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DESIGN OF TRAVELLING FORMWORK
A project report submitted in partial fulfillment of the requirements for the award of degree of
Bachelor of Technology
in
Civil Engineering
Submitted by
PRABHA V.T. LAHARI (08131A0144)
K. TARAKESWARA RAO (08131A0125)
Under the guidance of
Dr. L VENKAT, PhD
Associate Professor, Civil Engineering
DEPARTMENT OF CIVIL ENGINEERING
GAYATRI VIDYA PARISHAD COLLEGE OF ENGINEERING
(AUTONOMOUS)
MADHURAWADA, VISAKHAPATNAM -530048
(Affiliated to JNT University, Kakinada, A.P)
April 2012
CERTIFICATE
This is to certify that the project report entitled “DESIGN OF TRAVELLING
FORMWORK FOR SEGMENTAL BOX-GIRDER” is the bonafide work carried during
the academic year 2011-2012 by
P.V.T. Lahari (08131A0144)
K. Tarakeswara Rao (08131A0125)
under the guidance of Dr. L.Venkat (PhD), Associate Professor, is submitted to the
Department of Civil Engineering, GAYATRI VIDYA PARISHAD College of Engineering
(Autonomous), Visakhapatnam in partial fulfillment of the requirements for the award of
degree of ‘Bachelor of Technology’ in ‘Civil Engineering’.
Project Guide HOD – Civil Engineering
…………………… .…………………..
Dr. L Venkat, PhD., Dr. Manchikanti Srinivas, M.Tech, Ph.D.,
Associate Professor, Professor, HOD,
Civil Engineering Dept. Civil Engineering Dept.
ACKNOWLEDGEMENTS
We wish to express our sincere gratitude to our project guide Dr. L Venkat,
Associate Professor, Department of Civil Engineering, for his esteemed
guidance for the successful completion of the project and for his constant
inspiration and encouragement.
We are thankful to Prof. N S V V S J Gandhi, Principal, G V P College of
Engineering and Dr. M Srinivas, Head of the Department, Department of
Civil Engineering for encouraging us to take up an innovative project and for
constant source of inspiration.
We thank our faculty and non-teaching staff of the department of Civil
Engineering for their constant support and assistance.
Prabha Venkata Tarunya Lahari
K Tarakeswara Rao
i
ABSTRACT
The safety, stability, speed and economy are the major concerns of any construction. As
formwork provides support and containment to the fresh concrete and provides the structure
with size and shape and controls its alignment and position, it forms an important part of the
construction. This project discusses the design of a steel formwork system for a box-girder
used in segmental bridge constructions which can be pre-fabricated and can be reused. This
approach is to increase the speed of the construction as well as the efficiency keeping
economic aspects under consideration. In order to comprehend the idea of the project more
effectively, study of design of concrete formwork for wall, column, slab, raft using timber and
steel has also been made and comparison of these models is also studied. A box girder
formwork system with mechanical screw jacks, bolted joints for haunch, rails, steel channels
and plates as its components, which can be reused for segmental bridge construction, has been
designed and design of each of its components is discussed. The design approach is such that
a single cell box girder formwork is first designed with the help of STAAD software
considering the different kinds of loads it is subjected to. The load calculations, the
calculations of the ultimate bending moment and the ultimate deflection under loads, on each
component are discussed along with the behavior of the formwork system under the loads it is
subjected to and different approaches for the design are studied. Advantages of this model are
also discussed.
ii
TABLE OF CONTENTS
ABSTRACT i
LIST OF FIGURES v
LIST OF TABLES vi
Page No.
CHAPTER-1 INTRODUCTION 1
1.1 Formwork 1
1.2 Formwork System 1
1.3 Objective and Scope of the Project 2
CHAPTER-2 FORM WORK 3
2.1 Design Considerations 4
2.2 Formwork for Concrete 5
2.3 construction of formwork 7
2.4 Order and method of removing formwork 7
2.5 Effect of Formwork on Concrete Quality 7
2.6 Causes of Formwork Failure 8
2.7 Planning for Formwork 8
CHAPTER-3 LOADS ON CONCRETE FORMWORK 9
3.1 Vertical Loads 9
3.2 Lateral Load 9
iii
CHAPTER-4 WALL FORMWORK 11
4.1 Wooden Formwork for Wall 11
4.2 Steel Formwork for Wall 13
CHAPTER-5 COLUMN FORMWORK 17
5.1 Wooden Formwork for Column 17
5.2 Steel Formwork for Column 20
CHAPTER-6 FORMWORK FOR RAFT FOUNDATION 23
6.1 Wooden Formwork for Raft Foundation 23
6.2 Steel Formwork for Raft Foundation 25
CHAPTER-7 SLAB FORMWORK 28
7.1 Wooden Formwork for Slab 28
7.2 Steel Formwork for Slab 30
CHAPTER-8 COMPARISON BETWEEN STEEL
AND WOODEN FORMWORK 35
8.1 Wooden Formwork 35
8.2 Steel formwork 36
8.3 Steel forms compared with wooden formwork 36
3.4 Timber Form Materials and Accessories 36
iv
CHAPTER-9 TRAVELLING FORMWORK
FOR BOX-GIRDER 40
9.1 Design Components 41
9.2 Load Calculation 42
9.3 Design Approach 43
9.4 Design of Travelling Formwork 45
9.5 Mechanical Screw Jacks 53
9.6 Rail Section 53
9.7 Hinge Connections 56
CHAPTER-10 CONCLUSION 57
REFERENCES 58
v
LIST OF FIGURES
FIG. NO TITLE Page No.
Fig. 1 Typical formwork setup for a wall 7
Fig. 2 Wall formwork 11
Fig. 3 Cross-section of a wall form 16
Fig. 4 Loading on column (plan view) 18
Fig. 5 Components of column form 22
Fig. 6 Raft foundation formwork 23
Fig. 7 Components of slab formwork 30
Fig. 8 Typical wall form with components identified 37
Fig. 9 Parts of typical wall form 37
Fig. 10 Different types of ties 38
Fig. 11 A continuous single member tie 39
Fig. 12 Typical cross-section of a box-girder bridge 40
Fig. 13 Dimensions of a single cell formwork 40
Fig. 14 Lateral pressure distribution 43
Fig. 15 Upper plate and strips 45
Fig. 16 STAAD drawing showing the reactions at supports for Upper plate 46
Fig. 17 Lateral plate and strips 48
Fig. 18 Loading on major beams 49
Fig. 19 Reactions at supports 50
Fig. 20 Dimensions of lateral plate 50
Fig. 21 Lateral plate with horizontal strips and major beams 51
Fig. 22 Mechanical Screw Jacks 53
Fig. 23 Loading on rail 54
Fig. 24 Section of a rail 54
Fig. 25 Components of formwork for box-girder 55
Fig. 26 Hinged Connections 56
vi
LIST OF TABLES
S. No TABLE NO. TITLE Page No.
1 1 Chemical coefficient Cc 10
2 2 Unit weight coefficient Cw 10
3 3 Allowable Stresses and Pressures
for Plywood Formwork 34
4 4 Normal size of members for wooden formwork 35
1
Chapter-1
INTRODUCTION
In the present world and ever since the beginning of the civilization, the purpose of any
construction is to provide the structure with maximum strength so that it can resist all kinds of
deformations effectively while it is also aesthetically sound, safe and is according to the plan
and within the constraints of the economy, environmental regulations and the welfare of the
general society.
Concrete reinforced buildings are preferred to other types of structures in most major
constructions because of the advantages they offer over structures made with other building
materials. Concrete has many advantages over the other building materials like its property of
being a durable material that reduces the building maintenance costs and provides a longer
service life. Reinforced concrete possesses considerable strength for resisting seismic and
wind loads. These factors and others make the selection of reinforced concrete an economical
alternative. The construction of a concrete building requires ‘formwork’ to support the slabs
(horizontal formwork) as well as columns and walls (vertical formwork).
1.1Formwork
Formwork is defined as a temporary structure whose purpose is to provide support and
containment for fresh concrete until it can support itself. It molds concrete to the desired
shape and size, and controls its position and alignment.
Concrete forms are engineered structures that are required to support loads such as fresh
concrete, construction materials, equipment, workers, various impacts, and sometimes wind.
The forms must support all the applied loads without collapse or excessive deflection.
1.2 Formwork System
A formwork system is defined as “the total system of support for freshly placed concrete
including the mold or sheathing which contacts the concrete as well as supporting members,
hardware, and necessary bracing”.
Formwork provides support to the structure and is the largest component of the reinforced
concrete buildings and hence is the most important part of the construction of the structure, as
the safety of the structure depends on it. In the construction of formwork various methods
have been used based on the need and economy. Formwork cost accounts for 40 to 60 percent
2
of the cost of the concrete frame and for approximately 10 percent of the building cost. But
keeping the safety aspect in mind along with the economical aspects and the time factor, a
formwork has to be designed.
So far the formworks are built in place, used once and subsequently wrecked. With the
growing need to improve the quality of the structure with importance being given to the
economy and the time factor, the trend is to make use of the changing and ever-improving
technologies to make innovative developments in the design and construction of new types of
formworks that are pre-fabricated, assembled in large units, deployable and can be
continuously reused.
1.3 Objective and Scope of the Project
The main objective of our project hence, is to make use of technologies to design and develop
a travelling formwork of a segmental box-girder of a bridge that can be prefabricated,
assembled in large units, deployable and can be reused. The objective also includes the design
and analysis of various components of the box-girder under lateral loads, slab loads,
deflections etc., and to determine the failure that may occur due to various reasons and the
measures to be taken to prevent the failure. The design of steel and timber formworks for the
slab, wall, column and raft are also first discussed in order to better understand the formwork
system.
The design of such a formwork would improve safety, speed, and quality of the structure.
The aim of the project is to develop such a formwork for the box-girder that can be used in the
bridge construction which can further be developed for the design of other structures like
tunnels.
The box-girder designed is slightly different from the conventional box girders used for
bridges in that this box girder has bolted joints and vertical and horizontal hydraulic jacks to
reduce the size of the box both vertically and horizontally, after the casting is done so that it
can be moved from place to place and can be reused.
The formwork system and its various components and types of formwork like wood and steel
are first discussed in detail for slab, column, wall and raft before designing the travelling
formwork for box-girder. This is to understand better the formwork system so that a proper
design can be ensured.
3
Chapter-2
Formwork
Definition:
Any means or methods which provide temporary support, access, enhancement, or otherwise
facilitate the construction of permanent structures.
Necessity:
Temporary structures form the interface between design and construction. Most permanent
structures simply could not be built without temporary structures.
Impact on Schedule, Cost, and Quality
Losses in time and money will occur if the temporary structures are not planned and
coordinated with the same degree of thoroughness as the permanent structures.
A good formwork should satisfy the following requirements:
1. It should be strong enough to withstand all types of dead and live loads.
2. It should be rigidly constructed and efficiently propped and braced both horizontally
and vertically, so as to retain its shape.
3. The joints in the formwork should be tight against leakage of cement grout.
4. Construction of formwork should permit removal of various parts in desired sequences
without damage to the concrete.
5. The material of the formwork should be cheap, easily available and should be suitable
for reuse.
6. The formwork should be set accurately to the desired line and levels should have plane
surface.
2.1 Design Considerations
Safety
Designers must place the first priority on safety.IS codes, as well as other codes in the
industry, providing stringent performance specifications (how the system should work)
regarding temporary structures.
Formwork must be:
 Strong to carry the full load and side pressure from freshly placed concrete, together
with construction traffic and equipment, and
 Sound (made of good quality, durable materials)
4
Cost
Formwork can be the most expensive part of some construction projects. Designing cost-
effective solutions to temporary structures problems could easily be the competitive
advantage a contractor has over others. The designer must have a thorough knowledge of all
the options which will sufficiently solve the temporary structures problem.
Areas of cost reduction:
1. Planning for maximum reuse − A form designed for max reuse is stronger and more
expensive, but it can save on the total form cost.
2. Economical form construction
 Use shop-built-forms− provides greatest efficiency in working conditions and in
 The purchase and use of materials and tools;
 Create shop area on the site− to form sections too large or transportation cost too high;
 Use job-built− for small jobs, or where forms must be fitted to terrain;
 Buy prefabricated forms(large number of reuses)
 Rent prefab forms(better flexibility in regulating volume of work)
3. Setting and stripping
 Repeat the same functions to increase the crew efficiency as the job progresses
 Use metal clamp or special wedge pin connections that are secure, yet easy to
assemble and dismantle; and
 Add extra features that make handling, erection, and stripping easier such as handles,
lifting eyes.
4. Cranes and Hoists
 Size of form sections should be limited to the capacity of the largest crane planned for
the job.
 Stair towers may be completed early in the schedule to be used for moving men and
materials.
 Leave one bay open to permit mobile crane and concrete truck movement.
5. Bar Setting
 Form design can permit the rebar to be pre-assembled before installation (more
favorable condition)
6. Concrete Placement
 High lifts in wall construction make placing and vibration difficult.
Placing rate is limited by form design.
5
Unique Design Challenges
Temporary structures are subject to unique loading conditions which do not apply to a
permanent structure (fluctuating or dynamic loads, impact loads, and loads which change
position). Working within spatial constraints and cramped sites requires the most efficient
temporary structure so that workers still have room to maneuver safely.
It is always possible that an unforeseen condition could arise during an excavation due to
uncertainty of soil conditions. Designers must include an appropriate factor of safety in their
calculations or they may consider contingency plans for changing soil conditions.
Types of load that structures support are:
 Dead loads – permanent; including self-weight, floor covering, suspended ceiling,
partitions, etc.
 Live loads – not permanent; the location is not fixed; including furniture, equipment,
and occupants of buildings
 Wind load (exerts a pressure or suction on the exterior of a building);
 Other loads (hydrostatic pressure)
 If the load is applied suddenly, the effects of IMPACT must be accounted for.
Design specifications provide guidance for the design of structural members and their
connections. They have no legal standing on their own, but they can easily be adopted, by
reference, as part of a building code. i.e., ACI 318-99- Building Code Requirements for
Structural Concrete. The Specifications for Design of Wood Members are by National Design
Specifications for Wood Construction by American Forest and Paper Association.
2.2 Formwork for Concrete
Formwork development has paralleled the growth of concrete construction throughout the
20th century. The increasing acceptance of concrete as a major construction material presents
the form builder a new range of problems in the development of appropriate sheathing
materials and maintenance of rigid tolerances. Figure 1 shows a typical concrete wall
formwork setup.
6
Fig. 1 - Typical wall formwork setup
Formwork is a classic temporary structure in the sense that it is erected quickly, highly loaded
for a few hours during the concrete placement, and within a few days disassembled for future
reuse. Also classic in their temporary nature are the connections, braces, tie anchorages, and
adjustment devices which forms need.
For concrete formworks, the notion of "Temporary Structures" does not quite portray the
reality. Forms, its hardware and accessories are used over and over again over their life time.
Because of that it is necessary to use materials with high durability and easy to maintain. The
form design should be such that it can be erected and disassembled efficiently in order to
maximize productivity. The disassembly or stripping of forms depends on factors such as the
bond between concrete and the form, rigidity and shrinkage of concrete. Since early form
removal is desirable for their reuse, a reliable basis for determining the earliest possible
stripping time is necessary.
Some of the early signs to look for during stripping are no excessive deflection or distortion
and no evidence of cracking or other damage to the concrete due to the removal of the forms
or the form supports. In any event, forms must not be stripped until the concrete has hardened
enough to hold its own weight and any other weight it may be carrying. The surface must be
hard enough to remain undamaged and unmarked when reasonable care is used in stripping
the forms.
7
Traditionally, formwork was erected in place and wrecked after only one time of usage. Due
to high labor costs, it is more efficient and profitable to prefabricate forms, assemble them in
large units using mechanical devices, such as cranes to erect the forms and reuse them as
much as possible.
Lumber was once the predominant form material, but developments in the use of plywood,
metal, plastics, and other materials, together with the increasing use of specialized
accessories, have changed the picture.
2.3 Construction of formwork:
This normally involves the following operations:
1. Propping and centering
2. Shuttering
3. Provision of camber
4. Cleaning and surface treatment
2.4 Order and method of removing formwork:
The sequence of orders and method of removal of formwork are as follows:
1. Shuttering forming the vertical faces of walls beams and column sides should be
removed first as they bear no load but only retain the concrete.
2. Shuttering forming soffit of slabs should be removed next.
3. Shuttering forming soffit of beams, girders or other heavily loaded shuttering should
be removed in the end.
Rapid hardening cement, warm weather and light loading conditions allow early removal of
formwork. The formwork should under no circumstances be allowed to be removed until all
the concrete reaches strength of at least twice the stresses to which the concrete may be
subjected at the time of removal of formwork. All formworks should be eased gradually and
carefully in order to prevent the load being suddenly transferred to concrete.
2.5 Effect of Formwork on Concrete Quality
In designing and building formwork, the designer should aim for maximum economy without
sacrificing quality or safety. Size, shape, and alignment of slabs, beams, and other concrete
structural elements depend on accurate construction of the forms.
The forms must be:
8
 Sufficiently rigid under the construction loads to maintain the designed shape of the
concrete,
 Stable and strong enough to maintain large members in alignment, and
 Substantially constructed to withstand handling and reuse without losing their
dimensional integrity.
The formwork must remain in place until the concrete is strong enough to carry its own
weight, or the finished structure may be damaged.
2.6 Causes of Formwork Failure
Formwork failures are the cause of many accidents and building failures that occur during
concrete construction, usually when fresh concrete is being placed. Generally some
unexpected event causes one member to fail, then others become overloaded or misaligned
and the entire formwork structure collapses. The main causes of formwork failure are:
1. Improper stripping and shore removal
2. Inadequate bracing
3. Vibration
4. Unstable soil under mudsills (A plank, frame, or small footing on the ground used as a base
for a shore or post in formwork), shoring not plumb
5. Inadequate control of concrete placement
6. Lack of attention to formwork details.
2.7 Planning for Formwork
The engineer should plan for formwork at the time of making bid considering the following
factors:
 Placing schedule and stripping time requirements;
 Capacity of equipment available to handle form sections and materials;
 Capacity of mixing and placing equipment;
 Construction joints;
 Reuse of forms as affected by stripping time;
 Relative merits of job-built, shop-built and ready-made forms; and
 Weather (protection requirements and stripping time)
9
Chapter-3
LOADS ON CONCRETE FORMWORK
3.1 Vertical loads:
Vertical loads consist of dead and live loads. The weight of formwork plus the weight of the
reinforcement and freshly placed concrete is dead load. The live load includes the weight of
the workers, equipment, material storage, runways, and impact.
Vertical loads assumed for shoring and reshoring design for multi-storey construction should
include all loads transmitted from the floors above as dictated by the proposed construction
schedule. The formwork should be designed for a live load of not less than 50 lb/ft2 (2.4kPa)
of horizontal projection. When motorized carts are used, the live load should not be less than
75 lb/ft2 (3.6kPa).The design load for combined dead and live loads should not be less than
100 lb/ft2 (4.8kPa) or 125 lb/ft2 (6.0kPa) if motorized carts are used.
3.2 Lateral load:
For concrete having a slump of 175 mm or less and placed with normal internal vibration to a
depth of 1.2 m or less, formwork can be designed for a lateral pressure as follows, where
Pmax = maximum lateral pressure, kPa;
R =rate of placement, m/h;
T = temperature of concrete during placing, °C;
Cw = unit weight coefficient per Table 3;
And
Cc = chemistry coefficient per Table 2;
For columns
With a minimum of 30Cw kPa, but in no case greater than ‘ρgh’.
For walls with a rate of placement of less than 2.1 m/h and a placement height not exceeding
4.2 m
With a minimum of 30Cw kPa, but in no case greater than ‘ρgh’.
10
For walls with a placement rate less than 2.1 m/h where placement height exceeds 4.2 m, and
for all walls with a placement rate of 2.1 to 4.5 m/h
With a minimum of 30CwkPa, but in no case greater than ‘ρgh’.
The chemistry coefficient Cc is determined from Table 1:
Table 1- Chemical coefficient Cc
Chemical coefficient Cc
Types I, II, and III without retarders* 1.0
Types I, II, and III with a retarder 1.2
Other types or blends containing less than
70% slag
or 40% fly ash without retarders*
1.2
Other types or blends containing less than
70% slag
or 40% fly ash with a retarder*
1.4
Blends containing more than 70% slag or
40% fly ash
1.4
The unit weight coefficient Cw is determined from Table 2:
Table 2 - Unit weight co-efficient Cw
Unit weight co-efficient Cw
Density of concrete Cw
Less than 2240 kg/m3
But not less than 0.8
2240 to 2400 kg/m3
1.0
Greater than 2400 kg/m3
*Retarders include any admixture, such as a retarder, retarding water reducer, retarding
midrange water-reducing admixture, or high-range water-reducing admixture (super
plasticizer), that delays setting of concrete.
11
Chapter-4
WALL FORMWORK
Load calculations:
Assumptions
Rate of placement of concrete (R) = 1 m/hr. < 2.1 m/hr.
Temperature of concrete during placing (T) = 270
c
Height of the wall= 3 m.
We use OPC without retarders and assuming fresh concrete weight as 23 kg/m3
Hence cc= 1 and cw= 1.
Lateral loading on wall
……(1)
p= 24.84kN/m2
< 30kN/m2
Hence take p= 30 k/N/m2
(626psf)
Fig. 2 wall formwork
4.1 Wooden Formwork for Wall:
Ply wood:
Load on ply= 626psf (30kN/m2
)
To find the support spacing for plywood sheathing, assume the sheets of plywood are oriented
in the form panel with the face grain across the supports (strong direction). Table 3 shows that
the plywood of thickness will carry a pressure of 885psf (42.37kN/m2
) with supports
spacing of 8 in. This is also a convenient modular spacing for support of panel edges.
12
Wale spacing:
To determine wale spacing with 8” stud spacing, the load on each stud will be 535plf
(12.9kN/m). The studs must be supported by the wales so that the bending stress, the shear
stress, and the deflection in the studs do not exceed allowable levels.
If the studs have 3 or more spans, the maximum bending moment can be approximated from
the given formula.
.…(2)
Solving l gives,
.…. (3)
The allowable bending stress, Fb gives the allowable bending moment when multiplied by the
section modulus, S.
Use H16 timber beam which has bending capacity of 3kN-m.
Therefore L= 1.52 m.
But it should also satisfy the deflection criteria.
Hence <
L<
L< 1.016
Therefore take least of 2 values. Hence provide 1m spacing between wales.
Tie spacing:
For wales, determine the spacing and size of tie required. Loads on wale are actually point
loads from studs but are often treated as distributed loads.
For 1 m wale spacing, the equivalent distributed wale load,
W = 1×30= 30kN/m.
Using Eq. 2,
Solving l gives,
Using Eq.3,
13
The allowable bending stress, Fb gives the allowable bending moment when multiplied by the
section modulus, Z.
35,200 mm3
Mallow= 0.66× fy ×Z …. (4)
Mallow= 0.66×250×35,200= 5.8kN-m.
Therefore 1.39 m
Deflection criteria:
L = 1.52 m
Therefore take least of 2 values. Hence provide 1350 mm spacing between ties.
Find the required tie size:
Load on tie = tie spacing ×wale load
= 1.35×30= 40.5kN.
The tie must have a safe working capacity of at least 41kN; the best choice is probably a 4.5
ton capacity tie.
4.2 Steel Formwork for Wall:
Load coming on to the wall = 30kN/m2
Use steel plate of thickness 3 mm.
Consider steel plate as beam of c/s dimensions 3 m×3 mm.
Then bending capacity Mallow= 0.66× fy ×Z
Therefore = 4500 mm3
.
Using Eq. 4,
14
Mallow= 0.66×250×4500= 0.7425kN-m.
Using Eq. 3,
Deflection criteria:
L = 182 mm
Therefore take least of 2 values. Hence provide 180 mm spacing between studs.
If the studs have 3 or more spans, the maximum bending moment,
Solving l gives,
The allowable bending stress, Fb gives the allowable bending moment when multiplied by the
section modulus, Z.
2083.33 mm3
Using Eq. 4,
Mallow= 0.66× fy ×Z.
Mallow= 0.66×250×2083.333= 0.34kN-m.
Therefore
15
0.79 m
Deflection criteria:
L = 0.9 m
Therefore take least of 2 values. Hence provide 790 mm spacing between wales.
For wales, determine the spacing and size of tie required. Loads on wale are actually point
loads from studs but are often treated as distributed loads.
For 0.79 m wale spacing, the equivalent distributed wale load,
W= 0.79×30 = 23.7kN/m.
Using Eq. 3,
Solving l gives,
The allowable bending stress, Fb gives the allowable bending moment when multiplied by the
section modulus, Z.
35,200 mm3
Using Eq. 4,
Mallow= 0.66× fy ×Z.
Mallow= 0.66×250×35,200= 5.8kN-m.
Therefore
1.5 m
16
Deflection criteria:
L = 1.6 m
Therefore take least of 2 values. Hence provide 1500 mm spacing between ties.
Find the required tie size:
Load on tie = tie spacing × wale load = 1.5×23.7= 35.55kN.
The tie must have a safe working capacity of at least 36kN; the best choice is probably a 4 ton
capacity tie. The wall form c/s is shown in Figure 2.
Fig. 3 Cross-section of Timber Wall Form
17
Chapter-5
COLUMN FORMWORK
Load calculations:
Assumptions
Rate of placement of concrete (R) = 1 m/hr. < 2.1 m/hr.
Temperature of concrete during placing (T) = 270
.
Column dimensions 400 mm×400 mm.
We use OPC without retarders and assuming fresh concrete weight as 23 kg/m3
Hence cc= 1 and cw = 1.
Lateral loading on column
From Eq. 1
….. (1)
p = 24.84kN/m2
< 30kN/m2
Hence take p= 30 k/N/m2
5.1 Wooden Formwork for Column:
To find the support spacing for plywood sheathing, assume the sheets of plywood are oriented
in the form panel with the face grain across the supports (strong direction). Table 3 shows that
the plywood of thickness will carry a pressure of 885psf (42.37kN/m2) with supports
spacing of 8 in. This is also a convenient modular spacing for support of panel edges. The
loading on column form is shown in Figure 3.
18
Fig. 4 Loading on Column (plan view)
Wale spacing:
To determine wale spacing, with 8” stud spacing, the load on each stud will be 417plf
(9.1kN/m)
If the studs have 3 or more spans, the maximum bending moment can be approximated.
Using Eq. 2,
Solving l gives,
The allowable bending stress, Fb gives the allowable bending moment when multiplied by the
section modulus, S.
Use H16 timber beam which has bending capacity of 3kN-m.
19
Therefore L = 1.81 m for given loading of
But it should also satisfy the deflection criteria.
Hence <
L<
L< 1.1
Therefore take least of 2 values. Hence provide 1.1 m spacing between wales.
For wales, determine the spacing and size of tie required. Loads on wale are actually point
loads from studs but are often treated as distributed loads.
For 1.1 m wale spacing, the equivalent distributed wale load,
W = 1.1×30 = 33kN/m.
Using Eq. 2,
The allowable bending stress, Fb gives the allowable bending moment when multiplied by the
section modulus, Z.
Using Eq. 4,
Mallow= 0.66× fy ×Z.
Mallow= 0.66×250×4,200= 0.693kN-m > 0.45kN-m
Deflection criteria:
Provide ISA5030 for wales.
Load on each bolt at the end of wale = 6.6k.
20
5.2 Steel Formwork for Column:
Loading on plate:
Using Eq. 4,
Bending capacity of t mm thick plate = 0.66× fy ×Z
= 0.66×250×
= 27500× t2
N-mm.
But it should be greater than max.bending moment,
27500× t2
> 0.15×106
t > 2.33mm
Deflection criteria:
t > 3.001
Therefore‘t’ should be greater than 3 mm.
Hence take 3 mm plate.
For 0.2 m spacing load coming on to studs = 30×0.2 = 6kN/m.
If the studs have 3 or more spans, the maximum bending moment,
Solving l gives,
21
The allowable bending stress, Fb gives the allowable bending moment when multiplied by the
section modulus, Z.
2083.33 mm3
Using Eq. 4,
Mallow= 0.66× fy ×Z.
Mallow= 0.66×250×2083.333= 0.34kN-m.
Therefore
0.75 m
Deflection criteria:
L = 0.88 m
Therefore take least of 2 values. Hence provide 750 mm spacing between wales.
For wales, determine the spacing and size of tie required. Loads on wale are actually point
loads from studs but are often treated as distributed loads.
For 0.79 m wale spacing, the equivalent distributed wale load,
W = 0.75×30= 22.5kN/m.
The allowable bending stress, Fb gives the allowable bending moment when multiplied by the
section modulus, Z.
22
Using Eq. 4,
Mallow= 0.66× fy ×Z.
Mallow= 0.66×250×3,400= 0.56kN-m > 0.45kN-m
Deflection criteria:
Provide ISA5030 for wales.
Load on each bolt at the end of wale = 4.5kN
Fig. 5 components of column form
23
Chapter-6
FORMWORK FOR RAFT FOUNDATION
6.1 Wooden Formwork for Raft Foundation:
To find the support spacing for plywood sheathing, assume the sheets of plywood are oriented
in the form panel with the face grain across the supports (strong direction). Table 3 shows that
the plywood will carry a pressure of 885psf (42.37kN/m2
) with supports spacing of 8 in. This
is also a convenient modular spacing for support of panel edges.
Fig.6 raft foundation formwork
Wale spacing:
To determine the wale spacing: With an 8 in. stud spacing, the load on each stud will be
417plf (9.13kN/m2
). The studs must be supported by the wales so that the bending stress, the
shear stress, and the deflection in the studs do not exceed allowable levels.
If the studs have 3 or more spans, the maximum bending moment can be approximated from
the given Table 3,
Using Eq. 2,
Solving l gives,
The allowable bending stress, Fb gives the allowable bending moment when multiplied by the
section modulus, S.
24
Use H16 timber beam which has bending capacity of 3kN-m.
Therefore L=1.52 m.
But it should also satisfy the deflection criteria.
Hence <
L<
L< 1.016
Therefore take least of 2 values. Hence provide 1m spacing between wales.
For wales, determine the spacing and size of tie required. Loads on wale are actually point
loads from studs but are often treated as distributed loads.
For 1 m wale spacing, the equivalent distributed wale load,
W = 1×30= 30kN/m.
Using Eq. 2,
Solving l gives,
The allowable bending stress, Fb gives the allowable bending moment when multiplied by the
section modulus, Z.
35,200 mm3
Using Eq. 4,
Mallow= 0.66× fy ×Z.
Mallow= 0.66×250×35,200= 5.8kN-m.
Therefore
1.39 m
Deflection criteria:
25
L = 1.52 m
Therefore take least of 2 values. Hence provide 1350 mm spacing between ties.
Find the required tie size:
Load on tie = tie spacing ×wale load
= 1.35×30= 40.5kN.
The tie must have a safe working capacity of at least 41kN; the best choice is probably 4.5
ton tie.
6.2 Steel Formwork for Raft Foundation:
Load coming on to the wall = 30kN/m2
Use steel plate of thickness 3 mm.
Consider steel plate as beam of c/s dimensions 1 m×3 mm.
Then bending capacity Mallow= 0.66× fy ×Z.
Therefore = 1500 mm3
.
Using Eq. 4,
Mallow= 0.66×250×1500= 0.2475 kN-m.
Using Eq. 3,
Deflection criteria:
26
L = 182 mm
Therefore take least of 2 values. Hence provide 180 mm spacing between studs.
Load on studs= 0.18×30= 5.4kN/m2
.
If the studs have 3 or more spans, the maximum bending moment,
Solving l gives,
The allowable bending stress, Fb gives the allowable bending moment when multiplied by the
section modulus, Z.
2083.33 mm3
Using Eq. 4,
Mallow= 0.66× fy ×Z.
Mallow= 0.66×250×2083.333= 0.34kN-m.
Therefore
0.79 m
Deflection criteria:
L = 0.9 m
Therefore take least of 2 values. Hence provide 790 mm spacing between wales.
For wales, determine the spacing and size of tie required. Loads on wale are actually point
loads from studs but are often treated as distributed loads.
For 0.79 m wale spacing, the equivalent distributed wale load,
W = 0.79×30 = 23.7kN/m.
27
Using Eq. 2,
Solving l gives,
The allowable bending stress, Fb gives the allowable bending moment when multiplied by the
section modulus, Z.
35,200 mm3
Using Eq. 4,
Mallow= 0.66× fy ×Z.
Mallow= 0.66×250×35,200= 5.8kN-m.
Therefore
1.5 m
Deflection criteria:
L = 1.6m
Therefore take least of 2 values. Hence provide 1500 mm spacing between ties.
Find the required tie size:
Load on tie = tie spacing ×wale load
= 1.5×23.7= 35.55kN.
The tie must have a safe working capacity of at least 36kN; the best choice is probably 4 ton
capacity tie.
28
Chapter-7
SLAB FORMWORK
Load calculations:
Loading on slab:
Fresh concrete load of slab thickness 150 mm= 25×0.15 (including reinforcement)
= 3.75kN/m2
.
Live load on slab according to ACI 347 = 3.6kN/m2
Total load= 7.37kN/m2
Factored load= 12kN/m2
(250psf)
7.1 Wooden Formwork for Slab:
Loading on slab:
Fresh concrete load of slab thickness 150mm = 25×0.15 (including reinforcement)
= 3.75kN/m2
.
Live load on slab according to ACI 347 = 3.6kN/m2
Total load= 7.37kN/m2
Factored load= 12kN/m2
(250psf)
To find the support spacing for plywood sheathing, assume the sheets of plywood are oriented
in the form panel with the face grain across the supports (strong direction). Table 3 shows that
the plywood of thickness will carry a pressure of 265psf (12.68kN/m2) with supports
spacing of 16 in. This is also a convenient modular spacing for support of panel edges
Wale spacing:
With 16” stud spacing, the load on each stud will be 334plf (4.872kN/m)
If the studs have 3 or more spans, the maximum bending moment can be approximated from
the given Table 4,
Using Eq. 2,
Solving l gives,
29
The allowable bending stress, Fb gives the allowable bending moment when multiplied by the
section modulus, S.
Use H16 timber beam which has bending capacity of 3kN-m.
Therefore L=2.48 m.
But it should also satisfy the deflection criteria.
Hence <
L<
L< 1.11
Therefore take least of 2 values. Hence provide 1.1 m spacing between wales.
For wales, determine the spacing and size of tie required. Loads on wale are actually point
loads from studs but are often treated as distributed loads.
For 1.1 m wale spacing, the equivalent distributed wale load,
W = 1.1×12= 13.2kN/m (832plf)
Using Eq. 2,
Solving l gives,
The allowable bending stress, Fb gives the allowable bending moment when multiplied by the
section modulus, Z.
35,200 mm3
Using Eq. 4,
Mallow= 0.66× fy ×Z
Mallow= 0.66×250×35,200= 5.8kN-m.
Therefore
2.09m
30
Deflection criteria:
L = 1.52 m
Therefore take least of 2 values. Hence provide 1500 mm spacing between posts.
Finding the required post size:
Load on post = post spacing ×wale load
= 1.5×13.2= 19.8kN.
Assuming fcd= 75 N/mm2
Area required = 19.8×103
/75 = 264 mm2
Use 3.2 mm thick pipe,
External diameter of pipe = 33.7 mm.
Area provided= 306 mm2
Moment of inertia= 36100 mm4
Radius of gyration = = 10.8 mm
89.138
8.10
15001



r
KL
From the Table 9.1(a) in IS800-2007
fcd = 82 N/mm2
Load carrying capacity of post = 306×81.6= 25kN>19.8kN
Therefore, post of Ø33.7 mm with 3.3 mm thick is satisfying all the requirements.
Fig. 7 components of slab form (timber)
31
7.2 Steel Formwork for Slab:
Load on plate = 12kN/m2
Consider steel plate as beam of c/s dimensions 1 m×3 mm.
Using Eq. 4,
Then bending capacity Mallow= 0.66× fy ×Z.
Therefore = 1500 mm3
.
Using Eq. 4,
Mallow= 0.66×250×1500= 0.2475kN-m.
Using Eq. 3,
Deflection criteria:
L = 240 mm
Therefore take least of 2 values. Hence provide 240 mm spacing between studs.
Load on studs= 0.24×12= 2.88kN/m2
.
If the studs have 3 or more spans, the maximum bending moment,
Using Eq. 2,
Solving l gives,
The allowable bending stress, Fb gives the allowable bending moment when multiplied by the
section modulus, Z.
32
2083.33 mm3
Using Eq. 4,
Mallow= 0.66× fy ×Z.
Mallow= 0.66×250×2083.333= 0.34 kN-m.
Therefore
1.08m
Deflection criteria:
L = 1.13 m
Therefore take least of 2 values. Hence provide 1 m spacing between wales.
For wales, determine the spacing and size of tie required. Loads on wale are actually point
loads from studs but are often treated as distributed loads.
For 1 m wale spacing, the equivalent distributed wale load,
W = 1×12= 12kN/m.
Using Eq. 2,
Solving l gives,
The allowable bending stress, Fb gives the allowable bending moment when multiplied by the
section modulus, Z.
35,200 mm3
Using Eq. 4,
Mallow= 0.66× fy ×Z.
33
Mallow= 0.66×250×35,200= 5.8kN-m.
Therefore
2.2 m
Deflection criteria:
L = 2.23 m
Therefore take least of 2 values. Hence provide 2.2 m spacing between posts.
Post design:
Load coming on to each pole = 2.2×9.48= 21.1kN.
Assuming fcd= 90 N/mm2
Area required = 21.1×103
/75= 293.33 mm2
Use 3.2 mm thick pipe,
External diameter of pipe = 33.7 mm.
Area provided= 306 mm2
Moment of inertia= 36100 mm4
Radius of gyration = = 10.8 mm
89.138
8.10
15001



r
KL
From the Table9.1 (a) in IS800-2007
fcd = 82 N/mm2
Load carrying capacity of post = 306×81.6= 25kN> 21.1.
Therefore, post of Ø33.7 mm with 3.3 mm thick is satisfying all the requirements.
34
Table 3– Allowable Stresses and Pressures for Plywood Formwork
Allowable Stresses and Pressures for Plywood Formwork
35
Chapter-8
COMPARISON BETWEEN STEEL AND WOODEN
FORMWORK
Timber is the most common material used for formwork. The disadvantage with timber
formwork is that it will warp, swell and shrink. Application of water impermeable cost to the
surface of wood mitigates these defects.
The construction of formwork takes time and involves expenditure up to 20 to 25% of the
cost of the structure or even more. Design of these temporary structures is made to economic
expenditure. The operation of removing the formwork is known as stripping. Stripped
formwork can be reused. Reusable forms are known as panel forms and non-usable are called
stationary forms.
8.1 Wooden Formwork:
Timber for formwork should satisfy the following requirement:
It should be
1. well-seasoned
2. light in weight
3. easily workable with nails without splitting
4. free from loose knots
Normal sizes of members for timber formwork are shown in Table 1:
Table 4 - Normal size of members for wooden formwork
Sheeting for slabs, beam, column
side and beam bottom
25 mm to 40 mm thick
Joints, ledges
50 x 70 mm to 50 x 150 mm
Posts
75 x 100 mm to 100 x 100 mm
36
Resin bonded plywood sheets are attached to timber frames to make up panels of required
sizes. The cost of plywood formwork compares favorably with that of timber shuttering and it
may even prove cheaper in certain cases in view of the following considerations:
1. It is possible to have smooth finish in which case on cost in surface finishing is there.
2. By use of large size panels it is possible to effect saving in the labor cost of fixing and
dismantling.
3. Numbers of reuses are more as compared with timber shuttering. For estimation
purpose, number of reuses can be taken as 20 to 25.
8.2 Steel Formwork
This consists of panels fabricated out of thin steel plates stiffened along the edges by small
steel angles. The panel units can be held together through the use of suitable clamps or bolts
and nuts. The panels can be fabricated in large number in any desired modular shape or size.
Steel forms are largely used in large projects or in situation where large number reuses of the
shuttering is possible. This type of shuttering is considered most suitable for circular or
curved structures.
8.3 Steel forms compared with wooden formwork:
1. Steel forms are stronger, durable and have longer life than wooden formwork and their
reuses are more in number.
2. Steel forms can be installed and dismantled with greater ease and speed.
3. The quality of exposed concrete surface by using steel forms is good and such surfaces
need no further treatment.
4. Steel formwork does not absorb moisture from concrete.
5. Steel formwork does not shrink or warp.
8.4 Timber Form Materials and Accessories
Practically all formwork jobs require some lumber. A local supplier will advise what material
and sizes are in stock or promptly obtainable, and the designer or builder can proceed
accordingly. Figure 5 shows a typical wall form with its components. Figure 6 shows parts of
a typical wall form.
37
Fig. 8 - Typical wall form with components identified.
Fig. 9 - Parts of a typical wall form
38
Ties
In order to secure concrete forms against the lateral pressure of unhardened concrete, a
tensile unit called concrete form tie is used (they are also referred to as form clamps, coil ties,
rod clamps, snap ties, etc.). Figure 7 shows a typical single member tie.
Fig.10 Different types of ties
Ties are manufactured in two basic types:
 Continuous single member ties; in which the tensile unit is a single piece, have a
special holding device added for engaging the tensile unit against the exterior of the -
form shown in Figure 5. Some single member ties may be pulled as an entire unit from
the concrete; others are broken back a predetermined distance. Some are cut flush with
the concrete surface.
39
a) Straight tie with elastic tube
b) Threaded bar with unattached plastic sleeve
Fig. 11 – A continuous single member tie
 Internal disconnecting type ties, in which the tensile unit has an inner part with
threaded connections to removable external members generally, remain in the
concrete.
40
Chapter-9
TRAVELLING FORMWORK FOR BOX-GIRDER
The travelling formwork for one cell of a twin cell segmental box girder is considered for
design.
The dimensions of the formwork under consideration are shown in the Figure 8.
Fig. 12 Typical Cross-section of Box-girder Bridge
Single cell for which the travelling formwork is designed is as shown in the Figure 9.
Fig. 13. Dimensions of the single cell formwork
41
9.1 Design Components
Upper Steel Plate/ Slab: An upper steel plate is provided to bear the external loads and acts as
a slab to the whole system.
Lateral/Vertical Steel Plates: Lateral plates of steel are provided to resist the lateral loading
and to provide a shape in the form of walls to the system.
Strips: Vertical and Horizontal Strips are provided as supports to the upper and lateral plates
which are in turn supported by the major beams of ISMC 75 Back to back channels. Lateral
buckling of these members is possible due to their lesser depth and more width compared to
depth and hence strips at regular intervals are to be provided to prevent buckling.
Back to back ISMC75 Channels: Back to back ISMC75 channels are provided to resist the
torsion and to provide support to the slab, there is a gap provided between the back to back
channels to enable future enhancements.
Horizontal Mechanical Jack: One horizontal hydraulic jack is provided to facilitate the
movement of the slab formwork in the horizontal direction.
Vertical Mechanical Jack: Two vertical hydraulic jacks are provided based on the length of
the formwork. These facilitate the movement of the walls of the box girder in upward and
downward directions to the restricted lengths.
Hinged Connection: Hinged connections are provided at the two upper corners of the box i.e.,
for the haunch so that when the box has to be compressed for reuse, after the casting is done,
the corners can be folded.
Rails: Rails are provided at the bottom end of each vertical jack so that the formwork can be
moved forward or backward to the desired position for reuse.
The design of each and every component should be done with great care and based on the
standard specification codes. The length and number of the hydraulic jacks and the design of
bolts and rails also depends on the requirement criteria.
42
9.2 Load Calculation:
Loading ( On Upper plate/ slab):
Weight of fresh concrete = density× thickness
= 25×0.4 = 10kN/sq.m
Weight of plate (6 mm thick) =78.5×0.006
=0.471kN/sq.m
Hence, Live load = 75psf
= 75×0.04788kN/sq.m
= 3.591kN/sq.m
And total vertical load = 10 + 0.471 +3.591
= 14.062
= 15kN/sq.m (approx.)
Therefore, factored vertical load = 15×1.5 = 22.5kN/sq.m
Lateral load ( On vertical/lateral plates):
Assuming, Rate of pouring (R) = 1 m/hr
= 3.281 ft/hr
Temperature (T) = 27o
C
= 27 + 273= 300 K
According to ACI 347,
Lateral Pressure, 






T
R
p 9000150







300
281.3
9000150
43
= 248.43 psf = 11.89kN/sq.m
Factored load = 11.89×1.5 = 17.835kN/sq.m
Therefore, the envelope of the maximum pressure will show a hydrostatic pressure at a depth
below the form
150
43.248
 = 1.66 ft = 0.5 m
Hence, from the above calculation, till the depth of 0.5m the pressure distribution will be
linear, then it will be constant.
{1psf= 0.0478803kN/sq.m = 0.0208854 lb/sq.ft}
The envelope of lateral pressure distribution is shown in Figure 10:
Fig.14 Lateral Pressure Distribution
9.3 Design Approach
In order to design the components of the formwork, STAAD software is used. The upper
plate, lateral plates, beams (horizontal, central and cross members) are designed on STAAD
for the loads calculated as shown above and the results obtained for Bending Moments and
Deflections are compared with the calculated allowable stress and deflection. The number of
bays, number of members, the distance between each member is based on these values. The
suitable combination of the number of bays and the deflection and bending moment obtained
44
which are less than the allowable deflection and bending moment values respectively are
considered for the final design.
For example, for the upper plate design allowable bending moment value obtained from
calculations is 1.485kN-m and the allowable deflection value is 0.6944m. Then, for a vertical
load of 33.75kN/m (calculated) and thickness of the plate- 0.006m, length- 2m as fed in
STAAD, if we take 9 supports i.e., 8 bays (bay distance of 0.25m), the maximum deflection
obtained is 0.151m which exceeds allowable deflection and the maximum bending moment
value obtained is 0.223kN-m which is within the allowable limit. But as the deflection criteria
is not satisfied and hence not safe, we go for another number of bays like 5 or 6 bays
whichever satisfies the allowable deflection and the allowable bending moment criterion.
Calculation of Allowable Deflection and Allowable Bending Moment:
Allowable deflection limit =
360
span
Allowable Bending Stress =
Z
M
f 
Allowable Bending Moment = M = f ×Z





 

6
250
3
2 dbd
[‘f’ value for Mild steel
is 250 N/ sq.mm]
The obtained maximum bending moment and deflection values for all the components should
be within these limits.
45
9.4 Design of Travelling Formwork:
The design of various components of a travelling formwork mentioned in Chapter 7 is
discussed further. The upper plate is shown in Figure 11.
Fig.15 Upper plate and strips
Upper Plate/ Slab ( 6 bays and 7 supports including ends):
Thickness= 6 mm
Bay length= 0.333 m
Width= 1.5 m
Length= 2 m
From the above load calculation, vertical load on the plate= 22.5× width of the plate,
Vertical Load = 22.5× 1.5= 33.75kN/m
Allowable deflection= 250/360= 0.6944 mm
Allowable Bending Moment 




 

6
661500
25066.0 = 1.485kN-m
STAAD RESULTS:
Max. Deflection= 0.475 m < 0.6944 mm
46
Max. Bending moment= 0.396kN-m <1.485kN-m
Hence Safe.
Sometimes, even though the max.deflection and the max.bending moment obtained are within
the allowable limits, the design might not be considered if obtained max.deflection or bending
moments are too less than the allowable limits. Even if the values are appropriate the number
of bays could be very high, which is not economical. In these cases, combinations have to be
changed.
STAAD drawing showing the reactions at supports for Upper plate are shown in Figure 12:
Fig.16 STAAD drawing showing the reactions at supports for Upper plate.
Vertical Strips( 7 nos):
Vertical End Strips:
Depth= 6 cm
Width= 6 mm
Length= 1.5 m
For end strips, Loading= 22.5×0.33/2= 3.7125kN/m
47
Allowable deflection=
360
l
=
360
1000
8.0  = 2.22 mm
For Overhang portion, allowable deflection=
360
1000
35.0  = 0.97 mm
Allowable Bending Moment= 




 

6
50506
25066.0 = 0.41kN-m
STAAD RESULTS:
Max. deflection= 0.944 m < 2.22 mm
< 0.97 mm
Max. Bending moment= 0.24kN-m <0.41kN-m
Hence safe.
For Vertical end strips, depth of 6 mm and width of 6 cm are used and as shown above, it
satisfies the deflection and bending moment conditions.
But for the Vertical Intermediate strips, if same depth and bending moment are used and the
loading on them is twice than that of the Vertical End strips and in that case, the deflection
and Bending moment obtained are very high and exceed the allowable deflection and bending
moment.
So, depth, as it cannot be changed, we increase the width to 8 mm for Vertical Intermediate
strips to reduce the bending moment and deflection.
Vertical Intermediate Strips:
Depth= 6 cm
48
Width= 8 mm
For Central strips, Loading= 22.5×0.33= 7.425kN/m
Allowable Deflection=
360
l
360
1000
35.0  = 0.9777 mm
STAAD RESULTS:
Max. deflection= 0.772 mm< 0.9777 mm
Max. Bending moment= 0.46kN-m
Hence safe.
As the allowable deflection for overhang part (of length 0.35 mm) is more than that of the part
between supports (i.e., of length 0.8 mm), the obtained deflections can be compared for all the
parts with the allowable deflection of the overhanging part.
Major Beams (B/B ISMC 75 OF 2 nos):
To support the vertical members which are supports for slab, two major beams of back to
back ISMC 75 are provided. These are shown in the Figure 13:
Fig.17 Lateral Plate and Strips
The vertical members act as point loads on the two major beams as shown in Figure 14:
49
Fig.18 Loading on Major Beams
The vertical members act as point loads on the two cross members as shown above.
Length= 2 m
ISMC 75 channels section details:
Allowable deflection=
360
250
=
360
)333.022( 
= 3.7 mm
50
Allowable Bending Moment= 




 

1000
22.20
25066.0 = 6.666kN-m
STAAD RESULTS:
Max. deflection= 3.594 m < 3.7 mm
Max. Bending moment= 5.96kN-m < 6.666kN-m
Hence safe.
The reactions at supports are shown in Figure 15.
Fig.19 Reactions at Supports
Lateral/Vertical Plates:
Lateral plate is shown in Figure 16:
Fig.20 Dimensions of Lateral Plate
51
Thickness= 6 mm
Width= 2 m
Loading= 18×2 m= 36kN/m
6 Supports:
Allowable deflection =
360
1000
4.0  = 1.11 mm
Allowable Bending Moment= 




 

6
6610002
25066.0 = 1.98kN-m
STAAD RESULTS:
Max. deflection= 0.796 mm< 1.11 mm
Max. Bending moment= 0.61kN-m< 1.98kN-m
Hence Safe.
Horizontal Strips:
The horizontal strips and major beams are shown in Figure 17:
Fig.21 Lateral Plate with Horizontal Strips and Major Beams
52
Horizontal End Strips:
Allowable deflection= 







300300
101010
445.0 = 1.236 mm
Allowable Bending Moment= 




 

6
6060
525066.0 = 0.495kN-m
Max. deflection= 0.86 mm< 1.236 mm
Max. Bending Moment= 0.305kN-m
Reactions on major beam= 3.6kN, 3.6kN
Horizontal Intermediate Strips:
Allowable deflection= 




 
360
101010
445.0 = 1.230 mm
Allowable Bending Moment= 




 

6
8080
525066.0 = 0.85kN-m
Max. deflection= 0.726 mm
Max. Bending moment= 0.713kN-m
Reaction= 7.2kN, 7.2kN
Major Beams (B/B ISMC 75 of 2 nos):
The section details for the major beams are same as that of the major beams for the upper
plate.
Z (w.r.t X-axis)= 20.2 cu.m for single columns
Moment Capacity= )101010(2.2025066.0  = 6.666kN-m
Max. Moment= 1.44kN-m
Max.deflection= 0.673 mm
Allowable deflection= 




 

300
101010
400 = 1.11kN-m
53
Reactions:
At A= 18kN, At B= 18kN
9.5 Mechanical Screw Jacks:
Vertical Jacks:
4 Mechanical screw jacks of 4 tons capacity are used as the load coming on each one is 3.6
tons.
Horizontal Jacks:
4 mechanical screw jacks of 2 tons capacity are used as the load coming on each one is 1.8
tons.
These will be clamped to the major beams of the slab and the lateral plate.
The mechanical screw jacks that can be used are shown in Figure 18:
Fig.22 Mechanical Screw Jacks
9.6 Rail Section:
Rails are used to facilitate the movement or transfer of the formwork from one segment to the
next after the concrete is set.
The loading on the rail and the bending capacity are shown in Figure 19:
54
Fig. 23 Loading on Rail
Max BM = 11.25kN-m
Bending capacity = 12.6kN-m
Section of the rail that is used in the formwork floor is as shown in the Figure 20:
Fig.24 Section of a Rail
55
A drawing of the cross section of the box girder with the above described components is
shown in the Figure 21. The hinged connection at the haunch is showed in detail in Figure 22.
Fig.25 Components of Formwork for Box-girder
56
9.7 Hinge Connections:
Hinges are provided for haunch as the connections between the ends of upper slab and the
lateral plates to enable the folding of the formwork for reuse.
The hinged connections that are used for this purpose are as shown in the Figure 22:
Fig.26 Hinged Connections
57
Chapter-10
CONCLUSION
The summary report presented above discusses the design aspects of a travelling formwork
for a segmental box girder which can be prefabricated and reused. Prior to this the design of
steel and timber formworks for slab, raft, column and wall are also discussed in order to
understand the project better. A comparison between steel and wood formworks is discussed
along with the temporary structures. As the economy, speed and efficiency are the major
considerations of any project, an effort has been made to improve the efficiency of the project
by reducing the waste of time and material by designing a travelling formwork for a
segmental box girder. This formwork can be reused for one segment after another after the
concrete is set. This prefabricated formwork design and its components are discussed in the
report. The detailed design of each component using STAAD PRO software and the
calculations based on references and IS codes are presented. The model can be reused and
hence it is advantageous over various other formwork systems as it improves the work
efficiency by reducing the time taken for construction and wastage of material.
58
REFERENCES
1) Arch Alexander, “Design and Construction of Concrete Formwork”, The Civil
Engineering Handbook, Second Edition, Edited by W . F . Chen and J . Y . Richard
Liew, CRC Press 2002, Chapter-4.
2) Brand, R.E. 1975. Falsework and Access Scaffolds in Tubular Steel. McGraw-Hill,
New York.
3) Chen, W.F. and Mosallam, K.H. 1991. Concrete Buildings, Analysis for Safe
Construction. CRC Press, BocaRaton, FL.
4) Hurd, M.K. 1989. Formwork for Concrete, 6th ed. American Concrete Institute,
Detroit, MI.
5) Moore, C.E. 1977. Concrete Form Construction. Van Nostrand Reinhold, New York.
6) Peurifoy, P.E. 1976. Formwork for Concrete Structures. McGraw-Hill, New York.
7) Ratay, R.T. 1984. Handbook of Temporary Structures in Construction. McGraw-Hill,
New York.
8) Load calculations including vertical and lateral were based on ACI Committee 347
recommendations.
9) IS: 14687- 1999 Falsework for the Concrete Structures-Guidelines.

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B.Tech Research Paper

  • 1. DESIGN OF TRAVELLING FORMWORK A project report submitted in partial fulfillment of the requirements for the award of degree of Bachelor of Technology in Civil Engineering Submitted by PRABHA V.T. LAHARI (08131A0144) K. TARAKESWARA RAO (08131A0125) Under the guidance of Dr. L VENKAT, PhD Associate Professor, Civil Engineering DEPARTMENT OF CIVIL ENGINEERING GAYATRI VIDYA PARISHAD COLLEGE OF ENGINEERING (AUTONOMOUS) MADHURAWADA, VISAKHAPATNAM -530048 (Affiliated to JNT University, Kakinada, A.P) April 2012
  • 2. CERTIFICATE This is to certify that the project report entitled “DESIGN OF TRAVELLING FORMWORK FOR SEGMENTAL BOX-GIRDER” is the bonafide work carried during the academic year 2011-2012 by P.V.T. Lahari (08131A0144) K. Tarakeswara Rao (08131A0125) under the guidance of Dr. L.Venkat (PhD), Associate Professor, is submitted to the Department of Civil Engineering, GAYATRI VIDYA PARISHAD College of Engineering (Autonomous), Visakhapatnam in partial fulfillment of the requirements for the award of degree of ‘Bachelor of Technology’ in ‘Civil Engineering’. Project Guide HOD – Civil Engineering …………………… .………………….. Dr. L Venkat, PhD., Dr. Manchikanti Srinivas, M.Tech, Ph.D., Associate Professor, Professor, HOD, Civil Engineering Dept. Civil Engineering Dept.
  • 3. ACKNOWLEDGEMENTS We wish to express our sincere gratitude to our project guide Dr. L Venkat, Associate Professor, Department of Civil Engineering, for his esteemed guidance for the successful completion of the project and for his constant inspiration and encouragement. We are thankful to Prof. N S V V S J Gandhi, Principal, G V P College of Engineering and Dr. M Srinivas, Head of the Department, Department of Civil Engineering for encouraging us to take up an innovative project and for constant source of inspiration. We thank our faculty and non-teaching staff of the department of Civil Engineering for their constant support and assistance. Prabha Venkata Tarunya Lahari K Tarakeswara Rao
  • 4. i ABSTRACT The safety, stability, speed and economy are the major concerns of any construction. As formwork provides support and containment to the fresh concrete and provides the structure with size and shape and controls its alignment and position, it forms an important part of the construction. This project discusses the design of a steel formwork system for a box-girder used in segmental bridge constructions which can be pre-fabricated and can be reused. This approach is to increase the speed of the construction as well as the efficiency keeping economic aspects under consideration. In order to comprehend the idea of the project more effectively, study of design of concrete formwork for wall, column, slab, raft using timber and steel has also been made and comparison of these models is also studied. A box girder formwork system with mechanical screw jacks, bolted joints for haunch, rails, steel channels and plates as its components, which can be reused for segmental bridge construction, has been designed and design of each of its components is discussed. The design approach is such that a single cell box girder formwork is first designed with the help of STAAD software considering the different kinds of loads it is subjected to. The load calculations, the calculations of the ultimate bending moment and the ultimate deflection under loads, on each component are discussed along with the behavior of the formwork system under the loads it is subjected to and different approaches for the design are studied. Advantages of this model are also discussed.
  • 5. ii TABLE OF CONTENTS ABSTRACT i LIST OF FIGURES v LIST OF TABLES vi Page No. CHAPTER-1 INTRODUCTION 1 1.1 Formwork 1 1.2 Formwork System 1 1.3 Objective and Scope of the Project 2 CHAPTER-2 FORM WORK 3 2.1 Design Considerations 4 2.2 Formwork for Concrete 5 2.3 construction of formwork 7 2.4 Order and method of removing formwork 7 2.5 Effect of Formwork on Concrete Quality 7 2.6 Causes of Formwork Failure 8 2.7 Planning for Formwork 8 CHAPTER-3 LOADS ON CONCRETE FORMWORK 9 3.1 Vertical Loads 9 3.2 Lateral Load 9
  • 6. iii CHAPTER-4 WALL FORMWORK 11 4.1 Wooden Formwork for Wall 11 4.2 Steel Formwork for Wall 13 CHAPTER-5 COLUMN FORMWORK 17 5.1 Wooden Formwork for Column 17 5.2 Steel Formwork for Column 20 CHAPTER-6 FORMWORK FOR RAFT FOUNDATION 23 6.1 Wooden Formwork for Raft Foundation 23 6.2 Steel Formwork for Raft Foundation 25 CHAPTER-7 SLAB FORMWORK 28 7.1 Wooden Formwork for Slab 28 7.2 Steel Formwork for Slab 30 CHAPTER-8 COMPARISON BETWEEN STEEL AND WOODEN FORMWORK 35 8.1 Wooden Formwork 35 8.2 Steel formwork 36 8.3 Steel forms compared with wooden formwork 36 3.4 Timber Form Materials and Accessories 36
  • 7. iv CHAPTER-9 TRAVELLING FORMWORK FOR BOX-GIRDER 40 9.1 Design Components 41 9.2 Load Calculation 42 9.3 Design Approach 43 9.4 Design of Travelling Formwork 45 9.5 Mechanical Screw Jacks 53 9.6 Rail Section 53 9.7 Hinge Connections 56 CHAPTER-10 CONCLUSION 57 REFERENCES 58
  • 8. v LIST OF FIGURES FIG. NO TITLE Page No. Fig. 1 Typical formwork setup for a wall 7 Fig. 2 Wall formwork 11 Fig. 3 Cross-section of a wall form 16 Fig. 4 Loading on column (plan view) 18 Fig. 5 Components of column form 22 Fig. 6 Raft foundation formwork 23 Fig. 7 Components of slab formwork 30 Fig. 8 Typical wall form with components identified 37 Fig. 9 Parts of typical wall form 37 Fig. 10 Different types of ties 38 Fig. 11 A continuous single member tie 39 Fig. 12 Typical cross-section of a box-girder bridge 40 Fig. 13 Dimensions of a single cell formwork 40 Fig. 14 Lateral pressure distribution 43 Fig. 15 Upper plate and strips 45 Fig. 16 STAAD drawing showing the reactions at supports for Upper plate 46 Fig. 17 Lateral plate and strips 48 Fig. 18 Loading on major beams 49 Fig. 19 Reactions at supports 50 Fig. 20 Dimensions of lateral plate 50 Fig. 21 Lateral plate with horizontal strips and major beams 51 Fig. 22 Mechanical Screw Jacks 53 Fig. 23 Loading on rail 54 Fig. 24 Section of a rail 54 Fig. 25 Components of formwork for box-girder 55 Fig. 26 Hinged Connections 56
  • 9. vi LIST OF TABLES S. No TABLE NO. TITLE Page No. 1 1 Chemical coefficient Cc 10 2 2 Unit weight coefficient Cw 10 3 3 Allowable Stresses and Pressures for Plywood Formwork 34 4 4 Normal size of members for wooden formwork 35
  • 10. 1 Chapter-1 INTRODUCTION In the present world and ever since the beginning of the civilization, the purpose of any construction is to provide the structure with maximum strength so that it can resist all kinds of deformations effectively while it is also aesthetically sound, safe and is according to the plan and within the constraints of the economy, environmental regulations and the welfare of the general society. Concrete reinforced buildings are preferred to other types of structures in most major constructions because of the advantages they offer over structures made with other building materials. Concrete has many advantages over the other building materials like its property of being a durable material that reduces the building maintenance costs and provides a longer service life. Reinforced concrete possesses considerable strength for resisting seismic and wind loads. These factors and others make the selection of reinforced concrete an economical alternative. The construction of a concrete building requires ‘formwork’ to support the slabs (horizontal formwork) as well as columns and walls (vertical formwork). 1.1Formwork Formwork is defined as a temporary structure whose purpose is to provide support and containment for fresh concrete until it can support itself. It molds concrete to the desired shape and size, and controls its position and alignment. Concrete forms are engineered structures that are required to support loads such as fresh concrete, construction materials, equipment, workers, various impacts, and sometimes wind. The forms must support all the applied loads without collapse or excessive deflection. 1.2 Formwork System A formwork system is defined as “the total system of support for freshly placed concrete including the mold or sheathing which contacts the concrete as well as supporting members, hardware, and necessary bracing”. Formwork provides support to the structure and is the largest component of the reinforced concrete buildings and hence is the most important part of the construction of the structure, as the safety of the structure depends on it. In the construction of formwork various methods have been used based on the need and economy. Formwork cost accounts for 40 to 60 percent
  • 11. 2 of the cost of the concrete frame and for approximately 10 percent of the building cost. But keeping the safety aspect in mind along with the economical aspects and the time factor, a formwork has to be designed. So far the formworks are built in place, used once and subsequently wrecked. With the growing need to improve the quality of the structure with importance being given to the economy and the time factor, the trend is to make use of the changing and ever-improving technologies to make innovative developments in the design and construction of new types of formworks that are pre-fabricated, assembled in large units, deployable and can be continuously reused. 1.3 Objective and Scope of the Project The main objective of our project hence, is to make use of technologies to design and develop a travelling formwork of a segmental box-girder of a bridge that can be prefabricated, assembled in large units, deployable and can be reused. The objective also includes the design and analysis of various components of the box-girder under lateral loads, slab loads, deflections etc., and to determine the failure that may occur due to various reasons and the measures to be taken to prevent the failure. The design of steel and timber formworks for the slab, wall, column and raft are also first discussed in order to better understand the formwork system. The design of such a formwork would improve safety, speed, and quality of the structure. The aim of the project is to develop such a formwork for the box-girder that can be used in the bridge construction which can further be developed for the design of other structures like tunnels. The box-girder designed is slightly different from the conventional box girders used for bridges in that this box girder has bolted joints and vertical and horizontal hydraulic jacks to reduce the size of the box both vertically and horizontally, after the casting is done so that it can be moved from place to place and can be reused. The formwork system and its various components and types of formwork like wood and steel are first discussed in detail for slab, column, wall and raft before designing the travelling formwork for box-girder. This is to understand better the formwork system so that a proper design can be ensured.
  • 12. 3 Chapter-2 Formwork Definition: Any means or methods which provide temporary support, access, enhancement, or otherwise facilitate the construction of permanent structures. Necessity: Temporary structures form the interface between design and construction. Most permanent structures simply could not be built without temporary structures. Impact on Schedule, Cost, and Quality Losses in time and money will occur if the temporary structures are not planned and coordinated with the same degree of thoroughness as the permanent structures. A good formwork should satisfy the following requirements: 1. It should be strong enough to withstand all types of dead and live loads. 2. It should be rigidly constructed and efficiently propped and braced both horizontally and vertically, so as to retain its shape. 3. The joints in the formwork should be tight against leakage of cement grout. 4. Construction of formwork should permit removal of various parts in desired sequences without damage to the concrete. 5. The material of the formwork should be cheap, easily available and should be suitable for reuse. 6. The formwork should be set accurately to the desired line and levels should have plane surface. 2.1 Design Considerations Safety Designers must place the first priority on safety.IS codes, as well as other codes in the industry, providing stringent performance specifications (how the system should work) regarding temporary structures. Formwork must be:  Strong to carry the full load and side pressure from freshly placed concrete, together with construction traffic and equipment, and  Sound (made of good quality, durable materials)
  • 13. 4 Cost Formwork can be the most expensive part of some construction projects. Designing cost- effective solutions to temporary structures problems could easily be the competitive advantage a contractor has over others. The designer must have a thorough knowledge of all the options which will sufficiently solve the temporary structures problem. Areas of cost reduction: 1. Planning for maximum reuse − A form designed for max reuse is stronger and more expensive, but it can save on the total form cost. 2. Economical form construction  Use shop-built-forms− provides greatest efficiency in working conditions and in  The purchase and use of materials and tools;  Create shop area on the site− to form sections too large or transportation cost too high;  Use job-built− for small jobs, or where forms must be fitted to terrain;  Buy prefabricated forms(large number of reuses)  Rent prefab forms(better flexibility in regulating volume of work) 3. Setting and stripping  Repeat the same functions to increase the crew efficiency as the job progresses  Use metal clamp or special wedge pin connections that are secure, yet easy to assemble and dismantle; and  Add extra features that make handling, erection, and stripping easier such as handles, lifting eyes. 4. Cranes and Hoists  Size of form sections should be limited to the capacity of the largest crane planned for the job.  Stair towers may be completed early in the schedule to be used for moving men and materials.  Leave one bay open to permit mobile crane and concrete truck movement. 5. Bar Setting  Form design can permit the rebar to be pre-assembled before installation (more favorable condition) 6. Concrete Placement  High lifts in wall construction make placing and vibration difficult. Placing rate is limited by form design.
  • 14. 5 Unique Design Challenges Temporary structures are subject to unique loading conditions which do not apply to a permanent structure (fluctuating or dynamic loads, impact loads, and loads which change position). Working within spatial constraints and cramped sites requires the most efficient temporary structure so that workers still have room to maneuver safely. It is always possible that an unforeseen condition could arise during an excavation due to uncertainty of soil conditions. Designers must include an appropriate factor of safety in their calculations or they may consider contingency plans for changing soil conditions. Types of load that structures support are:  Dead loads – permanent; including self-weight, floor covering, suspended ceiling, partitions, etc.  Live loads – not permanent; the location is not fixed; including furniture, equipment, and occupants of buildings  Wind load (exerts a pressure or suction on the exterior of a building);  Other loads (hydrostatic pressure)  If the load is applied suddenly, the effects of IMPACT must be accounted for. Design specifications provide guidance for the design of structural members and their connections. They have no legal standing on their own, but they can easily be adopted, by reference, as part of a building code. i.e., ACI 318-99- Building Code Requirements for Structural Concrete. The Specifications for Design of Wood Members are by National Design Specifications for Wood Construction by American Forest and Paper Association. 2.2 Formwork for Concrete Formwork development has paralleled the growth of concrete construction throughout the 20th century. The increasing acceptance of concrete as a major construction material presents the form builder a new range of problems in the development of appropriate sheathing materials and maintenance of rigid tolerances. Figure 1 shows a typical concrete wall formwork setup.
  • 15. 6 Fig. 1 - Typical wall formwork setup Formwork is a classic temporary structure in the sense that it is erected quickly, highly loaded for a few hours during the concrete placement, and within a few days disassembled for future reuse. Also classic in their temporary nature are the connections, braces, tie anchorages, and adjustment devices which forms need. For concrete formworks, the notion of "Temporary Structures" does not quite portray the reality. Forms, its hardware and accessories are used over and over again over their life time. Because of that it is necessary to use materials with high durability and easy to maintain. The form design should be such that it can be erected and disassembled efficiently in order to maximize productivity. The disassembly or stripping of forms depends on factors such as the bond between concrete and the form, rigidity and shrinkage of concrete. Since early form removal is desirable for their reuse, a reliable basis for determining the earliest possible stripping time is necessary. Some of the early signs to look for during stripping are no excessive deflection or distortion and no evidence of cracking or other damage to the concrete due to the removal of the forms or the form supports. In any event, forms must not be stripped until the concrete has hardened enough to hold its own weight and any other weight it may be carrying. The surface must be hard enough to remain undamaged and unmarked when reasonable care is used in stripping the forms.
  • 16. 7 Traditionally, formwork was erected in place and wrecked after only one time of usage. Due to high labor costs, it is more efficient and profitable to prefabricate forms, assemble them in large units using mechanical devices, such as cranes to erect the forms and reuse them as much as possible. Lumber was once the predominant form material, but developments in the use of plywood, metal, plastics, and other materials, together with the increasing use of specialized accessories, have changed the picture. 2.3 Construction of formwork: This normally involves the following operations: 1. Propping and centering 2. Shuttering 3. Provision of camber 4. Cleaning and surface treatment 2.4 Order and method of removing formwork: The sequence of orders and method of removal of formwork are as follows: 1. Shuttering forming the vertical faces of walls beams and column sides should be removed first as they bear no load but only retain the concrete. 2. Shuttering forming soffit of slabs should be removed next. 3. Shuttering forming soffit of beams, girders or other heavily loaded shuttering should be removed in the end. Rapid hardening cement, warm weather and light loading conditions allow early removal of formwork. The formwork should under no circumstances be allowed to be removed until all the concrete reaches strength of at least twice the stresses to which the concrete may be subjected at the time of removal of formwork. All formworks should be eased gradually and carefully in order to prevent the load being suddenly transferred to concrete. 2.5 Effect of Formwork on Concrete Quality In designing and building formwork, the designer should aim for maximum economy without sacrificing quality or safety. Size, shape, and alignment of slabs, beams, and other concrete structural elements depend on accurate construction of the forms. The forms must be:
  • 17. 8  Sufficiently rigid under the construction loads to maintain the designed shape of the concrete,  Stable and strong enough to maintain large members in alignment, and  Substantially constructed to withstand handling and reuse without losing their dimensional integrity. The formwork must remain in place until the concrete is strong enough to carry its own weight, or the finished structure may be damaged. 2.6 Causes of Formwork Failure Formwork failures are the cause of many accidents and building failures that occur during concrete construction, usually when fresh concrete is being placed. Generally some unexpected event causes one member to fail, then others become overloaded or misaligned and the entire formwork structure collapses. The main causes of formwork failure are: 1. Improper stripping and shore removal 2. Inadequate bracing 3. Vibration 4. Unstable soil under mudsills (A plank, frame, or small footing on the ground used as a base for a shore or post in formwork), shoring not plumb 5. Inadequate control of concrete placement 6. Lack of attention to formwork details. 2.7 Planning for Formwork The engineer should plan for formwork at the time of making bid considering the following factors:  Placing schedule and stripping time requirements;  Capacity of equipment available to handle form sections and materials;  Capacity of mixing and placing equipment;  Construction joints;  Reuse of forms as affected by stripping time;  Relative merits of job-built, shop-built and ready-made forms; and  Weather (protection requirements and stripping time)
  • 18. 9 Chapter-3 LOADS ON CONCRETE FORMWORK 3.1 Vertical loads: Vertical loads consist of dead and live loads. The weight of formwork plus the weight of the reinforcement and freshly placed concrete is dead load. The live load includes the weight of the workers, equipment, material storage, runways, and impact. Vertical loads assumed for shoring and reshoring design for multi-storey construction should include all loads transmitted from the floors above as dictated by the proposed construction schedule. The formwork should be designed for a live load of not less than 50 lb/ft2 (2.4kPa) of horizontal projection. When motorized carts are used, the live load should not be less than 75 lb/ft2 (3.6kPa).The design load for combined dead and live loads should not be less than 100 lb/ft2 (4.8kPa) or 125 lb/ft2 (6.0kPa) if motorized carts are used. 3.2 Lateral load: For concrete having a slump of 175 mm or less and placed with normal internal vibration to a depth of 1.2 m or less, formwork can be designed for a lateral pressure as follows, where Pmax = maximum lateral pressure, kPa; R =rate of placement, m/h; T = temperature of concrete during placing, °C; Cw = unit weight coefficient per Table 3; And Cc = chemistry coefficient per Table 2; For columns With a minimum of 30Cw kPa, but in no case greater than ‘ρgh’. For walls with a rate of placement of less than 2.1 m/h and a placement height not exceeding 4.2 m With a minimum of 30Cw kPa, but in no case greater than ‘ρgh’.
  • 19. 10 For walls with a placement rate less than 2.1 m/h where placement height exceeds 4.2 m, and for all walls with a placement rate of 2.1 to 4.5 m/h With a minimum of 30CwkPa, but in no case greater than ‘ρgh’. The chemistry coefficient Cc is determined from Table 1: Table 1- Chemical coefficient Cc Chemical coefficient Cc Types I, II, and III without retarders* 1.0 Types I, II, and III with a retarder 1.2 Other types or blends containing less than 70% slag or 40% fly ash without retarders* 1.2 Other types or blends containing less than 70% slag or 40% fly ash with a retarder* 1.4 Blends containing more than 70% slag or 40% fly ash 1.4 The unit weight coefficient Cw is determined from Table 2: Table 2 - Unit weight co-efficient Cw Unit weight co-efficient Cw Density of concrete Cw Less than 2240 kg/m3 But not less than 0.8 2240 to 2400 kg/m3 1.0 Greater than 2400 kg/m3 *Retarders include any admixture, such as a retarder, retarding water reducer, retarding midrange water-reducing admixture, or high-range water-reducing admixture (super plasticizer), that delays setting of concrete.
  • 20. 11 Chapter-4 WALL FORMWORK Load calculations: Assumptions Rate of placement of concrete (R) = 1 m/hr. < 2.1 m/hr. Temperature of concrete during placing (T) = 270 c Height of the wall= 3 m. We use OPC without retarders and assuming fresh concrete weight as 23 kg/m3 Hence cc= 1 and cw= 1. Lateral loading on wall ……(1) p= 24.84kN/m2 < 30kN/m2 Hence take p= 30 k/N/m2 (626psf) Fig. 2 wall formwork 4.1 Wooden Formwork for Wall: Ply wood: Load on ply= 626psf (30kN/m2 ) To find the support spacing for plywood sheathing, assume the sheets of plywood are oriented in the form panel with the face grain across the supports (strong direction). Table 3 shows that the plywood of thickness will carry a pressure of 885psf (42.37kN/m2 ) with supports spacing of 8 in. This is also a convenient modular spacing for support of panel edges.
  • 21. 12 Wale spacing: To determine wale spacing with 8” stud spacing, the load on each stud will be 535plf (12.9kN/m). The studs must be supported by the wales so that the bending stress, the shear stress, and the deflection in the studs do not exceed allowable levels. If the studs have 3 or more spans, the maximum bending moment can be approximated from the given formula. .…(2) Solving l gives, .…. (3) The allowable bending stress, Fb gives the allowable bending moment when multiplied by the section modulus, S. Use H16 timber beam which has bending capacity of 3kN-m. Therefore L= 1.52 m. But it should also satisfy the deflection criteria. Hence < L< L< 1.016 Therefore take least of 2 values. Hence provide 1m spacing between wales. Tie spacing: For wales, determine the spacing and size of tie required. Loads on wale are actually point loads from studs but are often treated as distributed loads. For 1 m wale spacing, the equivalent distributed wale load, W = 1×30= 30kN/m. Using Eq. 2, Solving l gives, Using Eq.3,
  • 22. 13 The allowable bending stress, Fb gives the allowable bending moment when multiplied by the section modulus, Z. 35,200 mm3 Mallow= 0.66× fy ×Z …. (4) Mallow= 0.66×250×35,200= 5.8kN-m. Therefore 1.39 m Deflection criteria: L = 1.52 m Therefore take least of 2 values. Hence provide 1350 mm spacing between ties. Find the required tie size: Load on tie = tie spacing ×wale load = 1.35×30= 40.5kN. The tie must have a safe working capacity of at least 41kN; the best choice is probably a 4.5 ton capacity tie. 4.2 Steel Formwork for Wall: Load coming on to the wall = 30kN/m2 Use steel plate of thickness 3 mm. Consider steel plate as beam of c/s dimensions 3 m×3 mm. Then bending capacity Mallow= 0.66× fy ×Z Therefore = 4500 mm3 . Using Eq. 4,
  • 23. 14 Mallow= 0.66×250×4500= 0.7425kN-m. Using Eq. 3, Deflection criteria: L = 182 mm Therefore take least of 2 values. Hence provide 180 mm spacing between studs. If the studs have 3 or more spans, the maximum bending moment, Solving l gives, The allowable bending stress, Fb gives the allowable bending moment when multiplied by the section modulus, Z. 2083.33 mm3 Using Eq. 4, Mallow= 0.66× fy ×Z. Mallow= 0.66×250×2083.333= 0.34kN-m. Therefore
  • 24. 15 0.79 m Deflection criteria: L = 0.9 m Therefore take least of 2 values. Hence provide 790 mm spacing between wales. For wales, determine the spacing and size of tie required. Loads on wale are actually point loads from studs but are often treated as distributed loads. For 0.79 m wale spacing, the equivalent distributed wale load, W= 0.79×30 = 23.7kN/m. Using Eq. 3, Solving l gives, The allowable bending stress, Fb gives the allowable bending moment when multiplied by the section modulus, Z. 35,200 mm3 Using Eq. 4, Mallow= 0.66× fy ×Z. Mallow= 0.66×250×35,200= 5.8kN-m. Therefore 1.5 m
  • 25. 16 Deflection criteria: L = 1.6 m Therefore take least of 2 values. Hence provide 1500 mm spacing between ties. Find the required tie size: Load on tie = tie spacing × wale load = 1.5×23.7= 35.55kN. The tie must have a safe working capacity of at least 36kN; the best choice is probably a 4 ton capacity tie. The wall form c/s is shown in Figure 2. Fig. 3 Cross-section of Timber Wall Form
  • 26. 17 Chapter-5 COLUMN FORMWORK Load calculations: Assumptions Rate of placement of concrete (R) = 1 m/hr. < 2.1 m/hr. Temperature of concrete during placing (T) = 270 . Column dimensions 400 mm×400 mm. We use OPC without retarders and assuming fresh concrete weight as 23 kg/m3 Hence cc= 1 and cw = 1. Lateral loading on column From Eq. 1 ….. (1) p = 24.84kN/m2 < 30kN/m2 Hence take p= 30 k/N/m2 5.1 Wooden Formwork for Column: To find the support spacing for plywood sheathing, assume the sheets of plywood are oriented in the form panel with the face grain across the supports (strong direction). Table 3 shows that the plywood of thickness will carry a pressure of 885psf (42.37kN/m2) with supports spacing of 8 in. This is also a convenient modular spacing for support of panel edges. The loading on column form is shown in Figure 3.
  • 27. 18 Fig. 4 Loading on Column (plan view) Wale spacing: To determine wale spacing, with 8” stud spacing, the load on each stud will be 417plf (9.1kN/m) If the studs have 3 or more spans, the maximum bending moment can be approximated. Using Eq. 2, Solving l gives, The allowable bending stress, Fb gives the allowable bending moment when multiplied by the section modulus, S. Use H16 timber beam which has bending capacity of 3kN-m.
  • 28. 19 Therefore L = 1.81 m for given loading of But it should also satisfy the deflection criteria. Hence < L< L< 1.1 Therefore take least of 2 values. Hence provide 1.1 m spacing between wales. For wales, determine the spacing and size of tie required. Loads on wale are actually point loads from studs but are often treated as distributed loads. For 1.1 m wale spacing, the equivalent distributed wale load, W = 1.1×30 = 33kN/m. Using Eq. 2, The allowable bending stress, Fb gives the allowable bending moment when multiplied by the section modulus, Z. Using Eq. 4, Mallow= 0.66× fy ×Z. Mallow= 0.66×250×4,200= 0.693kN-m > 0.45kN-m Deflection criteria: Provide ISA5030 for wales. Load on each bolt at the end of wale = 6.6k.
  • 29. 20 5.2 Steel Formwork for Column: Loading on plate: Using Eq. 4, Bending capacity of t mm thick plate = 0.66× fy ×Z = 0.66×250× = 27500× t2 N-mm. But it should be greater than max.bending moment, 27500× t2 > 0.15×106 t > 2.33mm Deflection criteria: t > 3.001 Therefore‘t’ should be greater than 3 mm. Hence take 3 mm plate. For 0.2 m spacing load coming on to studs = 30×0.2 = 6kN/m. If the studs have 3 or more spans, the maximum bending moment, Solving l gives,
  • 30. 21 The allowable bending stress, Fb gives the allowable bending moment when multiplied by the section modulus, Z. 2083.33 mm3 Using Eq. 4, Mallow= 0.66× fy ×Z. Mallow= 0.66×250×2083.333= 0.34kN-m. Therefore 0.75 m Deflection criteria: L = 0.88 m Therefore take least of 2 values. Hence provide 750 mm spacing between wales. For wales, determine the spacing and size of tie required. Loads on wale are actually point loads from studs but are often treated as distributed loads. For 0.79 m wale spacing, the equivalent distributed wale load, W = 0.75×30= 22.5kN/m. The allowable bending stress, Fb gives the allowable bending moment when multiplied by the section modulus, Z.
  • 31. 22 Using Eq. 4, Mallow= 0.66× fy ×Z. Mallow= 0.66×250×3,400= 0.56kN-m > 0.45kN-m Deflection criteria: Provide ISA5030 for wales. Load on each bolt at the end of wale = 4.5kN Fig. 5 components of column form
  • 32. 23 Chapter-6 FORMWORK FOR RAFT FOUNDATION 6.1 Wooden Formwork for Raft Foundation: To find the support spacing for plywood sheathing, assume the sheets of plywood are oriented in the form panel with the face grain across the supports (strong direction). Table 3 shows that the plywood will carry a pressure of 885psf (42.37kN/m2 ) with supports spacing of 8 in. This is also a convenient modular spacing for support of panel edges. Fig.6 raft foundation formwork Wale spacing: To determine the wale spacing: With an 8 in. stud spacing, the load on each stud will be 417plf (9.13kN/m2 ). The studs must be supported by the wales so that the bending stress, the shear stress, and the deflection in the studs do not exceed allowable levels. If the studs have 3 or more spans, the maximum bending moment can be approximated from the given Table 3, Using Eq. 2, Solving l gives, The allowable bending stress, Fb gives the allowable bending moment when multiplied by the section modulus, S.
  • 33. 24 Use H16 timber beam which has bending capacity of 3kN-m. Therefore L=1.52 m. But it should also satisfy the deflection criteria. Hence < L< L< 1.016 Therefore take least of 2 values. Hence provide 1m spacing between wales. For wales, determine the spacing and size of tie required. Loads on wale are actually point loads from studs but are often treated as distributed loads. For 1 m wale spacing, the equivalent distributed wale load, W = 1×30= 30kN/m. Using Eq. 2, Solving l gives, The allowable bending stress, Fb gives the allowable bending moment when multiplied by the section modulus, Z. 35,200 mm3 Using Eq. 4, Mallow= 0.66× fy ×Z. Mallow= 0.66×250×35,200= 5.8kN-m. Therefore 1.39 m Deflection criteria:
  • 34. 25 L = 1.52 m Therefore take least of 2 values. Hence provide 1350 mm spacing between ties. Find the required tie size: Load on tie = tie spacing ×wale load = 1.35×30= 40.5kN. The tie must have a safe working capacity of at least 41kN; the best choice is probably 4.5 ton tie. 6.2 Steel Formwork for Raft Foundation: Load coming on to the wall = 30kN/m2 Use steel plate of thickness 3 mm. Consider steel plate as beam of c/s dimensions 1 m×3 mm. Then bending capacity Mallow= 0.66× fy ×Z. Therefore = 1500 mm3 . Using Eq. 4, Mallow= 0.66×250×1500= 0.2475 kN-m. Using Eq. 3, Deflection criteria:
  • 35. 26 L = 182 mm Therefore take least of 2 values. Hence provide 180 mm spacing between studs. Load on studs= 0.18×30= 5.4kN/m2 . If the studs have 3 or more spans, the maximum bending moment, Solving l gives, The allowable bending stress, Fb gives the allowable bending moment when multiplied by the section modulus, Z. 2083.33 mm3 Using Eq. 4, Mallow= 0.66× fy ×Z. Mallow= 0.66×250×2083.333= 0.34kN-m. Therefore 0.79 m Deflection criteria: L = 0.9 m Therefore take least of 2 values. Hence provide 790 mm spacing between wales. For wales, determine the spacing and size of tie required. Loads on wale are actually point loads from studs but are often treated as distributed loads. For 0.79 m wale spacing, the equivalent distributed wale load, W = 0.79×30 = 23.7kN/m.
  • 36. 27 Using Eq. 2, Solving l gives, The allowable bending stress, Fb gives the allowable bending moment when multiplied by the section modulus, Z. 35,200 mm3 Using Eq. 4, Mallow= 0.66× fy ×Z. Mallow= 0.66×250×35,200= 5.8kN-m. Therefore 1.5 m Deflection criteria: L = 1.6m Therefore take least of 2 values. Hence provide 1500 mm spacing between ties. Find the required tie size: Load on tie = tie spacing ×wale load = 1.5×23.7= 35.55kN. The tie must have a safe working capacity of at least 36kN; the best choice is probably 4 ton capacity tie.
  • 37. 28 Chapter-7 SLAB FORMWORK Load calculations: Loading on slab: Fresh concrete load of slab thickness 150 mm= 25×0.15 (including reinforcement) = 3.75kN/m2 . Live load on slab according to ACI 347 = 3.6kN/m2 Total load= 7.37kN/m2 Factored load= 12kN/m2 (250psf) 7.1 Wooden Formwork for Slab: Loading on slab: Fresh concrete load of slab thickness 150mm = 25×0.15 (including reinforcement) = 3.75kN/m2 . Live load on slab according to ACI 347 = 3.6kN/m2 Total load= 7.37kN/m2 Factored load= 12kN/m2 (250psf) To find the support spacing for plywood sheathing, assume the sheets of plywood are oriented in the form panel with the face grain across the supports (strong direction). Table 3 shows that the plywood of thickness will carry a pressure of 265psf (12.68kN/m2) with supports spacing of 16 in. This is also a convenient modular spacing for support of panel edges Wale spacing: With 16” stud spacing, the load on each stud will be 334plf (4.872kN/m) If the studs have 3 or more spans, the maximum bending moment can be approximated from the given Table 4, Using Eq. 2, Solving l gives,
  • 38. 29 The allowable bending stress, Fb gives the allowable bending moment when multiplied by the section modulus, S. Use H16 timber beam which has bending capacity of 3kN-m. Therefore L=2.48 m. But it should also satisfy the deflection criteria. Hence < L< L< 1.11 Therefore take least of 2 values. Hence provide 1.1 m spacing between wales. For wales, determine the spacing and size of tie required. Loads on wale are actually point loads from studs but are often treated as distributed loads. For 1.1 m wale spacing, the equivalent distributed wale load, W = 1.1×12= 13.2kN/m (832plf) Using Eq. 2, Solving l gives, The allowable bending stress, Fb gives the allowable bending moment when multiplied by the section modulus, Z. 35,200 mm3 Using Eq. 4, Mallow= 0.66× fy ×Z Mallow= 0.66×250×35,200= 5.8kN-m. Therefore 2.09m
  • 39. 30 Deflection criteria: L = 1.52 m Therefore take least of 2 values. Hence provide 1500 mm spacing between posts. Finding the required post size: Load on post = post spacing ×wale load = 1.5×13.2= 19.8kN. Assuming fcd= 75 N/mm2 Area required = 19.8×103 /75 = 264 mm2 Use 3.2 mm thick pipe, External diameter of pipe = 33.7 mm. Area provided= 306 mm2 Moment of inertia= 36100 mm4 Radius of gyration = = 10.8 mm 89.138 8.10 15001    r KL From the Table 9.1(a) in IS800-2007 fcd = 82 N/mm2 Load carrying capacity of post = 306×81.6= 25kN>19.8kN Therefore, post of Ø33.7 mm with 3.3 mm thick is satisfying all the requirements. Fig. 7 components of slab form (timber)
  • 40. 31 7.2 Steel Formwork for Slab: Load on plate = 12kN/m2 Consider steel plate as beam of c/s dimensions 1 m×3 mm. Using Eq. 4, Then bending capacity Mallow= 0.66× fy ×Z. Therefore = 1500 mm3 . Using Eq. 4, Mallow= 0.66×250×1500= 0.2475kN-m. Using Eq. 3, Deflection criteria: L = 240 mm Therefore take least of 2 values. Hence provide 240 mm spacing between studs. Load on studs= 0.24×12= 2.88kN/m2 . If the studs have 3 or more spans, the maximum bending moment, Using Eq. 2, Solving l gives, The allowable bending stress, Fb gives the allowable bending moment when multiplied by the section modulus, Z.
  • 41. 32 2083.33 mm3 Using Eq. 4, Mallow= 0.66× fy ×Z. Mallow= 0.66×250×2083.333= 0.34 kN-m. Therefore 1.08m Deflection criteria: L = 1.13 m Therefore take least of 2 values. Hence provide 1 m spacing between wales. For wales, determine the spacing and size of tie required. Loads on wale are actually point loads from studs but are often treated as distributed loads. For 1 m wale spacing, the equivalent distributed wale load, W = 1×12= 12kN/m. Using Eq. 2, Solving l gives, The allowable bending stress, Fb gives the allowable bending moment when multiplied by the section modulus, Z. 35,200 mm3 Using Eq. 4, Mallow= 0.66× fy ×Z.
  • 42. 33 Mallow= 0.66×250×35,200= 5.8kN-m. Therefore 2.2 m Deflection criteria: L = 2.23 m Therefore take least of 2 values. Hence provide 2.2 m spacing between posts. Post design: Load coming on to each pole = 2.2×9.48= 21.1kN. Assuming fcd= 90 N/mm2 Area required = 21.1×103 /75= 293.33 mm2 Use 3.2 mm thick pipe, External diameter of pipe = 33.7 mm. Area provided= 306 mm2 Moment of inertia= 36100 mm4 Radius of gyration = = 10.8 mm 89.138 8.10 15001    r KL From the Table9.1 (a) in IS800-2007 fcd = 82 N/mm2 Load carrying capacity of post = 306×81.6= 25kN> 21.1. Therefore, post of Ø33.7 mm with 3.3 mm thick is satisfying all the requirements.
  • 43. 34 Table 3– Allowable Stresses and Pressures for Plywood Formwork Allowable Stresses and Pressures for Plywood Formwork
  • 44. 35 Chapter-8 COMPARISON BETWEEN STEEL AND WOODEN FORMWORK Timber is the most common material used for formwork. The disadvantage with timber formwork is that it will warp, swell and shrink. Application of water impermeable cost to the surface of wood mitigates these defects. The construction of formwork takes time and involves expenditure up to 20 to 25% of the cost of the structure or even more. Design of these temporary structures is made to economic expenditure. The operation of removing the formwork is known as stripping. Stripped formwork can be reused. Reusable forms are known as panel forms and non-usable are called stationary forms. 8.1 Wooden Formwork: Timber for formwork should satisfy the following requirement: It should be 1. well-seasoned 2. light in weight 3. easily workable with nails without splitting 4. free from loose knots Normal sizes of members for timber formwork are shown in Table 1: Table 4 - Normal size of members for wooden formwork Sheeting for slabs, beam, column side and beam bottom 25 mm to 40 mm thick Joints, ledges 50 x 70 mm to 50 x 150 mm Posts 75 x 100 mm to 100 x 100 mm
  • 45. 36 Resin bonded plywood sheets are attached to timber frames to make up panels of required sizes. The cost of plywood formwork compares favorably with that of timber shuttering and it may even prove cheaper in certain cases in view of the following considerations: 1. It is possible to have smooth finish in which case on cost in surface finishing is there. 2. By use of large size panels it is possible to effect saving in the labor cost of fixing and dismantling. 3. Numbers of reuses are more as compared with timber shuttering. For estimation purpose, number of reuses can be taken as 20 to 25. 8.2 Steel Formwork This consists of panels fabricated out of thin steel plates stiffened along the edges by small steel angles. The panel units can be held together through the use of suitable clamps or bolts and nuts. The panels can be fabricated in large number in any desired modular shape or size. Steel forms are largely used in large projects or in situation where large number reuses of the shuttering is possible. This type of shuttering is considered most suitable for circular or curved structures. 8.3 Steel forms compared with wooden formwork: 1. Steel forms are stronger, durable and have longer life than wooden formwork and their reuses are more in number. 2. Steel forms can be installed and dismantled with greater ease and speed. 3. The quality of exposed concrete surface by using steel forms is good and such surfaces need no further treatment. 4. Steel formwork does not absorb moisture from concrete. 5. Steel formwork does not shrink or warp. 8.4 Timber Form Materials and Accessories Practically all formwork jobs require some lumber. A local supplier will advise what material and sizes are in stock or promptly obtainable, and the designer or builder can proceed accordingly. Figure 5 shows a typical wall form with its components. Figure 6 shows parts of a typical wall form.
  • 46. 37 Fig. 8 - Typical wall form with components identified. Fig. 9 - Parts of a typical wall form
  • 47. 38 Ties In order to secure concrete forms against the lateral pressure of unhardened concrete, a tensile unit called concrete form tie is used (they are also referred to as form clamps, coil ties, rod clamps, snap ties, etc.). Figure 7 shows a typical single member tie. Fig.10 Different types of ties Ties are manufactured in two basic types:  Continuous single member ties; in which the tensile unit is a single piece, have a special holding device added for engaging the tensile unit against the exterior of the - form shown in Figure 5. Some single member ties may be pulled as an entire unit from the concrete; others are broken back a predetermined distance. Some are cut flush with the concrete surface.
  • 48. 39 a) Straight tie with elastic tube b) Threaded bar with unattached plastic sleeve Fig. 11 – A continuous single member tie  Internal disconnecting type ties, in which the tensile unit has an inner part with threaded connections to removable external members generally, remain in the concrete.
  • 49. 40 Chapter-9 TRAVELLING FORMWORK FOR BOX-GIRDER The travelling formwork for one cell of a twin cell segmental box girder is considered for design. The dimensions of the formwork under consideration are shown in the Figure 8. Fig. 12 Typical Cross-section of Box-girder Bridge Single cell for which the travelling formwork is designed is as shown in the Figure 9. Fig. 13. Dimensions of the single cell formwork
  • 50. 41 9.1 Design Components Upper Steel Plate/ Slab: An upper steel plate is provided to bear the external loads and acts as a slab to the whole system. Lateral/Vertical Steel Plates: Lateral plates of steel are provided to resist the lateral loading and to provide a shape in the form of walls to the system. Strips: Vertical and Horizontal Strips are provided as supports to the upper and lateral plates which are in turn supported by the major beams of ISMC 75 Back to back channels. Lateral buckling of these members is possible due to their lesser depth and more width compared to depth and hence strips at regular intervals are to be provided to prevent buckling. Back to back ISMC75 Channels: Back to back ISMC75 channels are provided to resist the torsion and to provide support to the slab, there is a gap provided between the back to back channels to enable future enhancements. Horizontal Mechanical Jack: One horizontal hydraulic jack is provided to facilitate the movement of the slab formwork in the horizontal direction. Vertical Mechanical Jack: Two vertical hydraulic jacks are provided based on the length of the formwork. These facilitate the movement of the walls of the box girder in upward and downward directions to the restricted lengths. Hinged Connection: Hinged connections are provided at the two upper corners of the box i.e., for the haunch so that when the box has to be compressed for reuse, after the casting is done, the corners can be folded. Rails: Rails are provided at the bottom end of each vertical jack so that the formwork can be moved forward or backward to the desired position for reuse. The design of each and every component should be done with great care and based on the standard specification codes. The length and number of the hydraulic jacks and the design of bolts and rails also depends on the requirement criteria.
  • 51. 42 9.2 Load Calculation: Loading ( On Upper plate/ slab): Weight of fresh concrete = density× thickness = 25×0.4 = 10kN/sq.m Weight of plate (6 mm thick) =78.5×0.006 =0.471kN/sq.m Hence, Live load = 75psf = 75×0.04788kN/sq.m = 3.591kN/sq.m And total vertical load = 10 + 0.471 +3.591 = 14.062 = 15kN/sq.m (approx.) Therefore, factored vertical load = 15×1.5 = 22.5kN/sq.m Lateral load ( On vertical/lateral plates): Assuming, Rate of pouring (R) = 1 m/hr = 3.281 ft/hr Temperature (T) = 27o C = 27 + 273= 300 K According to ACI 347, Lateral Pressure,        T R p 9000150        300 281.3 9000150
  • 52. 43 = 248.43 psf = 11.89kN/sq.m Factored load = 11.89×1.5 = 17.835kN/sq.m Therefore, the envelope of the maximum pressure will show a hydrostatic pressure at a depth below the form 150 43.248  = 1.66 ft = 0.5 m Hence, from the above calculation, till the depth of 0.5m the pressure distribution will be linear, then it will be constant. {1psf= 0.0478803kN/sq.m = 0.0208854 lb/sq.ft} The envelope of lateral pressure distribution is shown in Figure 10: Fig.14 Lateral Pressure Distribution 9.3 Design Approach In order to design the components of the formwork, STAAD software is used. The upper plate, lateral plates, beams (horizontal, central and cross members) are designed on STAAD for the loads calculated as shown above and the results obtained for Bending Moments and Deflections are compared with the calculated allowable stress and deflection. The number of bays, number of members, the distance between each member is based on these values. The suitable combination of the number of bays and the deflection and bending moment obtained
  • 53. 44 which are less than the allowable deflection and bending moment values respectively are considered for the final design. For example, for the upper plate design allowable bending moment value obtained from calculations is 1.485kN-m and the allowable deflection value is 0.6944m. Then, for a vertical load of 33.75kN/m (calculated) and thickness of the plate- 0.006m, length- 2m as fed in STAAD, if we take 9 supports i.e., 8 bays (bay distance of 0.25m), the maximum deflection obtained is 0.151m which exceeds allowable deflection and the maximum bending moment value obtained is 0.223kN-m which is within the allowable limit. But as the deflection criteria is not satisfied and hence not safe, we go for another number of bays like 5 or 6 bays whichever satisfies the allowable deflection and the allowable bending moment criterion. Calculation of Allowable Deflection and Allowable Bending Moment: Allowable deflection limit = 360 span Allowable Bending Stress = Z M f  Allowable Bending Moment = M = f ×Z         6 250 3 2 dbd [‘f’ value for Mild steel is 250 N/ sq.mm] The obtained maximum bending moment and deflection values for all the components should be within these limits.
  • 54. 45 9.4 Design of Travelling Formwork: The design of various components of a travelling formwork mentioned in Chapter 7 is discussed further. The upper plate is shown in Figure 11. Fig.15 Upper plate and strips Upper Plate/ Slab ( 6 bays and 7 supports including ends): Thickness= 6 mm Bay length= 0.333 m Width= 1.5 m Length= 2 m From the above load calculation, vertical load on the plate= 22.5× width of the plate, Vertical Load = 22.5× 1.5= 33.75kN/m Allowable deflection= 250/360= 0.6944 mm Allowable Bending Moment         6 661500 25066.0 = 1.485kN-m STAAD RESULTS: Max. Deflection= 0.475 m < 0.6944 mm
  • 55. 46 Max. Bending moment= 0.396kN-m <1.485kN-m Hence Safe. Sometimes, even though the max.deflection and the max.bending moment obtained are within the allowable limits, the design might not be considered if obtained max.deflection or bending moments are too less than the allowable limits. Even if the values are appropriate the number of bays could be very high, which is not economical. In these cases, combinations have to be changed. STAAD drawing showing the reactions at supports for Upper plate are shown in Figure 12: Fig.16 STAAD drawing showing the reactions at supports for Upper plate. Vertical Strips( 7 nos): Vertical End Strips: Depth= 6 cm Width= 6 mm Length= 1.5 m For end strips, Loading= 22.5×0.33/2= 3.7125kN/m
  • 56. 47 Allowable deflection= 360 l = 360 1000 8.0  = 2.22 mm For Overhang portion, allowable deflection= 360 1000 35.0  = 0.97 mm Allowable Bending Moment=         6 50506 25066.0 = 0.41kN-m STAAD RESULTS: Max. deflection= 0.944 m < 2.22 mm < 0.97 mm Max. Bending moment= 0.24kN-m <0.41kN-m Hence safe. For Vertical end strips, depth of 6 mm and width of 6 cm are used and as shown above, it satisfies the deflection and bending moment conditions. But for the Vertical Intermediate strips, if same depth and bending moment are used and the loading on them is twice than that of the Vertical End strips and in that case, the deflection and Bending moment obtained are very high and exceed the allowable deflection and bending moment. So, depth, as it cannot be changed, we increase the width to 8 mm for Vertical Intermediate strips to reduce the bending moment and deflection. Vertical Intermediate Strips: Depth= 6 cm
  • 57. 48 Width= 8 mm For Central strips, Loading= 22.5×0.33= 7.425kN/m Allowable Deflection= 360 l 360 1000 35.0  = 0.9777 mm STAAD RESULTS: Max. deflection= 0.772 mm< 0.9777 mm Max. Bending moment= 0.46kN-m Hence safe. As the allowable deflection for overhang part (of length 0.35 mm) is more than that of the part between supports (i.e., of length 0.8 mm), the obtained deflections can be compared for all the parts with the allowable deflection of the overhanging part. Major Beams (B/B ISMC 75 OF 2 nos): To support the vertical members which are supports for slab, two major beams of back to back ISMC 75 are provided. These are shown in the Figure 13: Fig.17 Lateral Plate and Strips The vertical members act as point loads on the two major beams as shown in Figure 14:
  • 58. 49 Fig.18 Loading on Major Beams The vertical members act as point loads on the two cross members as shown above. Length= 2 m ISMC 75 channels section details: Allowable deflection= 360 250 = 360 )333.022(  = 3.7 mm
  • 59. 50 Allowable Bending Moment=         1000 22.20 25066.0 = 6.666kN-m STAAD RESULTS: Max. deflection= 3.594 m < 3.7 mm Max. Bending moment= 5.96kN-m < 6.666kN-m Hence safe. The reactions at supports are shown in Figure 15. Fig.19 Reactions at Supports Lateral/Vertical Plates: Lateral plate is shown in Figure 16: Fig.20 Dimensions of Lateral Plate
  • 60. 51 Thickness= 6 mm Width= 2 m Loading= 18×2 m= 36kN/m 6 Supports: Allowable deflection = 360 1000 4.0  = 1.11 mm Allowable Bending Moment=         6 6610002 25066.0 = 1.98kN-m STAAD RESULTS: Max. deflection= 0.796 mm< 1.11 mm Max. Bending moment= 0.61kN-m< 1.98kN-m Hence Safe. Horizontal Strips: The horizontal strips and major beams are shown in Figure 17: Fig.21 Lateral Plate with Horizontal Strips and Major Beams
  • 61. 52 Horizontal End Strips: Allowable deflection=         300300 101010 445.0 = 1.236 mm Allowable Bending Moment=         6 6060 525066.0 = 0.495kN-m Max. deflection= 0.86 mm< 1.236 mm Max. Bending Moment= 0.305kN-m Reactions on major beam= 3.6kN, 3.6kN Horizontal Intermediate Strips: Allowable deflection=        360 101010 445.0 = 1.230 mm Allowable Bending Moment=         6 8080 525066.0 = 0.85kN-m Max. deflection= 0.726 mm Max. Bending moment= 0.713kN-m Reaction= 7.2kN, 7.2kN Major Beams (B/B ISMC 75 of 2 nos): The section details for the major beams are same as that of the major beams for the upper plate. Z (w.r.t X-axis)= 20.2 cu.m for single columns Moment Capacity= )101010(2.2025066.0  = 6.666kN-m Max. Moment= 1.44kN-m Max.deflection= 0.673 mm Allowable deflection=         300 101010 400 = 1.11kN-m
  • 62. 53 Reactions: At A= 18kN, At B= 18kN 9.5 Mechanical Screw Jacks: Vertical Jacks: 4 Mechanical screw jacks of 4 tons capacity are used as the load coming on each one is 3.6 tons. Horizontal Jacks: 4 mechanical screw jacks of 2 tons capacity are used as the load coming on each one is 1.8 tons. These will be clamped to the major beams of the slab and the lateral plate. The mechanical screw jacks that can be used are shown in Figure 18: Fig.22 Mechanical Screw Jacks 9.6 Rail Section: Rails are used to facilitate the movement or transfer of the formwork from one segment to the next after the concrete is set. The loading on the rail and the bending capacity are shown in Figure 19:
  • 63. 54 Fig. 23 Loading on Rail Max BM = 11.25kN-m Bending capacity = 12.6kN-m Section of the rail that is used in the formwork floor is as shown in the Figure 20: Fig.24 Section of a Rail
  • 64. 55 A drawing of the cross section of the box girder with the above described components is shown in the Figure 21. The hinged connection at the haunch is showed in detail in Figure 22. Fig.25 Components of Formwork for Box-girder
  • 65. 56 9.7 Hinge Connections: Hinges are provided for haunch as the connections between the ends of upper slab and the lateral plates to enable the folding of the formwork for reuse. The hinged connections that are used for this purpose are as shown in the Figure 22: Fig.26 Hinged Connections
  • 66. 57 Chapter-10 CONCLUSION The summary report presented above discusses the design aspects of a travelling formwork for a segmental box girder which can be prefabricated and reused. Prior to this the design of steel and timber formworks for slab, raft, column and wall are also discussed in order to understand the project better. A comparison between steel and wood formworks is discussed along with the temporary structures. As the economy, speed and efficiency are the major considerations of any project, an effort has been made to improve the efficiency of the project by reducing the waste of time and material by designing a travelling formwork for a segmental box girder. This formwork can be reused for one segment after another after the concrete is set. This prefabricated formwork design and its components are discussed in the report. The detailed design of each component using STAAD PRO software and the calculations based on references and IS codes are presented. The model can be reused and hence it is advantageous over various other formwork systems as it improves the work efficiency by reducing the time taken for construction and wastage of material.
  • 67. 58 REFERENCES 1) Arch Alexander, “Design and Construction of Concrete Formwork”, The Civil Engineering Handbook, Second Edition, Edited by W . F . Chen and J . Y . Richard Liew, CRC Press 2002, Chapter-4. 2) Brand, R.E. 1975. Falsework and Access Scaffolds in Tubular Steel. McGraw-Hill, New York. 3) Chen, W.F. and Mosallam, K.H. 1991. Concrete Buildings, Analysis for Safe Construction. CRC Press, BocaRaton, FL. 4) Hurd, M.K. 1989. Formwork for Concrete, 6th ed. American Concrete Institute, Detroit, MI. 5) Moore, C.E. 1977. Concrete Form Construction. Van Nostrand Reinhold, New York. 6) Peurifoy, P.E. 1976. Formwork for Concrete Structures. McGraw-Hill, New York. 7) Ratay, R.T. 1984. Handbook of Temporary Structures in Construction. McGraw-Hill, New York. 8) Load calculations including vertical and lateral were based on ACI Committee 347 recommendations. 9) IS: 14687- 1999 Falsework for the Concrete Structures-Guidelines.