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Construction technology analysis and choice Second Edition Tony Bryan

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Construction technology analysis and choice Second Edition Tony Bryan Digital Instant Download Author(s): Tony Bryan ISBN(s): 9781405158749, 1405158743 Edition: Second edition File Details: PDF, 6.52 MB Year: 2010 Language: english
Construction Technology Analysis and Choice
Construction Technology Analysis and Choice Second Edition Tony Bryan University of the West of England A John Wiley & Sons, Ltd., Publication
This edition first published 2010 © 2005, 2010 Tony Bryan First published 2005 by Blackwell Publishing Ltd Second edition 2010 Blackwell Publishing was acquired by John Wiley & Sons in February 2007. Blackwell’s publishing programme has been merged with Wiley’s global Scientific, Technical, and Medical business to form Wiley-Blackwell. Registered office John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, United Kingdom Editorial offices 9600 Garsington Road, Oxford, OX4 2DQ, United Kingdom 350 Main Street, Malden, MA 02148-5020, USA For details of our global editorial offices, for customer services and for information about how to apply for permission to reuse the copyright material in this book please see our website at www.wiley.com/wiley-blackwell. The right of the author to be identified as the author of this work has been asserted in accordance with the Copyright, Designs and Patents Act 1988. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by the UK Copyright, Designs and Patents Act 1988, without the prior permission of the publisher. Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books. Designations used by companies to distinguish their products are often claimed as trademarks. All brand names and product names used in this book are trade names, service marks, trademarks or registered trademarks of their respective owners. The publisher is not associated with any product or vendor mentioned in this book. This publication is designed to provide accurate and authoritative information in regard to the subject matter covered. It is sold on the understanding that the publisher is not engaged in rendering professional services. If professional advice or other expert assistance is required, the services of a competent professional should be sought. Library of Congress Cataloging-in-Publication Data Bryan, Tony, 1947– Construction technology : analysis and choice / Tony Bryan. – 2nd ed. p. cm. Includes index. ISBN 978-1-4051-5874-9 (pbk. : alk. paper) 1. Building. I. Title. TH146.B82 2010 690′.837–dc22 2009038731 A catalogue record for this book is available from the British Library. Set in 10/12 pt Palatino by Toppan Best-set Premedia Limited Printed in Malaysia 1 2010
Contents Preface ix 䊏 PART 1 ANALYSIS 1 1 The Framework for Understanding 3 Process and knowledge 3 The initial suggestion 4 Carrying out the evaluation 4 Physical and social context 5 The basis of analysis 6 Knowledge needed for choice 7 Summary 8 2 Building Purpose and Performance 9 Activities, space and construction 9 Introduction to performance requirements 9 Environmental impact and sustainability 17 Summary 17 3 Common Forms – Specific Solutions 18 General and constructed forms 18 The emergence of general building forms 18 Uncertainty and risk 22 Summary 23 4 Construction Variables 24 The variables of construction – the outcome of choice 24 Choosing materials 25 Choosing shape 27 Choosing size 27 Spatial relationships 32 Joints and fixings 32 Summary 35 5 Defining Conditions 37 Physical and social conditions 37 Activity and construction-modifying environments 38 The dynamics of the system 38 Choice of interior elements of the building 42 Inside the construction itself 42 Summary 43 6 The Resource Base 44 Introduction 44 Materials – the primary resource 44 Knowledge and skill – the human resource 45 Production equipment – the technological resource 46 Money – the enabling resource 47 Summary 48 7 Design Concept 49 Linking design to construction choice – flows and transfers 49 Concept design – broad options 50 Physical performance and appearance – commodity, firmness and delight 50 Function of the whole, function of the parts 51 Summary 52 8 Appearance 53 Visualising attributes and response 53 Space and context 53 Physical space for the construction 55 The approach to analysis 56 Summary 56 9 Analysis of Physical Behaviour 57 Visualising conditions and response 57 Function and performance – a technical aim 57 Preventing failure – a technical objective 57 The role of observation and science in the analysis 58 The approach to analysis 59 Summary 59 10 Physical Behaviour Creating Environments 60 Aspects of environment 60 The building as a system 60 The dry environment 65 The warm environment 72 The light environment 78 The acoustic environment 82 The clean environment 86 The safe environment 88 The private environment 96 Summary 97
vi Contents 11 Physical Behaviour Under Load 98 Forces, external and internal 98 Basic structural members 100 Curving (and folding) structural members 104 Structural connections 105 Grid members – pin-jointed frames 107 Building structures – wind stability 108 Stress–strain and the choice of material 110 Structural analysis and design 111 Movements and structural behaviour 112 Stresses in the ground 112 The major structural forms 114 Summary 117 12 Physical Behaviour Over Time 119 Reliability: renewal, maintenance, repair and disposal 119 Basis of analysis 120 Soiling and cleaning 120 Durability of materials 121 Movements in components 124 Ground movement, settlement and subsidence 127 Movement and detailing 128 Wear of components 129 Summary 129 13 Manufacture and Assembly 130 Realisation of performance 130 Visualising stages and sequence 130 Analysis of operations, methods and resources 133 Materials and labour 135 Production equipment 136 Production options 141 Knowledge and expertise for the analysis of the process 148 Summary 149 14 Cost 150 Cost and value 150 Cost and price 151 Cost and time frames 151 Cost and cost data 152 Summary 154 15 Sustainability – Social Concern 155 Two major forces 155 Sustainability 156 Established influences and new concerns 156 Responding to the sustainability agenda 158 Buildings as systems 161 Renewable energy sources 168 Water and waste 170 Materials choice and detailing 172 Planning and design concepts 173 Emerging technologies 173 Summary 174 䊏 PART 2 CHOICE – HOUSE CONSTRUCTION 177 16 Applying the Framework to Housing 179 The need for an integrated approach 179 The basis of the case study 180 Summary 182 17 Floors 183 Upper floors 183 General forms for upper floors 183 Timber-joisted upper floors 184 Ground floors 191 Suspended ground floors 192 Ground-supported slab floors 195 Services and other elements 197 Site influences on choice of ground floors 197 Production operations for ground floors 198 The final choice 199 Summary 199 18 Roofs 201 Pitch and span 201 Other functions 201 Pitched roofs 202 Flat roofs 218 Summary 219 19 Walls 221 Wall types by function 221 General forms 221 Walls in the case study 224 Masonry cavity external walls 224 Openings in the external wall 233 Doors and windows – the components in the openings 236 The panel frame option 238 Party (separating) walls 241 Partition walls 242 Summary 243 20 Foundations 244 Basic function 244 Site investigation 246
Contents vii Foundation design 247 The strip foundation 247 Foundations for poor surface conditions 250 Economics of foundations 254 Basements 254 Summary 254 21 Services 256 Introduction 256 Analysis of services systems 257 Hot and cold water 257 Heating systems 263 Drainage 267 Electrical systems 273 Summary 279 䊏 PART 3 CHOICE – COMMERCIAL CONSTRUCTION 281 22 Applying the Framework to Commercial Buildings 283 The story so far 283 The way forward 285 The technological mix 287 Summary 289 23 Common Forms and Emerging Technologies 290 Introduction 290 UK commercial building through the twentieth century 291 Summary 298 24 Interface Design 299 Introduction 299 The enclosure–services interface 300 The enclosure–structure interface 302 The structure–services interface 305 Summary 306 25 Structural Skeletal Frames 307 Materials development and structural options 307 Reinforced concrete – performance 315 In situ reinforced concrete frames – production 317 Precast concrete frames – production 329 Structural steel – performance 330 Structural steel – fabrication and construction 333 Structure choice and overall design 337 Summary 338 26 Roof Structures 340 Introduction 340 Variety of structural form 341 Broad options 342 Construction details 348 Summary 352 27 Loadbearing Structural Walls 353 Broad options 353 Multi-storey construction 354 Single-storey industrial construction 359 Summary 363 28 Structure Below Ground 364 Introduction 364 Foundation design 364 Foundation types 366 Soil improvement 372 Basements 373 Large area industrial concrete ground floors 380 Summary 384 29 External Enclosure to Structural Frames 385 Introduction 385 External walls 385 Cavity brickwork 390 Cladding panels 392 Curtain walling 396 Facing materials 397 Lightweight cladding 403 Structural glazing 404 Roof construction 406 Summary 411 30 Internal Enclosure 412 Performance 412 Applied finishes 413 Component systems 414 Summary 421 31 Services – Scope and Space 422 Introduction 422 Scope 422 Space 424 Environmental services 424 Public health services 429 Power supply 432 Security 433 Operational services 435 The need for coordination 436
viii Contents Production sequence and contract time 437 Cost of services systems 438 Summary 438 32 Guide to Further Reading 440 What this book provides 440 Sources of information – authority, validity and relevance 440 Finding information 443 Using information – corroboration, confirmation and risk 444 Summary 444 Index 445
Preface This book has been prepared for those at the beginning of their career studying with a view to practise in one of the professions concerned with the construction of buildings. It is written for the novice who, with study and experience, will become an expert in his or her chosen field. The more fundamental ideas developed in the text may need to be revisited as experience grows and it is, therefore, hopefully a text that can be referred to in the early years of practice and maybe beyond. The book takes as its theme the process of choice: what the expert has to know and how the expert could think through the myriad deci- sions that have to be made about the design, production, maintenance and disposal of build- ings. While this involves a process of analysis, the basis of which is universally applicable, the final choice is dictated by context. The context is set by time and place, the nature of the activity to be undertaken in the building and the aspirations of its benefactor or client. The process of choice is seeking appro- priate solutions in a physical and cultural context. For a text of this nature it may seem to be dominated by words and not illustrations. The contention is that for the novice or the practis- ing professional faced with new ideas and situ- ations the explanation of possible solutions is required. Presenting a final working drawing may be the outcome of choice, but it is the process of analysis with its need for explana- tions that gives the confidence that it will perform and can be built in the context of the particular building. A picture only paints a thousand words if you already have the words to explain it. It is hoped that the reader will find that the text tells a good story, that the development of the ideas is logical and easy to follow, but perhaps above all that it is seen as valuable in the world of practice. It is hoped that the text will be illuminating and the illustrations supportive in providing the explanations of both the analysis and the solutions suggested for choice. The first part of the book focuses on the key areas of analysis that have to be considered to check that the proposed construction will perform (will not fail) and can be built. These two tests are seen as fundamental to the final choice. In order to carry out these analyses this book suggests that it is necessary to visualise not only the physical form of final construction, however outline or tentative, but also, equally importantly, its response to the dynamic condi- tions under which it has to perform. The key question is ‘What if I do it like this?’ The answer comes from an understanding of how it works and how it is built, this understanding coming from explanations of why things happen, drawing on knowledge from a number of other disciplines such as science and economics. Each of the areas of analysis presented in this book is independent, and therefore each analy- sis has to be separate, yet all have to be satisfac- tory before the final choice is made. Choice is a juggling act: checking a proposal in one area of analysis may suggest changes that will affect others. Structurally sound solutions may be dif- ficult to build or solutions that will last without maintenance too expensive as a capital invest- ment. The final choice must satisfy all the areas of analysis. The second and third parts of the book put analysis into practice, focusing on making the final choice. Given the approach identified in the first part of the book, with context being so important, the chapters in Parts 2 and 3 are written from the perspective of making choices for construction in the UK at the beginning of the twenty-first century. In Part 2 the focus is on housing, while Part 3 is concerned with the
x Preface commercial use and scale of building. While these both take place in the same physical and cultural environments, the way buildings are commissioned and designed varies. For mass housing the choice of technical solutions is made by the developer/builder and this leads to a convergence of detailing and specification for the construction. This current common form of house construction is presented in Part 2. In commercial building there is considerably more diversity in the use and scale of the building, leading to more variety in both the mix of tech- nologies and in detailing and specification. This greater need to consider broad options early in the design and to be clear about the potential for the technical solution is reflected in the approach developed in Part 3. The final chapter provides a guide to the wide range of published material that is available to develop knowledge beyond this book and par- ticularly to support the process of choice. The book itself gives no direct references. The notion of the framework for understanding developed in the book encourages the idea of seeking rel- evant and current information in the context of each project. It is hoped that this final chapter introduces the sources of information that will complement the approach developed in this book in order to put these ideas into practice. This book is written with the conviction that by focusing on the process of choice the range of theory and knowledge that is useful to prac- tice becomes explicit, making the link between knowledge and practice and between under- standing and experience clear. As study, and then practice, unfolds for each individual it is the power to reflect that develops understanding. It is hoped that the framework suggested in this book will help not just the process of choice but also the process of reflection. Readers should take from this text what understanding they can to use it to develop their own good judgement in what- ever part they play in the great enterprise of construction and the development of the built environment. Tony Bryan Book website at www.wiley.com/go/bryanconstructiontech2e Contains nearly 200 fully referenced, clear line drawings to download for free, as well as suggested learning activities for lecturers to incorporate into their teaching programmes.
Part 1 Analysis
1The Framework for Understanding This opening chapter outlines a framework to help develop an understanding of what has to be known in order to take decisions on how we should build. The framework suggests a way of going about selecting construction and identifies the knowledge that is required to make the choice. It is the framework that will be developed and used throughout the book. Process and knowledge This book provides examples of construction, showing how we currently build, and provides an introduction to the understanding necessary to explain how the construction works. These two types of knowledge are both vital to making decisions as to how we should create and main- tain buildings in the future. This book sets this knowledge in the context of the process of making choices for the construction. In practice, a great deal of knowledge exists of the types of construction we might use and the materials and details that might be specified. There is, however, the need for any proposed construc- tion works to answer the questions ‘Will it fail?’ and ‘Can it be built?’ Clearly it requires the answer to these two questions to be ‘No, it will not fail’ and ‘Yes, it can be built’. These categori- cal no and yes answers may be difficult to give in practice. There often needs to be some analysis to develop a level of confidence with which to make the choice. The amount of analysis required determines the level of under- standing and experience needed to provide the evaluation of the suggested solution before the decision is taken to put the final proposal into practice. It is this basic ability to make a suggestion of how a building might be constructed and then to carry out an evaluation asking the questions whether it will fail and whether it can be built that is developed in this book. The evaluation points to changes in the suggestion, which after re-evaluation will lead, through a series of refinements, to the specification and details to be adopted. This requires knowledge of what potential solutions might look like, with current practice and precedent as the major sources for an initial suggestion. It requires an understanding of what is necessary to be specified in order to describe the proposed construction in sufficient detail to carry out the evaluation. The ability to carry out the evaluation, on the other hand, is dependent on an ability to ‘see’ the proposal working in the dynamic systems of the physical and social conditions in which the building is to be built. This process of choice and the way it leads to the identification of the knowledge required is shown in Figure 1.1. It will be shown later that the process of choice is not just an analysis of the behaviour of physical performance. This evaluation of a proposal’s response to the dynamic physical, chemical and biological systems of nature is vital, but building also takes place in a social and cultural context. There will be an impera- tive to ensure that the resources and know-how are available to manufacture and assemble the construction. This will require knowledge of the available industrial systems. Further, it will be necessary to ensure that the cost of the solution
4 Analysis Analysis is monitored and that its social and environ- mental impact is audited. These will demand an understanding of both the economic and social systems in which the building is to be created. The initial suggestion If the process is suggestion and evaluation, and the starting point is suggestion, it is necessary to know how we make the initial suggestion. How do we make that first best guess? In most cases the suggestion is informed by precedents. It is necessary to have knowledge of current solutions and how they perform in practice. Something, somewhere, has been done before that gives clues as to how the new solu- tions might be formulated. In times where change is limited the particular circumstances will have been faced a number of times in the past and successful solutions will have evolved. The well-tried and tested solution needs only to be suggested and, with some evaluation to ensure the circumstances have not materially changed, can be immediately adopted. If the circumstances are changing, current solutions may still be the best starting point. They repre- sent not only a sound basis in performance but also an existing base of resources and know-how to manufacture and produce the materials and details. Evaluation may modify but not fundamentally change the solution. This, over time, gives rise to a number of general forms from which specific solutions can be derived. In some cases, perhaps where there are increasing user demands, or the structure of industrial practice is changing, then similar or related practice may have to be investigated. On the rare occasions where suggestions have to be derived from little or no existing previous work, a more fundamental understanding of the behaviour of the construction will have to be applied. While experts approach making suggestions based on their knowledge and experience, it is, in many ways, not necessary to know much at all to make suggestions. It is the evaluation that requires the expertise. Novices or casual observ- ers may make suggestions that may be hailed as brilliant observation, but in truth they have no way of knowing whether that particular sug- gestion is workable or not. It will take the expert to spot its potential and prove its worth through evaluation. The power of the expert to spot potential is probably associated with the ability to carry out a rapid, approximate evaluation before subject- ing the suggestion to more rigorous and explicit analysis. Carrying out the evaluation The heart of the success of the process of tech- nological choice lies in the ability to be able to carry out an evaluation. The need to carry out a series of analytical exercises determines the knowledge required and manner of its applica- tion. It requires a level of understanding to answer the question ‘What if we built the build- ing as proposed?’ While the suggestion and the ultimate solu- tion describe the construction in what appears to be a static detail, the evaluation of the sug- gested construction has to describe a dynamic Figure 1.1 Relationship of process of choice to knowledge required. Evaluation Construction detail Dynamic systems Suggestion Process of choice Knowledge required
The Framework for Understanding 5 Analysis system of behaviour (‘Will it fail?’) and a pro- duction process (‘Can it be built?’). The process starts with the client’s brief, the design then being devised from the require- ments of those who commission the works, and as a response to the social and physical context in which the building is to be built. It is against these criteria that failure will be judged. There will be many possible ways to construct a build- ing to achieve performance expressed in the client’s brief. The criteria for choice of the tech- nical solution come from the identification of the function of the parts and how they contrib- ute to the function of the building as a whole. The dynamic behaviour of the construction responding to changing conditions has to be understood, anticipating the modes of failure. Some specification of performance has to be established and then the suggestion has to be tested in the mind to assess the risk of failure within agreed design conditions. It is easy to see technology as only the final construction, an assembly of components and materials, the building as a static object. However, making the choice of what construc- tion should be adopted has to be rooted in an understanding of the construction as a dynamic system responding to changes in conditions and open to a failure to perform. It is necessary to be able to visualise not only the physical construction but also its behaviour under the conditions it will have to endure in its working life. Both of these are of equal importance. If the suggestion is not visu- alised correctly, its behaviour under analysis may be misinterpreted. If the dynamic system of behaviour is not visualised correctly, a flawed proposal may be adopted. Visualising the building as a dynamic system will involve iden- tifying the flows and transfers that take place both within the building and through the con- struction itself. These ideas are explained in Chapter 7. Technological choice demands skills in these areas of visualising the object and the systems, and then the conceptual manipulation of the systems acting on the construction to predict behaviour and assess the risk of failure. If the two basic questions to ask of a proposed solution are whether it will fail and whether it can be built, the criteria for choice come from an understanding not only of the potential dynamic flows and transfers when the building is in operation but also of the resources available. The performance of construction can only be realised if the resources are available to construct the building. This relies on the manu- facturing and assembly possibilities but will also include the existence of design expertise and the options for maintenance and disposal. Knowledge of available techniques and know- how for production is crucial to the choice of the final construction if it is to be successful in reality as well as on paper. As a design concept emerges, it is necessary to question what construction solutions may be used to fulfil the design requirements. It is then necessary to question whether this solu- tion is available with current technology and resources within any environmental, cost or time requirements. The resources available make the design a reality. Technology stands between the design of the building and the management of the resources. Choices can be made that may extend current production and design knowledge, but this must be recognised, and any costs involved in prototypes or training and the risks involved must be accepted before the final choice is made. The design and resources available condition the choice. These two areas are shown in Figure 1.2. These are the two areas that have to be understood before any analysis can be started leading to the final choice of construction. Physical and social context Figure 1.2 also indicates that before any choice for a specific building can be made it is neces- sary to understand something of the context in which it will be constructed. There needs to be some knowledge of the conditions that exist when and where the building is to be built, pos- sibly with some assessment of how conditions may change in the future.
6 Analysis Analysis Design Concept Resource Base Construction Physical behaviour Appearance Cost Social concerns Manufacture/ assembly Physical Context Cultural Context Figure 1.2 Framework of analysis. Construction takes place within, and has an impact on, the world in which it is undertaken. Some description of this world is necessary for both technical and socio-economic analyses. The world can be represented as a series of con- texts, both physical and cultural. The physical context includes nature and climate. These exert forces that act on the building; they provide the raw resources and may be adversely affected by the construction and operation of buildings. The physical context includes the surrounding development and the need for the design to respond to existing buildings and spaces. People and their social, economic and politi- cal systems create the cultural context. It needs a response to local, national and even global needs based on beliefs and fundamental world views of the relationship between individuals and between society and the other components of the natural world. The interaction between these two sets of con- texts has been brought into focus at the begin- ningofthetwenty-firstcenturybythemovement for sustainable development. The realisation that development cannot continue without consideration of its impact on the natural envi- ronment as well as established economic and social considerations calls for new knowledge associated with materials choice, energy use and waste disposal aspects of our chosen construction. There are, therefore, dangers in seeing these two sets of contexts as separate. However, it is still useful to consider them as having different dynamics, as, generally, in order to resolve technical questions, it is necessary to have an understanding of the physical context, while to evaluate the chance of a solution being success- fully applied requires an understanding of society, its economic and political systems. The basis of analysis Having identified the design concept and the resource base as providing the criteria for choice and having recognised the need to understand the physical and social context in which we build, it is possible to identify five areas of analysis as shown in Figure 1.2.
The Framework for Understanding 7 Analysis The design concept is the translation of the physical and social needs for the operation of the whole building into a scheme that identifies the function and performance of each of the parts. In order to achieve this, the design concept has to articulate both the arrangement and appearance of the spaces and the technical contribution each part of the construction will make to the creation and maintenance of the internal conditions. Two tests indicated in Figure 1.2 have to be applied to a suggestion to see if it complies with the design concept: • Does the physical behaviour of the construc- tion provide a building fulfilling its func- tions to the required performance level? • Does it provide the right attributes of appearance? The test for physical behaviour involves three separate areas of analysis: • Creating environments • Under load • Over time Three tests indicated in Figure 1.2 have to be applied to a suggestion to see if it is achievable with available resources: • Can it be produced, including its manufacture and assembly and the subsequent processes of maintenance and disposal, with existing skills and know-how in a reasonable time and at the required quality? • Are the resources available at reasonable cost? • Will it be compatible with the social concerns that currently exist? These resources are both natural (from the envi- ronment) and social, so both aspects have to be part of the evaluation. It is only possible to use resources that nature has provided. However, the level of economic development in a society will provide the capacity to process materials, develop the skills and machinery to work them, the intellectual capacity to undertake design and the provision of capital to invest in the enterprise of the construction itself. Both the technical properties of materials and the exist- ence of the knowledge to exploit them plus any environmental impact of their use must be analysed in evaluating a suggested form of construction. These seven areas of analysis (physical behaviour being three) that have to be under- taken are, by and large, unrelated to each other and each needs its own tools of analysis and knowledge base to be successfully applied. Carrying out one analysis may indicate the need for a change in the suggestion, but the change that is chosen may make the analysis of a previous aspect invalid. It is not until all the relevant areas of analysis are shown to be satis- factory that the suggestions can be adopted as the solution. These seven areas of analysis have potentially to be undertaken for all aspects of the construc- tion, from the overall structural system to the finest detail such as the screw that fixes the final fitting to a wall. The work in this is clearly overwhelming if it has to be carried out for every building that is constructed. Current practice can inform much of the process of choice. One of the most important decisions that experts take is, of all the thousands of choices that have to be made to fully specify the con- struction, which of the areas of analysis for which parts of the building are significant. Where, if analysis is not thought through, is the greatest risk of failure? It is not clear how experts make this judge- ment. One possible explanation is that while looking at a suggestion they make many rapid checks against the seven criteria. From their knowledge and experience they take a view on what is well within failure limits and where the risks of failure are higher. Knowledge needed for choice It is now possible to start to identify the knowl- edge that is required and the areas of under- standing that have to be developed in order to carry out a full evaluation. Although used in various combinations in the different areas of analysis, it is possible to put forward a tentative list of types of knowledge that will be required:
8 Analysis Analysis • Setting the performance levels as the criteria against which the evaluation will be made. • Defining the conditions under which per- formance has to be achieved. • Determining the fundamental behaviour of the construction that would lead to failure to meet performance requirements. • Identifying the materials’ properties that will govern the behaviour that could lead to failure. • Thinking through the behaviour of the par- ticular combination of materials and details under the conditions envisaged. • Identifying the process of manufacture and assembly together with the resources required to produce the building within quality, time, cost and safety limits. • The cost in economic, social and environ- mental terms of using a particular form of construction. The process of evaluation requires the building to be conceptualised in a number of ways. While the final building will be seen as a physical construction, ‘bricks and mortar’, it is necessary to perceive the building in a number of other ways when carrying out the evaluation. Initially, the construction has to be seen as ful- filling a set of functions with associated per- formance levels. For evaluation, the building has to be viewed as a series of physical systems responding dynamically to changing condi- tions. The building then has to be seen as a series of production operations with the resources required for the realisation of the design. All these will have economic, environ- mental and social implications that have to be understood. When all these can be mastered, choices can be made associated with an assess- ment of risk and with some confidence of a successful building. Summary 1. The process of choice is one of suggestions and evaluation that requires knowledge of the physical construction and the dynamic systems in which it will be built and will operate. 2. How a suggestion is generated, and the extent to which a formal evaluation has to be under- taken, depends on the scale and nature of any changes from current practice required by either the design or the resources available. 3. When there is a changing demand for buildings and rapidly developing technical knowl- edge, the role of experience changes from predominantly reproducing known solutions to the integration of experience into a process of analysis to explore the possibilities of failure in the modified or new solutions before they are built. 4. The design and the resource availability define the criteria for the evaluation. This has to be set within a physical and cultural context. 5. The suggestion will probably be based on precedent and this leads to general forms from which specific solutions can be derived. 6. The evaluation needs to be carried out through seven areas of analysis: appearance, behav- iour creating environments, behaviour under load, behaviour over time, manufacture and assembly, cost and social concerns. 7. This will involve constant reference to both production and design. The concern is for what will not fail and can be built.
2 Building Purpose and Performance Technology is used to mediate between the world as it is and the world as we want it. This chapter expands this idea, focusing on the users and their activities, introducing the functions expected of the building and how these have to be translated into a process of choice for the construction of each part. Activities, space and construction Buildings are often characterised by their overall purpose or function – house, factory, hospital, prison, etc. – and are often immediately recog- nisable although their architecture may vary. To understand the form of the building, it is neces- sary to understand the day-to-day activities that make up the function for which the building is commissioned. The construction will have to play its part in ensuring the well-being of these activities. The notion of well-being is normally associated with the people who use the spaces, but the building will have to protect the equip- ment being used and the storage of items associ- ated with the activities. Well-being of people also needs to include the requirements of the owner and the wider public, as buildings are social institutions and create the surrounding spaces. The majority of spaces in buildings have to accommodate people and consideration of their well-being becomes a dominant aspect of the performance of the construction. In some cases, such as the rooms for the early computers and specialist storage areas such as vaults and cold stores, the equipment housed in the building or the storage conditions dominate the require- ments. Designing for the well-being of people is essentially concerned with health, safety and comfort. Health should be understood as meaning both physical and mental health, both being a function of physical and social condi- tions created by the building. The owner may see a purpose beyond the simple support of activities, to include image and status. The surroundings in which the activities are undertaken have social signifi- cance and must form a feature of the design. Each society over time evolves common building forms for each purpose type that become recognisable within that society because of their size, arrangements of internal spaces and social statement. With this emergence of building form there is a need to develop appro- priate construction solutions. This process is dealt with in more detail in Chapter 3, but first this chapter explores the complex range of per- formance issues. These will be established pre- dominantly by the users’ activities, although later by the owner and then by government in the form of legislation on behalf of society as a whole. Introduction to performance requirements In order to explore the range of performance issues it is useful to engage in a mind experi- ment. The situation to be imagined is one where civilisation as we know it does not exist and the task is to provide shelter. The scenario is one of few resources of materials, labour
10 Analysis Analysis or knowledge. There is also little development of an economic system, so the whole design and production process has to be undertaken by the users. The mind experiment starts by asking which performance the user of the building would seek to satisfy first. The experi- ment can then be extended through time, assuming increasing resources and socialisa- tion, introducing additional requirements that would add value and utility and improve well-being. By undertaking this mind experiment it will be possible to introduce the needs of the user and hence the functions that he or she will require the building to fulfil. As the user is also, at least initially, the designer and builder of the shelter, he/she must decide on the construction. The experiment will, therefore, also start to introduce the ideas and knowledge that will be needed to make decisions on the construction of the building itself. All the issues and factors introduced here are still relevant today. In the beginning Given no immediate risk from attack, we can speculate that people would organise their technological endeavour in the following way. Thought would have to be given to the range of activities of everyday life that should be housed in the shelter. Initially this is likely to be very few, perhaps only sleeping, with most activity being undertaken outside depending on the prevailing climate. This will provide a defini- tion of size and any division of the internal space that needs to be made. It would be imme- diately recognised that these requirements for size and shape would be limited by the possible construction available. Some decision would have to be made as to how much effort should go into developing construction to match aspi- rations or use existing resources to satisfy immediate needs. The priority in terms of establishing functions for the building fabric would be to remain dry, a condition fundamental to the health and comfort of people and the storage of many natural products. This would be accompanied by the requirement to be warm, but it is possible that this will initially be achieved in combina- tion with other technologies. These would include clothing and the use of fire, which at this stage may or may not be associated with the construction of the shelter. As soon as any construction is contemplated the builder is immediately faced with achieving a stable structure and making some judgement on how long it may last. Although buildings may be erected for environmental control, their very existence demands considerations of stability and reliability if they are to be deemed satisfactory by the user. This will require the identification of possible modes of failure. At this early stage this would include how the con- struction might leak or fall down. This under- standing of the ways in which performance may be lost becomes crucial to directing effort to significant aspects of the solution. This would also lead to some questioning of what mainte- nance may be necessary and what parts may have to be renewed to continue the per- formance until the construction had to be aban- doned or demolished to make way for a new building. It would also become necessary to have some knowledge of the environmental conditions in which the construction has to maintain per- formance. This knowledge would be required to consider not only the environmental control but also the stability and reliability. These three become the key physical performance issues. External climatic conditions such as frequency and volume of rainfall will need to be assessed for the weatherproofing function. Damaging wind speeds and direction would need to be assessed for stability. It would, however, soon become clear that wind is a major factor in weatherproofing. Some of the most arduous weatherproofing conditions come with wind- driven rain. It is not possible to say what aspect of the environment needs to be known to assess durability until some choice of the basic materi- als is made. Specific decay agents in the envi- ronment degrade different materials. Linking materials to their generators of decay is just one more question that has to be answered in the
Building Purpose and Performance 11 Analysis quest for knowledge to make sensible choices for the construction. This assessment of external climate would soon reveal that often the more extreme condi- tions of open land are ameliorated by local natural features, that exposure can be modified by the position and orientation of the building which will limit the demands on the construc- tion and/or give better internal conditions. The next steps As the number of activities carried out in the building increases, the provision of good air may be the next priority for improvement of the construction. This is probably the next require- ment for health and comfort after dryness and warmth. Seeking a solution that would improve the quality of the air would probably involve ven- tilation since there is an abundance of good air outside. It would have to be recognised that the air outside may also be cold and that this will make the requirement for warmth more diffi- cult to achieve. This may mean that a solution for good air may only be possible when air tem- peratures outside are sufficiently high or air quality inside is particularly poor. Assuming that the active technologies of building services are not available, modification would be neces- sary in the existing construction. It would be necessary to use natural ventilation driven by wind pressures around the building. Openings would have to be introduced to ensure the exchange of air. Their position and size would have to be considered. It would be possible to introduce a level of control by providing shutters. The openings could eventually be as sophisticated as chimneys, but history tells us that these often come much later. It is important to note that the containment of the bad air is a direct result of employing con- struction to remain dry and warm. The air outside the building is almost certainly good. This realisation that the construction itself can create undesirable conditions should not go unnoticed. Changes introduced to fulfil new performance demands may change conditions that have always been satisfactory. This hap- pened towards the end of the twentieth century when a requirement for energy saving was satisfied by the introduction of insulation. Under some environmental conditions this led to condensation that has a deleterious effect on the basic requirement of keeping dry. This led to health problems for the users of the buildings. The introduction of new performance require- ments may also introduce failures in the con- struction that have previously not occurred. This happened in the condensation example, where dampness caused not only health prob- lems but also a deterioration of the construction materials themselves. In this mind experiment it is possible to speculate on a similar problem with the improvement in internal air quality. Given the lack of social organisation to produce more processed materials, the construction would almost certainly be made of relatively unmodified organic materials. In this case it might be speculated that if the poor air had a large component of smoke it would have permeated the construction. This would have effectively fumigated the organic materials and kept infestations or decay-promoting fungi and insects at bay. Improving internal air quality may change the conditions within the construction itself. This may allow significant numbers of some of the natural agents of decay to thrive, thereby reducing the life of the construction. More physical requirements This mind experiment continues on the assump- tion that no major threat to security arises. This would inevitably lead to a diversion of resources and may change the priorities of individuals or society in seeking improvements in their build- ings, although it may also lead to new types of buildings, such as defensive works. Given peaceful social development, the next priority may be difficult to identify. It may be that the infestation of insects and small animals that will be attracted to the improved internal environment becomes a problem. It
12 Analysis Analysis may be that in the harsh realities of life, and in the absence of any realisation of the health risks, these infestations would be tolerated. Measures to eliminate the larger animals, if not already considered as a danger, may now become important. At some time, however, infestation control would have to be included in the list of functions required of the construction to improve well-being. This is part of the more general requirement to keep the enclosed space clean. Internal surfaces that are dust- free, smooth and wipeable become desirable attributes where cleanliness becomes important to the health and comfort of the user. Having gained good clear air, more activities could be carried on indoors. It is, therefore, possible to imagine an increasing need for light to improve comfort levels and further extend the range of activities in the building. The choice is between natural and artificial means of lighting. Natural would involve openings, while artificial would only demand a safe place to support what would almost certainly be an independent light source. Although inde- pendent of the building, it would have an influ- ence on it. Perhaps the major influence it would have is in the increased risk from fire. While it may not be possible to improve the fire resist- ance of the whole building at this time, it would be sensible to employ non-combustible materi- als at least where the light source is to be mounted. Here we see the increased use of technologies independent of the building, seen by the user as an asset to the well-being of the activities, influ- encing the required functions of the construc- tion itself. Another requirement is for some measure of noise control. This would, of course, only become a concern if the external level of noise were somehow interfering with the overall sense of well-being. It may become a problem when the building has separate rooms for spe- cific activities. Noise from one activity may well be incompatible with the conditions necessary for another. Noise is a particular problem of civilisation, and especially for those societies that have advanced technologies. It also seems that it has a cultural basis in attitudes towards individual rights, privacy and intrusion. The technical considerations become more complex It is useful to view the need to consider noise performance from a different perspective. It may be that there is a need to modify the sound between outside and inside, yet the construc- tion used for the other requirements already has sufficient, if not excess, ability to perform as a sound barrier. With low performance expecta- tions the final form of construction is dictated by only a few of the functional requirements. As more functions are identified and the level of the required performance increases it becomes difficult to provide simple construction solu- tions. Composite solutions are necessary with different materials to satisfy different functions at the levels of performance that are required. The analysis of exactly how each part of the construction is interacting in providing the overall function becomes more difficult. The danger comes when changes are suggested. It is necessary to ensure that the change does not make a previously satisfactory performance critical so that the construction fails to perform, in an unexpected way. The trend towards lighter partitioning in housing has, by reducing the weight and changing natural vibration fre- quencies, reduced the sound transmission resistance. In the past this was normally more than satisfactory when partitions were thicker or made of denser material. The lighter, cheaper solution may become critical in some situations where the soundproofing performance of the heavier solution had always been taken for granted. The need for composite construction leads to the search for materials with properties matched to the specific functions. Processing or manufac- ture of materials allows these properties to be more accurately achieved. This not only changes the ability to gain performance but also influences the production resources required.
Building Purpose and Performance 13 Analysis Materials and manufacturing methods may also be changed to provide more economic buildings. The innovation may not be driven by performance but in order to seek production and cost gains. This may lead to performance failure in previously satisfactory solutions. Those responsible for the choice of construction must re-evaluate the possible performance fail- ures if construction is changed for production or cost advantages. Taking storage and equipment into account The environmental requirements that have been introduced are those necessary to maintain the well-being of the people who use the building. These can be summarised as: • Dryness • Warmth • Cleanliness • Light • Quiet Observations of this list will identify that, with only slight modifications (e.g. warmth needs to be more generally interpreted as temperature control), it could equally well be applied to maintaining the well-being of the equipment and stored items. The required internal condi- tions for storage and equipment may be differ- ent, even hostile to life as in the case of cold storage. They will still demand the same type of functions of the construction. There would, however, be changes in performance level due to the change in specification for the internal environment, even though the external condi- tion may be the same. In the example of cold storage, levels of insulation would be different. More significantly, the equipment and stored items, as well as the living occupants, will con- tribute to the internal environment with noise, smell, heat, fumes, etc. It may be that the con- struction is called on to moderate these effects by isolating storage from living areas by parti- tions. Independent technologies in the same room such as cooling of food may be applied using ideas such as evaporating water from a porous pot or a refrigerator. However, inde- pendent technologies may influence internal conditions. In the example of cooling food the porous pot releases vapour and the refrigerator releases heat. The dynamics of these changes in the internal environment due to occupants and independ- ent technologies in the building must become part of the analysis. Sealing up a building to reduce heat loss through air changes can lead to a build-up of vapour (if only from people breathing), which makes condensation more likely. Although the list of environmental require- ments generated for people will cover most circumstances associated with the equipment and storage in the building, it may in some situ- ations be incomplete. Some modern equipment has environmental operating requirements, such as the need for anti-static precautions, that may not currently be considered necessary for the well-being of people. What has to be achieved is a balanced solution to ensure the well-being of both the participants and the processes associated with the activities for which the building is required. What should be considered tolerable? Setting performance levels involves considering what is tolerable. What should be considered as normal limits to be maintained in the internal conditions? What external conditions should be allowed for in the design? These questions have to be answered in terms of risk and conse- quences. Extremes that happen rarely but have serious consequences to the well-being of the activity or even threaten life and property may well be taken into account. The more frequent events, even with lesser consequences, are also more likely to be taken into account. This is not independent of the economic resources available and social attitudes. In many parts of the world, earthquakes will occur, but the con- struction to minimise the risk to life is seen as increasing costs beyond that to be extended to
14 Analysis Analysis all sections of society. Similar circumstances have existed in the past with fire and building. Increasing wealth, effectively distributed in society, will affect what is considered tolerable, reflecting more demanding performance expectations. Generally, wide limits would be accepted for solutions at the beginning of our mind experi- ment, but as societies develop they seek to extend the range and level of demands. This often includes a requirement for a greater level of control as it defines a narrower band within which performance is deemed satisfactory. These trends place more demands on the solu- tions and failure is more likely. Some extremes that happen rarely have to be considered if they have serious consequences. One risk that comes from the internal activity that generates extreme conditions has already been raised. It is the issue of fire within the building. At the beginning of the mind experi- ment, while escape for people would be required, it is unlikely that there would be any expectation on the part of the user that any of the building would remain after a fire. Although fire is now rare in modern buildings, its conse- quences are such, particularly in risk to life, that it is currently deemed necessary for the con- struction to continue to maintain a selected range of performances both during and after the fire. This would almost certainly include stability, although insurance requirements may extend the performance range. External climatic extremes such as wind, flood, lightning and even earthquake may be considered. Design for flood may be sensible if the building is sited by water, for lightning if a tall building and for earthquake if the building is in an unstable region of the world. New threats created by increasing sophistica- tion of solutions are now emerging. Draught- free homes created to conserve heat may suffer from a build-up of radon gas if built in an area of the country where it occurs naturally in the rocks below the building. The chemical con- taminants in the soil on sites used for redundant industries threaten both the occupants and the fabric of the building itself. Introducing social requirements Having established the requirements for health and physical comfort, it is now necessary to consider the social aspects. In reality the consid- eration of performance for more social aspects does not come only when physical require- ments have been fully satisfied. Human endeav- our very quickly becomes a social activity and there grows a need for social organisation, establishing cultural norms, provision for lead- ership and political activities and an economic system for the exchange of goods and services. Buildings play their part in this process not only to house the activities but also in that they reflect, affirm and even become instruments for change as the cultural and economic order develops. As well as the issues of status and image, to be discussed later in this chapter, two other functions associated with well-being arise when society starts to develop. These are the require- ments for security and privacy. They are mainly associated with mental health, although the security risk, if it becomes a reality, may involve physical danger. The point at which people would take these functions into account would be dependent on the nature of the society that develops. They are not as predictable as the physical needs and may well have to be addressed before the desired level of physical comfort and safety is achieved. Security requirements will be dependent on the existence of a perceived threat. If the risks are seen as sufficient, technological inge- nuity, time and resources will be devoted to combating the threat if social devices such as the rule of law or treaties cannot be achieved. Threats come from both inside and outside a society, each of which pose different challenges to the technological skills of the builder. In the extreme, in buildings such as bunkers, the secu- rity threat dominates the design as the technol- ogy of survival becomes pitted against the technology of destruction. The requirement of privacy is much more rooted in the cultural attitudes to community. It is cultural interpretations of what activities
Building Purpose and Performance 15 Analysis should be shared and those that should be carried out in private that dictate the need to introduce this performance into buildings. Performance levels of privacy can be identified associated with the senses, visual and aural being the two main requirements of the build- ing influencing both the external envelope and normally demanding some division of internal space. The functions of the building that have a social origin often translate into aspects of phys- ical performance already introduced. Security makes structural demands on the fabric. Privacy determines many of the sound transmission requirements of construction. Influence of production resources As more functions are included and more materials are introduced, production resources and know-how have to develop. The relation- ship between the need for a building and the availability of the materials, skill and tools to produce it is always a determining factor in the choice of the construction. Access to production knowledge and expertise limits the pace of development of new solutions to achieve new performance. However, developments in mate- rials and production can also suggest different ways of achieving similar performance. This mind experiment has taken the perspec- tive of the purpose of the building and require- ments of the user. It is easy to forget that the means of realising that performance may need as much thought and ingenuity as the design and detailing of the fabric and structure of the building. In many old buildings it is easy to see how they work but often difficult to see how they might have been built without appreciat- ing the tools and skills available at the time. In many innovative buildings, detailing is often determined as much by manufacturing or erec- tion procedures as it is by satisfying perform- ance. The availability of manufacturing and assembly resources also determines the cost. The need to develop production procedure affects the time to construct and risk associated with a particular solution. All these contribute to the final quality of the building and its success judged by performance. Considering cost and value Throughout this mind experiment the question of cost and value will have to be considered. Buildings are usually costed in terms of money, but there are also considerations of cost to the environment and on the impact they may have on the society itself. The resources available to any society are limited and decisions have to be made as to how these should be allocated. As part of the culture these are the political deci- sions involving both the vision of the type of society that should emerge and the preferred methods of achieving it. It is from this cultural process that demand is initiated, the cost of resources determined and value assigned. Buildings will only be commissioned when the cost of a building that performs to an ade- quate standard is considered good value. If the costs are too great, decisions have to be taken on eliminating functions, reducing performance or changing production methods. These changes have to ensure that the building is still consid- ered as value for money. Assigning this cost requires that at least a broad outline of both the construction and the production methods is known. At some point in the process the deci- sion to proceed to full design and production based on estimated cost has to be made. For buildings that can be produced using well- developed current forms of construction this decision can be made very early with some cer- tainty. For a project where there are few prec- edents, possible solutions may have to be investigated before cost can be established with sufficient certainty to take the decision to proceed. It is, however, always a requirement to set cost limits as early as possible and then develop the final solution with these costs in mind. Building for status and image Status and image will at some time in the development of society start to influence the
16 Analysis Analysis requirements of the building. This may be reflected in the size of the space provided over and above that strictly required for the physical satisfaction of the activity itself. It may be asso- ciated with the quality of the materials used being acknowledged as expensive. These expen- sive materials must have the ability to perform their physical tasks without failure, but they could have been replaced by a less expensive alternative. These requirements are often then overlaid with issues of art and fashion and sym- bolism. The influence of these should not be underestimated, but a full discussion of their nature and form is inappropriate in this text. The pressures of status and image are not just related to statements of wealth and position. We all need to make statements and feel com- fortable about our place in society related to the prevailing cultural norms. It has to be recog- nised that these cultural norms can be highly regionalised, being associated with tribes or nations, although improved communication seems to reduce this variability. We all care about what our buildings look like and the envi- ronment they create. Using and being associ- ated with buildings that match the psychological demands of the activities carried out in the building is very important to our mental well-being. These issues become associated with aesthet- ics, the visual and deeper, even spiritual, quality of beauty of both natural and manufactured articles. These are the aspects of the world that satisfy our feelings rather than our physical needs. Buildings intrude into the rural land- scape and create the cityscape. Their shape, form, colour and ornamentation have a signifi- cant impact on our lives. Control from society and legislation All social groups have cultural norms of behav- iour that limit the actions of individuals and impose sanctions for transgressions. This even- tually has to be formalised into legislation, some of which will start to impinge on the choices that may be made for construction. Direct leg- islation is normally associated with public health, limiting the use of scarce resources or the position and appearance of whole build- ings. Once manufacture and assembly start, there are laws associated with the health and safety of operatives and people in the surround- ing area. All these will have to be acknowledged and satisfied in the final choice. If the choice of con- struction is made in the sprit of responsibility within the cultural norms, it should not domi- nate the solutions chosen. Legislation is for the protection of those who use the buildings and should, therefore, be easy to accommodate into a process whose objectives include satisfying social and individual needs. In reality the law on these matters can be slow to change and may be drafted such that its inter- pretation becomes a matter of opinion. These factors can spur or inhibit technological change, but it is clear that in an advanced society those responsible for the choice of construction have to be aware of the law and its interpretation. There is much legislation that will indirectly influence the choice of construction, although predicting and understanding the links are more difficult. Contracts become necessary between the organisations that undertake dif- ferent parts of the building process. This legisla- tion affects decisions on the construction and what risks they carry. The knowledge and expe- rience that the organisation has then influence the choices made for the construction of the building. Clients, users and change of purpose Another complication that arises as society develops is that individuals who become the owner/occupiers commission fewer buildings. It is now possible for those who commission the work to be an investment company who pass on the task of operating the building to another company for use by yet another group of people. This does not nullify the idea that satisfying the needs of the user should govern the perform- ance of the construction solutions. It is the pro- vision of space that ensures that the desired activities can be carried out efficiently and effec- tively by the user that gives value and utility to a building. Those who commission the build-
Building Purpose and Performance 17 Analysis ing may have objectives such as investment, but these will generally only succeed if the purpose of the building and its performance are satisfactory. Even when relatively simple relationships between client and initial occupation exist, the purpose of the building is likely to change with time. These can be quite dramatic changes such as churches to flats, but most are much more subtle. Changing practices in medicine have made many old hospital designs inefficient and the general electronic information revolu- tion has changed the basic activities carried out in many offices. Increasingly the operators of buildings (as opposed to the users) see the building as part of the business’s efficiency. This gives different value to maintenance, alter- ations and refurbishment and makes the build- ing a more integrated part of the facilities as a whole. This leads to the questions about the whole life costs. More expensive initial options may be better value over the life of the building, reducing operating costs and increasing effi- ciency and well-being. Environmental impact and sustainability This long-term view of the building leads to wider questions about environmental impact. Construction has always had a local impact on the environment; it takes resources, changes ecosystems, consumes energy and creates waste. The society in both our mind experiment and now in reality has grown more prosperous; infrastructures have improved, allowing the growth of manufacturing and materials process- ing to serve an expanding population with ever higher performance expectations. The environ- mental impact of technologies chosen for indi- vidual buildings can now contribute to global consequences. This demands yet more analysis, with new knowledge required in order to make choices about the technology we employ for our build- ings. It will lead to different solutions being favoured, innovation and risk. The story continues. Summary 1. The purpose of the building is to support the activity to be carried out in the building using both physical and social criteria. 2. Both physical and social functions of the building lead to physical performance requirements covering environmental, structural and reliability aspects of the construction. These require- ments lead to performance expectations and hence definitions of failure. 3. Choice of construction can only be made in the knowledge of the environments in which the construction operates and an understanding of the mechanisms or actions that lead to failure. 4. The other factors to be considered in making the choice of construction include production resources and know-how, cost, legislation and the need to consider the whole life of the building and its environmental impact.
3 Common Forms – Specific Solutions This section develops the idea that in any society there is a recognisable set of common building forms. These common forms will be drawn from a range of generic types that are then worked into various specific solutions. The generic type and constructed form are two distinct ways of identifying the construction that is adopted for a building. The conceptual generic type is characterised by its arrangements of components and action in achieving performance. The physical constructed solution has defined materials, size and shape of components, joints and fixings. This construction solution becomes specific to an individual building, although the building may be repeated many times and the detail may work in many buildings. General and constructed forms In any society at any time there is a pattern of needs that supports a recognisable series of common building forms. For each of these building forms there will be an interrelated set of construction solutions to cope with the size of the building and the resources affordable for each. Construction solutions are derived from a limited set of generic types. Technological choice often starts with the selection of an appropriate general form that is then developed into a detailed construction solution for a spe- cific building. The ability to describe a building in these two forms, the general form and constructed form, at the early concept stage in the design of a building is most important. It should be the big idea from which the individual details can be developed so they work together to ensure the performance of the building as a whole. The emergence of general building forms It appears that the prime determinant of the construction of a building is related to space. The users’ demands will translate fundamen- tally into spaces and their size and interrelation- ships will suggest the scale and shape of the building. At the domestic scale small cellular spaces lock together, while many commercial or public buildings require more voluminous spaces, often with smaller associated spaces such as toilets, to form the building as a working unit. Construction solutions are directly related to this demand for space. Most significantly it influences the structure, but these choices have inevitable consequences on the solutions avail- able for the construction of the enclosure and other elements of the building. Currently there is a wide range of spatial requirements both on plan and in the height required that leads to the use of a range of struc- tural forms. Three general groups of structural form can be identified: • Loadbearing walls • Skeletal frames • Long-span roofs Each of these will create a range of building forms, some examples of which are shown in Figure 3.1. Each building form will be made up of a combination of a range of structural
Common Forms – Specific Solutions 19 Analysis elements. An example of a generic structural element is the beam. With its structural action in bending it appears in cellular loadbearing construction as joists for the floor and a lintel over an opening, in skeletal frames as a main structural member and in the long-span roof in a portal frame. This generic type has been adapted for specific solutions using different materials to achieve the required characteristics: great strength, small deflections, small section size, low weight, good looks, low cost, fast erec- tion. Each of these characteristics will have a greater or lesser significance in a specific build- ing. In a house the joist will most likely be timber; in the skeletal frame the beam will gen- erally be steel or reinforced concrete. The portal frame is most likely to be made from steel, but for a building of the right use, scale and size it could be made from reinforced concrete or even from timber in a laminated form. While the ability to enclose the space is the primary determinant of the generic form, design and resource conditions will lead to a dominant economic detailed solution. This leads to two ways of thinking about a building, each having it own vocabulary to describe the solution. Early in the selection of the construction it is helpful to think about the elements of the build- ing in generic terms. This can then be developed into a full description of the constructed form, including specification of materials, joints and fixings. Generic elemental – domestic, loadbearing walls One widespread use for the loadbearing wall form is the house. Described in their ele- mental form, houses in the UK at the beginning of the twenty-first century employ a semi- permeable (cavity) construction for all external walls to provide (with internal cell walls) a stable dry box. This box will be roofed with a tiled covering supported on a trussed rafter structure taking the loads directly to the external walls. This means that any internal loadbearing walls need not extend to roof level. Suspended floors will be joisted, often taking advantage of internal walls to limit spans, making some ground-floor partitions loadbearing. Ground floors may be ground supported or suspended floors depending on the site and ground conditions. Foundations are most likely to be strip footings unless the ground conditions are very poor. This form is shown in Figure 3.2. Many houses built in the first half of the twentieth century and still in use were not con- structed like this. Many have solid permeable walls and have roofs made from individual structural members (rafters, purlins, struts and hangers) which, when acting as a whole, require internal wall support. Later in the twentieth century the width of terraced houses reduced and cross wall construction, where only walls Figure 3.1 Typical form associated with types of structure. Loadbearing Skeletal frame Long span roof
20 Analysis Analysis between the houses are loadbearing, became an option. This lost the stabilising effect of the box but allowed a range of less expensive external back and front walls to be chosen. As the loadbearing wall solution is developed into multi-storey flats other elemental forms have to be employed. Floors with greater sound and fire performance requirements become more economical as slabs, not joisted, even though the spans might not have changed sig- nificantly. The loadbearing walls may become prefabricated, taking advantage of the repeti- tions floor by floor to gain a production advantage. As this arrangement is developed into multi- storey blocks, the alternative structural form of the skeletal frames will become an economic alternative, even though the plan layout still shows walls dividing the building into small spaces with limited floor spans that made the loadbearing wall option viable. Constructed form – domestic, loadbearing walls None of the generic descriptions talks about the material, the shape or size of the components or the joints and fixings employed. They give the elements general names and describe them in terms of their general form or how they perform. For the constructed form, details have to be worked out to ensure economic sizes and man- ufacturing techniques. From this a recognisable physical constructed form will appear. The con- structed form of the generic elements shown in Figure 3.2 is given in Figure 3.3. This shows concrete single-lap interlocking roof tiles sup- ported on timber battens over felt fixed to timber-trussed rafters jointed with galvanised steel gang-nail plates. The external walls are masonry, although timber frame is a viable alternative. The wall may be constructed of brick outer skin and block or timber framed Figure 3.2 Generic description of house construction. Semi-permeable cavity wall Internal wall carrying floor loads Tiled pitched roof Trussed rafter roof structure Joisted first floor Ground supported floor Strip foundations Non-loadbearing partition
Common Forms – Specific Solutions 21 Analysis Figure 3.3 Constructed form description of house construction. Brick outer leaf with block or timber frame inner leaf connected with wall ties with insulation in cavity Inner block wall with plaster or plasterboard finish Concrete single lap tiles fixed to timber battens over sarking felt Timber truss created with galvanised steel nail plates Timber joists bearing on inner wall with chipboard decking and plasterboard for ceiling Insulated solid ground floor with fill (hardcore) under concrete slab Plain concrete strip foundations Timber stud partition with plasterboard skin Insulation panels for the inner leaf. This is unlikely to meet the requirements to limit the passage of heat. The most cost effective way to limit heat loss in the winter condition (loss of heat from warmed inside air) is by insulation incorpo- rated into the wall. In summer the design condi- tion is heat gain from outside. As this gain is predominantly from direct radiant heat from the sun, shading or thermal capacity (not shown in Figure 3.3) may be better actions than insulation. The floors are timber joist supported by resting either directly on the inner leaf or on galvanised steel joist hangers and finished with chipboard sheet flooring. As the ground-floor partition walls carry the joists they are con- structed with concrete blocks. However, as the trussed rafters only transfer load to the external walls the first-floor partitions only need to be timber stud with plasterboard finish, as long as they can provide appropriate levels of sound insulation. Plasterboard has been used for the ceilings and as a finish for the downstairs block- work, although gypsum plaster may be used on any block walls in the house. The external wall would have to be modified below ground and the foundation would be a strip of plain concrete. The size of each of these components has to be chosen. Common components, such as the brick or the standard range of windows, have been developed in appropriate sizes to work with the domestic scale and perform- ance levels. The size of some components, such as the trussed rafters and floor joists, has to be designed to the size and use of the building. In the same way as houses in the past have been different to the construction shown in Figures 3.2 and 3.3 there is no reason to suspect that either generic forms or the physical solu- tions will endure into the future. They will evolve and develop to meet new design needs and resource conditions.
22 Analysis Analysis Other general forms and current practice Buildings using skeletal frames and long-span roofs show a greater variety of both generic elemental types and physical construction solu- tions. To try to catalogue them here is not appropriate. However, a few examples serve to introduce these forms as both generic and phys- ical entities. The skeletal frame structure has beams, columns, slabs and some means of ensuring overall stability. This basic format can be repeated to generate large buildings both on plan and in height. These structures will, however, need internal structural columns or walls, thus imposing some limits on clear internal space. Where this structural form has no current rivals is in its ability to achieve great heights with relatively open internal spaces. The physical constructed form is generated in either steel or reinforced concrete. The reinforced concrete can be either precast or in situ. These materials can then be mixed between the elements. Most steel solutions have steel beams and columns but concrete floors and either concrete or steel wind-stability provision. Reinforced concrete structures nor- mally have reinforced concrete members throughout, but the development of flat slabs as spanning structures has eliminated the need for beams. Long-span roof structures are used for indus- trial, retail, storage, exhibition, sports venues and other activities that need large floor space under the roof. They are normally only single- storey, although they may require considerable internal clear height. Some buildings used for these purposes are not large, and so although termed long span because of their potential the generic forms may be used for buildings of modest scale. Long-span roofs have perhaps the greatest variety of generic elemental forms to be developed into construction forms. Both plane and three-dimensional structures in flat and curved forms have been developed in steel and reinforced concrete and even timber and aluminium. Both skeletal and long-span structures have to be enclosed. The enclosing fabric can nor- mally be supported and restrained by the struc- ture and there is a wide range of options for the external walling. Again, generic forms such as cladding or facings can be identified, with con- structed solution in materials such as metal, concrete, glass or brickwork being chosen for the specific building. The different structural forms tend to use different enclosure solutions. In long-span structures the building often requires less openings, and reducing the weight of the fabric allows economic gains to be made in the structure. This leads to sheet cladding in metals with heavier forms such as brickwork used only around the building at ground level, where it can be supported directly on the ground. In the multi-storey skeletal form the interaction of the enclosure and the structure plus the need for performance often lead to more complex construction. Building services To illustrate the idea of the general form and the specific solution, descriptions have been given for the construction of the structure and enclo- sure elements. Buildings also include a group of technologies collectively known as building services. It is not the intention of this chapter to introduce their general forms and possible solu- tions. This is not because they are any less sig- nificant in supporting the everyday use of the building and the well-being of the occupants. Each building will have to be resolved with a mix of structure, enclosure and service systems to meet the performance expectations of the building. Hopefully in this chapter the point about general and specific forms has been made with the examples of structure and enclosure. The general forms and possible solutions for services will be introduced in later chapters in the book. Uncertainty and risk Where change is slow, there is the opportunity for current detailed solutions to be adopted
Common Forms – Specific Solutions 23 Analysis with little modification from one similar build- ing to another. There is always danger in assum- ing two building to be the same, but if the general form is robust and not being applied close to a failure cusp the solution can be sug- gested in detail without much analysis, with little risk. As the pace of change increases, initial choice may deviate from currently detailed and even generic forms. The initial suggestion becomes based on an understanding of generic forms that then need to be thought through in detail. Initially this may only need some alterations in materials or detailing, but as demands become more divergent from common practice then alternative elemental generic forms in new combinations may be more appropriate. In making any technological choice it is important to be aware of the uncertainty and risk in adopting a particular solution. The technical risk is one of failure in perform- ance. As with any risk it must be weighed against the consequences. Consequences that lead to loss of life always require careful atten- tion. Where the consequence is interruptions in the operation of the building, the severity of the loss will have to be evaluated against the risk of failure. Whatever the pace of change, the choice of construction is based on an understanding of the action of the generic form and the performance of the detailed design and availa- bility of resources to construct the specific solution. Summary 1. Elements and components have a limited range of conceptual generic forms based on their action in achieving performance. 2. Detailed construction solutions have to be chosen for specific design and resource conditions and are therefore ultimately specific to an individual building, although the building may be repeated and one detail may work in more than one building. 3. Within each society a range of common building forms and economic construction solutions arise which normally form the basis for choice for subsequent construction solutions. 4. Particularly in times of change, the process of choice has to include analysis that recognises the uncertainties and risks for each individual building in both failing to achieve design performance and acknowledging the reality of available resources.
4 Construction Variables This chapter explores the variables that define construction: materials, shape, size and spatial rela- tionships. It introduces the reality of deviations in assessing whether the components will fit together and perform. The chapter concludes with a section on the specific aspects of jointing and fixing as the process by which the parts of the building can contribute to the behaviour of the whole. The variables of construction – the outcome of choice It is important to recognise at the start what aspects of the physical construction can be varied in order to achieve the desired perform- ance of the building. Identifying what can be varied also identifies what has to be chosen and specified if an unambiguous solution is to be defined. Choices have to be made for the materials to be formed into components that have a defined shape and size. Each component has then to be given a spatial relationship with other compo- nents together with the joints and fixings neces- sary for them to act as a whole building. This simple identification of the variables is repre- sented in Figure 4.1. Defining the final physical arrangements of the construction involves a specification for each of the component parts of the building, including any joints and fixings, detailed in assemblies of components to create the final building. This specification will have to include: • The material of which components are to be made and the quality of that material • The shape into which the material has to be formed • The size of each component, giving dimen- sions sufficient to define the shape • The relationship of each part either to an absolute position defined by a reference framework or relative to another part of the construction or the surrounding environ- ment This specification determines the space that the components and their joints will occupy. It may be in competition for this space with other parts of the construction and/or the usable space of the building itself. The choice of construction cannot be confirmed until this has been checked and it has been established that there is a unique space for each part of the building. Joints and fixings also need to be identified by their component parts, their material, shape and size and spatial relationships, as they them- selves are part of the assembly. These assem- blies are then connected (where they are often identified as junctions) into the whole building. Any components associated with junctions also have to be specified. The process of choice is about defining the components, their materials, shape and size and their spatial relationships, including the joints and fixings necessary to complete the building. The focus of technological knowledge is taking decisions about these variables to create a build- ing that is safe and has utility. This is a technical choice that has to be made following the crea- tion of a design concept and coming before the management of the production process. Yet it is a choice that has to be made in the full knowl- edge of the design requirements and the avail- able production resources.
Construction Variables 25 Analysis Figure 4.1 Variables or outcome of choice. spatial arrangement size shape joints fixings Components Assemblies Buildings materials Choosing materials Specifying materials is a process of matching the properties of the materials to the perform- ance requirements. This is not, however, inde- pendent of size and shape, for all materials have all properties to some degree or another. We only choose to exploit certain properties when their value is such that, in economic quantities and at sizes and shapes that can be produced, transported and fitted within the space availa- ble, they will perform at the required level. Buildings are perhaps the largest manufac- tured items widely used throughout all socie- ties in the world. They demand relatively high quantities of materials at reasonable cost and it is, therefore, not surprising that, historically, materials used for everyday buildings are those with high bulk, locally available and with limited process costs. Increasing economic wealth and its attendant higher levels of infra- structure allow the use of materials requiring greater processing off site and less need to rely on local materials. With economic development comes the possibility for transfer of production activity to factories remote from the site, which in turn gives opportunities to use a wider range of materials than a wholly site-based process. The materials that have been dominant in building in the past are timber and stone, with lime, limited amounts of iron for fixings, lead and glass. Fired clay for bricks and tiles has been used for some time in the UK, but up to just before the turn of the nineteenth century these would have been only used locally, par- ticularly in the conurbations where there was a sufficiently large market close to the kiln site. In rural areas such as Devon, soil was still being used for agricultural cottages up to the end of the nineteenth century. Perhaps the two materials that have made the greatest impact on the size and scale of eve- ryday building have been steel and concrete. The superior strength properties have allowed greater loads to be carried on smaller sections but in particular have introduced the possibility of smaller, efficient spanning members such as beams. This opened the way to large, com- paratively voluminous building to a wider group of building clients. In the last half of the twentieth century there was an increasing number of materials introduced into buildings. More metals such as copper and aluminium now are used, particularly in services. Plastic has made a considerable impact but only where its relatively high cost can be justified by thin- sectioned components. Processing and manu- facturing developments have offered some old materials new opportunities, with techniques such as laminating timbers. As well as increasing the range of materials, developments have been made that offer more grades with greater quality control of the more traditional materials, allowing even finer choices to match performance with cost. All this demands increasing knowledge. Evaluating the more recently formulated materials is more dif- ficult for many have not yet stood the test of time. More materials introduce more possibili- ties for incompatibility so even well-tried and tested materials may fail in new combinations. Adverse reactions between materials and between materials and the environment may threaten durability in ways that have to be imagined before an analysis can be undertaken. In imagining failures it is possible to argue that all failures are ultimately materials failures.
26 Analysis Analysis It is also possible to argue that the failure of the material is always the consequence of a previ- ous sequence of events and therefore never the direct fault of the material. The usefulness of this argument possibly lies in accepting that both are true. In considering the behaviour of the material, it is necessary to identify the sig- nificant events in the life of a component when a coincidence of conditions may lead to failure. The events that lead to failure will determine which properties of the material will become critical. Significant events may well be during manufacture, assembly or during the life of the building. Understanding the production process as well as the behaviour of the finished building is vital, for the most demanding event in the life of a component may well be in storage, han- dling or as part of a partially erected building. An example of this is a precast, reinforced con- crete pile where transporting and in particular driving induce entirely different stresses in the materials than when it is under load as a foundation. Materials – health, safety and the environment While it is the properties of a material that may identify it for use in a building, there are reasons why it may not be preferred or even excluded from the ultimate choice. Cost and the availabil- ity of local manufacturing techniques have already been introduced, but aspects of health, safety and the environment also have to be considered. There are many reasons why a material may be hazardous to health, particularly during the manufacturing and assembly processes, and these will be discussed in more detail in Chapter 13 in the section on health and safety. However, materials have also to be evaluated against their impact on the environment and their contribution to sustainable development. Society is reassessing its relationship with the natural environment and the demands and stresses we place on it. Much of the concern is associated with our development as a techno- logical society. This new thinking is bound to play a major part in the future in the way we build buildings. Such concerns as energy use, biodiversity, waste and pollution can be directly affected by our choice of building materials. In assessing a material for its environmental impact it is necessary to trace its entire history, often known as cradle-to-grave analysis. We can only use the materials provided by nature. Any material that finishes up in a building will have been part of an ecosystem that will be altered by the removal of the resource we require to make and shape our components. In many cases the effect will be local and nature will have the capacity to restore the balance in a short amount of time. However, as the volume of development increases and infrastructure becomes available to exploit resources on a large scale, the restorative powers of nature may be severely tested. The impact becomes more than local to the extent that the exploita- tion of the earth’s resources begins to have global implications. This is the fear at the beginning of the twenty-first century. Concerns associated with resource depletion, loss of biodiversity and global warming are all affected by decisions to use certain materials in buildings. This is not just in the extraction of materials but also in their transport, for the business of building materials is now part of global trade. There may be a preference for a renewable resource if this can be identified. Processing and manufacture use energy and produce waste and pollution. In an attempt to compare the impact of producing materials we use the idea of embodied energy or embodied carbon. It is the sum of the energy or carbon used to extract and process materials normally calculated up to the delivery to the site gate. Where components are delivered to site, the energy or carbon used in manufacture may vary even if they are made of the same material. This is discussed in more detail in Chapter 15. Assessment of embodied energy or carbon allows not only comparisons between materials but also the evaluation of using recycled mate- rial where process energy may be less than that of the original conversion. Waste and pollution
Construction Variables 27 Analysis also pose a major problem in that returning the by-products of processing to nature may place a burden on the environment it is not capable of dealing with. Disposal strategies are a major concern in evaluating the environmental impact of the choice of materials. Disposal is of concern not only at the stage of manufacture and assembly but also at the end of the life of the building itself. Specifying materials where the recycling opportunities are limited and the disposal and pollution costs may be high will have to be another part of the analysis of the environmental impact of the choice of construction. Choosing shape The shaping of components can bring great ben- efits in terms of performance. It can give strength by corrugating comparatively thin materials and can provide ornament and finish to satisfy appearance requirements. It has a particular role to play at joints and at points of fixing, where shaping such as grooves and rebates can be the major contribution to achieving function. Shaping is, however, dependent on manufac- turing processes that require skills, tools and machinery. This adds cost to the component that has to be justified by its utility or a saving in material. It is also dependent on the material chosen, not only for its ability to be worked with current process skills and technology but also for its ability to be worked to fine enough devia- tions (precision) to achieve the allowable toler- ances required for performance. Early construction methods exhibit the char- acteristic of minimal working or shaping of the raw materials. Exploiting shape comes with increased resources where skills and manufac- turing technique become available. Shaping is achieved either by forming the shape directly from a formless material or by working from simple shapes available from the natural form of the raw material. In some cases these are combined where a crude shape is formed and then refined by removing material to work towards the final form. Shaping has to be related to an appropriate manufacturing process. Techniques such as casting, rolling or extruding can shape a form- less material such as concrete, clay or hot metal. Cutting or machining can then reduce materials to refine or modify the shape. Parts can be added by fixing additional pieces to make complex shapes from simpler forms. Simple forms can also be bent, pressed, beaten or forged into more complex shapes. These processes introduce a range of materials properties associ- ated with workability. They may make a mate- rial with all the properties for performance unusable or at least too expensive to use. Many of these processes are essentially factory based; the range of methods that can be undertaken on site is still limited in most cases by individual skill and tools, leaving pouring, cutting and attaching with some bending as the predominant shaping processes. Choosing shape and appreciating its per- formance value and production cost is a major consideration in technological choice. It has par- ticular significance in the issues of deviations and fit, to be discussed later in this chapter. Where parts with complex shapes have to fit together, there will be particular demands on accuracy that limit the ability of the assembly to accommodate distortions. Hence, while shaping of individual components leads to many oppor- tunities in jointing and fixing, this must be con- sidered carefully in terms of the components’ relationship to the assembly of which they form a part. Choosing size So far it has been established that the level of performance required from the construction leads to the initial choice of material based on a match between the function and a property that can be exploited economically. It has also been established that, for each material, certain proc- esses such as cutting or shaping may be avail- able to make best use of the material and facilitate assemblies that function as whole ele- ments of the building. It is now necessary to
28 Analysis Analysis establish dimensions sufficient to define the shape, allow manufacture and ensure assembly. In the process of choice it may be that there is a limit to the size of the component that will determine the choice of material and/or the shape. This limit may be associated with the need to fit together with other components or there may be manufacturing/handling limita- tions. It may be that visually the size of the component confounds the design vision. It is helpful to see the establishing of dimen- sions in three phases working towards a manu- facturing or working specification: • Gross size – based on performance • Coordinated size – based on incorporation with other components • Working size – based on jointing, fixing, deviations and movement The gross size will be determined by perform- ance. It represents a minimum size for water- proof materials to keep out the rain or for structural elements to support the loads. It will, therefore, identify the scale and proportion to the solution and may even show at an early stage that a solution is not possible with that material with the chosen shaping in the space available for the construction itself. If the gross size appears to be sensible to achieve performance economically and within the space available, it is then necessary to look at the dimensions in terms of the detail and how the parts of the construction will go together. This is common, for instance, where the major component is incorporated into brick or block- work. This is illustrated in Figure 4.2 for the sizing of the depth of a concrete lintel over an opening in brickwork. Structural calculations may show that the lintel only has to be 125mm deep. However, the co-ordinating depth of a brick course is 75mm (65mm for the brick and 10mm for the joint), so the lintel would have to have a coordinated size of 150mm. Establishing coordinating sizes becomes particularly significant in more industrialised and prefabricated buildings that are often Figure 4.2 Sizing depth of lintel. Working depth 140 ± 2 mm Span Load Lintel Structural depth 125 mm (a) Gross depth based on strength performance (b) Co-ordinated depth based on brick courses (c) Working depth based on joints and deviations Lintel 75 mm brick courses Co-ordinated depth 150 mm Lintel 10 mm mortar joint
Construction Variables 29 Analysis designed within a dimensional discipline around a module, leading to a basic or modular size being established. The most common module is likely to be 300mm. When selecting factory-made components available from man- ufacturers’ catalogues, the economics of pro- duction means that they are often only available in a limited number of sizes. Although these will be based on a module most likely to max- imise their potential for integration with other components, they do limit the choice without incurring additional cost. The coordinating size does not take into account: • The need for space for joints and fixings • Allowance for deviations and movement These have to be considered together, as in many cases the joints will have to allow for the deviations and movement, and the fixings will have to accommodate both deviations and movements if the assembly is to fit together on site and maintain its integrity in operation. Consideration of these aspects will lead to a working or manufacturing size. Joints are a necessary part of the assembly process to ensure fit in that they can take up deviations in components. Fixings are required to hold assemblies together and these also take up space. Sometimes the joint is also the fixing. The material of the joint and the fixings dictates their own dimensions (with its own deviations). If the fixing is in addition to the joint and this cannot be accommodated completely within the component or in the joint, space has to be pro- vided for the fixing itself. This will have to include any access required to complete the fixing on site. In some cases thought has to be given to the space necessary to remove the fixing for repair or maintenance. In the example of the lintel the joints in the brickwork are 10mm. This will be a mortar joint that will allow for deviations in the brick. It is now possible to establish the working size for the lintel at 140mm. For a full specification of the depth it is necessary to be clear that in the manufacture of the lintel any deviation from the 140mm will have to be limited as these also have to be accommodated in the 10mm mortar joint. Figure 4.2 suggests an allowable deviation or tolerance of ±2mm. It is now necessary to ensure that the material can be manufactured or worked within these deviations or there is a risk that the lintel will not fit with the brickwork. Working sizes also have to take into account any allowance for dimensional changes that may take place during the life of the compo- nent. These are known as movements or inher- ent deviations, as they are inherent in the materials chosen, and these are discussed in more detail in Chapter 12. Dimensional deviation and fit When establishing a working size and thinking about how assemblies might fit together, it is necessary to think about three things: • The size of the space into which the compo- nent has to fit • The size of the component and its position in the space • The gap that will be formed between compo- nents for the joint/fixings Generally a component can be said to fit if it can be positioned within the space so that the gaps allow for effective fixing and jointing. During construction, all of these – the space, the component and its position and the gap – will vary: they will all need to have tolerances established. In what is often thought of as traditional con- struction, trade processes control fit. Procedures such as building in and cut to fit allow for dimensions to be set by the construction itself as the work proceeds. It requires judgement as to how much reduction should be made for fixings, jointing materials, gaps or movements, but these are part of the craft tradition. It is not a question of analysis but one of common prac- tice. One person can take all the deviations into account at one point in the assembly procedure in one judgement. With the use of components and the develop- ment of prefabricated construction, building in and cutting to fit is no longer an option. There
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hundred piastres. She was soon able to purchase a better house, where she not only gave the man more nourishing food, but sent for a teacher to instruct him how to read and write. He had so improved in appearance by this time, and had profited so well by the wise conversation of Zubeydeh, that he was quite like another person, and those who had known him in his poverty no longer recognized him. For this reason, the Caliph, who soon repented of his anger towards Zubeydeh and made every effort to recover her, was unable to find any trace of him. Mesrour sought day and night through the streets of Baghdad, but as Zubeydeh never left the wood-cutter’s house, all his search was in vain, and the Caliph was like one distracted. “One day, as the wood-cutter was on his way to the forest, he was met by three persons, who desired to hire his asses for the day. ‘But,’ said he, ‘I make my living from the wood which the asses carry to the city.’ ‘What profit do you make upon each load?’ asked one of the men. ‘If it is a good load, I often make fifty piastres,’ answered the wood-cutter. ‘Well,’ said the men, ‘we will give you two hundred piastres as the hire of each ass, for one day.’ The wood-cutter, who had not expected such an extraordinary offer, was about to accept it at once, when he reflected that he had obeyed in all things the advice of Zubeydeh, and ought not to take such a step without her consent. He thereupon requested the men to wait while he returned home and consulted his wife. ‘You have done right, O my lord!’ said Zubeydeh: ‘I commend your prudence, and am quite willing that you should accept the offer of the men, as the money will purchase other asses and repay you for the loss of the day’s profit, if the persons should not return.’ “Now the three men were three celebrated robbers, who had amassed a vast treasure, which they kept concealed in a cave in one of the neighboring mountains. They hired the donkeys in order to transport this treasure to a barque in which they had taken passage to Bassora, where they intended to establish themselves as rich foreign merchants. But Allah, who governs all things, allows the plans of the wicked to prosper for a time, only that he may throw
them into more utter ruin at the last. The robbers went to their secret cave with the donkeys and loaded them with all their spoils— great sacks of gold, of rubies, diamonds and emeralds, which the beasts were scarcely strong enough to carry. On their way to the river below Baghdad, where the boat was waiting for them, two of them stopped to drink at a well, while the other went on with the asses. Said one of the twain to the other: “Let us kill our comrade, that we may have the greater treasure.” He at once agreed, and they had no sooner overtaken the third robber, than the first, with one stroke of his sabre, made his head fly from his body. The two then proceeded together for a short distance, when the murderer said: ‘I must have more than half of the treasure, because I killed our comrade.’ ‘If you begin by claiming more than half, you will in the end claim the whole,’ said the other robber, who refused to agree. They presently set upon each other with their swords, and after fighting for some time, both of them received so many wounds that they fell dead in the road. “The asses, finding that no one was driving them any longer, took, from habit, the road to the wood-cutter’s house, where they arrived safely, with the treasure upon their backs. Great was the amazement of their master, who, at Zubeydeh’s command, carried the heavy sacks into the house. But when he had opened one of them, and the splendor of the jewels filled the whole room, Zubeydeh exclaimed: ‘God is great! Now, indeed, I see that my conduct is acceptable to Him, and that His hand hurries my design more swiftly to its completion.’ But, as she knew not what had happened to the robbers, and supposed that the owner of the treasure would have his loss proclaimed in the bazaars, she determined to keep the sacks closed for the space of a moon, after which, according to the law, they would become her property, if they had not been claimed in the mean time. Of course, no proclamation of the loss was made, and at the end of the moon, she considered that she had a just right to the treasure, which, upon computation proved to be even greater than that of the Caliph Haroun Al-Raschid.
“She commanded the wood-cutter to send her at once the most renowned architect of Baghdad, whom she directed to build, exactly opposite to the Caliph’s Palace, another palace which should surpass in splendor any thing that had ever been beheld. For the purchase of the materials and the hire of the workmen, she gave him a hundred thousand pieces of gold. ‘If men ask,’ said she, ‘for whom you are building the palace, tell them it is for the son of a foreign king.’ The architect employed all the workmen in Baghdad, and followed her instructions so well, that in two months the palace was finished. The like of it had never been seen, and the Caliph’s palace faded before its magnificence as the face of the moon fades when the sun has risen above the horizon. The walls were of marble, white as snow; the gates of ivory, inlaid with pearl; the domes were gilded, so that when the sun shone, the eye could not look upon them; and from a great fountain of silver, in the court-yard, a jet of rose-colored water, which diffused an agreeable odor, leaped into air. Of this palace it might be said, in the words of the poet: ‘Truly it resembles Paradise; or is it the lost House of Irem, built from the treasures of King Sheddad? May kindness dwell upon the lips of the lord of this palace, and charity find refuge in his heart, that he be adjudged worthy to enjoy such splendor!’ “During the building of the palace, Zubeydeh employed the best masters in teaching the wood-cutter all the accomplishments which his present condition required that he should possess. In a short time he was a very pattern of elegance in his manner; his words were choice and spoken with dignity and propriety, and his demeanor was that of one born to command rather than to obey. When she had succeeded to the full extent of her wishes, she commenced teaching him to play chess, and spent several hours a day in this manner, until he finally played with a skill equal to her own. By this time, the palace was completed, and after having purchased horses and slaves, and every thing necessary to the maintenance of a princely household, Zubeydeh and the wood-cutter took possession of it during the night, in order that they might not be observed by the Caliph. Zubeydeh bade the wood-cutter
remember the promise he had made her. She still retained her own apartments, with a number of female slaves to attend her, and she now presented to him, as a harem becoming a prince, twenty Circassian girls, each one fairer than the morning-star. “The next morning she called the wood-cutter, and addressed him thus: ‘You see, my lord! what I have done for you. You remember in what misery I found you, and how, by your following my advice, every thing was changed. I intend to exalt you still higher, and in order that my plans may not be frustrated, I now ask you to promise that you will obey me in all things, for a month from this time.’ Zubeydeh made this demand, for she knew how quickly a change of fortune may change a man’s character, and how he will soon come to look upon that as a right which Allah granted him as a boon. But the wood-cutter threw himself at her feet, and said: ‘O Queen! it is for you to command, and it is for me to obey. You have taught me understanding and wisdom; you have given me the wealth of kings. May Allah forget me, if I forget to give you, in return, gratitude and obedience.’ ‘Go, then,’ continued Zubeydeh, ‘mount this horse, and attended by twenty slaves on horseback, visit the coffee-house in the great bazaar. Take with thee a purse of three thousand pieces of gold, and as thou goest on thy way, scatter a handful occasionally among the beggars. Take thy seat in the coffee-house, where thou wilt see the Vizier’s son, who is a skilful player of chess. He will challenge the multitude to play with him, and when no one accepts, do thou engage him for a thousand pieces of gold. Thou wilt win; but pay him the thousand pieces as if thou hadst lost, give two hundred pieces to the master of the coffee-house, divide two hundred pieces among the attendants, and scatter the remainder among the beggars.’ “The wood-cutter performed all that Zubeydeh commanded. He accepted the challenge of the Vizier’s son, won the game, yet paid him a thousand pieces of gold as if he had lost, and then rode back to the palace, followed by the acclamations of the multitude, who were loud in their praises of his beauty, the elegance of his speech, his unbounded munificence, and the splendor of his attendance.
Every day he visited the coffee-house, gave two hundred pieces of gold to the master, two hundred to the servants, and distributed six hundred among the beggars. But the Vizier’s son, overcome with chagrin at his defeat, remained at home, where, in a few days, he sickened and died. These things coming to the Vizier’s ear, he felt a great desire to see the foreign prince, whose wealth and generosity were the talk of all Baghdad; and as he believed himself to be the greatest chess-player in the world, he determined to challenge him to a game. He thereupon visited the coffee-house, where he had not remained long when the wood-cutter made his appearance, in even greater splendor than before. This was in accordance with the instructions of Zubeydeh, who was informed of all that had taken place. He at once accepted the Vizier’s challenge to play, for a stake of two thousand pieces of gold. After a hard-fought battle, the Vizier was fairly beaten, but the wood-cutter paid him the two thousand pieces of gold, as if he had lost the game, gave away another thousand as usual, and retired to his palace. “The Vizier took his defeat so much to heart, that his chagrin, combined with grief for the loss of his son, carried him off in a few days. This circumstance brought the whole history to the ears of Haroun Al-Raschid himself, who was immediately seized with a strong desire to play chess with the foreign prince, not doubting but that, as he had always beaten his Vizier, he would be more than a match for the new antagonist. Accordingly he sent an officer to the palace of the wood-cutter, with a message that the Commander of the Faithful desired to offer his hospitality to the son of the foreign king. By Zubeydeh’s advice, the invitation was accepted, and the officer speedily returned to Haroun Al-Raschid, to whom he gave such a description of the magnificence of the new palace, that the Caliph’s mouth began to water, and he exclaimed: ‘By Allah! I must look to this. No man, who has not the ring of Solomon on his finger, shall surpass me in my own capital!’ In a short time the wood-cutter arrived, attired in such splendor that the day seemed brighter for his appearance, and attended by forty black slaves, in dresses of crimson silk, with turbans of white and gold, and golden swords by
their sides. They formed a double row from the court-yard to the throne-hall where the Caliph sat, and up the avenue thus formed the wood-cutter advanced, preceded by two slaves in dresses of cloth- of-silver, who placed at the Caliph’s feet two crystal goblets filled with rubies and emeralds of immense size. The Caliph, delighted with this superb present, rose, embraced the supposed prince, and seated him by his side. From the great wealth displayed by the wood-cutter, and the perfect grace and propriety of his manners, the Caliph suspected that he was no less a personage than the son of the King of Cathay. “After a handsome repast had been served, the Caliph proposed a game of chess, stating that he had heard much of the prince’s skill in playing. ‘After I shall have played with you, O Commander of the Faithful!’ said the wood-cutter, ‘you will hear no more of my skill.’ The Caliph was charmed with the modesty of this speech, and the compliment to himself, and they immediately began to play. The wood-cutter, although he might easily have beaten the Caliph, suffered the latter to win the first game, which put him into the best humor possible. But when the second game had been played, and the wood-cutter was the victor, he perceived that the Caliph’s face became dark, and his good-humor was gone. ‘You are too generous to your servant, O Caliph!’ said he; ‘had you not given me this success as an encouragement, I should have lost a second time.’ At these words Haroun smiled, and they played a third game, which the wood-cutter purposely allowed him to win. Such was the counsel given to him by Zubeydeh, who said: ‘If thou permittest him to win the first game, he will be so well pleased, that thou mayest venture to defeat him on the second game. Then, when he has won the third game, thy having been once victorious will magnify his opinion of his own skill; for where we never suffer defeat, we at last regard our conquests with indifference.’ “The result was precisely as Zubeydeh had predicted. The Caliph was charmed with the foreign prince, and in a few days made him his Vizier. The wood-cutter filled his exalted station with dignity and judgment, and became at once a great favorite with the people of
Baghdad. The month of obedience which he promised to Zubeydeh was now drawing to a close, when she said to him: ‘Cease to visit the Caliph, and do not leave thy palace for two or three days. When the Caliph sends for thee, return for answer that thou art ill.’ She foresaw that the Caliph would then come to see his Vizier, and gave the wood-cutter complete instructions, concerning what he should say and do. “Haroun Al-Raschid no sooner heard of the illness of his Vizier, than he went personally to his palace, to see him. He was amazed at the size and splendor of the edifice. ‘Truly,’ said he, striking his hands together, ‘this man hath found the ring of Solomon, which compels the assistance of the genii. In all my life I have never seen such a palace as this.’ He found the Vizier reclining on a couch of cloth-of- gold, in a chamber, the walls whereof were of mother-of-pearl, and the floor of ivory. There was a fountain of perfumed water in the centre, and beside it stood a jasmine-tree, growing in a vase of crystal. ‘How is this?’ said the Caliph, seating himself on one end of the couch; ‘a man whom the genii serve, should have the secrets of health in his hands.’ ‘It is no fever,’ said the Vizier; ‘but the other day as I was washing myself in the fountain, before the evening prayer, I stooped too near the jasmine tree, and one of its thorns scratched my left arm.’ ‘What!’ cried the Caliph, in amazement; ‘the scratch of a blunt jasmine-thorn has made you ill!’. ‘You wonder at it, no doubt, O Commander of the Faithful!’ said the Vizier; ‘because, only a few months ago, you saw that I was insensible to the fangs of a serpent, which had fastened upon my heel.’ ‘There is no God but God!’ exclaimed Haroun Al-Raschid, as by these words he recognized the poor wood-cutter, who had passed under the window of his palace —‘hast thou indeed found the ring of Solomon?—and where is the woman whom Mesrour, at my command, brought to thee?’ “‘She is here!’ said Zubeydeh, entering the door. She turned towards the Caliph, and slightly lifting her veil, showed him her face, more beautiful than ever. Haroun, with a cry of joy, was on the point of clasping her in his arms, when he stopped suddenly, and said: ‘But thou art now the wife of that man.’ ‘Not so, great Caliph!’
exclaimed the Vizier who rose to his feet, now that there was no longer any need to affect illness; ‘from the day that she entered my house, I have never seen her face. By the beard of the Prophet, she is not less pure than she is wise. It is she who has made me all that I am. Obedience to her was the seed from which the tree of my fortune has grown.’ Zubeydeh then knelt at the Caliph’s feet, and said: ‘O Commander of the Faithful, restore me to the light of your favor. I swear to you that I am not less your wife than when the cloud of your anger overshadowed me. This honorable man has never ceased to respect me. My thoughtless words led you to send me forth to take the place of the serpent, but I have now shown you that a wife may also be to her husband as the staff, whereon he leans for support; as the camel, which bringeth him riches; as the tent, which shelters and protects him; as the bath, which maketh him comely, and as the lamp, whereby his steps are enlightened.’ “Haroun Al-Raschid had long since bitterly repented of his rashness and cruelty. He now saw in what had happened, the hand of Allah, who had turned that which he had intended as a punishment, into a triumph. He restored Zubeydeh at once to his favor, and to the wood-cutter, whom he still retained as Vizier, he gave his eldest daughter in marriage. All the citizens of Baghdad took part in the festivities, which lasted two weeks, and the Caliph, to commemorate his gratitude, built a superb mosque, which is called the Mosque of the Restoration to this very day. The Vizier nobly requited all the pains which the Sultana Zubeydeh had taken with his education, and showed so much wisdom and justice in his administration of the laws, that the Caliph never had occasion to be dissatisfied with him. Thus they all lived together in the utmost happiness and concord, until they were each, in turn, visited by the Terminator of Delights and the Separator of Companions.” So ended Achmet’s story; but without the moonlight, the tall Ethiopian palms and the soothing pipe, as accessories, I fear that this reproduction of it retains little of the charm which I found in the original. It was followed by other and wilder tales, stamped in every part with the unmistakable signet of the Orient. They were all
characterized by the belief in an inevitable Destiny, which seems to be the informing soul of all Oriental literature. This belief affords every liberty to the poet and romancer, and the Arabic authors have not scrupled to make liberal use of it. There is no hazard in surrounding your hero with all sorts of real and imaginary dangers, or in heaping up obstacles in the path of his designs, when you know that his destiny obliges him to overcome them. He becomes, for the time, the impersonation of Fate, and circumstances yield before him. You see, plainly, that he was chosen, in the beginning, to do the very thing which he accomplishes, in the end. If a miracle is needed for his success, it is not withheld. Difficulties crowd upon him to the last, only that the final triumph may be more complete and striking. Yet with all these violations of probability, the Oriental tales exhibit a great fertility of invention and sparkle with touches of genuine human nature. The deep and absorbing interest with which the unlettered Arabs listen to their recital—the hold which they have upon the popular heart of the East—attests their value, as illustrations of Eastern life. From Poetry we frequently passed to Religion, and Achmet was astonished to find me familiar not only with Mohammed, but with Ali and Abdullah and Abu-talib, and with many incidents of the Prophet’s life, which were new to him. The Persian chronicles were fresh in my memory, and all the wonders related of Mohammed by that solemn old biographer, Mohammed Bekr, came up again as vividly as when I first read them. We compared notes, he repeated passages of the Koran, and so the Giaour and the True Believer discussed the nature of their faith, but always ended by passing beyond Prophet and Apostle, to the one great and good God, who is equally merciful to all men. I could sincerely adopt the first article of his faith: “La illah il’ Allah!” “There is no God but God,” while he was equally ready to accept the first commandment of mine.
CHAPTER XX. FROM SHENDY TO KHARTOUM. Arrival at Shendy—Appearance of the Town—Shendy in Former Days—We Touch at El Metemma—The Nile beyond Shendy—Flesh Diet vs. Vegetables—We Escape Shipwreck—A Walk on Shore—The Rapids of Derreira—Djebel Gerri—The Twelfth Cataract—Night in the Mountain Gorge—Crocodiles—A Drink of Mareesa—My Birth-Day—Fair Wind— Approach to Khartoum—The Junction of the Two Niles—Appearance of the City—We Drop Anchor. The morning after visiting the ruins of Meroë I reached the old Ethiopian town of Shendy. It lies about half a mile from the river, but the massive fort and palace of the Governor are built on the water’s edge. Several spreading sycamore trees gave a grace to the shore, which would otherwise have been dull and tame. Naked Ethiopians were fishing or washing their clothes in the water, and some of them, as they held their long, scarlet-edged mantles above their heads, to dry in the wind and sun, showed fine, muscular figures. The women had hideous faces, but symmetrical and well developed forms. A group of Egyptian soldiers watched us from the bank before the palace, and several personages on horseback, one of whom appeared to be the Governor himself, were hailing the ferry boat, which was just about putting off with a heavy load of natives. We ran the boat to the shore, at a landing-place just above the palace. The banks of the river were covered with fields of cucumbers and beans, the latter brilliant with white and purple blossoms and filled with the murmuring sound of bees. Achmet, the raïs and I walked up to the capital—the famous Shendy, once the great mart of trade for the regions between the Red Sea and Dar-Fūr. On the way we met numbers of women with water-jars. They wore no veils, but certainly needed them, for their faces were of a broad, semi-negro character, and repulsively plain. The town is built in a straggling
manner, along a low, sandy ridge, and is upwards of a mile in length, though it probably does not contain more than ten thousand inhabitants. The houses are mud, of course, but rough and filthy, and many of them are the same circular tokuls of mats and palm- sticks as I had already noticed in the smaller villages. The only decent dwelling which I saw had been just erected by a Dongolese merchant. There was a mosque, with a low mud minaret, but neither in this nor in any other respect did the place compare with El Mekheyref. The bazaar resembled a stable, having a passage through the centre, shaded with mats, and stalls on either side, some of which contained donkeys and others merchants. The goods displayed were principally blue and white cotton stuffs of coarse quality, beads, trinkets and the like. It was market-day, but the people had not yet assembled. A few screens of matting, erected on sticks, were the only preparations which had been made. The whole appearance of the place was that of poverty and desertion. Beyond the clusters of huts, and a mud wall, which ran along the eastern side of the town, the Desert extended to the horizon—a hot, white plain, dotted with clumps of thorns. On our return to the boat, the raïs pointed out the spot where, in 1822, Ismaïl Pasha and his soldiers were burned to death by Mek Nemr (King Leopard), the last monarch of Shendy. The bloody revenge taken by Mohammed Bey Defterdar (son-in-law of Mohammed Ali), for that act, sealed the fate of the kingdom. The seat of the Egyptian government in Soudân was fixed at Khartoum, which in a few years became also the centre of trade, and now flourishes at the expense of Shendy and El Metemma. Burckhardt, who visited Shendy during the reign of King Leopard, devotes much space to a description of the trade of the town at that time. It was then in the height of its prosperity, and the resort of merchants from Arabia, Abyssinia, Egypt, and even Syria and Asia Minor. It was also one of the chief slave-marts of Central Africa, in which respect it has since been superseded by Obeid, in Kordofan. The only commerce which has been left to Shendy is that with Djidda and the other Arabian ports, by way of Sowakin, on the Red
Sea—a caravan journey of fourteen days, through the country of Takka, infested by the wild tribes of the Hallengas and Hadendoas. Mek Nemr, according to Burckhardt, was of the Djaaleyn tribe, who are descendants of the Beni Koreish, of Yemen, and still retain the pure Arabian features. I was afterwards, during my stay in Khartoum, enabled to verify the declaration of the same traveller, that all the tribes of Ethiopia between the Nile and the Red Sea are of unmixed Arab stock. The palace of the Governor, which was a building of considerable extent, had heavy circular bastions, which were defended by cannon. Its position, on the bank of the Nile, was much more agreeable than that of the city, and the garrison had settled around it, forming a small village on its eastern side. The white walls and latticed windows of the palace reminded me of Cairo, and I anticipated a pleasant residence within its walls, on my return to Shendy. As I wished to reach Khartoum as soon as possible I did not call upon the Governor, but sent him the letter of recommendation from Yagheshir Bey. From Shendy, one sees the group of palms which serves as a landmark to El Metemma, the capital of a former Ethiopian Kingdom, further up the Nile, on its opposite bank. This is the starting point for caravans to Merawe and Dongola through the Beyooda Desert. We passed its port about noon, and stopped a few minutes to let the raïs pay his compliments to the owner of our vessel, who was on shore. He was a little old man, with a long staff, and dressed like the meanest Arab, although he was shekh of half a dozen villages, and had a servant leading a fine Dongolese horse behind him. The boat of Khalim Bey, agent of the Governor of Berber and Shendy, was at the landing place, and we saw the Bey, a tall, handsome Turk in a rich blue and crimson dress, who sent a servant to ask my name and character. The scenery of the Nile, southward from Shendy, is again changed. The tropical rains which fall occasionally at Abou-Hammed and scantily at Berber, are here periodical, and there is no longer the same striking contrast between desert and garden land. The plains extending inward from the river are covered with a growth of bushes
and coarse grass, which also appears in patches on the sides of the mountains. The inhabitants cultivate but a narrow strip of beans and dourra along the river, but own immense flocks of sheep and goats, which afford their principal sustenance. I noticed many fields of the grain called dookhn, of which they plant a larger quantity than of dourra. Mutton, however, is the Ethiopian’s greatest delicacy. Notwithstanding this is one of the warmest climates in the world, the people eat meat whenever they can get it, and greatly prefer it to vegetable food. The sailors and camel-drivers, whose principal food is dourra, are, notwithstanding a certain quality of endurance, as weak as children, when compared with an able-bodied European, and they universally attribute this weakness to their diet. This is a fact for the lank vegetarians to explain. My experience coincided with that of the Ethiopians, and I ascribed no small share of my personal health and strength, which the violent alternations of heat and cold during the journey had not shaken in the least, to the fact of my having fared sumptuously every day. After leaving Shendy, the Nile makes a bend to the west, and we went along slowly all the afternoon, with a side-wind. The shores were not so highly cultivated as those we had passed, and low hills of yellow sand began to show themselves on either hand. The villages were groups of mud tokuls, with high, conical roofs, and the negro type of face appeared much more frequently among the inhabitants—the result of amalgamation with slaves. We saw numbers of young crocodiles which my sailors delighted to frighten by shouting and throwing sticks at them, as they sunned themselves on the sand. Wild geese and ducks were abundant, and the quiet little coves along the shore were filled with their young brood. During the day a large hawk or vulture dashed down to within a yard of the deck in the attempt to snatch a piece of my black ram, which Beshir had just killed. The next morning we had a narrow escape from shipwreck. The wind blew strong from the north, as we reached a twist in the river, where our course for several miles lay to the north-west, obliging the men to take in sail and tow the vessel. They had reached the
turning-point and the sail was blowing loose, while two sailors lay out on the long, limber yard, trying to reef, when a violent gust pulled the rope out of the hands of the man on shore, and we were carried into the stream. The steersman put the helm hard up, and made for the point of an island which lay opposite, but the current was so strong that we could not reach it. It blew a gale, and the Nile was rough with waves. Between the island and the southern shore lay a cluster of sharp, black rocks, and for a few minutes we appeared to be driving directly upon them. The raïs and sailors, with many cries of “O Prophet! O Apostle!” gave themselves up to their fate; but the strength of the current saved us. Our bow just grazed the edge of the last rock, and we were blown across to the opposite shore, where we struck hard upon the sand and were obliged to remain two hours, until the wind abated. I was vexed and impatient at first, but remembering the effect of a pipe upon a similar occasion, I took one, and soon became calm enough to exclaim: “it is the will of Allah!” While the boat was making such slow headway, I went ashore and walked an hour or two among the fields of beans and dourra. The plains for several miles inland were covered with dry grass and thorn-trees, and only needed irrigation to bloom as a garden. The sun was warm, the bean-fields alive with bees, and the wind took a rich summer fragrance from the white and purple blossoms. Near one of the huts, I accosted a woman who was weeding among the dourra. She told me that her husband had deserted her and taken another wife, leaving her the charge of their two children. He had also taken her three cows and given them to his new wife, so that her only means of support was to gather the dry grass and sell it in the villages. I gave her a few piastres, which she received gratefully. In the afternoon we passed the main bend of the river, and were able to make use of the wind, which by this time was light. The sailor who had been left ashore during the gale overtook us, by walking a distance of eight or ten miles and swimming one of the smaller arms of the river. The western bank of the river now became broken and hilly, occasionally overhung by bluffs of gravelly soil, of a
dark red color. On the top of one of the hills there was a wall, which the raïs pointed out to me as kadeem (ancient), but it appeared too dilapidated to repay the trouble of a visit. On the following day, the scenery became remarkably wild and picturesque. After passing the village of Derreira, on the right bank, the Nile was studded with islands of various sizes, rising like hillocks from the water, and all covered with the most luxuriant vegetation. The mimosa, the acacia, the palm, the sycamore and the nebbuk flourished together in rank growth, with a profusion of smaller shrubs, and all were matted together with wild green creepers, which dropped their long streamers of pink and purple blossoms into the water. Reefs of black rock, over which the waves foamed impetuously, made the navigation intricate and dangerous. The banks of the river were high and steep, and covered with bushes and rank grass, above which the rustling blades of the dourra glittered in the sun. The country was thickly populated, and the inhabitants were mostly of the Shygheean tribe—from Dar Shygheea, the region between Dongola and Berber. The sakias were tended by Dinka slaves, as black as ebony, and with coarse, brutish faces. At one point on the eastern shore, opposite the island of Bendi, the natives had collected all their live stock, but for what purpose I could not learn. The shore was covered with hundreds of camels, donkeys, sheep, cows and goats, carefully kept in separate herds. After threading ten miles of those island bowers, we approached Djebel Gerri, which we had seen all day, ahead of us. The Nile, instead of turning westward around the flank of the mountain, as I had anticipated from the features of the landscape, made a sudden bend to the south, between a thick cluster of islands, and entered the hills. At this point there was a rapid, extending half-way across the river. The natives call it a shellàl (cataract), although it deserves the name no more than the cataracts of Assouan and Wadi-Halfa. Adopting the term, however, which has been sanctioned by long usage, this is the Twelfth Cataract of the Nile, and the last one which the traveller meets before reaching the mountains of Abyssinia. The
stream is very narrow, compressed between high hills of naked red sandstone rock. At sunset we were completely shut in the savage solitude, and there we seemed likely to remain, for the wind came from all quarters by turns, and jammed the vessel against the rocks more than once. The narrow terraces of soil on the sides of the mountains were covered with dense beds of long, dry grass, and as we lay moored to the rocks, I climbed up to one of these, in spite of the raïs’s warnings that I should fall in with lions and serpents. I lay down in the warm grass, and watched the shadows deepen in the black gorge, as the twilight died away. The zikzak or crocodile-bird twittered along the shore, and, after it became quite dark, the stillness was occasionally broken by the snort of a hippopotamus, as he thrust his huge head above water, or by the yell of a hyena prowling among the hills. Talk of the pleasure of reading a traveller’s adventures in strange lands! There is no pleasure equal to that of living them: neither the anticipation nor the memory of such a scene as I witnessed that evening, can approach the fascination of the reality. I was awakened after midnight by the motion of the vessel, and looking out of my shelter as I lay, could see that we were slowly gliding through the foldings of the stony mountains. The moon rode high and bright, over the top of a peak in front, and the sound of my prow, as it occasionally grated against the rocks, alone disturbed the stillness of the wild pass. Once the wind fell, and the men were obliged to make fast to a rock, but before morning we had emerged from the mountains and were moored to the bank, to await daylight for the passage of the last rapid. In the mouth of the pass lies an island, which rises into a remarkable conical peak, about seven hundred feet in height. It is called the Rowyàn (thirst assuaged), while a lofty summit of the range of Gerri bears the name of Djebel Attshàn (the Mountain of Thirst). The latter stands on a basis of arid sand, whence its name, but the Rowyàn is encircled by the arms of the Nile. In the Wady Beit-Naga, some three or four hours’ journey eastward from the river, are the ruined temples of Naga and Mesowuràt, described by
Hoskins. The date of their erection has been ascertained by Lepsius to be coeval with that of Meroë. We here saw many crocodiles, basking on the warm sand-banks. One group of five were enormous monsters, three of them being at least fifteen, and the other two twenty feet in length. They lazily dragged their long bodies into the water as we approached, but returned after we had passed. The zikzaks were hopping familiarly about them, on the sand, and I have no doubt that they do service to the crocodiles in the manner related by the Arabs. The river was still studded with islands—some mere fragments of rock covered with bushes, and some large level tracts, flourishing with rich fields of cotton and dourra. About noon, we passed a village on the eastern bank, and I sent Ali and Beshir ashore to procure supplies, for my ram was finished. Ali found only one fowl, which the people did not wish to sell, but, Turk-like, he took it forcibly and gave them the usual price. Beshir found some mareesa, a fermented drink made of dourra, and for two piastres procured two jars of it, holding two gallons each, which were brought down to the boat by a pair of sturdy Dinka women, whose beauty was almost a match for Bakhita. The mareesa had an agreeable flavor and very little intoxicating property. I noticed, however, that after Beshir had drunk nearly a gallon, he sang and danced rather more than usual, and had much to say of a sweetheart of his, who lived in El- Metemma, and who bore the charming name of Gammerò- Betahadjerò. Bakhita, after drinking an equal portion, complained to me bitterly of my white sheep, which had nibbed off the ends of the woolly twists adorning her head, but I comforted her by the present of half a piastre, for the purpose of buying mutton-fat. As the wind fell, at sunset, we reached a long slope of snowy sand, on the island of Aūssee. Achmet went to the huts of the inhabitants, where he was kindly received and furnished with milk. I walked for an hour up and down the beautiful beach, breathing the mild, cool evening air, heavy with delicious odors. The glassy Nile beside me reflected the last orange-red hues of sunset, and the evening star, burning with a white, sparry lustre, made a long track
of light across his breast. I remembered that it was my birth-day— the fourth time I had spent my natal anniversary in a foreign land. The first had been in Germany, the second in Italy, the third in Mexico, and now the last, in the wild heart of Africa. They were all pleasant, but this was the best of all. When I returned to the vessel, I found my carpet and cushions spread on the sand, and Ali waiting with my pipe. The evening entertainment commenced: I was listening to an Arabian tale, and watching the figures of the boatmen, grouped around a fire they had kindled in a field of dookhn, when the wind came up with a sudden gust and blew out the folds of my idle flag. Instantly the sand was kicked over the brands, the carpet taken up, all hands called on board, and we dashed away on the dark river with light hearts. I rose before sunrise the next morning, and found the wind unchanged. We were sailing between low shores covered with grain- fields, and a sandy island lay in front. The raïs no sooner saw me than he called my attention to the tops of some palm-trees that appeared on the horizon, probably six or eight miles distant. They grew in the gardens of Khartoum! We reached the point of the broad, level island that divides the waters of the two Niles, and could soon distinguish the single minaret and buildings of the city. A boat, coming down from the White Nile, passed us on the right, and another, bound for Khartoum, led us up the Blue Nile. The proper division between the two rivers is the point of land upon which Khartoum is built, but the channel separating it from the island opposite is very narrow, and the streams do not fully meet and mingle their waters till the island is passed. The city presented a picturesque—and to my eyes, accustomed to the mud huts of the Ethiopian villages—a really stately appearance, as we drew near. The line of buildings extended for more than a mile along the river, and many of the houses were embowered in gardens of palm, acacia, orange and tamarind trees. The Palace of the Pasha had a certain appearance of dignity, though its walls were only unburnt brick, and his hareem, a white, two-story building, looked cool and elegant amid the palms that shaded it. Egyptian soldiers, in
their awkward, half-Frank costume, were lounging on the bank before the Palace, and slaves of inky blackness, resplendent in white and red livery, were departing on donkeys on their various errands. The slope of the bank was broken at short intervals by water-mills, and files of men with skins, and women with huge earthen jars on their heads, passed up and down between the water’s edge and the openings of the narrow lanes leading between the gardens into the city. The boat of the Governor of Berber, rowed by twelve black slaves, put off from shore, and moved slowly down stream, against the north wind, as we drew up and moored the America below the garden of the Catholic Mission. It was the twelfth of January; I had made the journey from Assouan to Khartoum in twenty-six days, and from Cairo in fifty-seven.
CHAPTER XXI. LIFE IN KHARTOUM. The American Flag—A Rencontre—Search for a House—The Austrian Consular Agent—Description of his Residence—The Garden—The Menagerie—Barbaric Pomp and State—Picturesque Character of the Society of Khartoum—Foundation and Growth of the City—Its Appearance—The Population—Unhealthiness of the Climate— Assembly of Ethiopian Chieftains—Visit of Two Shekhs—Dinner and Fireworks. At the time of my arrival in Khartoum, there were not more than a dozen vessels in port, and the only one which would pass for respectable in Egypt was the Pasha’s dahabiyeh. I had but an open merchant-boat, yet my green tent and flag gave it quite a showy air, and I saw that it created some little sensation among the spectators. The people looked at the flag with astonishment, for the stars and stripes had never before been seen in Khartoum. At the earnest prayer of the raïs, who was afraid the boat would be forcibly impressed into the service of the Government, and was anxious to get back to his sick family in El Metemma, I left the flag flying until he was ready to leave. Old Bakhita, in her dumb, ignorant way, expressed great surprise and grief when she learned that Achmet and I were going to desert the vessel. She had an indefinite idea that we had become part and parcel of it, and would remain on board for the rest of our lives. I took Achmet and started immediately in search of a house, as in those lands a traveller who wishes to be respectable, must take a residence on arriving at a city, even if he only intends to stay two or three days. Over the mud walls on either side of the lane leading up from the water, I could look into wildernesses of orange, date, fig, and pomegranate trees, oleanders in bloom and trailing vines. We entered a tolerable street, cleanly swept, and soon came to a coffee-
house. Two or three persons were standing at the door, one of whom—a fat, contented-looking Turk—eyed Achmet sharply. The two looked at each other a moment in mutual doubt and astonishment, and then fell into each other’s arms. It was a Syrian merchant, whom Achmet had known in Cairo and Beyrout. “O master!” said he, his dark face radiant with delight, as he clasped the hand of the Syrian: “there never was such a lucky journey as this!” The merchant, who had been two years in Khartoum, accompanied us in our search. We went first to the residence of the shekh of the quarter, who was not at home. Two small boys, the sons of one of a detachment of Egyptian physicians, who had recently arrived, received me. They complained bitterly of Soudân, and longed to get back again to Cairo. We then went to the Governor of the city, but he was absent in Kordofan. Finally, in wandering about the streets, we met a certain Ali Effendi, who took us to a house which would be vacant the next day. It was a large mud palace, containing an outer and inner divan, two sleeping- rooms, a kitchen, store-rooms, apartments for servants, and an inclosed court-yard and stables, all of which were to be had at one hundred piastres a month—an exorbitant price, as I afterwards learned. Before engaging it, I decided to ask the advice of the Austrian Consular Agent, Dr. Reitz, for whom I had letters from the English and Austrian Consuls in Cairo. He received me with true German cordiality, and would hear of nothing else but that I should immediately take possession of an unoccupied room in his house. Accordingly the same day of my arrival beheld me installed in luxurious quarters, with one of the most brave, generous and independent of men as my associate. As the Consul’s residence was the type of a house of the best class in Khartoum, a description of it may give some idea of life in the place, under the most agreeable circumstances. The ground-plot was one hundred and thirty paces square, and surrounded by a high mud wall. Inside of this stood the dwelling, which was about half that length, and separated from it by a narrow garden and court- yard. Entering the court by the gate, a flight of steps conducted to
the divan, or reception-room, in the second story. From the open ante-chamber one might look to the south over the gray wastes of Sennaar, or, if the sun was near his setting, see a reach in the White Nile, flashing like the point of an Arab spear. The divan had a cushioned seat around three sides, and matting on the floor, and was really a handsome room, although its walls were mud, covered with a thin coating of lime, and its roof palm-logs overlaid with coarse matting, on which rested a layer of mud a foot thick. In the second story were also the Consular Office and a sleeping-room. The basement contained the kitchen, store-rooms, and servants’ rooms. The remainder of the house was only one story in height, and had a balcony looking on the garden, and completely embowered in flowering vines. The only rooms were the dining-hall, with cushioned divans on each side and a drapery of the Austrian colors at the end, and my apartment, which overlooked a small garden-court, wherein two large ostriches paced up and down, and a company of wild geese and wild swine made continual discord. The court at the entrance communicated with the stables, which contained the Consul’s horses—a white steed, of the pure Arabian-blood of Nedjid, and the red stallion appropriated to my use, which was sent by the King of Dar-Fūr to Lattif Pasha, and presented by him to the Consul. A hejin, or trained dromedary, of unusual size, stood in the court, and a tame lioness was tied to a stake in the corner. She was a beautiful and powerful beast, and I never passed her without taking her head between my knees, or stroking her tawny hide until she leaned against me like a cat and licked my hand. Passing through a side-door into the garden, we came upon a whole menagerie of animals. Under the long arbors, covered with luxuriant grape-vines, stood two surly hyenas, a wild ass from the mountains of the Atbara, and an Abyssinian mule. A tall marabout (a bird of the crane species, with a pouch-bill) stalked about the garden, occasionally bending a hinge in the middle of his long legs, and doubling them backwards, so that he used half of them for a seat. Adjoining the stable was a large sheep-yard, in which were gathered together gazelles, strange varieties of sheep and goats
from the countries of the White Nile, a virgin-crane, and a large antilopus leucoryx, from Kordofan, with curved horns four feet in length. My favorite, however, was the leopard, which was a most playful and affectionate creature except at meal-time. He was not more than half grown, and had all the wiles of an intelligent kitten, climbing his post and springing upon me, or creeping up slyly and seizing my ankle in his mouth. The garden, which was watered by a well and string of buckets turned by an ox, had a rich variety of fruit- trees. The grape season was just over, though I had a few of the last bunches; figs were ripening from day to day, oranges and lemons were in fruit and flower, bananas blooming for another crop, and the pomegranate and kiskteh, or custard-apple, hung heavy on the branches. There was also a plantation of date-trees and sugar-cane, and a great number of ornamental shrubs. In all these picturesque features of my residence in Khartoum, I fully realized that I had at last reached Central Africa. In our mode of life, also, there was a rich flavor of that barbaric pomp and state which one involuntarily associates with the name of Soudân. We arose at dawn, and at sunrise were in the saddle. Sometimes I mounted the red stallion, of the wild breed of Dar-Fūr, and sometimes one of the Consul’s tall and fleet dromedaries. Six dark attendants, in white and scarlet dresses, followed us on dromedaries and two grooms on foot ran before us, to clear a way through the streets. After passing through Khartoum, we frequently made long excursions up the banks of the two Niles, or out upon the boundless plain between them. In this way, I speedily became familiar with the city and its vicinity, and as, on our return, I always accompanied the Consul on all his visits to the various dignitaries, I had every opportunity of studying the peculiar life of the place, and gaining some idea of its governing principles. As the only city of Central Africa which has a regular communication with the Mediterranean (by which it occasionally receives a ray of light from the civilized world beyond), it has become a capital on a small scale, and its society is a curious compound of Christian, Turk and Barbarian. On the same day, I have had a whole sheep set before me, in the house
of an Ethiopian Princess, who wore a ring in her nose; taken coffee and sherbet with the Pasha; and drank tea, prepared in the true English style, in the parlor of a European. When to these remarkable contrasts is added the motley character of its native population, embracing representatives from almost every tribe between Dar-Fūr and the Red Sea, between Egypt and the Negro kingdoms of the White Nile, it will readily be seen how rich a field of observation Khartoum offers to the traveller. Nevertheless, those who reside there, almost without exception, bestow upon the city and country all possible maledictions. Considered as a place of residence, other questions come into play, and they are perhaps not far wrong. Khartoum is the most remarkable—I had almost said the only example of physical progress in Africa, in this century. Where, thirty years ago, there was not even a dwelling, unless it might be the miserable tokul, or straw hut of the Ethiopian Fellah, now stands a city of some thirty or forty thousand inhabitants, daily increasing in size and importance, and gradually drawing into its mart the commerce of the immense regions of Central Africa. Its foundation, I believe, is due to Ismaïl Pasha (son of Mohammed Ali), who, during his conquests of the kingdoms of Shendy and Sennaar, in the years 1821 and 1822, recognized the importance, in a military and commercial sense, of establishing a post at the confluence of the two Niles. Mohammed Bey Defterdar, who succeeded him, seconded the plan, and ere long it was determined to make Khartoum, on account of its central position, the capital of the Egyptian pashalik of Soudân. Standing at the mouth of the Blue Nile, which flows down from the gold and iron mountains of Abyssinia, and of the White Nile, the only avenue to a dozen Negro kingdoms, rich in ivory and gum, and being nearly equidistant from the conquered provinces of Sennaar, Kordofan, Shendy and Berber, it speedily outgrew the old Ethiopian cities, and drew to itself the greater part of their wealth and commercial activity. Now it is the metropolis of all the eastern part of Soudân, and the people speak of it in much the same style as the Egyptians speak of their beloved Cairo.
The town is larger, cleaner and better built than any of the cities of Upper Egypt, except perhaps Siout. It extends for about a mile along the bank of the Blue Nile, facing the north, and is three- quarters of a mile in its greatest breadth. The part next the river is mostly taken up with the gardens and dwellings of Beys and other government officers, and wealthy merchants. The gardens of the Pasha, of Moussa Bey, Musakar Bey and the Catholic Mission are all large and beautiful, and towards evening, when the north wind rises, shower the fragrance of their orange and mimosa blossoms over the whole town. The dwellings, which stand in them, cover a large space of ground, but are, for the most part, only one story in height, as the heavy summer rains would speedily beat down mud walls of greater height. The Pasha’s palace, which was built during the year previous to my visit, is of burnt brick, much of which was taken from the ancient Christian ruins of Abou-Haràss, on the Blue Nile. It is a quadrangular building, three hundred feet square, with a large open court in the centre. Its front formed one side of a square, which, when complete, will be surrounded by other offices of government. For Soudân, it is a building of some pretension, and the Pasha took great pride in exhibiting it. He told me that the Arab shekhs who visited him would not believe that it was the work of man alone. Allah must have helped him to raise such a wonderful structure. It has an inclosed arched corridor in front, in the Italian style, and a square tower over the entrance. At the time of my visit Abdallah Effendi was building a very handsome two-story house of burnt brick, and the Catholic priests intended erecting another, as soon as they should have established themselves permanently. Within a few months, large additions had been made to the bazaar, while the houses of the slaves, on the outskirts of the city, were constantly springing up like ant-hills. There is no plan whatever in the disposition of the buildings. Each man surrounds his property with a mud wall, regardless of its location with respect to others, and in going from one point to another, one is obliged to make the most perplexing zigzags. I rarely ventured far on foot, as I soon became bewildered in the labyrinth
of blank walls. When mounted on the Consul’s tallest dromedary, I looked down on the roofs of the native houses, and could take my bearings without difficulty. All the mysteries of the lower life of Khartoum were revealed to me, from such a lofty post. On each side I looked into pent yards where the miserable Arab and Negro families lazily basked in the sun during the day, or into the filthy nests where they crawled at night. The swarms of children which they bred in those dens sat naked in the dust, playing with vile yellow dogs, and sometimes a lean burden camel stood in the corner. The only furniture to be seen was a water-skin, a few pots and jars, a basket or two, and sometimes an angareb, or coarse wooden frame covered with a netting of ropes, and serving as seat and bed. Nearly half the population of the place are slaves, brought from the mountains above Fazogl, or from the land of the Dinkas, on the White Nile. One’s commiseration of these degraded races is almost overcome by his disgust with their appearance and habits, and I found even the waste plain that stretches towards Sennaar a relief after threading the lanes of the quarters where they live. Notwithstanding the nature of its population, Khartoum is kept commendably neat and clean. It will be a lucky day for Rome and Florence when their streets exhibit no more filth than those of this African city. The bazaars only are swept every morning, but the wind performs this office for the remainder of the streets. The soog, or market, is held in a free space, opening upon the inland plain, where the country people bring their sheep, fowls, camels, dourra, vegetables and other common products. The slaughtering of animals takes place every morning on the banks of the Blue Nile, east of the city, which is thus entirely free from the effluvia arising therefrom. Here the sheep, cows, goats and camels are killed, skinned and quartered in the open air, and it is no unusual thing to see thirty or forty butchers at work on as many different animals, each surrounded by an attendant group of vultures, hawks, cranes, crows and other carnivorous birds. They are never molested by the people, and we sometimes rode through thousands of them, which had so
gorged themselves that they scarcely took the trouble to move out of our way. The place labors under the disadvantage of being the most unhealthy part of one of the most unhealthy regions in the world. From the southern frontier of Nubia, where the tropical rains begin to fall, to the table-land of Abyssinia on the south, and as far up the White Nile as has yet been explored, Soudân is devastated by fevers of the most malignant character. The summers are fatal to at least one-half of the Turks, Egyptians and Europeans who make their residence there, and the natives themselves, though the mortality is not so great among them, rarely pass through the year without an attack of fever. I arrived during the most healthy part of the year, and yet of all the persons I saw, three-fourths were complaining of some derangement of the system. The military hospital, which I visited, was filled with cases of fever, dysentery and small-pox. I was in such good bodily condition from my journey through the Desert that I could scarcely conceive the sensation of sickness, and the generous diet and invigorating exercise I enjoyed secured me from all fear of an attack. Travellers are not agreed as to the cause of this mortality in Soudân. Some attribute it to the presence of infusoriæ in the water; yet we drank the pure, mountain-born flood of the Blue Nile, and filtered it beforehand. I am disposed to side with Russegger, who accounts for it entirely by the miasma arising from decayed vegetation, during the intense heats. The country around Khartoum is a dead level; the only mountain to be seen is the long ridge of Djebel Gerrari, twelve miles to the north. Behind the town, the White Nile curves to the east, and during the inundation his waters extend even to the suburbs, almost insulating the place. The unusual sickness of the winter of 1852 might be accounted for by the inundation of the previous summer, which was so much higher than ordinary that the people were obliged to erect dykes to keep the water out of the streets. The opposite bank of the river is considered more healthy; and in the town of Halfay, only ten miles distant, the average mortality is much less.
I was fortunate in reaching Khartoum at a very interesting period. All the principal shekhs of the different tribes between the Nile and the Red Sea were then collected there, and as Dr. Reitz was on friendly terms with all of them, I had the opportunity of making their acquaintance, and could have readily procured a safe-conduct through their territories, if I had been disposed to make explorations in that direction. During the summer there had been trouble in the neighborhood of Sennaar, and a general movement against the Egyptian rule was feared. In October and November, however, Moussa Bey made a campaign in the regions about and beyond the Atbara, and returned with the chief malcontents in chains. They were afterwards liberated, but had been retained in Khartoum until some disputed questions should be settled. On the night of my arrival, the Consul received a visit of ceremony from the two principal ones: Hamed, the chief shekh of the Bishàrees, and Owd-el-Kerim, son of the great shekh of the Shukorees, which inhabit the wide territory between the Atbara and the Blue Nile. They were accompanied by several attendants, and by Mohammed Kheyr, the commander of the Shygheean cavalry employed in the late expedition. The latter was a fierce-looking black in rich Turkish costume. Hamed was a man of middle size, black, but with straight features and a mild, serious expression of face. He was dressed in white, as well as his attendant whose bushy hair was twisted into countless strings and pierced with a new wooden skewer. The Shukoree shekh arrived last. We were seated on the divan, and all rose when he entered. He was a tall, powerful man, with large, jet-black eyes and a bold, fierce face. He wore a white turban and flowing robes of the same color, with a fringe and stripe of crimson around the border. The Consul advanced to the edge of the carpet to meet him, when the shekh opened his arms and the two fell upon each other’s necks. Coffee and pipes were then served, and water was brought for the washing preparatory to dinner. Hamed and the Shygheean captain washed only their hands, but the great Owd-el-Kerim washed his hands, face and feet, and occupied nearly a quarter of an hour at his
devotions, bowing his head many times to the earth and repeating the name of Allah with deep emphasis. We passed through the garden to the dining-room, where the shekhs were greatly amazed at seeing a table set in European style. They all failed in managing the knives and forks, except Owd-el-Kerim, who watched the Consul and myself, and did his part with dignity. Achmet had made a vermicelli soup, which they eyed very suspiciously, and did not venture to take more than a few mouthfuls. They no doubt went away with the full belief that the Franks devour worms. They were at a loss how to attack the roast mutton, until I carved it for them, but did such execution with their fingers among the stews and salads that the dishes were soon emptied. After they had again partaken of coffee and pipes in the divan, the Consul ordered two or three rockets, which had been left from his Christmas celebration, to be sent up in order to satisfy the curiosity of his guests, who had heard much of those wonderful fires, which had amazed all Khartoum, three weeks before. The shekhs and attendants were grouped on the balcony, when the first rocket-shot hissing into the air, drew its fiery curve through the darkness, and burst into a rain of yellow stars. “Wallah!” and “Mashallah!” were echoed from mouth to mouth, and the desert chiefs could scarcely contain themselves, from astonishment and delight. The second rocket went up quite near to us, and sooner than was expected. Hamed, the Bishàree shekh, was so startled that he threw both his arms around the Consul and held fast for dear life, and even the great Owd-el-Kerim drew a long breath and ejaculated, “God is great!” They then took their leave, deeply impressed with the knowledge and wisdom of the Franks.
CHAPTER XXII. VISITS IN KHARTOUM. Visit to the Catholic Mission—Dr. Knoblecher, the Apostolic Vicar—Moussa Bey—Visit to Lattif Pasha—Reception—The Pasha’s Palace—Lions—We Dine with the Pasha—Ceremonies upon the Occasion—Music—The Guests—The Franks in Khartoum—Dr. Péney—Visit to the Sultana Nasra—An Ethiopian Dinner—Character of the Sultana. On the day of my arrival, Dr. Reitz proposed a visit to Dr. Knoblecher, the Apostolic Vicar of the Catholic Missions in Central Africa, who had returned to Khartoum about twenty days previous. The Vicar’s name was already familiar to me, from the account of his voyage up the White Nile in 1850, which was published in the German journals during his visit to Europe, and it had been my design to propose joining his party, in case he had carried out his plan of making a second voyage in the winter of 1852. He ascended as far as lat. 4° north, or about sixty miles beyond the point reached by D’Arnaud and Werne, and therefore stands at the head of Nilotic explorers. Preceded by two attendants, we walked through the town to the Catholic Mission, a spacious one-story building in a large garden near the river. Entering a court, in the centre of which grew a tall tamarind tree, we were received by an Italian monk, in flowing robes, who conducted us into a second court, inclosed by the residence of the Vicar. Here we met two other priests, a German and a Hungarian, dressed in flowing Oriental garments. They ushered us into a large room, carpeted with matting, and with a comfortable divan around the sides. The windows looked into a garden, which was filled with orange, fig and banana trees, and fragrant with jasmine and mimosa blossoms. We had scarcely seated ourselves, when the monks rose and remained standing, while Dr. Knoblecher
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    Construction technology analysisand choice Second Edition Tony Bryan Digital Instant Download Author(s): Tony Bryan ISBN(s): 9781405158749, 1405158743 Edition: Second edition File Details: PDF, 6.52 MB Year: 2010 Language: english
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  • 9.
    Construction Technology Analysis andChoice Second Edition Tony Bryan University of the West of England A John Wiley & Sons, Ltd., Publication
  • 10.
    This edition firstpublished 2010 © 2005, 2010 Tony Bryan First published 2005 by Blackwell Publishing Ltd Second edition 2010 Blackwell Publishing was acquired by John Wiley & Sons in February 2007. Blackwell’s publishing programme has been merged with Wiley’s global Scientific, Technical, and Medical business to form Wiley-Blackwell. Registered office John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, United Kingdom Editorial offices 9600 Garsington Road, Oxford, OX4 2DQ, United Kingdom 350 Main Street, Malden, MA 02148-5020, USA For details of our global editorial offices, for customer services and for information about how to apply for permission to reuse the copyright material in this book please see our website at www.wiley.com/wiley-blackwell. The right of the author to be identified as the author of this work has been asserted in accordance with the Copyright, Designs and Patents Act 1988. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by the UK Copyright, Designs and Patents Act 1988, without the prior permission of the publisher. Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books. Designations used by companies to distinguish their products are often claimed as trademarks. All brand names and product names used in this book are trade names, service marks, trademarks or registered trademarks of their respective owners. The publisher is not associated with any product or vendor mentioned in this book. This publication is designed to provide accurate and authoritative information in regard to the subject matter covered. It is sold on the understanding that the publisher is not engaged in rendering professional services. If professional advice or other expert assistance is required, the services of a competent professional should be sought. Library of Congress Cataloging-in-Publication Data Bryan, Tony, 1947– Construction technology : analysis and choice / Tony Bryan. – 2nd ed. p. cm. Includes index. ISBN 978-1-4051-5874-9 (pbk. : alk. paper) 1. Building. I. Title. TH146.B82 2010 690′.837–dc22 2009038731 A catalogue record for this book is available from the British Library. Set in 10/12 pt Palatino by Toppan Best-set Premedia Limited Printed in Malaysia 1 2010
  • 11.
    Contents Preface ix 䊏 PART1 ANALYSIS 1 1 The Framework for Understanding 3 Process and knowledge 3 The initial suggestion 4 Carrying out the evaluation 4 Physical and social context 5 The basis of analysis 6 Knowledge needed for choice 7 Summary 8 2 Building Purpose and Performance 9 Activities, space and construction 9 Introduction to performance requirements 9 Environmental impact and sustainability 17 Summary 17 3 Common Forms – Specific Solutions 18 General and constructed forms 18 The emergence of general building forms 18 Uncertainty and risk 22 Summary 23 4 Construction Variables 24 The variables of construction – the outcome of choice 24 Choosing materials 25 Choosing shape 27 Choosing size 27 Spatial relationships 32 Joints and fixings 32 Summary 35 5 Defining Conditions 37 Physical and social conditions 37 Activity and construction-modifying environments 38 The dynamics of the system 38 Choice of interior elements of the building 42 Inside the construction itself 42 Summary 43 6 The Resource Base 44 Introduction 44 Materials – the primary resource 44 Knowledge and skill – the human resource 45 Production equipment – the technological resource 46 Money – the enabling resource 47 Summary 48 7 Design Concept 49 Linking design to construction choice – flows and transfers 49 Concept design – broad options 50 Physical performance and appearance – commodity, firmness and delight 50 Function of the whole, function of the parts 51 Summary 52 8 Appearance 53 Visualising attributes and response 53 Space and context 53 Physical space for the construction 55 The approach to analysis 56 Summary 56 9 Analysis of Physical Behaviour 57 Visualising conditions and response 57 Function and performance – a technical aim 57 Preventing failure – a technical objective 57 The role of observation and science in the analysis 58 The approach to analysis 59 Summary 59 10 Physical Behaviour Creating Environments 60 Aspects of environment 60 The building as a system 60 The dry environment 65 The warm environment 72 The light environment 78 The acoustic environment 82 The clean environment 86 The safe environment 88 The private environment 96 Summary 97
  • 12.
    vi Contents 11 PhysicalBehaviour Under Load 98 Forces, external and internal 98 Basic structural members 100 Curving (and folding) structural members 104 Structural connections 105 Grid members – pin-jointed frames 107 Building structures – wind stability 108 Stress–strain and the choice of material 110 Structural analysis and design 111 Movements and structural behaviour 112 Stresses in the ground 112 The major structural forms 114 Summary 117 12 Physical Behaviour Over Time 119 Reliability: renewal, maintenance, repair and disposal 119 Basis of analysis 120 Soiling and cleaning 120 Durability of materials 121 Movements in components 124 Ground movement, settlement and subsidence 127 Movement and detailing 128 Wear of components 129 Summary 129 13 Manufacture and Assembly 130 Realisation of performance 130 Visualising stages and sequence 130 Analysis of operations, methods and resources 133 Materials and labour 135 Production equipment 136 Production options 141 Knowledge and expertise for the analysis of the process 148 Summary 149 14 Cost 150 Cost and value 150 Cost and price 151 Cost and time frames 151 Cost and cost data 152 Summary 154 15 Sustainability – Social Concern 155 Two major forces 155 Sustainability 156 Established influences and new concerns 156 Responding to the sustainability agenda 158 Buildings as systems 161 Renewable energy sources 168 Water and waste 170 Materials choice and detailing 172 Planning and design concepts 173 Emerging technologies 173 Summary 174 䊏 PART 2 CHOICE – HOUSE CONSTRUCTION 177 16 Applying the Framework to Housing 179 The need for an integrated approach 179 The basis of the case study 180 Summary 182 17 Floors 183 Upper floors 183 General forms for upper floors 183 Timber-joisted upper floors 184 Ground floors 191 Suspended ground floors 192 Ground-supported slab floors 195 Services and other elements 197 Site influences on choice of ground floors 197 Production operations for ground floors 198 The final choice 199 Summary 199 18 Roofs 201 Pitch and span 201 Other functions 201 Pitched roofs 202 Flat roofs 218 Summary 219 19 Walls 221 Wall types by function 221 General forms 221 Walls in the case study 224 Masonry cavity external walls 224 Openings in the external wall 233 Doors and windows – the components in the openings 236 The panel frame option 238 Party (separating) walls 241 Partition walls 242 Summary 243 20 Foundations 244 Basic function 244 Site investigation 246
  • 13.
    Contents vii Foundation design247 The strip foundation 247 Foundations for poor surface conditions 250 Economics of foundations 254 Basements 254 Summary 254 21 Services 256 Introduction 256 Analysis of services systems 257 Hot and cold water 257 Heating systems 263 Drainage 267 Electrical systems 273 Summary 279 䊏 PART 3 CHOICE – COMMERCIAL CONSTRUCTION 281 22 Applying the Framework to Commercial Buildings 283 The story so far 283 The way forward 285 The technological mix 287 Summary 289 23 Common Forms and Emerging Technologies 290 Introduction 290 UK commercial building through the twentieth century 291 Summary 298 24 Interface Design 299 Introduction 299 The enclosure–services interface 300 The enclosure–structure interface 302 The structure–services interface 305 Summary 306 25 Structural Skeletal Frames 307 Materials development and structural options 307 Reinforced concrete – performance 315 In situ reinforced concrete frames – production 317 Precast concrete frames – production 329 Structural steel – performance 330 Structural steel – fabrication and construction 333 Structure choice and overall design 337 Summary 338 26 Roof Structures 340 Introduction 340 Variety of structural form 341 Broad options 342 Construction details 348 Summary 352 27 Loadbearing Structural Walls 353 Broad options 353 Multi-storey construction 354 Single-storey industrial construction 359 Summary 363 28 Structure Below Ground 364 Introduction 364 Foundation design 364 Foundation types 366 Soil improvement 372 Basements 373 Large area industrial concrete ground floors 380 Summary 384 29 External Enclosure to Structural Frames 385 Introduction 385 External walls 385 Cavity brickwork 390 Cladding panels 392 Curtain walling 396 Facing materials 397 Lightweight cladding 403 Structural glazing 404 Roof construction 406 Summary 411 30 Internal Enclosure 412 Performance 412 Applied finishes 413 Component systems 414 Summary 421 31 Services – Scope and Space 422 Introduction 422 Scope 422 Space 424 Environmental services 424 Public health services 429 Power supply 432 Security 433 Operational services 435 The need for coordination 436
  • 14.
    viii Contents Production sequenceand contract time 437 Cost of services systems 438 Summary 438 32 Guide to Further Reading 440 What this book provides 440 Sources of information – authority, validity and relevance 440 Finding information 443 Using information – corroboration, confirmation and risk 444 Summary 444 Index 445
  • 15.
    Preface This book hasbeen prepared for those at the beginning of their career studying with a view to practise in one of the professions concerned with the construction of buildings. It is written for the novice who, with study and experience, will become an expert in his or her chosen field. The more fundamental ideas developed in the text may need to be revisited as experience grows and it is, therefore, hopefully a text that can be referred to in the early years of practice and maybe beyond. The book takes as its theme the process of choice: what the expert has to know and how the expert could think through the myriad deci- sions that have to be made about the design, production, maintenance and disposal of build- ings. While this involves a process of analysis, the basis of which is universally applicable, the final choice is dictated by context. The context is set by time and place, the nature of the activity to be undertaken in the building and the aspirations of its benefactor or client. The process of choice is seeking appro- priate solutions in a physical and cultural context. For a text of this nature it may seem to be dominated by words and not illustrations. The contention is that for the novice or the practis- ing professional faced with new ideas and situ- ations the explanation of possible solutions is required. Presenting a final working drawing may be the outcome of choice, but it is the process of analysis with its need for explana- tions that gives the confidence that it will perform and can be built in the context of the particular building. A picture only paints a thousand words if you already have the words to explain it. It is hoped that the reader will find that the text tells a good story, that the development of the ideas is logical and easy to follow, but perhaps above all that it is seen as valuable in the world of practice. It is hoped that the text will be illuminating and the illustrations supportive in providing the explanations of both the analysis and the solutions suggested for choice. The first part of the book focuses on the key areas of analysis that have to be considered to check that the proposed construction will perform (will not fail) and can be built. These two tests are seen as fundamental to the final choice. In order to carry out these analyses this book suggests that it is necessary to visualise not only the physical form of final construction, however outline or tentative, but also, equally importantly, its response to the dynamic condi- tions under which it has to perform. The key question is ‘What if I do it like this?’ The answer comes from an understanding of how it works and how it is built, this understanding coming from explanations of why things happen, drawing on knowledge from a number of other disciplines such as science and economics. Each of the areas of analysis presented in this book is independent, and therefore each analy- sis has to be separate, yet all have to be satisfac- tory before the final choice is made. Choice is a juggling act: checking a proposal in one area of analysis may suggest changes that will affect others. Structurally sound solutions may be dif- ficult to build or solutions that will last without maintenance too expensive as a capital invest- ment. The final choice must satisfy all the areas of analysis. The second and third parts of the book put analysis into practice, focusing on making the final choice. Given the approach identified in the first part of the book, with context being so important, the chapters in Parts 2 and 3 are written from the perspective of making choices for construction in the UK at the beginning of the twenty-first century. In Part 2 the focus is on housing, while Part 3 is concerned with the
  • 16.
    x Preface commercial useand scale of building. While these both take place in the same physical and cultural environments, the way buildings are commissioned and designed varies. For mass housing the choice of technical solutions is made by the developer/builder and this leads to a convergence of detailing and specification for the construction. This current common form of house construction is presented in Part 2. In commercial building there is considerably more diversity in the use and scale of the building, leading to more variety in both the mix of tech- nologies and in detailing and specification. This greater need to consider broad options early in the design and to be clear about the potential for the technical solution is reflected in the approach developed in Part 3. The final chapter provides a guide to the wide range of published material that is available to develop knowledge beyond this book and par- ticularly to support the process of choice. The book itself gives no direct references. The notion of the framework for understanding developed in the book encourages the idea of seeking rel- evant and current information in the context of each project. It is hoped that this final chapter introduces the sources of information that will complement the approach developed in this book in order to put these ideas into practice. This book is written with the conviction that by focusing on the process of choice the range of theory and knowledge that is useful to prac- tice becomes explicit, making the link between knowledge and practice and between under- standing and experience clear. As study, and then practice, unfolds for each individual it is the power to reflect that develops understanding. It is hoped that the framework suggested in this book will help not just the process of choice but also the process of reflection. Readers should take from this text what understanding they can to use it to develop their own good judgement in what- ever part they play in the great enterprise of construction and the development of the built environment. Tony Bryan Book website at www.wiley.com/go/bryanconstructiontech2e Contains nearly 200 fully referenced, clear line drawings to download for free, as well as suggested learning activities for lecturers to incorporate into their teaching programmes.
  • 17.
  • 19.
    1The Framework forUnderstanding This opening chapter outlines a framework to help develop an understanding of what has to be known in order to take decisions on how we should build. The framework suggests a way of going about selecting construction and identifies the knowledge that is required to make the choice. It is the framework that will be developed and used throughout the book. Process and knowledge This book provides examples of construction, showing how we currently build, and provides an introduction to the understanding necessary to explain how the construction works. These two types of knowledge are both vital to making decisions as to how we should create and main- tain buildings in the future. This book sets this knowledge in the context of the process of making choices for the construction. In practice, a great deal of knowledge exists of the types of construction we might use and the materials and details that might be specified. There is, however, the need for any proposed construc- tion works to answer the questions ‘Will it fail?’ and ‘Can it be built?’ Clearly it requires the answer to these two questions to be ‘No, it will not fail’ and ‘Yes, it can be built’. These categori- cal no and yes answers may be difficult to give in practice. There often needs to be some analysis to develop a level of confidence with which to make the choice. The amount of analysis required determines the level of under- standing and experience needed to provide the evaluation of the suggested solution before the decision is taken to put the final proposal into practice. It is this basic ability to make a suggestion of how a building might be constructed and then to carry out an evaluation asking the questions whether it will fail and whether it can be built that is developed in this book. The evaluation points to changes in the suggestion, which after re-evaluation will lead, through a series of refinements, to the specification and details to be adopted. This requires knowledge of what potential solutions might look like, with current practice and precedent as the major sources for an initial suggestion. It requires an understanding of what is necessary to be specified in order to describe the proposed construction in sufficient detail to carry out the evaluation. The ability to carry out the evaluation, on the other hand, is dependent on an ability to ‘see’ the proposal working in the dynamic systems of the physical and social conditions in which the building is to be built. This process of choice and the way it leads to the identification of the knowledge required is shown in Figure 1.1. It will be shown later that the process of choice is not just an analysis of the behaviour of physical performance. This evaluation of a proposal’s response to the dynamic physical, chemical and biological systems of nature is vital, but building also takes place in a social and cultural context. There will be an impera- tive to ensure that the resources and know-how are available to manufacture and assemble the construction. This will require knowledge of the available industrial systems. Further, it will be necessary to ensure that the cost of the solution
  • 20.
    4 Analysis Analysis is monitoredand that its social and environ- mental impact is audited. These will demand an understanding of both the economic and social systems in which the building is to be created. The initial suggestion If the process is suggestion and evaluation, and the starting point is suggestion, it is necessary to know how we make the initial suggestion. How do we make that first best guess? In most cases the suggestion is informed by precedents. It is necessary to have knowledge of current solutions and how they perform in practice. Something, somewhere, has been done before that gives clues as to how the new solu- tions might be formulated. In times where change is limited the particular circumstances will have been faced a number of times in the past and successful solutions will have evolved. The well-tried and tested solution needs only to be suggested and, with some evaluation to ensure the circumstances have not materially changed, can be immediately adopted. If the circumstances are changing, current solutions may still be the best starting point. They repre- sent not only a sound basis in performance but also an existing base of resources and know-how to manufacture and produce the materials and details. Evaluation may modify but not fundamentally change the solution. This, over time, gives rise to a number of general forms from which specific solutions can be derived. In some cases, perhaps where there are increasing user demands, or the structure of industrial practice is changing, then similar or related practice may have to be investigated. On the rare occasions where suggestions have to be derived from little or no existing previous work, a more fundamental understanding of the behaviour of the construction will have to be applied. While experts approach making suggestions based on their knowledge and experience, it is, in many ways, not necessary to know much at all to make suggestions. It is the evaluation that requires the expertise. Novices or casual observ- ers may make suggestions that may be hailed as brilliant observation, but in truth they have no way of knowing whether that particular sug- gestion is workable or not. It will take the expert to spot its potential and prove its worth through evaluation. The power of the expert to spot potential is probably associated with the ability to carry out a rapid, approximate evaluation before subject- ing the suggestion to more rigorous and explicit analysis. Carrying out the evaluation The heart of the success of the process of tech- nological choice lies in the ability to be able to carry out an evaluation. The need to carry out a series of analytical exercises determines the knowledge required and manner of its applica- tion. It requires a level of understanding to answer the question ‘What if we built the build- ing as proposed?’ While the suggestion and the ultimate solu- tion describe the construction in what appears to be a static detail, the evaluation of the sug- gested construction has to describe a dynamic Figure 1.1 Relationship of process of choice to knowledge required. Evaluation Construction detail Dynamic systems Suggestion Process of choice Knowledge required
  • 21.
    The Framework forUnderstanding 5 Analysis system of behaviour (‘Will it fail?’) and a pro- duction process (‘Can it be built?’). The process starts with the client’s brief, the design then being devised from the require- ments of those who commission the works, and as a response to the social and physical context in which the building is to be built. It is against these criteria that failure will be judged. There will be many possible ways to construct a build- ing to achieve performance expressed in the client’s brief. The criteria for choice of the tech- nical solution come from the identification of the function of the parts and how they contrib- ute to the function of the building as a whole. The dynamic behaviour of the construction responding to changing conditions has to be understood, anticipating the modes of failure. Some specification of performance has to be established and then the suggestion has to be tested in the mind to assess the risk of failure within agreed design conditions. It is easy to see technology as only the final construction, an assembly of components and materials, the building as a static object. However, making the choice of what construc- tion should be adopted has to be rooted in an understanding of the construction as a dynamic system responding to changes in conditions and open to a failure to perform. It is necessary to be able to visualise not only the physical construction but also its behaviour under the conditions it will have to endure in its working life. Both of these are of equal importance. If the suggestion is not visu- alised correctly, its behaviour under analysis may be misinterpreted. If the dynamic system of behaviour is not visualised correctly, a flawed proposal may be adopted. Visualising the building as a dynamic system will involve iden- tifying the flows and transfers that take place both within the building and through the con- struction itself. These ideas are explained in Chapter 7. Technological choice demands skills in these areas of visualising the object and the systems, and then the conceptual manipulation of the systems acting on the construction to predict behaviour and assess the risk of failure. If the two basic questions to ask of a proposed solution are whether it will fail and whether it can be built, the criteria for choice come from an understanding not only of the potential dynamic flows and transfers when the building is in operation but also of the resources available. The performance of construction can only be realised if the resources are available to construct the building. This relies on the manu- facturing and assembly possibilities but will also include the existence of design expertise and the options for maintenance and disposal. Knowledge of available techniques and know- how for production is crucial to the choice of the final construction if it is to be successful in reality as well as on paper. As a design concept emerges, it is necessary to question what construction solutions may be used to fulfil the design requirements. It is then necessary to question whether this solu- tion is available with current technology and resources within any environmental, cost or time requirements. The resources available make the design a reality. Technology stands between the design of the building and the management of the resources. Choices can be made that may extend current production and design knowledge, but this must be recognised, and any costs involved in prototypes or training and the risks involved must be accepted before the final choice is made. The design and resources available condition the choice. These two areas are shown in Figure 1.2. These are the two areas that have to be understood before any analysis can be started leading to the final choice of construction. Physical and social context Figure 1.2 also indicates that before any choice for a specific building can be made it is neces- sary to understand something of the context in which it will be constructed. There needs to be some knowledge of the conditions that exist when and where the building is to be built, pos- sibly with some assessment of how conditions may change in the future.
  • 22.
    6 Analysis Analysis Design Concept ResourceBase Construction Physical behaviour Appearance Cost Social concerns Manufacture/ assembly Physical Context Cultural Context Figure 1.2 Framework of analysis. Construction takes place within, and has an impact on, the world in which it is undertaken. Some description of this world is necessary for both technical and socio-economic analyses. The world can be represented as a series of con- texts, both physical and cultural. The physical context includes nature and climate. These exert forces that act on the building; they provide the raw resources and may be adversely affected by the construction and operation of buildings. The physical context includes the surrounding development and the need for the design to respond to existing buildings and spaces. People and their social, economic and politi- cal systems create the cultural context. It needs a response to local, national and even global needs based on beliefs and fundamental world views of the relationship between individuals and between society and the other components of the natural world. The interaction between these two sets of con- texts has been brought into focus at the begin- ningofthetwenty-firstcenturybythemovement for sustainable development. The realisation that development cannot continue without consideration of its impact on the natural envi- ronment as well as established economic and social considerations calls for new knowledge associated with materials choice, energy use and waste disposal aspects of our chosen construction. There are, therefore, dangers in seeing these two sets of contexts as separate. However, it is still useful to consider them as having different dynamics, as, generally, in order to resolve technical questions, it is necessary to have an understanding of the physical context, while to evaluate the chance of a solution being success- fully applied requires an understanding of society, its economic and political systems. The basis of analysis Having identified the design concept and the resource base as providing the criteria for choice and having recognised the need to understand the physical and social context in which we build, it is possible to identify five areas of analysis as shown in Figure 1.2.
  • 23.
    The Framework forUnderstanding 7 Analysis The design concept is the translation of the physical and social needs for the operation of the whole building into a scheme that identifies the function and performance of each of the parts. In order to achieve this, the design concept has to articulate both the arrangement and appearance of the spaces and the technical contribution each part of the construction will make to the creation and maintenance of the internal conditions. Two tests indicated in Figure 1.2 have to be applied to a suggestion to see if it complies with the design concept: • Does the physical behaviour of the construc- tion provide a building fulfilling its func- tions to the required performance level? • Does it provide the right attributes of appearance? The test for physical behaviour involves three separate areas of analysis: • Creating environments • Under load • Over time Three tests indicated in Figure 1.2 have to be applied to a suggestion to see if it is achievable with available resources: • Can it be produced, including its manufacture and assembly and the subsequent processes of maintenance and disposal, with existing skills and know-how in a reasonable time and at the required quality? • Are the resources available at reasonable cost? • Will it be compatible with the social concerns that currently exist? These resources are both natural (from the envi- ronment) and social, so both aspects have to be part of the evaluation. It is only possible to use resources that nature has provided. However, the level of economic development in a society will provide the capacity to process materials, develop the skills and machinery to work them, the intellectual capacity to undertake design and the provision of capital to invest in the enterprise of the construction itself. Both the technical properties of materials and the exist- ence of the knowledge to exploit them plus any environmental impact of their use must be analysed in evaluating a suggested form of construction. These seven areas of analysis (physical behaviour being three) that have to be under- taken are, by and large, unrelated to each other and each needs its own tools of analysis and knowledge base to be successfully applied. Carrying out one analysis may indicate the need for a change in the suggestion, but the change that is chosen may make the analysis of a previous aspect invalid. It is not until all the relevant areas of analysis are shown to be satis- factory that the suggestions can be adopted as the solution. These seven areas of analysis have potentially to be undertaken for all aspects of the construc- tion, from the overall structural system to the finest detail such as the screw that fixes the final fitting to a wall. The work in this is clearly overwhelming if it has to be carried out for every building that is constructed. Current practice can inform much of the process of choice. One of the most important decisions that experts take is, of all the thousands of choices that have to be made to fully specify the con- struction, which of the areas of analysis for which parts of the building are significant. Where, if analysis is not thought through, is the greatest risk of failure? It is not clear how experts make this judge- ment. One possible explanation is that while looking at a suggestion they make many rapid checks against the seven criteria. From their knowledge and experience they take a view on what is well within failure limits and where the risks of failure are higher. Knowledge needed for choice It is now possible to start to identify the knowl- edge that is required and the areas of under- standing that have to be developed in order to carry out a full evaluation. Although used in various combinations in the different areas of analysis, it is possible to put forward a tentative list of types of knowledge that will be required:
  • 24.
    8 Analysis Analysis • Settingthe performance levels as the criteria against which the evaluation will be made. • Defining the conditions under which per- formance has to be achieved. • Determining the fundamental behaviour of the construction that would lead to failure to meet performance requirements. • Identifying the materials’ properties that will govern the behaviour that could lead to failure. • Thinking through the behaviour of the par- ticular combination of materials and details under the conditions envisaged. • Identifying the process of manufacture and assembly together with the resources required to produce the building within quality, time, cost and safety limits. • The cost in economic, social and environ- mental terms of using a particular form of construction. The process of evaluation requires the building to be conceptualised in a number of ways. While the final building will be seen as a physical construction, ‘bricks and mortar’, it is necessary to perceive the building in a number of other ways when carrying out the evaluation. Initially, the construction has to be seen as ful- filling a set of functions with associated per- formance levels. For evaluation, the building has to be viewed as a series of physical systems responding dynamically to changing condi- tions. The building then has to be seen as a series of production operations with the resources required for the realisation of the design. All these will have economic, environ- mental and social implications that have to be understood. When all these can be mastered, choices can be made associated with an assess- ment of risk and with some confidence of a successful building. Summary 1. The process of choice is one of suggestions and evaluation that requires knowledge of the physical construction and the dynamic systems in which it will be built and will operate. 2. How a suggestion is generated, and the extent to which a formal evaluation has to be under- taken, depends on the scale and nature of any changes from current practice required by either the design or the resources available. 3. When there is a changing demand for buildings and rapidly developing technical knowl- edge, the role of experience changes from predominantly reproducing known solutions to the integration of experience into a process of analysis to explore the possibilities of failure in the modified or new solutions before they are built. 4. The design and the resource availability define the criteria for the evaluation. This has to be set within a physical and cultural context. 5. The suggestion will probably be based on precedent and this leads to general forms from which specific solutions can be derived. 6. The evaluation needs to be carried out through seven areas of analysis: appearance, behav- iour creating environments, behaviour under load, behaviour over time, manufacture and assembly, cost and social concerns. 7. This will involve constant reference to both production and design. The concern is for what will not fail and can be built.
  • 25.
    2 Building Purposeand Performance Technology is used to mediate between the world as it is and the world as we want it. This chapter expands this idea, focusing on the users and their activities, introducing the functions expected of the building and how these have to be translated into a process of choice for the construction of each part. Activities, space and construction Buildings are often characterised by their overall purpose or function – house, factory, hospital, prison, etc. – and are often immediately recog- nisable although their architecture may vary. To understand the form of the building, it is neces- sary to understand the day-to-day activities that make up the function for which the building is commissioned. The construction will have to play its part in ensuring the well-being of these activities. The notion of well-being is normally associated with the people who use the spaces, but the building will have to protect the equip- ment being used and the storage of items associ- ated with the activities. Well-being of people also needs to include the requirements of the owner and the wider public, as buildings are social institutions and create the surrounding spaces. The majority of spaces in buildings have to accommodate people and consideration of their well-being becomes a dominant aspect of the performance of the construction. In some cases, such as the rooms for the early computers and specialist storage areas such as vaults and cold stores, the equipment housed in the building or the storage conditions dominate the require- ments. Designing for the well-being of people is essentially concerned with health, safety and comfort. Health should be understood as meaning both physical and mental health, both being a function of physical and social condi- tions created by the building. The owner may see a purpose beyond the simple support of activities, to include image and status. The surroundings in which the activities are undertaken have social signifi- cance and must form a feature of the design. Each society over time evolves common building forms for each purpose type that become recognisable within that society because of their size, arrangements of internal spaces and social statement. With this emergence of building form there is a need to develop appro- priate construction solutions. This process is dealt with in more detail in Chapter 3, but first this chapter explores the complex range of per- formance issues. These will be established pre- dominantly by the users’ activities, although later by the owner and then by government in the form of legislation on behalf of society as a whole. Introduction to performance requirements In order to explore the range of performance issues it is useful to engage in a mind experi- ment. The situation to be imagined is one where civilisation as we know it does not exist and the task is to provide shelter. The scenario is one of few resources of materials, labour
  • 26.
    10 Analysis Analysis or knowledge.There is also little development of an economic system, so the whole design and production process has to be undertaken by the users. The mind experiment starts by asking which performance the user of the building would seek to satisfy first. The experi- ment can then be extended through time, assuming increasing resources and socialisa- tion, introducing additional requirements that would add value and utility and improve well-being. By undertaking this mind experiment it will be possible to introduce the needs of the user and hence the functions that he or she will require the building to fulfil. As the user is also, at least initially, the designer and builder of the shelter, he/she must decide on the construction. The experiment will, therefore, also start to introduce the ideas and knowledge that will be needed to make decisions on the construction of the building itself. All the issues and factors introduced here are still relevant today. In the beginning Given no immediate risk from attack, we can speculate that people would organise their technological endeavour in the following way. Thought would have to be given to the range of activities of everyday life that should be housed in the shelter. Initially this is likely to be very few, perhaps only sleeping, with most activity being undertaken outside depending on the prevailing climate. This will provide a defini- tion of size and any division of the internal space that needs to be made. It would be imme- diately recognised that these requirements for size and shape would be limited by the possible construction available. Some decision would have to be made as to how much effort should go into developing construction to match aspi- rations or use existing resources to satisfy immediate needs. The priority in terms of establishing functions for the building fabric would be to remain dry, a condition fundamental to the health and comfort of people and the storage of many natural products. This would be accompanied by the requirement to be warm, but it is possible that this will initially be achieved in combina- tion with other technologies. These would include clothing and the use of fire, which at this stage may or may not be associated with the construction of the shelter. As soon as any construction is contemplated the builder is immediately faced with achieving a stable structure and making some judgement on how long it may last. Although buildings may be erected for environmental control, their very existence demands considerations of stability and reliability if they are to be deemed satisfactory by the user. This will require the identification of possible modes of failure. At this early stage this would include how the con- struction might leak or fall down. This under- standing of the ways in which performance may be lost becomes crucial to directing effort to significant aspects of the solution. This would also lead to some questioning of what mainte- nance may be necessary and what parts may have to be renewed to continue the per- formance until the construction had to be aban- doned or demolished to make way for a new building. It would also become necessary to have some knowledge of the environmental conditions in which the construction has to maintain per- formance. This knowledge would be required to consider not only the environmental control but also the stability and reliability. These three become the key physical performance issues. External climatic conditions such as frequency and volume of rainfall will need to be assessed for the weatherproofing function. Damaging wind speeds and direction would need to be assessed for stability. It would, however, soon become clear that wind is a major factor in weatherproofing. Some of the most arduous weatherproofing conditions come with wind- driven rain. It is not possible to say what aspect of the environment needs to be known to assess durability until some choice of the basic materi- als is made. Specific decay agents in the envi- ronment degrade different materials. Linking materials to their generators of decay is just one more question that has to be answered in the
  • 27.
    Building Purpose andPerformance 11 Analysis quest for knowledge to make sensible choices for the construction. This assessment of external climate would soon reveal that often the more extreme condi- tions of open land are ameliorated by local natural features, that exposure can be modified by the position and orientation of the building which will limit the demands on the construc- tion and/or give better internal conditions. The next steps As the number of activities carried out in the building increases, the provision of good air may be the next priority for improvement of the construction. This is probably the next require- ment for health and comfort after dryness and warmth. Seeking a solution that would improve the quality of the air would probably involve ven- tilation since there is an abundance of good air outside. It would have to be recognised that the air outside may also be cold and that this will make the requirement for warmth more diffi- cult to achieve. This may mean that a solution for good air may only be possible when air tem- peratures outside are sufficiently high or air quality inside is particularly poor. Assuming that the active technologies of building services are not available, modification would be neces- sary in the existing construction. It would be necessary to use natural ventilation driven by wind pressures around the building. Openings would have to be introduced to ensure the exchange of air. Their position and size would have to be considered. It would be possible to introduce a level of control by providing shutters. The openings could eventually be as sophisticated as chimneys, but history tells us that these often come much later. It is important to note that the containment of the bad air is a direct result of employing con- struction to remain dry and warm. The air outside the building is almost certainly good. This realisation that the construction itself can create undesirable conditions should not go unnoticed. Changes introduced to fulfil new performance demands may change conditions that have always been satisfactory. This hap- pened towards the end of the twentieth century when a requirement for energy saving was satisfied by the introduction of insulation. Under some environmental conditions this led to condensation that has a deleterious effect on the basic requirement of keeping dry. This led to health problems for the users of the buildings. The introduction of new performance require- ments may also introduce failures in the con- struction that have previously not occurred. This happened in the condensation example, where dampness caused not only health prob- lems but also a deterioration of the construction materials themselves. In this mind experiment it is possible to speculate on a similar problem with the improvement in internal air quality. Given the lack of social organisation to produce more processed materials, the construction would almost certainly be made of relatively unmodified organic materials. In this case it might be speculated that if the poor air had a large component of smoke it would have permeated the construction. This would have effectively fumigated the organic materials and kept infestations or decay-promoting fungi and insects at bay. Improving internal air quality may change the conditions within the construction itself. This may allow significant numbers of some of the natural agents of decay to thrive, thereby reducing the life of the construction. More physical requirements This mind experiment continues on the assump- tion that no major threat to security arises. This would inevitably lead to a diversion of resources and may change the priorities of individuals or society in seeking improvements in their build- ings, although it may also lead to new types of buildings, such as defensive works. Given peaceful social development, the next priority may be difficult to identify. It may be that the infestation of insects and small animals that will be attracted to the improved internal environment becomes a problem. It
  • 28.
    12 Analysis Analysis may bethat in the harsh realities of life, and in the absence of any realisation of the health risks, these infestations would be tolerated. Measures to eliminate the larger animals, if not already considered as a danger, may now become important. At some time, however, infestation control would have to be included in the list of functions required of the construction to improve well-being. This is part of the more general requirement to keep the enclosed space clean. Internal surfaces that are dust- free, smooth and wipeable become desirable attributes where cleanliness becomes important to the health and comfort of the user. Having gained good clear air, more activities could be carried on indoors. It is, therefore, possible to imagine an increasing need for light to improve comfort levels and further extend the range of activities in the building. The choice is between natural and artificial means of lighting. Natural would involve openings, while artificial would only demand a safe place to support what would almost certainly be an independent light source. Although inde- pendent of the building, it would have an influ- ence on it. Perhaps the major influence it would have is in the increased risk from fire. While it may not be possible to improve the fire resist- ance of the whole building at this time, it would be sensible to employ non-combustible materi- als at least where the light source is to be mounted. Here we see the increased use of technologies independent of the building, seen by the user as an asset to the well-being of the activities, influ- encing the required functions of the construc- tion itself. Another requirement is for some measure of noise control. This would, of course, only become a concern if the external level of noise were somehow interfering with the overall sense of well-being. It may become a problem when the building has separate rooms for spe- cific activities. Noise from one activity may well be incompatible with the conditions necessary for another. Noise is a particular problem of civilisation, and especially for those societies that have advanced technologies. It also seems that it has a cultural basis in attitudes towards individual rights, privacy and intrusion. The technical considerations become more complex It is useful to view the need to consider noise performance from a different perspective. It may be that there is a need to modify the sound between outside and inside, yet the construc- tion used for the other requirements already has sufficient, if not excess, ability to perform as a sound barrier. With low performance expecta- tions the final form of construction is dictated by only a few of the functional requirements. As more functions are identified and the level of the required performance increases it becomes difficult to provide simple construction solu- tions. Composite solutions are necessary with different materials to satisfy different functions at the levels of performance that are required. The analysis of exactly how each part of the construction is interacting in providing the overall function becomes more difficult. The danger comes when changes are suggested. It is necessary to ensure that the change does not make a previously satisfactory performance critical so that the construction fails to perform, in an unexpected way. The trend towards lighter partitioning in housing has, by reducing the weight and changing natural vibration fre- quencies, reduced the sound transmission resistance. In the past this was normally more than satisfactory when partitions were thicker or made of denser material. The lighter, cheaper solution may become critical in some situations where the soundproofing performance of the heavier solution had always been taken for granted. The need for composite construction leads to the search for materials with properties matched to the specific functions. Processing or manufac- ture of materials allows these properties to be more accurately achieved. This not only changes the ability to gain performance but also influences the production resources required.
  • 29.
    Building Purpose andPerformance 13 Analysis Materials and manufacturing methods may also be changed to provide more economic buildings. The innovation may not be driven by performance but in order to seek production and cost gains. This may lead to performance failure in previously satisfactory solutions. Those responsible for the choice of construction must re-evaluate the possible performance fail- ures if construction is changed for production or cost advantages. Taking storage and equipment into account The environmental requirements that have been introduced are those necessary to maintain the well-being of the people who use the building. These can be summarised as: • Dryness • Warmth • Cleanliness • Light • Quiet Observations of this list will identify that, with only slight modifications (e.g. warmth needs to be more generally interpreted as temperature control), it could equally well be applied to maintaining the well-being of the equipment and stored items. The required internal condi- tions for storage and equipment may be differ- ent, even hostile to life as in the case of cold storage. They will still demand the same type of functions of the construction. There would, however, be changes in performance level due to the change in specification for the internal environment, even though the external condi- tion may be the same. In the example of cold storage, levels of insulation would be different. More significantly, the equipment and stored items, as well as the living occupants, will con- tribute to the internal environment with noise, smell, heat, fumes, etc. It may be that the con- struction is called on to moderate these effects by isolating storage from living areas by parti- tions. Independent technologies in the same room such as cooling of food may be applied using ideas such as evaporating water from a porous pot or a refrigerator. However, inde- pendent technologies may influence internal conditions. In the example of cooling food the porous pot releases vapour and the refrigerator releases heat. The dynamics of these changes in the internal environment due to occupants and independ- ent technologies in the building must become part of the analysis. Sealing up a building to reduce heat loss through air changes can lead to a build-up of vapour (if only from people breathing), which makes condensation more likely. Although the list of environmental require- ments generated for people will cover most circumstances associated with the equipment and storage in the building, it may in some situ- ations be incomplete. Some modern equipment has environmental operating requirements, such as the need for anti-static precautions, that may not currently be considered necessary for the well-being of people. What has to be achieved is a balanced solution to ensure the well-being of both the participants and the processes associated with the activities for which the building is required. What should be considered tolerable? Setting performance levels involves considering what is tolerable. What should be considered as normal limits to be maintained in the internal conditions? What external conditions should be allowed for in the design? These questions have to be answered in terms of risk and conse- quences. Extremes that happen rarely but have serious consequences to the well-being of the activity or even threaten life and property may well be taken into account. The more frequent events, even with lesser consequences, are also more likely to be taken into account. This is not independent of the economic resources available and social attitudes. In many parts of the world, earthquakes will occur, but the con- struction to minimise the risk to life is seen as increasing costs beyond that to be extended to
  • 30.
    14 Analysis Analysis all sectionsof society. Similar circumstances have existed in the past with fire and building. Increasing wealth, effectively distributed in society, will affect what is considered tolerable, reflecting more demanding performance expectations. Generally, wide limits would be accepted for solutions at the beginning of our mind experi- ment, but as societies develop they seek to extend the range and level of demands. This often includes a requirement for a greater level of control as it defines a narrower band within which performance is deemed satisfactory. These trends place more demands on the solu- tions and failure is more likely. Some extremes that happen rarely have to be considered if they have serious consequences. One risk that comes from the internal activity that generates extreme conditions has already been raised. It is the issue of fire within the building. At the beginning of the mind experi- ment, while escape for people would be required, it is unlikely that there would be any expectation on the part of the user that any of the building would remain after a fire. Although fire is now rare in modern buildings, its conse- quences are such, particularly in risk to life, that it is currently deemed necessary for the con- struction to continue to maintain a selected range of performances both during and after the fire. This would almost certainly include stability, although insurance requirements may extend the performance range. External climatic extremes such as wind, flood, lightning and even earthquake may be considered. Design for flood may be sensible if the building is sited by water, for lightning if a tall building and for earthquake if the building is in an unstable region of the world. New threats created by increasing sophistica- tion of solutions are now emerging. Draught- free homes created to conserve heat may suffer from a build-up of radon gas if built in an area of the country where it occurs naturally in the rocks below the building. The chemical con- taminants in the soil on sites used for redundant industries threaten both the occupants and the fabric of the building itself. Introducing social requirements Having established the requirements for health and physical comfort, it is now necessary to consider the social aspects. In reality the consid- eration of performance for more social aspects does not come only when physical require- ments have been fully satisfied. Human endeav- our very quickly becomes a social activity and there grows a need for social organisation, establishing cultural norms, provision for lead- ership and political activities and an economic system for the exchange of goods and services. Buildings play their part in this process not only to house the activities but also in that they reflect, affirm and even become instruments for change as the cultural and economic order develops. As well as the issues of status and image, to be discussed later in this chapter, two other functions associated with well-being arise when society starts to develop. These are the require- ments for security and privacy. They are mainly associated with mental health, although the security risk, if it becomes a reality, may involve physical danger. The point at which people would take these functions into account would be dependent on the nature of the society that develops. They are not as predictable as the physical needs and may well have to be addressed before the desired level of physical comfort and safety is achieved. Security requirements will be dependent on the existence of a perceived threat. If the risks are seen as sufficient, technological inge- nuity, time and resources will be devoted to combating the threat if social devices such as the rule of law or treaties cannot be achieved. Threats come from both inside and outside a society, each of which pose different challenges to the technological skills of the builder. In the extreme, in buildings such as bunkers, the secu- rity threat dominates the design as the technol- ogy of survival becomes pitted against the technology of destruction. The requirement of privacy is much more rooted in the cultural attitudes to community. It is cultural interpretations of what activities
  • 31.
    Building Purpose andPerformance 15 Analysis should be shared and those that should be carried out in private that dictate the need to introduce this performance into buildings. Performance levels of privacy can be identified associated with the senses, visual and aural being the two main requirements of the build- ing influencing both the external envelope and normally demanding some division of internal space. The functions of the building that have a social origin often translate into aspects of phys- ical performance already introduced. Security makes structural demands on the fabric. Privacy determines many of the sound transmission requirements of construction. Influence of production resources As more functions are included and more materials are introduced, production resources and know-how have to develop. The relation- ship between the need for a building and the availability of the materials, skill and tools to produce it is always a determining factor in the choice of the construction. Access to production knowledge and expertise limits the pace of development of new solutions to achieve new performance. However, developments in mate- rials and production can also suggest different ways of achieving similar performance. This mind experiment has taken the perspec- tive of the purpose of the building and require- ments of the user. It is easy to forget that the means of realising that performance may need as much thought and ingenuity as the design and detailing of the fabric and structure of the building. In many old buildings it is easy to see how they work but often difficult to see how they might have been built without appreciat- ing the tools and skills available at the time. In many innovative buildings, detailing is often determined as much by manufacturing or erec- tion procedures as it is by satisfying perform- ance. The availability of manufacturing and assembly resources also determines the cost. The need to develop production procedure affects the time to construct and risk associated with a particular solution. All these contribute to the final quality of the building and its success judged by performance. Considering cost and value Throughout this mind experiment the question of cost and value will have to be considered. Buildings are usually costed in terms of money, but there are also considerations of cost to the environment and on the impact they may have on the society itself. The resources available to any society are limited and decisions have to be made as to how these should be allocated. As part of the culture these are the political deci- sions involving both the vision of the type of society that should emerge and the preferred methods of achieving it. It is from this cultural process that demand is initiated, the cost of resources determined and value assigned. Buildings will only be commissioned when the cost of a building that performs to an ade- quate standard is considered good value. If the costs are too great, decisions have to be taken on eliminating functions, reducing performance or changing production methods. These changes have to ensure that the building is still consid- ered as value for money. Assigning this cost requires that at least a broad outline of both the construction and the production methods is known. At some point in the process the deci- sion to proceed to full design and production based on estimated cost has to be made. For buildings that can be produced using well- developed current forms of construction this decision can be made very early with some cer- tainty. For a project where there are few prec- edents, possible solutions may have to be investigated before cost can be established with sufficient certainty to take the decision to proceed. It is, however, always a requirement to set cost limits as early as possible and then develop the final solution with these costs in mind. Building for status and image Status and image will at some time in the development of society start to influence the
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    16 Analysis Analysis requirements ofthe building. This may be reflected in the size of the space provided over and above that strictly required for the physical satisfaction of the activity itself. It may be asso- ciated with the quality of the materials used being acknowledged as expensive. These expen- sive materials must have the ability to perform their physical tasks without failure, but they could have been replaced by a less expensive alternative. These requirements are often then overlaid with issues of art and fashion and sym- bolism. The influence of these should not be underestimated, but a full discussion of their nature and form is inappropriate in this text. The pressures of status and image are not just related to statements of wealth and position. We all need to make statements and feel com- fortable about our place in society related to the prevailing cultural norms. It has to be recog- nised that these cultural norms can be highly regionalised, being associated with tribes or nations, although improved communication seems to reduce this variability. We all care about what our buildings look like and the envi- ronment they create. Using and being associ- ated with buildings that match the psychological demands of the activities carried out in the building is very important to our mental well-being. These issues become associated with aesthet- ics, the visual and deeper, even spiritual, quality of beauty of both natural and manufactured articles. These are the aspects of the world that satisfy our feelings rather than our physical needs. Buildings intrude into the rural land- scape and create the cityscape. Their shape, form, colour and ornamentation have a signifi- cant impact on our lives. Control from society and legislation All social groups have cultural norms of behav- iour that limit the actions of individuals and impose sanctions for transgressions. This even- tually has to be formalised into legislation, some of which will start to impinge on the choices that may be made for construction. Direct leg- islation is normally associated with public health, limiting the use of scarce resources or the position and appearance of whole build- ings. Once manufacture and assembly start, there are laws associated with the health and safety of operatives and people in the surround- ing area. All these will have to be acknowledged and satisfied in the final choice. If the choice of con- struction is made in the sprit of responsibility within the cultural norms, it should not domi- nate the solutions chosen. Legislation is for the protection of those who use the buildings and should, therefore, be easy to accommodate into a process whose objectives include satisfying social and individual needs. In reality the law on these matters can be slow to change and may be drafted such that its inter- pretation becomes a matter of opinion. These factors can spur or inhibit technological change, but it is clear that in an advanced society those responsible for the choice of construction have to be aware of the law and its interpretation. There is much legislation that will indirectly influence the choice of construction, although predicting and understanding the links are more difficult. Contracts become necessary between the organisations that undertake dif- ferent parts of the building process. This legisla- tion affects decisions on the construction and what risks they carry. The knowledge and expe- rience that the organisation has then influence the choices made for the construction of the building. Clients, users and change of purpose Another complication that arises as society develops is that individuals who become the owner/occupiers commission fewer buildings. It is now possible for those who commission the work to be an investment company who pass on the task of operating the building to another company for use by yet another group of people. This does not nullify the idea that satisfying the needs of the user should govern the perform- ance of the construction solutions. It is the pro- vision of space that ensures that the desired activities can be carried out efficiently and effec- tively by the user that gives value and utility to a building. Those who commission the build-
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    Building Purpose andPerformance 17 Analysis ing may have objectives such as investment, but these will generally only succeed if the purpose of the building and its performance are satisfactory. Even when relatively simple relationships between client and initial occupation exist, the purpose of the building is likely to change with time. These can be quite dramatic changes such as churches to flats, but most are much more subtle. Changing practices in medicine have made many old hospital designs inefficient and the general electronic information revolu- tion has changed the basic activities carried out in many offices. Increasingly the operators of buildings (as opposed to the users) see the building as part of the business’s efficiency. This gives different value to maintenance, alter- ations and refurbishment and makes the build- ing a more integrated part of the facilities as a whole. This leads to the questions about the whole life costs. More expensive initial options may be better value over the life of the building, reducing operating costs and increasing effi- ciency and well-being. Environmental impact and sustainability This long-term view of the building leads to wider questions about environmental impact. Construction has always had a local impact on the environment; it takes resources, changes ecosystems, consumes energy and creates waste. The society in both our mind experiment and now in reality has grown more prosperous; infrastructures have improved, allowing the growth of manufacturing and materials process- ing to serve an expanding population with ever higher performance expectations. The environ- mental impact of technologies chosen for indi- vidual buildings can now contribute to global consequences. This demands yet more analysis, with new knowledge required in order to make choices about the technology we employ for our build- ings. It will lead to different solutions being favoured, innovation and risk. The story continues. Summary 1. The purpose of the building is to support the activity to be carried out in the building using both physical and social criteria. 2. Both physical and social functions of the building lead to physical performance requirements covering environmental, structural and reliability aspects of the construction. These require- ments lead to performance expectations and hence definitions of failure. 3. Choice of construction can only be made in the knowledge of the environments in which the construction operates and an understanding of the mechanisms or actions that lead to failure. 4. The other factors to be considered in making the choice of construction include production resources and know-how, cost, legislation and the need to consider the whole life of the building and its environmental impact.
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    3 Common Forms– Specific Solutions This section develops the idea that in any society there is a recognisable set of common building forms. These common forms will be drawn from a range of generic types that are then worked into various specific solutions. The generic type and constructed form are two distinct ways of identifying the construction that is adopted for a building. The conceptual generic type is characterised by its arrangements of components and action in achieving performance. The physical constructed solution has defined materials, size and shape of components, joints and fixings. This construction solution becomes specific to an individual building, although the building may be repeated many times and the detail may work in many buildings. General and constructed forms In any society at any time there is a pattern of needs that supports a recognisable series of common building forms. For each of these building forms there will be an interrelated set of construction solutions to cope with the size of the building and the resources affordable for each. Construction solutions are derived from a limited set of generic types. Technological choice often starts with the selection of an appropriate general form that is then developed into a detailed construction solution for a spe- cific building. The ability to describe a building in these two forms, the general form and constructed form, at the early concept stage in the design of a building is most important. It should be the big idea from which the individual details can be developed so they work together to ensure the performance of the building as a whole. The emergence of general building forms It appears that the prime determinant of the construction of a building is related to space. The users’ demands will translate fundamen- tally into spaces and their size and interrelation- ships will suggest the scale and shape of the building. At the domestic scale small cellular spaces lock together, while many commercial or public buildings require more voluminous spaces, often with smaller associated spaces such as toilets, to form the building as a working unit. Construction solutions are directly related to this demand for space. Most significantly it influences the structure, but these choices have inevitable consequences on the solutions avail- able for the construction of the enclosure and other elements of the building. Currently there is a wide range of spatial requirements both on plan and in the height required that leads to the use of a range of struc- tural forms. Three general groups of structural form can be identified: • Loadbearing walls • Skeletal frames • Long-span roofs Each of these will create a range of building forms, some examples of which are shown in Figure 3.1. Each building form will be made up of a combination of a range of structural
  • 35.
    Common Forms –Specific Solutions 19 Analysis elements. An example of a generic structural element is the beam. With its structural action in bending it appears in cellular loadbearing construction as joists for the floor and a lintel over an opening, in skeletal frames as a main structural member and in the long-span roof in a portal frame. This generic type has been adapted for specific solutions using different materials to achieve the required characteristics: great strength, small deflections, small section size, low weight, good looks, low cost, fast erec- tion. Each of these characteristics will have a greater or lesser significance in a specific build- ing. In a house the joist will most likely be timber; in the skeletal frame the beam will gen- erally be steel or reinforced concrete. The portal frame is most likely to be made from steel, but for a building of the right use, scale and size it could be made from reinforced concrete or even from timber in a laminated form. While the ability to enclose the space is the primary determinant of the generic form, design and resource conditions will lead to a dominant economic detailed solution. This leads to two ways of thinking about a building, each having it own vocabulary to describe the solution. Early in the selection of the construction it is helpful to think about the elements of the build- ing in generic terms. This can then be developed into a full description of the constructed form, including specification of materials, joints and fixings. Generic elemental – domestic, loadbearing walls One widespread use for the loadbearing wall form is the house. Described in their ele- mental form, houses in the UK at the beginning of the twenty-first century employ a semi- permeable (cavity) construction for all external walls to provide (with internal cell walls) a stable dry box. This box will be roofed with a tiled covering supported on a trussed rafter structure taking the loads directly to the external walls. This means that any internal loadbearing walls need not extend to roof level. Suspended floors will be joisted, often taking advantage of internal walls to limit spans, making some ground-floor partitions loadbearing. Ground floors may be ground supported or suspended floors depending on the site and ground conditions. Foundations are most likely to be strip footings unless the ground conditions are very poor. This form is shown in Figure 3.2. Many houses built in the first half of the twentieth century and still in use were not con- structed like this. Many have solid permeable walls and have roofs made from individual structural members (rafters, purlins, struts and hangers) which, when acting as a whole, require internal wall support. Later in the twentieth century the width of terraced houses reduced and cross wall construction, where only walls Figure 3.1 Typical form associated with types of structure. Loadbearing Skeletal frame Long span roof
  • 36.
    20 Analysis Analysis between thehouses are loadbearing, became an option. This lost the stabilising effect of the box but allowed a range of less expensive external back and front walls to be chosen. As the loadbearing wall solution is developed into multi-storey flats other elemental forms have to be employed. Floors with greater sound and fire performance requirements become more economical as slabs, not joisted, even though the spans might not have changed sig- nificantly. The loadbearing walls may become prefabricated, taking advantage of the repeti- tions floor by floor to gain a production advantage. As this arrangement is developed into multi- storey blocks, the alternative structural form of the skeletal frames will become an economic alternative, even though the plan layout still shows walls dividing the building into small spaces with limited floor spans that made the loadbearing wall option viable. Constructed form – domestic, loadbearing walls None of the generic descriptions talks about the material, the shape or size of the components or the joints and fixings employed. They give the elements general names and describe them in terms of their general form or how they perform. For the constructed form, details have to be worked out to ensure economic sizes and man- ufacturing techniques. From this a recognisable physical constructed form will appear. The con- structed form of the generic elements shown in Figure 3.2 is given in Figure 3.3. This shows concrete single-lap interlocking roof tiles sup- ported on timber battens over felt fixed to timber-trussed rafters jointed with galvanised steel gang-nail plates. The external walls are masonry, although timber frame is a viable alternative. The wall may be constructed of brick outer skin and block or timber framed Figure 3.2 Generic description of house construction. Semi-permeable cavity wall Internal wall carrying floor loads Tiled pitched roof Trussed rafter roof structure Joisted first floor Ground supported floor Strip foundations Non-loadbearing partition
  • 37.
    Common Forms –Specific Solutions 21 Analysis Figure 3.3 Constructed form description of house construction. Brick outer leaf with block or timber frame inner leaf connected with wall ties with insulation in cavity Inner block wall with plaster or plasterboard finish Concrete single lap tiles fixed to timber battens over sarking felt Timber truss created with galvanised steel nail plates Timber joists bearing on inner wall with chipboard decking and plasterboard for ceiling Insulated solid ground floor with fill (hardcore) under concrete slab Plain concrete strip foundations Timber stud partition with plasterboard skin Insulation panels for the inner leaf. This is unlikely to meet the requirements to limit the passage of heat. The most cost effective way to limit heat loss in the winter condition (loss of heat from warmed inside air) is by insulation incorpo- rated into the wall. In summer the design condi- tion is heat gain from outside. As this gain is predominantly from direct radiant heat from the sun, shading or thermal capacity (not shown in Figure 3.3) may be better actions than insulation. The floors are timber joist supported by resting either directly on the inner leaf or on galvanised steel joist hangers and finished with chipboard sheet flooring. As the ground-floor partition walls carry the joists they are con- structed with concrete blocks. However, as the trussed rafters only transfer load to the external walls the first-floor partitions only need to be timber stud with plasterboard finish, as long as they can provide appropriate levels of sound insulation. Plasterboard has been used for the ceilings and as a finish for the downstairs block- work, although gypsum plaster may be used on any block walls in the house. The external wall would have to be modified below ground and the foundation would be a strip of plain concrete. The size of each of these components has to be chosen. Common components, such as the brick or the standard range of windows, have been developed in appropriate sizes to work with the domestic scale and perform- ance levels. The size of some components, such as the trussed rafters and floor joists, has to be designed to the size and use of the building. In the same way as houses in the past have been different to the construction shown in Figures 3.2 and 3.3 there is no reason to suspect that either generic forms or the physical solu- tions will endure into the future. They will evolve and develop to meet new design needs and resource conditions.
  • 38.
    22 Analysis Analysis Other generalforms and current practice Buildings using skeletal frames and long-span roofs show a greater variety of both generic elemental types and physical construction solu- tions. To try to catalogue them here is not appropriate. However, a few examples serve to introduce these forms as both generic and phys- ical entities. The skeletal frame structure has beams, columns, slabs and some means of ensuring overall stability. This basic format can be repeated to generate large buildings both on plan and in height. These structures will, however, need internal structural columns or walls, thus imposing some limits on clear internal space. Where this structural form has no current rivals is in its ability to achieve great heights with relatively open internal spaces. The physical constructed form is generated in either steel or reinforced concrete. The reinforced concrete can be either precast or in situ. These materials can then be mixed between the elements. Most steel solutions have steel beams and columns but concrete floors and either concrete or steel wind-stability provision. Reinforced concrete structures nor- mally have reinforced concrete members throughout, but the development of flat slabs as spanning structures has eliminated the need for beams. Long-span roof structures are used for indus- trial, retail, storage, exhibition, sports venues and other activities that need large floor space under the roof. They are normally only single- storey, although they may require considerable internal clear height. Some buildings used for these purposes are not large, and so although termed long span because of their potential the generic forms may be used for buildings of modest scale. Long-span roofs have perhaps the greatest variety of generic elemental forms to be developed into construction forms. Both plane and three-dimensional structures in flat and curved forms have been developed in steel and reinforced concrete and even timber and aluminium. Both skeletal and long-span structures have to be enclosed. The enclosing fabric can nor- mally be supported and restrained by the struc- ture and there is a wide range of options for the external walling. Again, generic forms such as cladding or facings can be identified, with con- structed solution in materials such as metal, concrete, glass or brickwork being chosen for the specific building. The different structural forms tend to use different enclosure solutions. In long-span structures the building often requires less openings, and reducing the weight of the fabric allows economic gains to be made in the structure. This leads to sheet cladding in metals with heavier forms such as brickwork used only around the building at ground level, where it can be supported directly on the ground. In the multi-storey skeletal form the interaction of the enclosure and the structure plus the need for performance often lead to more complex construction. Building services To illustrate the idea of the general form and the specific solution, descriptions have been given for the construction of the structure and enclo- sure elements. Buildings also include a group of technologies collectively known as building services. It is not the intention of this chapter to introduce their general forms and possible solu- tions. This is not because they are any less sig- nificant in supporting the everyday use of the building and the well-being of the occupants. Each building will have to be resolved with a mix of structure, enclosure and service systems to meet the performance expectations of the building. Hopefully in this chapter the point about general and specific forms has been made with the examples of structure and enclosure. The general forms and possible solutions for services will be introduced in later chapters in the book. Uncertainty and risk Where change is slow, there is the opportunity for current detailed solutions to be adopted
  • 39.
    Common Forms –Specific Solutions 23 Analysis with little modification from one similar build- ing to another. There is always danger in assum- ing two building to be the same, but if the general form is robust and not being applied close to a failure cusp the solution can be sug- gested in detail without much analysis, with little risk. As the pace of change increases, initial choice may deviate from currently detailed and even generic forms. The initial suggestion becomes based on an understanding of generic forms that then need to be thought through in detail. Initially this may only need some alterations in materials or detailing, but as demands become more divergent from common practice then alternative elemental generic forms in new combinations may be more appropriate. In making any technological choice it is important to be aware of the uncertainty and risk in adopting a particular solution. The technical risk is one of failure in perform- ance. As with any risk it must be weighed against the consequences. Consequences that lead to loss of life always require careful atten- tion. Where the consequence is interruptions in the operation of the building, the severity of the loss will have to be evaluated against the risk of failure. Whatever the pace of change, the choice of construction is based on an understanding of the action of the generic form and the performance of the detailed design and availa- bility of resources to construct the specific solution. Summary 1. Elements and components have a limited range of conceptual generic forms based on their action in achieving performance. 2. Detailed construction solutions have to be chosen for specific design and resource conditions and are therefore ultimately specific to an individual building, although the building may be repeated and one detail may work in more than one building. 3. Within each society a range of common building forms and economic construction solutions arise which normally form the basis for choice for subsequent construction solutions. 4. Particularly in times of change, the process of choice has to include analysis that recognises the uncertainties and risks for each individual building in both failing to achieve design performance and acknowledging the reality of available resources.
  • 40.
    4 Construction Variables Thischapter explores the variables that define construction: materials, shape, size and spatial rela- tionships. It introduces the reality of deviations in assessing whether the components will fit together and perform. The chapter concludes with a section on the specific aspects of jointing and fixing as the process by which the parts of the building can contribute to the behaviour of the whole. The variables of construction – the outcome of choice It is important to recognise at the start what aspects of the physical construction can be varied in order to achieve the desired perform- ance of the building. Identifying what can be varied also identifies what has to be chosen and specified if an unambiguous solution is to be defined. Choices have to be made for the materials to be formed into components that have a defined shape and size. Each component has then to be given a spatial relationship with other compo- nents together with the joints and fixings neces- sary for them to act as a whole building. This simple identification of the variables is repre- sented in Figure 4.1. Defining the final physical arrangements of the construction involves a specification for each of the component parts of the building, including any joints and fixings, detailed in assemblies of components to create the final building. This specification will have to include: • The material of which components are to be made and the quality of that material • The shape into which the material has to be formed • The size of each component, giving dimen- sions sufficient to define the shape • The relationship of each part either to an absolute position defined by a reference framework or relative to another part of the construction or the surrounding environ- ment This specification determines the space that the components and their joints will occupy. It may be in competition for this space with other parts of the construction and/or the usable space of the building itself. The choice of construction cannot be confirmed until this has been checked and it has been established that there is a unique space for each part of the building. Joints and fixings also need to be identified by their component parts, their material, shape and size and spatial relationships, as they them- selves are part of the assembly. These assem- blies are then connected (where they are often identified as junctions) into the whole building. Any components associated with junctions also have to be specified. The process of choice is about defining the components, their materials, shape and size and their spatial relationships, including the joints and fixings necessary to complete the building. The focus of technological knowledge is taking decisions about these variables to create a build- ing that is safe and has utility. This is a technical choice that has to be made following the crea- tion of a design concept and coming before the management of the production process. Yet it is a choice that has to be made in the full knowl- edge of the design requirements and the avail- able production resources.
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    Construction Variables 25 Analysis Figure4.1 Variables or outcome of choice. spatial arrangement size shape joints fixings Components Assemblies Buildings materials Choosing materials Specifying materials is a process of matching the properties of the materials to the perform- ance requirements. This is not, however, inde- pendent of size and shape, for all materials have all properties to some degree or another. We only choose to exploit certain properties when their value is such that, in economic quantities and at sizes and shapes that can be produced, transported and fitted within the space availa- ble, they will perform at the required level. Buildings are perhaps the largest manufac- tured items widely used throughout all socie- ties in the world. They demand relatively high quantities of materials at reasonable cost and it is, therefore, not surprising that, historically, materials used for everyday buildings are those with high bulk, locally available and with limited process costs. Increasing economic wealth and its attendant higher levels of infra- structure allow the use of materials requiring greater processing off site and less need to rely on local materials. With economic development comes the possibility for transfer of production activity to factories remote from the site, which in turn gives opportunities to use a wider range of materials than a wholly site-based process. The materials that have been dominant in building in the past are timber and stone, with lime, limited amounts of iron for fixings, lead and glass. Fired clay for bricks and tiles has been used for some time in the UK, but up to just before the turn of the nineteenth century these would have been only used locally, par- ticularly in the conurbations where there was a sufficiently large market close to the kiln site. In rural areas such as Devon, soil was still being used for agricultural cottages up to the end of the nineteenth century. Perhaps the two materials that have made the greatest impact on the size and scale of eve- ryday building have been steel and concrete. The superior strength properties have allowed greater loads to be carried on smaller sections but in particular have introduced the possibility of smaller, efficient spanning members such as beams. This opened the way to large, com- paratively voluminous building to a wider group of building clients. In the last half of the twentieth century there was an increasing number of materials introduced into buildings. More metals such as copper and aluminium now are used, particularly in services. Plastic has made a considerable impact but only where its relatively high cost can be justified by thin- sectioned components. Processing and manu- facturing developments have offered some old materials new opportunities, with techniques such as laminating timbers. As well as increasing the range of materials, developments have been made that offer more grades with greater quality control of the more traditional materials, allowing even finer choices to match performance with cost. All this demands increasing knowledge. Evaluating the more recently formulated materials is more dif- ficult for many have not yet stood the test of time. More materials introduce more possibili- ties for incompatibility so even well-tried and tested materials may fail in new combinations. Adverse reactions between materials and between materials and the environment may threaten durability in ways that have to be imagined before an analysis can be undertaken. In imagining failures it is possible to argue that all failures are ultimately materials failures.
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    26 Analysis Analysis It isalso possible to argue that the failure of the material is always the consequence of a previ- ous sequence of events and therefore never the direct fault of the material. The usefulness of this argument possibly lies in accepting that both are true. In considering the behaviour of the material, it is necessary to identify the sig- nificant events in the life of a component when a coincidence of conditions may lead to failure. The events that lead to failure will determine which properties of the material will become critical. Significant events may well be during manufacture, assembly or during the life of the building. Understanding the production process as well as the behaviour of the finished building is vital, for the most demanding event in the life of a component may well be in storage, han- dling or as part of a partially erected building. An example of this is a precast, reinforced con- crete pile where transporting and in particular driving induce entirely different stresses in the materials than when it is under load as a foundation. Materials – health, safety and the environment While it is the properties of a material that may identify it for use in a building, there are reasons why it may not be preferred or even excluded from the ultimate choice. Cost and the availabil- ity of local manufacturing techniques have already been introduced, but aspects of health, safety and the environment also have to be considered. There are many reasons why a material may be hazardous to health, particularly during the manufacturing and assembly processes, and these will be discussed in more detail in Chapter 13 in the section on health and safety. However, materials have also to be evaluated against their impact on the environment and their contribution to sustainable development. Society is reassessing its relationship with the natural environment and the demands and stresses we place on it. Much of the concern is associated with our development as a techno- logical society. This new thinking is bound to play a major part in the future in the way we build buildings. Such concerns as energy use, biodiversity, waste and pollution can be directly affected by our choice of building materials. In assessing a material for its environmental impact it is necessary to trace its entire history, often known as cradle-to-grave analysis. We can only use the materials provided by nature. Any material that finishes up in a building will have been part of an ecosystem that will be altered by the removal of the resource we require to make and shape our components. In many cases the effect will be local and nature will have the capacity to restore the balance in a short amount of time. However, as the volume of development increases and infrastructure becomes available to exploit resources on a large scale, the restorative powers of nature may be severely tested. The impact becomes more than local to the extent that the exploita- tion of the earth’s resources begins to have global implications. This is the fear at the beginning of the twenty-first century. Concerns associated with resource depletion, loss of biodiversity and global warming are all affected by decisions to use certain materials in buildings. This is not just in the extraction of materials but also in their transport, for the business of building materials is now part of global trade. There may be a preference for a renewable resource if this can be identified. Processing and manufacture use energy and produce waste and pollution. In an attempt to compare the impact of producing materials we use the idea of embodied energy or embodied carbon. It is the sum of the energy or carbon used to extract and process materials normally calculated up to the delivery to the site gate. Where components are delivered to site, the energy or carbon used in manufacture may vary even if they are made of the same material. This is discussed in more detail in Chapter 15. Assessment of embodied energy or carbon allows not only comparisons between materials but also the evaluation of using recycled mate- rial where process energy may be less than that of the original conversion. Waste and pollution
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    Construction Variables 27 Analysis alsopose a major problem in that returning the by-products of processing to nature may place a burden on the environment it is not capable of dealing with. Disposal strategies are a major concern in evaluating the environmental impact of the choice of materials. Disposal is of concern not only at the stage of manufacture and assembly but also at the end of the life of the building itself. Specifying materials where the recycling opportunities are limited and the disposal and pollution costs may be high will have to be another part of the analysis of the environmental impact of the choice of construction. Choosing shape The shaping of components can bring great ben- efits in terms of performance. It can give strength by corrugating comparatively thin materials and can provide ornament and finish to satisfy appearance requirements. It has a particular role to play at joints and at points of fixing, where shaping such as grooves and rebates can be the major contribution to achieving function. Shaping is, however, dependent on manufac- turing processes that require skills, tools and machinery. This adds cost to the component that has to be justified by its utility or a saving in material. It is also dependent on the material chosen, not only for its ability to be worked with current process skills and technology but also for its ability to be worked to fine enough devia- tions (precision) to achieve the allowable toler- ances required for performance. Early construction methods exhibit the char- acteristic of minimal working or shaping of the raw materials. Exploiting shape comes with increased resources where skills and manufac- turing technique become available. Shaping is achieved either by forming the shape directly from a formless material or by working from simple shapes available from the natural form of the raw material. In some cases these are combined where a crude shape is formed and then refined by removing material to work towards the final form. Shaping has to be related to an appropriate manufacturing process. Techniques such as casting, rolling or extruding can shape a form- less material such as concrete, clay or hot metal. Cutting or machining can then reduce materials to refine or modify the shape. Parts can be added by fixing additional pieces to make complex shapes from simpler forms. Simple forms can also be bent, pressed, beaten or forged into more complex shapes. These processes introduce a range of materials properties associ- ated with workability. They may make a mate- rial with all the properties for performance unusable or at least too expensive to use. Many of these processes are essentially factory based; the range of methods that can be undertaken on site is still limited in most cases by individual skill and tools, leaving pouring, cutting and attaching with some bending as the predominant shaping processes. Choosing shape and appreciating its per- formance value and production cost is a major consideration in technological choice. It has par- ticular significance in the issues of deviations and fit, to be discussed later in this chapter. Where parts with complex shapes have to fit together, there will be particular demands on accuracy that limit the ability of the assembly to accommodate distortions. Hence, while shaping of individual components leads to many oppor- tunities in jointing and fixing, this must be con- sidered carefully in terms of the components’ relationship to the assembly of which they form a part. Choosing size So far it has been established that the level of performance required from the construction leads to the initial choice of material based on a match between the function and a property that can be exploited economically. It has also been established that, for each material, certain proc- esses such as cutting or shaping may be avail- able to make best use of the material and facilitate assemblies that function as whole ele- ments of the building. It is now necessary to
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    28 Analysis Analysis establish dimensionssufficient to define the shape, allow manufacture and ensure assembly. In the process of choice it may be that there is a limit to the size of the component that will determine the choice of material and/or the shape. This limit may be associated with the need to fit together with other components or there may be manufacturing/handling limita- tions. It may be that visually the size of the component confounds the design vision. It is helpful to see the establishing of dimen- sions in three phases working towards a manu- facturing or working specification: • Gross size – based on performance • Coordinated size – based on incorporation with other components • Working size – based on jointing, fixing, deviations and movement The gross size will be determined by perform- ance. It represents a minimum size for water- proof materials to keep out the rain or for structural elements to support the loads. It will, therefore, identify the scale and proportion to the solution and may even show at an early stage that a solution is not possible with that material with the chosen shaping in the space available for the construction itself. If the gross size appears to be sensible to achieve performance economically and within the space available, it is then necessary to look at the dimensions in terms of the detail and how the parts of the construction will go together. This is common, for instance, where the major component is incorporated into brick or block- work. This is illustrated in Figure 4.2 for the sizing of the depth of a concrete lintel over an opening in brickwork. Structural calculations may show that the lintel only has to be 125mm deep. However, the co-ordinating depth of a brick course is 75mm (65mm for the brick and 10mm for the joint), so the lintel would have to have a coordinated size of 150mm. Establishing coordinating sizes becomes particularly significant in more industrialised and prefabricated buildings that are often Figure 4.2 Sizing depth of lintel. Working depth 140 ± 2 mm Span Load Lintel Structural depth 125 mm (a) Gross depth based on strength performance (b) Co-ordinated depth based on brick courses (c) Working depth based on joints and deviations Lintel 75 mm brick courses Co-ordinated depth 150 mm Lintel 10 mm mortar joint
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    Construction Variables 29 Analysis designedwithin a dimensional discipline around a module, leading to a basic or modular size being established. The most common module is likely to be 300mm. When selecting factory-made components available from man- ufacturers’ catalogues, the economics of pro- duction means that they are often only available in a limited number of sizes. Although these will be based on a module most likely to max- imise their potential for integration with other components, they do limit the choice without incurring additional cost. The coordinating size does not take into account: • The need for space for joints and fixings • Allowance for deviations and movement These have to be considered together, as in many cases the joints will have to allow for the deviations and movement, and the fixings will have to accommodate both deviations and movements if the assembly is to fit together on site and maintain its integrity in operation. Consideration of these aspects will lead to a working or manufacturing size. Joints are a necessary part of the assembly process to ensure fit in that they can take up deviations in components. Fixings are required to hold assemblies together and these also take up space. Sometimes the joint is also the fixing. The material of the joint and the fixings dictates their own dimensions (with its own deviations). If the fixing is in addition to the joint and this cannot be accommodated completely within the component or in the joint, space has to be pro- vided for the fixing itself. This will have to include any access required to complete the fixing on site. In some cases thought has to be given to the space necessary to remove the fixing for repair or maintenance. In the example of the lintel the joints in the brickwork are 10mm. This will be a mortar joint that will allow for deviations in the brick. It is now possible to establish the working size for the lintel at 140mm. For a full specification of the depth it is necessary to be clear that in the manufacture of the lintel any deviation from the 140mm will have to be limited as these also have to be accommodated in the 10mm mortar joint. Figure 4.2 suggests an allowable deviation or tolerance of ±2mm. It is now necessary to ensure that the material can be manufactured or worked within these deviations or there is a risk that the lintel will not fit with the brickwork. Working sizes also have to take into account any allowance for dimensional changes that may take place during the life of the compo- nent. These are known as movements or inher- ent deviations, as they are inherent in the materials chosen, and these are discussed in more detail in Chapter 12. Dimensional deviation and fit When establishing a working size and thinking about how assemblies might fit together, it is necessary to think about three things: • The size of the space into which the compo- nent has to fit • The size of the component and its position in the space • The gap that will be formed between compo- nents for the joint/fixings Generally a component can be said to fit if it can be positioned within the space so that the gaps allow for effective fixing and jointing. During construction, all of these – the space, the component and its position and the gap – will vary: they will all need to have tolerances established. In what is often thought of as traditional con- struction, trade processes control fit. Procedures such as building in and cut to fit allow for dimensions to be set by the construction itself as the work proceeds. It requires judgement as to how much reduction should be made for fixings, jointing materials, gaps or movements, but these are part of the craft tradition. It is not a question of analysis but one of common prac- tice. One person can take all the deviations into account at one point in the assembly procedure in one judgement. With the use of components and the develop- ment of prefabricated construction, building in and cutting to fit is no longer an option. There
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    Exploring the Varietyof Random Documents with Different Content
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    hundred piastres. Shewas soon able to purchase a better house, where she not only gave the man more nourishing food, but sent for a teacher to instruct him how to read and write. He had so improved in appearance by this time, and had profited so well by the wise conversation of Zubeydeh, that he was quite like another person, and those who had known him in his poverty no longer recognized him. For this reason, the Caliph, who soon repented of his anger towards Zubeydeh and made every effort to recover her, was unable to find any trace of him. Mesrour sought day and night through the streets of Baghdad, but as Zubeydeh never left the wood-cutter’s house, all his search was in vain, and the Caliph was like one distracted. “One day, as the wood-cutter was on his way to the forest, he was met by three persons, who desired to hire his asses for the day. ‘But,’ said he, ‘I make my living from the wood which the asses carry to the city.’ ‘What profit do you make upon each load?’ asked one of the men. ‘If it is a good load, I often make fifty piastres,’ answered the wood-cutter. ‘Well,’ said the men, ‘we will give you two hundred piastres as the hire of each ass, for one day.’ The wood-cutter, who had not expected such an extraordinary offer, was about to accept it at once, when he reflected that he had obeyed in all things the advice of Zubeydeh, and ought not to take such a step without her consent. He thereupon requested the men to wait while he returned home and consulted his wife. ‘You have done right, O my lord!’ said Zubeydeh: ‘I commend your prudence, and am quite willing that you should accept the offer of the men, as the money will purchase other asses and repay you for the loss of the day’s profit, if the persons should not return.’ “Now the three men were three celebrated robbers, who had amassed a vast treasure, which they kept concealed in a cave in one of the neighboring mountains. They hired the donkeys in order to transport this treasure to a barque in which they had taken passage to Bassora, where they intended to establish themselves as rich foreign merchants. But Allah, who governs all things, allows the plans of the wicked to prosper for a time, only that he may throw
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    them into moreutter ruin at the last. The robbers went to their secret cave with the donkeys and loaded them with all their spoils— great sacks of gold, of rubies, diamonds and emeralds, which the beasts were scarcely strong enough to carry. On their way to the river below Baghdad, where the boat was waiting for them, two of them stopped to drink at a well, while the other went on with the asses. Said one of the twain to the other: “Let us kill our comrade, that we may have the greater treasure.” He at once agreed, and they had no sooner overtaken the third robber, than the first, with one stroke of his sabre, made his head fly from his body. The two then proceeded together for a short distance, when the murderer said: ‘I must have more than half of the treasure, because I killed our comrade.’ ‘If you begin by claiming more than half, you will in the end claim the whole,’ said the other robber, who refused to agree. They presently set upon each other with their swords, and after fighting for some time, both of them received so many wounds that they fell dead in the road. “The asses, finding that no one was driving them any longer, took, from habit, the road to the wood-cutter’s house, where they arrived safely, with the treasure upon their backs. Great was the amazement of their master, who, at Zubeydeh’s command, carried the heavy sacks into the house. But when he had opened one of them, and the splendor of the jewels filled the whole room, Zubeydeh exclaimed: ‘God is great! Now, indeed, I see that my conduct is acceptable to Him, and that His hand hurries my design more swiftly to its completion.’ But, as she knew not what had happened to the robbers, and supposed that the owner of the treasure would have his loss proclaimed in the bazaars, she determined to keep the sacks closed for the space of a moon, after which, according to the law, they would become her property, if they had not been claimed in the mean time. Of course, no proclamation of the loss was made, and at the end of the moon, she considered that she had a just right to the treasure, which, upon computation proved to be even greater than that of the Caliph Haroun Al-Raschid.
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    “She commanded thewood-cutter to send her at once the most renowned architect of Baghdad, whom she directed to build, exactly opposite to the Caliph’s Palace, another palace which should surpass in splendor any thing that had ever been beheld. For the purchase of the materials and the hire of the workmen, she gave him a hundred thousand pieces of gold. ‘If men ask,’ said she, ‘for whom you are building the palace, tell them it is for the son of a foreign king.’ The architect employed all the workmen in Baghdad, and followed her instructions so well, that in two months the palace was finished. The like of it had never been seen, and the Caliph’s palace faded before its magnificence as the face of the moon fades when the sun has risen above the horizon. The walls were of marble, white as snow; the gates of ivory, inlaid with pearl; the domes were gilded, so that when the sun shone, the eye could not look upon them; and from a great fountain of silver, in the court-yard, a jet of rose-colored water, which diffused an agreeable odor, leaped into air. Of this palace it might be said, in the words of the poet: ‘Truly it resembles Paradise; or is it the lost House of Irem, built from the treasures of King Sheddad? May kindness dwell upon the lips of the lord of this palace, and charity find refuge in his heart, that he be adjudged worthy to enjoy such splendor!’ “During the building of the palace, Zubeydeh employed the best masters in teaching the wood-cutter all the accomplishments which his present condition required that he should possess. In a short time he was a very pattern of elegance in his manner; his words were choice and spoken with dignity and propriety, and his demeanor was that of one born to command rather than to obey. When she had succeeded to the full extent of her wishes, she commenced teaching him to play chess, and spent several hours a day in this manner, until he finally played with a skill equal to her own. By this time, the palace was completed, and after having purchased horses and slaves, and every thing necessary to the maintenance of a princely household, Zubeydeh and the wood-cutter took possession of it during the night, in order that they might not be observed by the Caliph. Zubeydeh bade the wood-cutter
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    remember the promisehe had made her. She still retained her own apartments, with a number of female slaves to attend her, and she now presented to him, as a harem becoming a prince, twenty Circassian girls, each one fairer than the morning-star. “The next morning she called the wood-cutter, and addressed him thus: ‘You see, my lord! what I have done for you. You remember in what misery I found you, and how, by your following my advice, every thing was changed. I intend to exalt you still higher, and in order that my plans may not be frustrated, I now ask you to promise that you will obey me in all things, for a month from this time.’ Zubeydeh made this demand, for she knew how quickly a change of fortune may change a man’s character, and how he will soon come to look upon that as a right which Allah granted him as a boon. But the wood-cutter threw himself at her feet, and said: ‘O Queen! it is for you to command, and it is for me to obey. You have taught me understanding and wisdom; you have given me the wealth of kings. May Allah forget me, if I forget to give you, in return, gratitude and obedience.’ ‘Go, then,’ continued Zubeydeh, ‘mount this horse, and attended by twenty slaves on horseback, visit the coffee-house in the great bazaar. Take with thee a purse of three thousand pieces of gold, and as thou goest on thy way, scatter a handful occasionally among the beggars. Take thy seat in the coffee-house, where thou wilt see the Vizier’s son, who is a skilful player of chess. He will challenge the multitude to play with him, and when no one accepts, do thou engage him for a thousand pieces of gold. Thou wilt win; but pay him the thousand pieces as if thou hadst lost, give two hundred pieces to the master of the coffee-house, divide two hundred pieces among the attendants, and scatter the remainder among the beggars.’ “The wood-cutter performed all that Zubeydeh commanded. He accepted the challenge of the Vizier’s son, won the game, yet paid him a thousand pieces of gold as if he had lost, and then rode back to the palace, followed by the acclamations of the multitude, who were loud in their praises of his beauty, the elegance of his speech, his unbounded munificence, and the splendor of his attendance.
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    Every day hevisited the coffee-house, gave two hundred pieces of gold to the master, two hundred to the servants, and distributed six hundred among the beggars. But the Vizier’s son, overcome with chagrin at his defeat, remained at home, where, in a few days, he sickened and died. These things coming to the Vizier’s ear, he felt a great desire to see the foreign prince, whose wealth and generosity were the talk of all Baghdad; and as he believed himself to be the greatest chess-player in the world, he determined to challenge him to a game. He thereupon visited the coffee-house, where he had not remained long when the wood-cutter made his appearance, in even greater splendor than before. This was in accordance with the instructions of Zubeydeh, who was informed of all that had taken place. He at once accepted the Vizier’s challenge to play, for a stake of two thousand pieces of gold. After a hard-fought battle, the Vizier was fairly beaten, but the wood-cutter paid him the two thousand pieces of gold, as if he had lost the game, gave away another thousand as usual, and retired to his palace. “The Vizier took his defeat so much to heart, that his chagrin, combined with grief for the loss of his son, carried him off in a few days. This circumstance brought the whole history to the ears of Haroun Al-Raschid himself, who was immediately seized with a strong desire to play chess with the foreign prince, not doubting but that, as he had always beaten his Vizier, he would be more than a match for the new antagonist. Accordingly he sent an officer to the palace of the wood-cutter, with a message that the Commander of the Faithful desired to offer his hospitality to the son of the foreign king. By Zubeydeh’s advice, the invitation was accepted, and the officer speedily returned to Haroun Al-Raschid, to whom he gave such a description of the magnificence of the new palace, that the Caliph’s mouth began to water, and he exclaimed: ‘By Allah! I must look to this. No man, who has not the ring of Solomon on his finger, shall surpass me in my own capital!’ In a short time the wood-cutter arrived, attired in such splendor that the day seemed brighter for his appearance, and attended by forty black slaves, in dresses of crimson silk, with turbans of white and gold, and golden swords by
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    their sides. Theyformed a double row from the court-yard to the throne-hall where the Caliph sat, and up the avenue thus formed the wood-cutter advanced, preceded by two slaves in dresses of cloth- of-silver, who placed at the Caliph’s feet two crystal goblets filled with rubies and emeralds of immense size. The Caliph, delighted with this superb present, rose, embraced the supposed prince, and seated him by his side. From the great wealth displayed by the wood-cutter, and the perfect grace and propriety of his manners, the Caliph suspected that he was no less a personage than the son of the King of Cathay. “After a handsome repast had been served, the Caliph proposed a game of chess, stating that he had heard much of the prince’s skill in playing. ‘After I shall have played with you, O Commander of the Faithful!’ said the wood-cutter, ‘you will hear no more of my skill.’ The Caliph was charmed with the modesty of this speech, and the compliment to himself, and they immediately began to play. The wood-cutter, although he might easily have beaten the Caliph, suffered the latter to win the first game, which put him into the best humor possible. But when the second game had been played, and the wood-cutter was the victor, he perceived that the Caliph’s face became dark, and his good-humor was gone. ‘You are too generous to your servant, O Caliph!’ said he; ‘had you not given me this success as an encouragement, I should have lost a second time.’ At these words Haroun smiled, and they played a third game, which the wood-cutter purposely allowed him to win. Such was the counsel given to him by Zubeydeh, who said: ‘If thou permittest him to win the first game, he will be so well pleased, that thou mayest venture to defeat him on the second game. Then, when he has won the third game, thy having been once victorious will magnify his opinion of his own skill; for where we never suffer defeat, we at last regard our conquests with indifference.’ “The result was precisely as Zubeydeh had predicted. The Caliph was charmed with the foreign prince, and in a few days made him his Vizier. The wood-cutter filled his exalted station with dignity and judgment, and became at once a great favorite with the people of
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    Baghdad. The monthof obedience which he promised to Zubeydeh was now drawing to a close, when she said to him: ‘Cease to visit the Caliph, and do not leave thy palace for two or three days. When the Caliph sends for thee, return for answer that thou art ill.’ She foresaw that the Caliph would then come to see his Vizier, and gave the wood-cutter complete instructions, concerning what he should say and do. “Haroun Al-Raschid no sooner heard of the illness of his Vizier, than he went personally to his palace, to see him. He was amazed at the size and splendor of the edifice. ‘Truly,’ said he, striking his hands together, ‘this man hath found the ring of Solomon, which compels the assistance of the genii. In all my life I have never seen such a palace as this.’ He found the Vizier reclining on a couch of cloth-of- gold, in a chamber, the walls whereof were of mother-of-pearl, and the floor of ivory. There was a fountain of perfumed water in the centre, and beside it stood a jasmine-tree, growing in a vase of crystal. ‘How is this?’ said the Caliph, seating himself on one end of the couch; ‘a man whom the genii serve, should have the secrets of health in his hands.’ ‘It is no fever,’ said the Vizier; ‘but the other day as I was washing myself in the fountain, before the evening prayer, I stooped too near the jasmine tree, and one of its thorns scratched my left arm.’ ‘What!’ cried the Caliph, in amazement; ‘the scratch of a blunt jasmine-thorn has made you ill!’. ‘You wonder at it, no doubt, O Commander of the Faithful!’ said the Vizier; ‘because, only a few months ago, you saw that I was insensible to the fangs of a serpent, which had fastened upon my heel.’ ‘There is no God but God!’ exclaimed Haroun Al-Raschid, as by these words he recognized the poor wood-cutter, who had passed under the window of his palace —‘hast thou indeed found the ring of Solomon?—and where is the woman whom Mesrour, at my command, brought to thee?’ “‘She is here!’ said Zubeydeh, entering the door. She turned towards the Caliph, and slightly lifting her veil, showed him her face, more beautiful than ever. Haroun, with a cry of joy, was on the point of clasping her in his arms, when he stopped suddenly, and said: ‘But thou art now the wife of that man.’ ‘Not so, great Caliph!’
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    exclaimed the Vizierwho rose to his feet, now that there was no longer any need to affect illness; ‘from the day that she entered my house, I have never seen her face. By the beard of the Prophet, she is not less pure than she is wise. It is she who has made me all that I am. Obedience to her was the seed from which the tree of my fortune has grown.’ Zubeydeh then knelt at the Caliph’s feet, and said: ‘O Commander of the Faithful, restore me to the light of your favor. I swear to you that I am not less your wife than when the cloud of your anger overshadowed me. This honorable man has never ceased to respect me. My thoughtless words led you to send me forth to take the place of the serpent, but I have now shown you that a wife may also be to her husband as the staff, whereon he leans for support; as the camel, which bringeth him riches; as the tent, which shelters and protects him; as the bath, which maketh him comely, and as the lamp, whereby his steps are enlightened.’ “Haroun Al-Raschid had long since bitterly repented of his rashness and cruelty. He now saw in what had happened, the hand of Allah, who had turned that which he had intended as a punishment, into a triumph. He restored Zubeydeh at once to his favor, and to the wood-cutter, whom he still retained as Vizier, he gave his eldest daughter in marriage. All the citizens of Baghdad took part in the festivities, which lasted two weeks, and the Caliph, to commemorate his gratitude, built a superb mosque, which is called the Mosque of the Restoration to this very day. The Vizier nobly requited all the pains which the Sultana Zubeydeh had taken with his education, and showed so much wisdom and justice in his administration of the laws, that the Caliph never had occasion to be dissatisfied with him. Thus they all lived together in the utmost happiness and concord, until they were each, in turn, visited by the Terminator of Delights and the Separator of Companions.” So ended Achmet’s story; but without the moonlight, the tall Ethiopian palms and the soothing pipe, as accessories, I fear that this reproduction of it retains little of the charm which I found in the original. It was followed by other and wilder tales, stamped in every part with the unmistakable signet of the Orient. They were all
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    characterized by thebelief in an inevitable Destiny, which seems to be the informing soul of all Oriental literature. This belief affords every liberty to the poet and romancer, and the Arabic authors have not scrupled to make liberal use of it. There is no hazard in surrounding your hero with all sorts of real and imaginary dangers, or in heaping up obstacles in the path of his designs, when you know that his destiny obliges him to overcome them. He becomes, for the time, the impersonation of Fate, and circumstances yield before him. You see, plainly, that he was chosen, in the beginning, to do the very thing which he accomplishes, in the end. If a miracle is needed for his success, it is not withheld. Difficulties crowd upon him to the last, only that the final triumph may be more complete and striking. Yet with all these violations of probability, the Oriental tales exhibit a great fertility of invention and sparkle with touches of genuine human nature. The deep and absorbing interest with which the unlettered Arabs listen to their recital—the hold which they have upon the popular heart of the East—attests their value, as illustrations of Eastern life. From Poetry we frequently passed to Religion, and Achmet was astonished to find me familiar not only with Mohammed, but with Ali and Abdullah and Abu-talib, and with many incidents of the Prophet’s life, which were new to him. The Persian chronicles were fresh in my memory, and all the wonders related of Mohammed by that solemn old biographer, Mohammed Bekr, came up again as vividly as when I first read them. We compared notes, he repeated passages of the Koran, and so the Giaour and the True Believer discussed the nature of their faith, but always ended by passing beyond Prophet and Apostle, to the one great and good God, who is equally merciful to all men. I could sincerely adopt the first article of his faith: “La illah il’ Allah!” “There is no God but God,” while he was equally ready to accept the first commandment of mine.
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    CHAPTER XX. FROM SHENDYTO KHARTOUM. Arrival at Shendy—Appearance of the Town—Shendy in Former Days—We Touch at El Metemma—The Nile beyond Shendy—Flesh Diet vs. Vegetables—We Escape Shipwreck—A Walk on Shore—The Rapids of Derreira—Djebel Gerri—The Twelfth Cataract—Night in the Mountain Gorge—Crocodiles—A Drink of Mareesa—My Birth-Day—Fair Wind— Approach to Khartoum—The Junction of the Two Niles—Appearance of the City—We Drop Anchor. The morning after visiting the ruins of Meroë I reached the old Ethiopian town of Shendy. It lies about half a mile from the river, but the massive fort and palace of the Governor are built on the water’s edge. Several spreading sycamore trees gave a grace to the shore, which would otherwise have been dull and tame. Naked Ethiopians were fishing or washing their clothes in the water, and some of them, as they held their long, scarlet-edged mantles above their heads, to dry in the wind and sun, showed fine, muscular figures. The women had hideous faces, but symmetrical and well developed forms. A group of Egyptian soldiers watched us from the bank before the palace, and several personages on horseback, one of whom appeared to be the Governor himself, were hailing the ferry boat, which was just about putting off with a heavy load of natives. We ran the boat to the shore, at a landing-place just above the palace. The banks of the river were covered with fields of cucumbers and beans, the latter brilliant with white and purple blossoms and filled with the murmuring sound of bees. Achmet, the raïs and I walked up to the capital—the famous Shendy, once the great mart of trade for the regions between the Red Sea and Dar-Fūr. On the way we met numbers of women with water-jars. They wore no veils, but certainly needed them, for their faces were of a broad, semi-negro character, and repulsively plain. The town is built in a straggling
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    manner, along alow, sandy ridge, and is upwards of a mile in length, though it probably does not contain more than ten thousand inhabitants. The houses are mud, of course, but rough and filthy, and many of them are the same circular tokuls of mats and palm- sticks as I had already noticed in the smaller villages. The only decent dwelling which I saw had been just erected by a Dongolese merchant. There was a mosque, with a low mud minaret, but neither in this nor in any other respect did the place compare with El Mekheyref. The bazaar resembled a stable, having a passage through the centre, shaded with mats, and stalls on either side, some of which contained donkeys and others merchants. The goods displayed were principally blue and white cotton stuffs of coarse quality, beads, trinkets and the like. It was market-day, but the people had not yet assembled. A few screens of matting, erected on sticks, were the only preparations which had been made. The whole appearance of the place was that of poverty and desertion. Beyond the clusters of huts, and a mud wall, which ran along the eastern side of the town, the Desert extended to the horizon—a hot, white plain, dotted with clumps of thorns. On our return to the boat, the raïs pointed out the spot where, in 1822, Ismaïl Pasha and his soldiers were burned to death by Mek Nemr (King Leopard), the last monarch of Shendy. The bloody revenge taken by Mohammed Bey Defterdar (son-in-law of Mohammed Ali), for that act, sealed the fate of the kingdom. The seat of the Egyptian government in Soudân was fixed at Khartoum, which in a few years became also the centre of trade, and now flourishes at the expense of Shendy and El Metemma. Burckhardt, who visited Shendy during the reign of King Leopard, devotes much space to a description of the trade of the town at that time. It was then in the height of its prosperity, and the resort of merchants from Arabia, Abyssinia, Egypt, and even Syria and Asia Minor. It was also one of the chief slave-marts of Central Africa, in which respect it has since been superseded by Obeid, in Kordofan. The only commerce which has been left to Shendy is that with Djidda and the other Arabian ports, by way of Sowakin, on the Red
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    Sea—a caravan journeyof fourteen days, through the country of Takka, infested by the wild tribes of the Hallengas and Hadendoas. Mek Nemr, according to Burckhardt, was of the Djaaleyn tribe, who are descendants of the Beni Koreish, of Yemen, and still retain the pure Arabian features. I was afterwards, during my stay in Khartoum, enabled to verify the declaration of the same traveller, that all the tribes of Ethiopia between the Nile and the Red Sea are of unmixed Arab stock. The palace of the Governor, which was a building of considerable extent, had heavy circular bastions, which were defended by cannon. Its position, on the bank of the Nile, was much more agreeable than that of the city, and the garrison had settled around it, forming a small village on its eastern side. The white walls and latticed windows of the palace reminded me of Cairo, and I anticipated a pleasant residence within its walls, on my return to Shendy. As I wished to reach Khartoum as soon as possible I did not call upon the Governor, but sent him the letter of recommendation from Yagheshir Bey. From Shendy, one sees the group of palms which serves as a landmark to El Metemma, the capital of a former Ethiopian Kingdom, further up the Nile, on its opposite bank. This is the starting point for caravans to Merawe and Dongola through the Beyooda Desert. We passed its port about noon, and stopped a few minutes to let the raïs pay his compliments to the owner of our vessel, who was on shore. He was a little old man, with a long staff, and dressed like the meanest Arab, although he was shekh of half a dozen villages, and had a servant leading a fine Dongolese horse behind him. The boat of Khalim Bey, agent of the Governor of Berber and Shendy, was at the landing place, and we saw the Bey, a tall, handsome Turk in a rich blue and crimson dress, who sent a servant to ask my name and character. The scenery of the Nile, southward from Shendy, is again changed. The tropical rains which fall occasionally at Abou-Hammed and scantily at Berber, are here periodical, and there is no longer the same striking contrast between desert and garden land. The plains extending inward from the river are covered with a growth of bushes
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    and coarse grass,which also appears in patches on the sides of the mountains. The inhabitants cultivate but a narrow strip of beans and dourra along the river, but own immense flocks of sheep and goats, which afford their principal sustenance. I noticed many fields of the grain called dookhn, of which they plant a larger quantity than of dourra. Mutton, however, is the Ethiopian’s greatest delicacy. Notwithstanding this is one of the warmest climates in the world, the people eat meat whenever they can get it, and greatly prefer it to vegetable food. The sailors and camel-drivers, whose principal food is dourra, are, notwithstanding a certain quality of endurance, as weak as children, when compared with an able-bodied European, and they universally attribute this weakness to their diet. This is a fact for the lank vegetarians to explain. My experience coincided with that of the Ethiopians, and I ascribed no small share of my personal health and strength, which the violent alternations of heat and cold during the journey had not shaken in the least, to the fact of my having fared sumptuously every day. After leaving Shendy, the Nile makes a bend to the west, and we went along slowly all the afternoon, with a side-wind. The shores were not so highly cultivated as those we had passed, and low hills of yellow sand began to show themselves on either hand. The villages were groups of mud tokuls, with high, conical roofs, and the negro type of face appeared much more frequently among the inhabitants—the result of amalgamation with slaves. We saw numbers of young crocodiles which my sailors delighted to frighten by shouting and throwing sticks at them, as they sunned themselves on the sand. Wild geese and ducks were abundant, and the quiet little coves along the shore were filled with their young brood. During the day a large hawk or vulture dashed down to within a yard of the deck in the attempt to snatch a piece of my black ram, which Beshir had just killed. The next morning we had a narrow escape from shipwreck. The wind blew strong from the north, as we reached a twist in the river, where our course for several miles lay to the north-west, obliging the men to take in sail and tow the vessel. They had reached the
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    turning-point and thesail was blowing loose, while two sailors lay out on the long, limber yard, trying to reef, when a violent gust pulled the rope out of the hands of the man on shore, and we were carried into the stream. The steersman put the helm hard up, and made for the point of an island which lay opposite, but the current was so strong that we could not reach it. It blew a gale, and the Nile was rough with waves. Between the island and the southern shore lay a cluster of sharp, black rocks, and for a few minutes we appeared to be driving directly upon them. The raïs and sailors, with many cries of “O Prophet! O Apostle!” gave themselves up to their fate; but the strength of the current saved us. Our bow just grazed the edge of the last rock, and we were blown across to the opposite shore, where we struck hard upon the sand and were obliged to remain two hours, until the wind abated. I was vexed and impatient at first, but remembering the effect of a pipe upon a similar occasion, I took one, and soon became calm enough to exclaim: “it is the will of Allah!” While the boat was making such slow headway, I went ashore and walked an hour or two among the fields of beans and dourra. The plains for several miles inland were covered with dry grass and thorn-trees, and only needed irrigation to bloom as a garden. The sun was warm, the bean-fields alive with bees, and the wind took a rich summer fragrance from the white and purple blossoms. Near one of the huts, I accosted a woman who was weeding among the dourra. She told me that her husband had deserted her and taken another wife, leaving her the charge of their two children. He had also taken her three cows and given them to his new wife, so that her only means of support was to gather the dry grass and sell it in the villages. I gave her a few piastres, which she received gratefully. In the afternoon we passed the main bend of the river, and were able to make use of the wind, which by this time was light. The sailor who had been left ashore during the gale overtook us, by walking a distance of eight or ten miles and swimming one of the smaller arms of the river. The western bank of the river now became broken and hilly, occasionally overhung by bluffs of gravelly soil, of a
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    dark red color.On the top of one of the hills there was a wall, which the raïs pointed out to me as kadeem (ancient), but it appeared too dilapidated to repay the trouble of a visit. On the following day, the scenery became remarkably wild and picturesque. After passing the village of Derreira, on the right bank, the Nile was studded with islands of various sizes, rising like hillocks from the water, and all covered with the most luxuriant vegetation. The mimosa, the acacia, the palm, the sycamore and the nebbuk flourished together in rank growth, with a profusion of smaller shrubs, and all were matted together with wild green creepers, which dropped their long streamers of pink and purple blossoms into the water. Reefs of black rock, over which the waves foamed impetuously, made the navigation intricate and dangerous. The banks of the river were high and steep, and covered with bushes and rank grass, above which the rustling blades of the dourra glittered in the sun. The country was thickly populated, and the inhabitants were mostly of the Shygheean tribe—from Dar Shygheea, the region between Dongola and Berber. The sakias were tended by Dinka slaves, as black as ebony, and with coarse, brutish faces. At one point on the eastern shore, opposite the island of Bendi, the natives had collected all their live stock, but for what purpose I could not learn. The shore was covered with hundreds of camels, donkeys, sheep, cows and goats, carefully kept in separate herds. After threading ten miles of those island bowers, we approached Djebel Gerri, which we had seen all day, ahead of us. The Nile, instead of turning westward around the flank of the mountain, as I had anticipated from the features of the landscape, made a sudden bend to the south, between a thick cluster of islands, and entered the hills. At this point there was a rapid, extending half-way across the river. The natives call it a shellàl (cataract), although it deserves the name no more than the cataracts of Assouan and Wadi-Halfa. Adopting the term, however, which has been sanctioned by long usage, this is the Twelfth Cataract of the Nile, and the last one which the traveller meets before reaching the mountains of Abyssinia. The
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    stream is verynarrow, compressed between high hills of naked red sandstone rock. At sunset we were completely shut in the savage solitude, and there we seemed likely to remain, for the wind came from all quarters by turns, and jammed the vessel against the rocks more than once. The narrow terraces of soil on the sides of the mountains were covered with dense beds of long, dry grass, and as we lay moored to the rocks, I climbed up to one of these, in spite of the raïs’s warnings that I should fall in with lions and serpents. I lay down in the warm grass, and watched the shadows deepen in the black gorge, as the twilight died away. The zikzak or crocodile-bird twittered along the shore, and, after it became quite dark, the stillness was occasionally broken by the snort of a hippopotamus, as he thrust his huge head above water, or by the yell of a hyena prowling among the hills. Talk of the pleasure of reading a traveller’s adventures in strange lands! There is no pleasure equal to that of living them: neither the anticipation nor the memory of such a scene as I witnessed that evening, can approach the fascination of the reality. I was awakened after midnight by the motion of the vessel, and looking out of my shelter as I lay, could see that we were slowly gliding through the foldings of the stony mountains. The moon rode high and bright, over the top of a peak in front, and the sound of my prow, as it occasionally grated against the rocks, alone disturbed the stillness of the wild pass. Once the wind fell, and the men were obliged to make fast to a rock, but before morning we had emerged from the mountains and were moored to the bank, to await daylight for the passage of the last rapid. In the mouth of the pass lies an island, which rises into a remarkable conical peak, about seven hundred feet in height. It is called the Rowyàn (thirst assuaged), while a lofty summit of the range of Gerri bears the name of Djebel Attshàn (the Mountain of Thirst). The latter stands on a basis of arid sand, whence its name, but the Rowyàn is encircled by the arms of the Nile. In the Wady Beit-Naga, some three or four hours’ journey eastward from the river, are the ruined temples of Naga and Mesowuràt, described by
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    Hoskins. The dateof their erection has been ascertained by Lepsius to be coeval with that of Meroë. We here saw many crocodiles, basking on the warm sand-banks. One group of five were enormous monsters, three of them being at least fifteen, and the other two twenty feet in length. They lazily dragged their long bodies into the water as we approached, but returned after we had passed. The zikzaks were hopping familiarly about them, on the sand, and I have no doubt that they do service to the crocodiles in the manner related by the Arabs. The river was still studded with islands—some mere fragments of rock covered with bushes, and some large level tracts, flourishing with rich fields of cotton and dourra. About noon, we passed a village on the eastern bank, and I sent Ali and Beshir ashore to procure supplies, for my ram was finished. Ali found only one fowl, which the people did not wish to sell, but, Turk-like, he took it forcibly and gave them the usual price. Beshir found some mareesa, a fermented drink made of dourra, and for two piastres procured two jars of it, holding two gallons each, which were brought down to the boat by a pair of sturdy Dinka women, whose beauty was almost a match for Bakhita. The mareesa had an agreeable flavor and very little intoxicating property. I noticed, however, that after Beshir had drunk nearly a gallon, he sang and danced rather more than usual, and had much to say of a sweetheart of his, who lived in El- Metemma, and who bore the charming name of Gammerò- Betahadjerò. Bakhita, after drinking an equal portion, complained to me bitterly of my white sheep, which had nibbed off the ends of the woolly twists adorning her head, but I comforted her by the present of half a piastre, for the purpose of buying mutton-fat. As the wind fell, at sunset, we reached a long slope of snowy sand, on the island of Aūssee. Achmet went to the huts of the inhabitants, where he was kindly received and furnished with milk. I walked for an hour up and down the beautiful beach, breathing the mild, cool evening air, heavy with delicious odors. The glassy Nile beside me reflected the last orange-red hues of sunset, and the evening star, burning with a white, sparry lustre, made a long track
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    of light acrosshis breast. I remembered that it was my birth-day— the fourth time I had spent my natal anniversary in a foreign land. The first had been in Germany, the second in Italy, the third in Mexico, and now the last, in the wild heart of Africa. They were all pleasant, but this was the best of all. When I returned to the vessel, I found my carpet and cushions spread on the sand, and Ali waiting with my pipe. The evening entertainment commenced: I was listening to an Arabian tale, and watching the figures of the boatmen, grouped around a fire they had kindled in a field of dookhn, when the wind came up with a sudden gust and blew out the folds of my idle flag. Instantly the sand was kicked over the brands, the carpet taken up, all hands called on board, and we dashed away on the dark river with light hearts. I rose before sunrise the next morning, and found the wind unchanged. We were sailing between low shores covered with grain- fields, and a sandy island lay in front. The raïs no sooner saw me than he called my attention to the tops of some palm-trees that appeared on the horizon, probably six or eight miles distant. They grew in the gardens of Khartoum! We reached the point of the broad, level island that divides the waters of the two Niles, and could soon distinguish the single minaret and buildings of the city. A boat, coming down from the White Nile, passed us on the right, and another, bound for Khartoum, led us up the Blue Nile. The proper division between the two rivers is the point of land upon which Khartoum is built, but the channel separating it from the island opposite is very narrow, and the streams do not fully meet and mingle their waters till the island is passed. The city presented a picturesque—and to my eyes, accustomed to the mud huts of the Ethiopian villages—a really stately appearance, as we drew near. The line of buildings extended for more than a mile along the river, and many of the houses were embowered in gardens of palm, acacia, orange and tamarind trees. The Palace of the Pasha had a certain appearance of dignity, though its walls were only unburnt brick, and his hareem, a white, two-story building, looked cool and elegant amid the palms that shaded it. Egyptian soldiers, in
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    their awkward, half-Frankcostume, were lounging on the bank before the Palace, and slaves of inky blackness, resplendent in white and red livery, were departing on donkeys on their various errands. The slope of the bank was broken at short intervals by water-mills, and files of men with skins, and women with huge earthen jars on their heads, passed up and down between the water’s edge and the openings of the narrow lanes leading between the gardens into the city. The boat of the Governor of Berber, rowed by twelve black slaves, put off from shore, and moved slowly down stream, against the north wind, as we drew up and moored the America below the garden of the Catholic Mission. It was the twelfth of January; I had made the journey from Assouan to Khartoum in twenty-six days, and from Cairo in fifty-seven.
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    CHAPTER XXI. LIFE INKHARTOUM. The American Flag—A Rencontre—Search for a House—The Austrian Consular Agent—Description of his Residence—The Garden—The Menagerie—Barbaric Pomp and State—Picturesque Character of the Society of Khartoum—Foundation and Growth of the City—Its Appearance—The Population—Unhealthiness of the Climate— Assembly of Ethiopian Chieftains—Visit of Two Shekhs—Dinner and Fireworks. At the time of my arrival in Khartoum, there were not more than a dozen vessels in port, and the only one which would pass for respectable in Egypt was the Pasha’s dahabiyeh. I had but an open merchant-boat, yet my green tent and flag gave it quite a showy air, and I saw that it created some little sensation among the spectators. The people looked at the flag with astonishment, for the stars and stripes had never before been seen in Khartoum. At the earnest prayer of the raïs, who was afraid the boat would be forcibly impressed into the service of the Government, and was anxious to get back to his sick family in El Metemma, I left the flag flying until he was ready to leave. Old Bakhita, in her dumb, ignorant way, expressed great surprise and grief when she learned that Achmet and I were going to desert the vessel. She had an indefinite idea that we had become part and parcel of it, and would remain on board for the rest of our lives. I took Achmet and started immediately in search of a house, as in those lands a traveller who wishes to be respectable, must take a residence on arriving at a city, even if he only intends to stay two or three days. Over the mud walls on either side of the lane leading up from the water, I could look into wildernesses of orange, date, fig, and pomegranate trees, oleanders in bloom and trailing vines. We entered a tolerable street, cleanly swept, and soon came to a coffee-
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    house. Two orthree persons were standing at the door, one of whom—a fat, contented-looking Turk—eyed Achmet sharply. The two looked at each other a moment in mutual doubt and astonishment, and then fell into each other’s arms. It was a Syrian merchant, whom Achmet had known in Cairo and Beyrout. “O master!” said he, his dark face radiant with delight, as he clasped the hand of the Syrian: “there never was such a lucky journey as this!” The merchant, who had been two years in Khartoum, accompanied us in our search. We went first to the residence of the shekh of the quarter, who was not at home. Two small boys, the sons of one of a detachment of Egyptian physicians, who had recently arrived, received me. They complained bitterly of Soudân, and longed to get back again to Cairo. We then went to the Governor of the city, but he was absent in Kordofan. Finally, in wandering about the streets, we met a certain Ali Effendi, who took us to a house which would be vacant the next day. It was a large mud palace, containing an outer and inner divan, two sleeping- rooms, a kitchen, store-rooms, apartments for servants, and an inclosed court-yard and stables, all of which were to be had at one hundred piastres a month—an exorbitant price, as I afterwards learned. Before engaging it, I decided to ask the advice of the Austrian Consular Agent, Dr. Reitz, for whom I had letters from the English and Austrian Consuls in Cairo. He received me with true German cordiality, and would hear of nothing else but that I should immediately take possession of an unoccupied room in his house. Accordingly the same day of my arrival beheld me installed in luxurious quarters, with one of the most brave, generous and independent of men as my associate. As the Consul’s residence was the type of a house of the best class in Khartoum, a description of it may give some idea of life in the place, under the most agreeable circumstances. The ground-plot was one hundred and thirty paces square, and surrounded by a high mud wall. Inside of this stood the dwelling, which was about half that length, and separated from it by a narrow garden and court- yard. Entering the court by the gate, a flight of steps conducted to
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    the divan, orreception-room, in the second story. From the open ante-chamber one might look to the south over the gray wastes of Sennaar, or, if the sun was near his setting, see a reach in the White Nile, flashing like the point of an Arab spear. The divan had a cushioned seat around three sides, and matting on the floor, and was really a handsome room, although its walls were mud, covered with a thin coating of lime, and its roof palm-logs overlaid with coarse matting, on which rested a layer of mud a foot thick. In the second story were also the Consular Office and a sleeping-room. The basement contained the kitchen, store-rooms, and servants’ rooms. The remainder of the house was only one story in height, and had a balcony looking on the garden, and completely embowered in flowering vines. The only rooms were the dining-hall, with cushioned divans on each side and a drapery of the Austrian colors at the end, and my apartment, which overlooked a small garden-court, wherein two large ostriches paced up and down, and a company of wild geese and wild swine made continual discord. The court at the entrance communicated with the stables, which contained the Consul’s horses—a white steed, of the pure Arabian-blood of Nedjid, and the red stallion appropriated to my use, which was sent by the King of Dar-Fūr to Lattif Pasha, and presented by him to the Consul. A hejin, or trained dromedary, of unusual size, stood in the court, and a tame lioness was tied to a stake in the corner. She was a beautiful and powerful beast, and I never passed her without taking her head between my knees, or stroking her tawny hide until she leaned against me like a cat and licked my hand. Passing through a side-door into the garden, we came upon a whole menagerie of animals. Under the long arbors, covered with luxuriant grape-vines, stood two surly hyenas, a wild ass from the mountains of the Atbara, and an Abyssinian mule. A tall marabout (a bird of the crane species, with a pouch-bill) stalked about the garden, occasionally bending a hinge in the middle of his long legs, and doubling them backwards, so that he used half of them for a seat. Adjoining the stable was a large sheep-yard, in which were gathered together gazelles, strange varieties of sheep and goats
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    from the countriesof the White Nile, a virgin-crane, and a large antilopus leucoryx, from Kordofan, with curved horns four feet in length. My favorite, however, was the leopard, which was a most playful and affectionate creature except at meal-time. He was not more than half grown, and had all the wiles of an intelligent kitten, climbing his post and springing upon me, or creeping up slyly and seizing my ankle in his mouth. The garden, which was watered by a well and string of buckets turned by an ox, had a rich variety of fruit- trees. The grape season was just over, though I had a few of the last bunches; figs were ripening from day to day, oranges and lemons were in fruit and flower, bananas blooming for another crop, and the pomegranate and kiskteh, or custard-apple, hung heavy on the branches. There was also a plantation of date-trees and sugar-cane, and a great number of ornamental shrubs. In all these picturesque features of my residence in Khartoum, I fully realized that I had at last reached Central Africa. In our mode of life, also, there was a rich flavor of that barbaric pomp and state which one involuntarily associates with the name of Soudân. We arose at dawn, and at sunrise were in the saddle. Sometimes I mounted the red stallion, of the wild breed of Dar-Fūr, and sometimes one of the Consul’s tall and fleet dromedaries. Six dark attendants, in white and scarlet dresses, followed us on dromedaries and two grooms on foot ran before us, to clear a way through the streets. After passing through Khartoum, we frequently made long excursions up the banks of the two Niles, or out upon the boundless plain between them. In this way, I speedily became familiar with the city and its vicinity, and as, on our return, I always accompanied the Consul on all his visits to the various dignitaries, I had every opportunity of studying the peculiar life of the place, and gaining some idea of its governing principles. As the only city of Central Africa which has a regular communication with the Mediterranean (by which it occasionally receives a ray of light from the civilized world beyond), it has become a capital on a small scale, and its society is a curious compound of Christian, Turk and Barbarian. On the same day, I have had a whole sheep set before me, in the house
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    of an EthiopianPrincess, who wore a ring in her nose; taken coffee and sherbet with the Pasha; and drank tea, prepared in the true English style, in the parlor of a European. When to these remarkable contrasts is added the motley character of its native population, embracing representatives from almost every tribe between Dar-Fūr and the Red Sea, between Egypt and the Negro kingdoms of the White Nile, it will readily be seen how rich a field of observation Khartoum offers to the traveller. Nevertheless, those who reside there, almost without exception, bestow upon the city and country all possible maledictions. Considered as a place of residence, other questions come into play, and they are perhaps not far wrong. Khartoum is the most remarkable—I had almost said the only example of physical progress in Africa, in this century. Where, thirty years ago, there was not even a dwelling, unless it might be the miserable tokul, or straw hut of the Ethiopian Fellah, now stands a city of some thirty or forty thousand inhabitants, daily increasing in size and importance, and gradually drawing into its mart the commerce of the immense regions of Central Africa. Its foundation, I believe, is due to Ismaïl Pasha (son of Mohammed Ali), who, during his conquests of the kingdoms of Shendy and Sennaar, in the years 1821 and 1822, recognized the importance, in a military and commercial sense, of establishing a post at the confluence of the two Niles. Mohammed Bey Defterdar, who succeeded him, seconded the plan, and ere long it was determined to make Khartoum, on account of its central position, the capital of the Egyptian pashalik of Soudân. Standing at the mouth of the Blue Nile, which flows down from the gold and iron mountains of Abyssinia, and of the White Nile, the only avenue to a dozen Negro kingdoms, rich in ivory and gum, and being nearly equidistant from the conquered provinces of Sennaar, Kordofan, Shendy and Berber, it speedily outgrew the old Ethiopian cities, and drew to itself the greater part of their wealth and commercial activity. Now it is the metropolis of all the eastern part of Soudân, and the people speak of it in much the same style as the Egyptians speak of their beloved Cairo.
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    The town islarger, cleaner and better built than any of the cities of Upper Egypt, except perhaps Siout. It extends for about a mile along the bank of the Blue Nile, facing the north, and is three- quarters of a mile in its greatest breadth. The part next the river is mostly taken up with the gardens and dwellings of Beys and other government officers, and wealthy merchants. The gardens of the Pasha, of Moussa Bey, Musakar Bey and the Catholic Mission are all large and beautiful, and towards evening, when the north wind rises, shower the fragrance of their orange and mimosa blossoms over the whole town. The dwellings, which stand in them, cover a large space of ground, but are, for the most part, only one story in height, as the heavy summer rains would speedily beat down mud walls of greater height. The Pasha’s palace, which was built during the year previous to my visit, is of burnt brick, much of which was taken from the ancient Christian ruins of Abou-Haràss, on the Blue Nile. It is a quadrangular building, three hundred feet square, with a large open court in the centre. Its front formed one side of a square, which, when complete, will be surrounded by other offices of government. For Soudân, it is a building of some pretension, and the Pasha took great pride in exhibiting it. He told me that the Arab shekhs who visited him would not believe that it was the work of man alone. Allah must have helped him to raise such a wonderful structure. It has an inclosed arched corridor in front, in the Italian style, and a square tower over the entrance. At the time of my visit Abdallah Effendi was building a very handsome two-story house of burnt brick, and the Catholic priests intended erecting another, as soon as they should have established themselves permanently. Within a few months, large additions had been made to the bazaar, while the houses of the slaves, on the outskirts of the city, were constantly springing up like ant-hills. There is no plan whatever in the disposition of the buildings. Each man surrounds his property with a mud wall, regardless of its location with respect to others, and in going from one point to another, one is obliged to make the most perplexing zigzags. I rarely ventured far on foot, as I soon became bewildered in the labyrinth
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    of blank walls.When mounted on the Consul’s tallest dromedary, I looked down on the roofs of the native houses, and could take my bearings without difficulty. All the mysteries of the lower life of Khartoum were revealed to me, from such a lofty post. On each side I looked into pent yards where the miserable Arab and Negro families lazily basked in the sun during the day, or into the filthy nests where they crawled at night. The swarms of children which they bred in those dens sat naked in the dust, playing with vile yellow dogs, and sometimes a lean burden camel stood in the corner. The only furniture to be seen was a water-skin, a few pots and jars, a basket or two, and sometimes an angareb, or coarse wooden frame covered with a netting of ropes, and serving as seat and bed. Nearly half the population of the place are slaves, brought from the mountains above Fazogl, or from the land of the Dinkas, on the White Nile. One’s commiseration of these degraded races is almost overcome by his disgust with their appearance and habits, and I found even the waste plain that stretches towards Sennaar a relief after threading the lanes of the quarters where they live. Notwithstanding the nature of its population, Khartoum is kept commendably neat and clean. It will be a lucky day for Rome and Florence when their streets exhibit no more filth than those of this African city. The bazaars only are swept every morning, but the wind performs this office for the remainder of the streets. The soog, or market, is held in a free space, opening upon the inland plain, where the country people bring their sheep, fowls, camels, dourra, vegetables and other common products. The slaughtering of animals takes place every morning on the banks of the Blue Nile, east of the city, which is thus entirely free from the effluvia arising therefrom. Here the sheep, cows, goats and camels are killed, skinned and quartered in the open air, and it is no unusual thing to see thirty or forty butchers at work on as many different animals, each surrounded by an attendant group of vultures, hawks, cranes, crows and other carnivorous birds. They are never molested by the people, and we sometimes rode through thousands of them, which had so
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    gorged themselves thatthey scarcely took the trouble to move out of our way. The place labors under the disadvantage of being the most unhealthy part of one of the most unhealthy regions in the world. From the southern frontier of Nubia, where the tropical rains begin to fall, to the table-land of Abyssinia on the south, and as far up the White Nile as has yet been explored, Soudân is devastated by fevers of the most malignant character. The summers are fatal to at least one-half of the Turks, Egyptians and Europeans who make their residence there, and the natives themselves, though the mortality is not so great among them, rarely pass through the year without an attack of fever. I arrived during the most healthy part of the year, and yet of all the persons I saw, three-fourths were complaining of some derangement of the system. The military hospital, which I visited, was filled with cases of fever, dysentery and small-pox. I was in such good bodily condition from my journey through the Desert that I could scarcely conceive the sensation of sickness, and the generous diet and invigorating exercise I enjoyed secured me from all fear of an attack. Travellers are not agreed as to the cause of this mortality in Soudân. Some attribute it to the presence of infusoriæ in the water; yet we drank the pure, mountain-born flood of the Blue Nile, and filtered it beforehand. I am disposed to side with Russegger, who accounts for it entirely by the miasma arising from decayed vegetation, during the intense heats. The country around Khartoum is a dead level; the only mountain to be seen is the long ridge of Djebel Gerrari, twelve miles to the north. Behind the town, the White Nile curves to the east, and during the inundation his waters extend even to the suburbs, almost insulating the place. The unusual sickness of the winter of 1852 might be accounted for by the inundation of the previous summer, which was so much higher than ordinary that the people were obliged to erect dykes to keep the water out of the streets. The opposite bank of the river is considered more healthy; and in the town of Halfay, only ten miles distant, the average mortality is much less.
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    I was fortunatein reaching Khartoum at a very interesting period. All the principal shekhs of the different tribes between the Nile and the Red Sea were then collected there, and as Dr. Reitz was on friendly terms with all of them, I had the opportunity of making their acquaintance, and could have readily procured a safe-conduct through their territories, if I had been disposed to make explorations in that direction. During the summer there had been trouble in the neighborhood of Sennaar, and a general movement against the Egyptian rule was feared. In October and November, however, Moussa Bey made a campaign in the regions about and beyond the Atbara, and returned with the chief malcontents in chains. They were afterwards liberated, but had been retained in Khartoum until some disputed questions should be settled. On the night of my arrival, the Consul received a visit of ceremony from the two principal ones: Hamed, the chief shekh of the Bishàrees, and Owd-el-Kerim, son of the great shekh of the Shukorees, which inhabit the wide territory between the Atbara and the Blue Nile. They were accompanied by several attendants, and by Mohammed Kheyr, the commander of the Shygheean cavalry employed in the late expedition. The latter was a fierce-looking black in rich Turkish costume. Hamed was a man of middle size, black, but with straight features and a mild, serious expression of face. He was dressed in white, as well as his attendant whose bushy hair was twisted into countless strings and pierced with a new wooden skewer. The Shukoree shekh arrived last. We were seated on the divan, and all rose when he entered. He was a tall, powerful man, with large, jet-black eyes and a bold, fierce face. He wore a white turban and flowing robes of the same color, with a fringe and stripe of crimson around the border. The Consul advanced to the edge of the carpet to meet him, when the shekh opened his arms and the two fell upon each other’s necks. Coffee and pipes were then served, and water was brought for the washing preparatory to dinner. Hamed and the Shygheean captain washed only their hands, but the great Owd-el-Kerim washed his hands, face and feet, and occupied nearly a quarter of an hour at his
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    devotions, bowing hishead many times to the earth and repeating the name of Allah with deep emphasis. We passed through the garden to the dining-room, where the shekhs were greatly amazed at seeing a table set in European style. They all failed in managing the knives and forks, except Owd-el-Kerim, who watched the Consul and myself, and did his part with dignity. Achmet had made a vermicelli soup, which they eyed very suspiciously, and did not venture to take more than a few mouthfuls. They no doubt went away with the full belief that the Franks devour worms. They were at a loss how to attack the roast mutton, until I carved it for them, but did such execution with their fingers among the stews and salads that the dishes were soon emptied. After they had again partaken of coffee and pipes in the divan, the Consul ordered two or three rockets, which had been left from his Christmas celebration, to be sent up in order to satisfy the curiosity of his guests, who had heard much of those wonderful fires, which had amazed all Khartoum, three weeks before. The shekhs and attendants were grouped on the balcony, when the first rocket-shot hissing into the air, drew its fiery curve through the darkness, and burst into a rain of yellow stars. “Wallah!” and “Mashallah!” were echoed from mouth to mouth, and the desert chiefs could scarcely contain themselves, from astonishment and delight. The second rocket went up quite near to us, and sooner than was expected. Hamed, the Bishàree shekh, was so startled that he threw both his arms around the Consul and held fast for dear life, and even the great Owd-el-Kerim drew a long breath and ejaculated, “God is great!” They then took their leave, deeply impressed with the knowledge and wisdom of the Franks.
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    CHAPTER XXII. VISITS INKHARTOUM. Visit to the Catholic Mission—Dr. Knoblecher, the Apostolic Vicar—Moussa Bey—Visit to Lattif Pasha—Reception—The Pasha’s Palace—Lions—We Dine with the Pasha—Ceremonies upon the Occasion—Music—The Guests—The Franks in Khartoum—Dr. Péney—Visit to the Sultana Nasra—An Ethiopian Dinner—Character of the Sultana. On the day of my arrival, Dr. Reitz proposed a visit to Dr. Knoblecher, the Apostolic Vicar of the Catholic Missions in Central Africa, who had returned to Khartoum about twenty days previous. The Vicar’s name was already familiar to me, from the account of his voyage up the White Nile in 1850, which was published in the German journals during his visit to Europe, and it had been my design to propose joining his party, in case he had carried out his plan of making a second voyage in the winter of 1852. He ascended as far as lat. 4° north, or about sixty miles beyond the point reached by D’Arnaud and Werne, and therefore stands at the head of Nilotic explorers. Preceded by two attendants, we walked through the town to the Catholic Mission, a spacious one-story building in a large garden near the river. Entering a court, in the centre of which grew a tall tamarind tree, we were received by an Italian monk, in flowing robes, who conducted us into a second court, inclosed by the residence of the Vicar. Here we met two other priests, a German and a Hungarian, dressed in flowing Oriental garments. They ushered us into a large room, carpeted with matting, and with a comfortable divan around the sides. The windows looked into a garden, which was filled with orange, fig and banana trees, and fragrant with jasmine and mimosa blossoms. We had scarcely seated ourselves, when the monks rose and remained standing, while Dr. Knoblecher
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