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Structural Steel and Timber Design EV306 Project Report

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  • 1. Structural Steel and Timber Design EV306 Project Report Double Storey Steel Building Student Name : Herry Hartono Student ID : 1001128753 Course : Civil Engineering Lecturer : Mr. Taha MJ Aleisawy Date of Submission : Monday, 5th of August 2013 Faculty of Engineering, Technology and Built Environment 2013
  • 2. STUDENT STATEMENT I hereby declare that design project entitles “Double Storey Steel Building” submitted to Mr. Taha, has followed the procedure as mentioned in British Standard 5950-1:2000. The design here submitted is original work done by the guidance of Mr. Taha, STAADPro lab tutor and Mr. Lee, Structural Steel and Timber Design lecturer. This design has applied the ethics from design process until the final proposed design. Safety measures have also been included in the design so as to uphold the public safety. This design is submitted in the fulfilment of the completion of the Structural Steel and Timber Design course. Designs embodies in this report have not been submitted by any other person, university or institute. Herry Hartono 1001128753
  • 3. ABSTRACT This project is to design a double storey steel building by using structural design software, STAAD Pro 2007. Design of this building follows the British Standards 5950-1:2000. Several dead loads and live load are imposed on columns, beams, purlins and truss members that are made of Universal Beam and angle section. The design is checked for its maximum capacity (compression, tension and shearing) to guarantee its safety. Most importantly, the section was not merely chosen, but it satisfies certain important criteria. The design obtained from the STAAD.Pro analysis was verified by the hand-calculation and it was proven to be an effective design for the building.
  • 4. ACKNOWLEDGEMENT I owe a debt of gratitude to Mr. Taha, my STAAD.Pro lab tutor, for his assistance, supports, guidance and advices which inspired me throughout this semester. He has taught me many things that I need to complete this design project. It is also my duty to record my thankfulness to Mr. Lee, my Structural Steel and Timber Design lecturer, who has given us precious knowledge and made the subjects easily- understandable. Without the assistances and guidance from both my lecturer and my tutor, completion of this design project would not have been possible.
  • 5. TABLE OF CONTENTS Chapter 1 – Introduction to Steel Structure 1.1. Steel Definition ……………………………………………………………… 1 1.2. History of Steel ……………………………………………………………… 3 1.3. Steel Structure Element 1.3.1. Truss ……………………………………………………………… 4 1.3.2. Beam ……………………………………………………………… 5 1.3.3. Column …………………………………………………………… 7 1.4. Merits and Limitations of Steel Structure …………………………………… 9 1.5. STAAD.Pro 2007 Review …………………………………………………… 10 Chapter 2 – Project Design 2.1. Problem Statement …………………………………………………………... 11 2.2. Problem Formulation ………………………………………………………… 12 2.3. Design Specification ………………………………………………………… 13 2.4. Potential Problem ……………………………………………………………. 15 2.5. Safety Measures ……………………………………………………………... 16 Chapter 3 – STAAD.Pro Analysis and Results 3.1. Project Design Approach ……………………………………………………. 17 3.2. Detailed Engineering Analysis and Design …………………………………. 19 3.3. STAAD.Pro Analysis Results ……………………………………………….. 24 Chapter 4 – Hand Calculation Results 30 Discussion 43 Conclusion 52 References 53
  • 6. CHAPTER 1 – INTRODUCTION TO STEEL STRUCTURE 1.1. STEEL DEFINITION Gary S. Berman (n.d.) stated that steel is a common building material used throughout the construction industry. It forms the skeleton for the building or structure and basically holds everything together. Steel is widely used as a building material. It is because of its design simplicity, mechanical properties and ease and speed of construction. If there is any extension needed on a steel structure, the new structures can be just welded or bolted to the existing structure. And, still it will give the same strength. Steel has a variety of properties to suit different requirements which are strength, ductility, weldability and corrosion resistance. Besides, steel has also a special feature. It will not break directly when it is loaded with excessive loading. It will buckle first, until it reaches its maximum capacity, then only it fails. This feature is explained in the Figure 1.1. (William, n.d., Chapter 1) Figure 1.1. Stress – Strain Curve of Steel (“True Stress – True Strain Curve,” n.d.) Steel will go through the yield point before it reaches the ultimate stress. Usually, the steel structure will be designed on its yield point. Reason being is to save cost since the steel structure is expensive. So, basically, the steel is stretched until it deforms to its yield point. Thus, the steel structure length is extended and the needs of more steel pieces can be reduced. Steel is shaped into several sections for the construction purposes which are I-section (Universal Beam), H-section (Universal Column), circular hollow section (CHS), rectangular
  • 7. hollow section (RHS), square hollow section (SHS), unequal angles, equal angles, double angles and many other shapes. This is why steel is preferred to be used in the construction as compared of concrete and timber. There are many sections available in the market. The engineer only needs to choose which design suits his design requirements. Other than that, this might cut off the cost of construction as well. The chosen design unquestionably satisfies the building requirements. Figure 1.2. Steel Structure Shapes (“Structural Steel,” n.d.)
  • 8. 1.2. HISTORY OF STEEL During the Pre-100 AD, steel has been produced on a small scale for thousands of years. Turkey was the first location of the first steel excavated. It was 4000 years old. Roman, Iberian and Chinese civilisations used steel to construct weapons. However, they were not capable in production steel yet, therefore, its uses was limited and subject to very long production times. Comes to year 300 BC – 1700 AD, steel called Damascus had been produced. It was back in India around 300 BC, during the Crusades of the Middle Ages that it required its legendary status. Damascus steel could be bent under pressure without breaking but could also hold its edge and the civilisation that mastered its production were feared. (Serisier, 2011) On the year 1855 AD, the production of steel was eased by the invention of Bessemer process in 1866 by British metallurgist, Sir Henry Bessemer. He realised that the molten iron unites readily with oxygen. So a strong blast of air through molten pig iron should convert the pig iron into steel by reducing its carbon content. At first, the carbon content was reduced too much, and further experimentation led to the addition of spiegeleisen – a compound of iron, manganese and carbon – to the Bessemer process. The manganese removes the excess oxygen in the form of manganese oxide, which passes into the slag and the carbon remains behind, converting the molten iron into steel. The blast of air through the molten pig iron, followed by the addition of a small quantity of molten Spiegel, converts the large mass of molten pig iron into steel in just minutes, without any additional fuel. (Spoerl, n.d.) In 1950, Bessemer process has become outdated, and was replaced by the introduction of basic oxygen steelmaking (BOS) which limits impurities and can even process old scrap metal into steel, lowering wastage and increasing efficiency. Nowadays, BOS has been widely used for steelmaking process. (Serisier, 2011) Steel is a predictable material and during the 1990’s, the industry had implemented new procedures for designing steel structures. Structural design has evolved, mostly due to the necessity caused by earthquakes. Until the 1970’s, structures were designed using proven formulas, but the calculations were done by hand. Today, software is already available on the PC for the structural analysis which provides faster calculation compared to hand. (Berman, n.d.)
  • 9. 1.3. STEEL STRUCTURE ELEMENT 1.3.1. TRUSS A truss is a triangular framework of elements that act primarily in tension and compression. When loads are applied to a truss only at the joints, forces are transmitted only in the direction of each of its members. Hence, the members only experience tension or compression force. There is not bending moment occurred. Truss has a high strength to weight ratio and consequently is used in many structures, from bridges, to roof supports, to space stations. (“Bridge Designer,” n.d.) Truss usually is very light, but very stiff form of construction. Before the welding was developed (pre 1930s), the truss was connected by truss girders. Rolled section and plate sizes were of limited range as well. (“Truss Bridges,” n.d.) Truss is considered expensive to fabricate today, being labour intensive, and maintenance issues have to be carefully addresses. However, they can still show advantages in particular application such as footbridges and railway bridges. Typical spans in one form or other can range from 40 m to 500 m. (“Truss Bridges,” n.d.) Figure 1.3. State Highway Bridge No. 16 over the Kickapoo River, Vernon County, WI (“Bridge Contest,” n.d.) The benefits of using trusses in the construction are: (“Construction Component,” n.d.)  Time saving – delay minimization  Cost saving – easily remodelled, repair and maintain  Materials saving – less material, high bearing strength  Labor saving – construction time reduction
  • 10. However, the truss has also disadvantages. It needs to be wasted if not properly designed. Other than that, sometimes, the structure can have a zero member force. It means the member does not carry any internal force. So it can be considered as material waste. (“Advantages of Truss Bridges,” n.d.) On this project, truss was used to design the roof of the double storey steel building. Truss will carry the all loading imposed on the roof, including wind load, live load and roof insulation (dead load). From loading applied on the roof, will be transferred into compression and tension loading in the truss members and will eventually go to the column that supports it. Most of the times, the roof truss comes with purlins to connect or become a bridge between a roof truss to another. 1.3.2. BEAM A structural beam is a component used in construction to add strength to any structure or design. Manufactured of steel, concrete or wood, the structural beam is typically used to span an open element of a structure, as well as to give support underneath a very heavy component of a structure. I beam (Universal Beam) is the most common type of beam used. Concrete structural beam manufacture often involves a steel I beam as the reinforcement in concrete for use in building bridges, buildings, and other concrete structures. Besides, channel section and angle are sometimes used also for the beam. (“What is a Structural Beam,” n.d.). Beside concrete and steel, beam can be made of plastic and wood. Below are the common sections that are used for the beam design. Figure 1.4. Beam Sections (“Members Subjected to Flexural Loads,” n.d.)
  • 11. On the construction, there are some combinations of beam supports that can be installed. Different combination of the supports, the response of the beam towards the applied load would be different as well. The most common combinations used are cantilever beam (fixed – free) and simply-supported beam (pin – roller or pin – pin). Figure 1.5. Cantilever Beam (“Understanding Calculus,” n.d.) Figure 1.6. Simply-Supported Beam (Prashant, 2013) Problem that usually beam has is bending. Why bending? Because it is loaded with lateral loading. Therefore, if it is observed from the cross sectional area of the beam (assumed the loading is imposed from the top), the top part of the beam will experience axial compression, whereas the bottom part will experience axial tension. According to the Tata Steel (n.d.), the bending strength may be limited by material strength, lateral-torsional buckling or local buckling. Three types of failure on beam structure are material failure causing a plastic hinge to form (bending), lateral torsional buckling along the length of the beam, and local buckling of the beam cross section. (a) (b)
  • 12. (c) (d) Figure 1.7. Types of Beam Failure: (a) Plastic Hinge, (b) Side Buckling, (c) Web Buckling and (d) Flange Buckling (Tata Steel, n.d.) On this project, the beam section used is Universal Beam (I-Beam). Since the beams are all primary beams, therefore, they have to be checked for its web bearing and web buckling. Most importantly, the shear buckling, shear capacity, moment capacity and allowable deflection must be checked first before assigning a section. This is to ensure the safety of the building constructed. 1.3.3. COLUMN Column is a vertical structural member that transmits the load from ceiling/ roof slab and beam, including its self-weight to the foundation. Columns are normally subjected to a pure compressive load. The most common used columns are RCC (Reinforced Concrete) columns. (Arun, n.d.) Caprani (n.d.) mentioned two main parameters governing column design.  Bracing: if the column can sway, additional moments are generated through the P – δ effect. This does not affect braced column.  Slenderness ratio: The effective length divided by the lateral dimension of the column. Low values indicate a crushing failure, while high values denote buckling.
  • 13. Figure 1.8. Effective Length of Different Supports Combination of Column (“Basic Calculation of Column Buckling,” n.d.) There are many sections that can be used for the column such as channel section and angle section. However, H-section (Universal Column) is the most commonly used section. Figure 1.9. H-Section Steel Column (“H-Section Steel Column,” n.d.) The steel column can also fail if the design is not done properly. A long compression member may fail due to buckling stress whereas the short compression member may fail due to yielding of material. Buckling of a column may occur even the maximum stresses in the material are less than the yield point of the material. Buckling means lateral deflection of the column. (“Definition of Column,” 2011) Figure 1.10. Column Buckling (“The Cardington Fire Test,” n.d.)
  • 14. On this project, the column is designed by using Universal Beam instead of Universal Column. Universal Beam will be more vulnerable to buckle as compared of Universal Column. Universal Column has approximately the same magnitude of flange width and web length, whereas, the Universal Beam has the web length greater than the flange width. Therefore, web buckling might happen on UB column. Nevertheless, if the design is done properly according to the specification, it is hoped the section will not show any sign of failure. 1.4. MERITS AND LIMITATIONS OF STEEL STRUCTURE Steel structures have been the main choice nowadays in the construction because of many advantages that it offers. Fast construction is the main reason why many company or contractor goes for steel structure instead of concrete or timber. Other than that, steel structure can be extended easily if necessary. According to Adeli (n.d.), the following are the advantages of adapting steel structures in the construction:  High strength/ weight ratio – dead weight of steel structures is relatively small. Thus property makes steel a very attractive structural material for high-rise buildings, long- span bridges, and structures located on soft ground.  Ductility – steel passes through large plastic deformation before failure.  Predictable material properties – steel properties do not change considerably with time.  Quality of construction – produced high-quality product.  Ease of repair  Adaptation of prefabrication – suitable for mass construction.  Repetitive use – can be reused after being disassembled.  Expanding existing structures – easily expanded by adding new bays or wings.  Fatigue strength – steel has good fatigue strength. However, steel structure has also some disadvantages that have to be taken into consideration of choosing as the building materials:  More expensive compared to concrete and timber.
  • 15.  Need to have fireproofing in order to not lose its strength.  Susceptible to corrosion. There might need to apply corrosion-resistant chemicals.  Susceptible to buckling (more slender). Thereafter, a structural engineer must be very wise in choosing the section of materials for the building. Steel structures do give a lot of advantages as compared to the concrete and timber, but it still depends on the application and location of the building itself. 1.5. STAAD.PRO 2007 REVIEW STAAD in STAADPro stands for Structural Analysis and Design. It is the most well- known engineering structural design software. According to “STAAD.Pro V8i” (n.d.), STAAD.Pro is the structural engineering professional’s choice for steel, concrete, timber, aluminium and cold-formed steel design of virtually any structure though its flexible modelling environment, advanced features, and fluent data collaboration. Figure 1.11. STAAD.Pro 2007 New Project Interface STAAD.Pro is a comprehensive integrated FEA (Finite Element Analysis) and design solution, including a state of the art used interface, visualization tools and integrated codes. It is able to analyse a structure exposed to dynamic response, soil structure interaction of wind, earthquake and moving loads. (Ramkumar, n.d.)
  • 16. CHAPTER 2 – PROJECT DESIGN 2.1. PROBLEM STATEMENT A two storey building is going to be constructed in urgent. Both storey of the building will be used as an office where there will be loading imposed on it. A lot of documents will be stored in the office for the administrative work. Other than that, there will be many computers, photocopy machines and shelves on the office room. In order to get the office building finish earlier, steel structures is the best choice. Hence, the beam, column and the roof truss are designed by using the steel structures. However, there are only 2 sections available in the market; angle section and UB (Universal Beam) section. It is decided to use the UB section for the all beams and columns, and angle section is used for the roof truss members and purlins. Before determining the size of UB or angle to be used, it is needed to calculate the actual loading on respective beam or column or truss. The roof truss will be loaded by wind uplift, the weight of roof insulation membrane. Additionally, first storey slab will be loaded by ¾” acoustical hung ceiling, mechanical, electrical and lighting, roof insulation membrane, finished flooring from second storey floor and live load. For the first storey floor, it will be loaded by finished flooring and live load. After all the loadings have been considered, only then the section of the UB or angle used can be determined. Section chosen must have the capacity larger of the actual so that the building will not fail. Figure 2.1. Double Storey Building Design 1st storey slab 1st storey floor Roof
  • 17. 2.2. PROBLEM FORMULATION Office of double storey building is designed with trusses supporting the roof. The building dimension is as follow:  Spacing between trusses is 3.5 m (2 bays)  Truss (triangular) of length of bottom chord of 6 m and height of 1.5 m  Length and width of the building are 7 m and 6 m, respectively  Height of first storey and second storey are 4 m and 3.5 m, respectively  Each storey supported by four columns at every corner The loading at roof, first storey slab and first storey floor are as follow:  Roof  ⁄  ⁄  First Storey Slab  ⁄  ⁄  ⁄ ⁄  ⁄  ⁄  ⁄  First Storey Floor  ⁄  ⁄  ⁄ The section chosen and design procedure for the building design must follow the BS 5950-1:2000. The steel grade is S275. Universal Beam is used for all columns design (first storey and second storey). Universal Beam is also used for all beams design. In addition, for the roof truss, angle section is chosen for the design of all the internal members, assuming all the connection in the truss is welded.
  • 18. Speaking about the connection, the four first storey columns are welded to the foundation at the bottom part and they are fixed-supported. It is fixed-supported to prevent the building from swaying that might occur due to wind loading from the side and most likely cause the building to collapse. Equally important, the connection between the other beams and columns on the intermediate nodes of the building are welded too, but they are pin- connected since the rotation of one beam or column will affect another beam or column connected in the same joint. The adequate sections for the building are to be determined by hand calculation and STAAD.Pro analysis. The analysis is to be done using STAAD.Pro software. At the same time, sections need to be checked for its maximum capacity (shear, bending, flexural, etc.). The results of software analysis and hand calculation are compared. 2.3. DESIGN SPECIFICATION Project Description This project is to design a building by using structural design software, STAAD.Pro 2007 (Structural Analysis and Design). This software allows the user to determine the section of the structure and eventually will analyse and simulate the designed structure to determine the structure response to the applied load. Objectives The objective of this project is to design double storey steel office building with an adequate section of steel structure. Both storeys will be used as office room for all the employees. Therefore, it will carry a lot of loadings. All columns, beams and roof truss members are designed by using steel material of different sections. Beams and columns will be designed by using Universal Beam whereas the roof truss members and purlins will be designed by using angle section. Specification  First storey o Four columns at corners (4 @4 m) – UB Section o Floor made of steel with thickness of 0.03 m o Height of first storey office is 4 m o Width and length of first storey office are 6 m and 7 m, respectively
  • 19.  Second storey o Four column at corners (4 @3.5 m) – UB Section o Floor made of steel with thickness of 0.03 m o Beams supporting floor (2 @6 m and 2 @7 m) – UB Section o Height of second storey office is 3.5 m o Width and length of first storey office are 6 m and 7 m, respectively  Roof truss o Roof truss has the length of bottom chord of 6 m o Height of roof truss is 1.5 m o Angle roof slope is 26.57o o Spacing between trusses is 3.5 m (2 bays) o Truss members is designed using single unequal angle section (compression and tension members) o Purlins connected the trusses is also designed using angle section Success Criteria All the steel structures chosen for the building design must be able to support all the loadings applied on the building or at least adequate, not to let the building to collapse. The loading has actually been multiplied to the factor for the conservative purposes. Sometimes, the loading might be more or less to the actual loading. If it is less, it does not matter, if it is more, it has been controlled by the factored loading. The failure can be therefore prevented. Budget The whole construction project is estimated to worth 40 million Malaysian Ringgit. High budget is due to the usage of the steel structures. Table 1. Design Specification
  • 20. 2.4. POTENTIAL PROBLEM The main potential problem of this project is the delay in completion. The reasons to the problem can be explained more clearly by fish bone diagram below. Figure 2.2. Fish Bone Diagram From the fish bone diagram above, the factors causing the construction problem can be observed. Resource is the usual problem that a construction project has. Lack of workers especially skilled workers normally will affect the speed of construction. Besides, the unproductive machineries such as old machineries will also slow down the speed construction since it cannot promise the good efficiency while operating. On the other hand, requirements from local authority can become a barrier on the flexibility of building design. The design needs to be revised and the designer has to come out with new drawings that follow the local building codes. Ultimately, this will drag following process of construction. Environment is one of the concerns in the construction. Bad environment can delay the construction as well. For the steel structure, if it rains the whole day during the construction, the welding of the structure joins cannot be done. Other than that, the rain might corrode the steel structure too if there is no extra care put on the structure. However, the environmental problem is an inevitable problem. What human can do is try to set the time of Construction Delay ResourcesMaterials Environment Design Authority Geotechnical Unproductive machineries Unskilled labours Lack of workers Hard to get permission Must follow the building codes Effect to the structureWeather Condition Low Soil Bearing Capacity Different depth of foundation Section Availability Late Delivery Revisions Non- adequate drawings Change of nature of work
  • 21. construction properly, for example do the construction not in a rainy season or conserve the steel structure by using anti-corrosion chemicals. Equally important, the on-time arrival of the materials will actually speed up the construction process. Yet it is still subject to the availability of the materials themselves. If the section is available, it is expected to arrive early and the construction can be preceded. However, sometimes, the section chosen by the structural engineer is rare. Hence, it is needed to get it ordered from some other place. The arrival of the materials will then depend on some factors. There might be interruption in the middle of transportation. This will then lead to the delay of construction. Lastly, the geotechnical problem (soil) will have effect on the construction. A proper site investigation will actually reduce the delay caused by this factor. Site investigation is done to determine the bearing capacity of the soil and then to determine the type of foundation needed. Since this project only covers a small area of ground, most of the times, a geotechnical engineer will not check every section of small area of the building, and assume that all the bearing capacity is the same throughout the whole area of the building stands on. Yet, in real case, this might not be correct. A strength of the soil can differ significantly even in a small area of coverage. Therefore, a proper site investigation will prevent the construction delay by removing the foundation problem. 2.5. SAFETY MEASURES Although the design has confirmed the BS 5950-1:2000, some factors of safety still have to be considered. Factors of safety for this project are as follow:  Loading must not exceed the loading capacity of the section chosen for the building.  Section must be inspected frequently to check if there is any defect (corrosion). If there is, a prompt action must be immediately taken in order to prevent the collapse.  Roof truss slope angle is designed not more than 30o . If it is changed to more than 30o , the serviceability of the purlins needs to be checked.  Steel structure must not be in contact with high temperature objects such as fire. It might lose its strength.
  • 22. CHAPTER 3 – STAAD.PRO ANALYSIS AND RESULTS 3.1. PROJECT DESIGN APPROACH a. Two dimensional design of the building was drawn. Figure 3.1. Two Dimensional Drawing of the Building b. The two dimensional drawing was rendered to get the three dimensional drawing. Beams and purlins of roof truss were added. Plates were assigned to the roof, first storey floor and second storey floor. Figure 3.2. Three Dimensional Drawing of the Building c. The supports (fixed at the bottom) were assigned to the structure. The plate thickness was assigned (4 mm of aluminium for roof and 30 mm of steel for flooring). Other than that, the section for the structure was also chosen. i. UB for columns and beams ii. Single unequal angle for truss members and purlins
  • 23. Figure 3.3. Building with Assigned Section and Plate Thickness d. The mesh was created on the plate to analyse the response of elements of the structure to the applied loading. Figure 3.4. Mesh Plates in the Structure e. Loadings were applied to the structure Figure 3.5. Building with Plate Loading
  • 24. 3.2. DETAILED ENGINEERING ANALYSIS AND DESIGN On this building design, the section, thickness and material chosen are as follow. 1. Figure 3.6. Roof Purlins Number of Purlins 10 Purlins Spacing 1.68 m Length of Purlin 3.50 m Material Steel Section Single Unequal Angle Section Designation 80 x 60 x 7 L Thickness 7.00 mm Moment of Inertia 59.0 cm4 Radius of Gyration rb 2.51 cm ra 1.74 cm rv 1.28 cm Elastic Modulus 10.7 cm3 Area of Section 9.38 cm2 Table 2. Roof Purlin Details
  • 25. 2. Figure 3.7. Roof Truss Number of Trusses 3 Trusses Spacing 3.50 m Length of Truss Bottom Chord 6.00 m Height of the Truss 1.50 m Roof Sloping Angle 26.57o Material Steel Section Single Unequal Angle Section Designation 65 x 50 x 5 L Thickness 5 mm Moment of Inertia 23.2 cm4 Radius of Gyration rb 2.05 cm ra 1.47 cm rv 1.07 cm Elastic Modulus 5.14 cm3 Area of Section 5.54 cm2 Table 3. Roof Truss Details
  • 26. 3. Figure 3.8. Beams Number of Beams 4 Length of Beam 2 @6 m and 2 @7 m Material Steel Section Universal Beam (I-Beam) Section Designation 356 x 171 x 57 UB Depth of Section 358.0 mm Width of Section 172.2 mm Thickness Web 8.10 mm Flange 13.0 mm Moment of Inertia 16000 cm4 Radius of Gyration rx 14.9 cm ry 3.91 cm Elastic Modulus 896 cm3 Plastic Modulus 1010 cm3 Area of Section 72.6 cm2 Table 4. Beam Details
  • 27. 4. Figure 3.9. Columns Number of Columns 8 Length of Column 4 @4 m and 4 @3.5 m Material Steel Section Universal Beam (I-Beam) Section Designation 406 x 178 x 54 UB Depth of Section 402.6 mm Width of Section 177.7 mm Thickness Web 7.70 mm Flange 10.9 mm Moment of Inertia 18700 cm4 Radius of Gyration rx 16.5 cm ry 3.85 cm Elastic Modulus 930 cm3 Plastic Modulus 1060 cm3 Area of Section 69.0 cm2 Table 5. Column Details
  • 28. 5. Figure 3.10. Aluminium Roof Plate Number of Plate 8 Thickness of Plate 4.00 mm Material Aluminium Unit Weight 27.0 kN/m3 Table 6. Roof Details 6. Figure 3.11. Steel Floor/ Slab Plate Number of Plate 2 Thickness of Plate 30.0 mm Material Steel Unit Weight 77.0 kN/m3 Table 7. Floor/ Slab Details
  • 29. 3.3. STAAD.PRO ANALYSIS RESULTS After the analysis, STAAD.Pro was able to show if there is any failed members. Yet with the design above, there was no failed beams detected. However, the plate bending and the beam stresses were clearly observed. Figure 3.12. Deflected Shape of Structure after Analysis on STAAD.Pro Table 8. Deflection of First Storey Slab
  • 30. Table 9. Deflection of First Storey Floor Figure 3.13. Forces Acting on the Structure
  • 31. 20 20 20 20 40 40 40 40 1 2 3 4 13 14 23.4 38.4 Mz(kNm) 3 3 3 3 6 6 6 6 9 9 9 9 1 2 3 3.5 14 17 8.36 -0.269 Mz(kNm) Figure 3.14. First Storey Column Stress Figure 3.15. Bending Moment Diagram of First Storey Column Figure 3.16. Second Storey Column Stress Figure 3.17. Bending Moment Diagram of Second Storey Column
  • 32. 100 100 100 100 200 200 200 200 0.2 0.4 0.6 0.7 193 204 -166 -173 Mz(kNm) Figure 3.18. 7 m Beam Stress (Middle Element of the Mesh Beam) Figure 3.19. Bending Moment Diagram of 7 m Beam (Middle Element of the Mesh Beam) Figure 3.20. 6 m Beam Stress (Middle Element of the Mesh Beam) Figure 3.21. Bending Moment Diagram of 6 m Beam (Middle Element of the Mesh Beam) 50 50 50 50 100 100 100 100 0.2 0.4 0.6 261 262 -76.1 -70.3 Mz(kNm)
  • 33. 0.07 0.07 0.07 0.07 0.14 0.14 0.14 0.14 0.5 1 1.5 5 9 -0.139 0.066 Mz(kNm) 0.07 0.07 0.07 0.07 0.14 0.14 0.14 0.14 0.1 0.2 0.30.335 5 361 -0.129 -0.086 Mz(kNm) Figure 3.22. Truss Member Stress (Maximum Tension) Figure 3.23. Bending Moment Diagram of Truss Member (Maximum Tension) Figure 3.24. Truss Member Stress (Maximum Compression – End Element of the Member) Figure 3.25. Bending Moment Diagram of Truss Member (Maximum Compression – End Element of the Member)
  • 34. 0.30 0.30 0.30 0.30 0.60 0.60 0.60 0.60 0.90 0.90 0.90 0.90 0.2 0.4 0.6 0.7 374 25 -0.483 -0.833 Mz(kNm) Figure 3.26. Purlin Stress (Middle Element of the Mesh Beam) Figure 3.27. Bending Moment Diagram of Purlin (Middle Element of the Mesh Beam)
  • 35. CHAPTER 4 – HAND CALCULATION RESULTS
  • 36. DISCUSSION On this project, a double storey steel building was designed by using STAAD.Pro 2007, structural analysis software. The double storey is to be used as an office. The whole building is made of steel, including the beams, columns, roof truss members, roof purlins and slabs. This is to accelerate the construction process since the office building is needed urgently. As aforementioned on the problem formulation, there are types of loading imposed to the structure; wind load, live load and dead load. Wind load is the load that hit the roof and usually causes an uplift force. The dead load mostly comes from the structure weight and finishing or lighting suspended on the slab. Dead load can be said as the permanent load that will always be on the structure. On the other hand, live load comes from the weight of employees in the office. Live load is the temporary load since the employees only will be in the office during working hours. Before the analysis was done, the design was modelled out. The two dimensional drawing of the building was constructed. Thereafter, the two dimensional drawing was rendered to obtain the three dimensional building. All necessary beams or purlins and plates were added. Aluminium plate of 4 mm thickness was used for the roof plate. In addition, steel plate of 30 mm thickness was used for the floor or slab of the first storey and second storey of the building. After the thickness of the plates was assigned, the section of the beams, columns, purlins and truss members was chosen. Purlins supporting the roof plates were designed by using the 80 x 60 x 7 L single unequal angle section. These roof purlins were supported by the three roof trusses which were designed by using 65 x 50 x 5 L single unequal angle section. The roof trusses were supported by four columns at every corner with the length of 3.5 m (height of second storey). The section chosen for column design is 406 x 178 x 54 UB. On the second storey, the steel plate floor is supported by the four beams at every side. For these beams, 356 x 171 x 57 UB was chosen. These beams will carry the loading from the steel plate floor of second storey and transferred it to the first storey columns. The columns for the first storey are using the same section as the second storey columns (406 x 178 x 54 UB). This is to simplify the construction process and not to confuse the worker. From the first storey columns, the loading will be transferred to the foundation. Talking about the first storey steel plate floor, it was not supported by any beam at the side. This is because the plate is supported wholly by the ground underneath it.
  • 37. After the section assignment has been done, the supports were assigned to the structure. The structure was fixed-supported at the bottom (first storey columns to the foundations). Thereafter, the loading was assigned accordingly to the structure. Before that, mesh has to be generated on all plates on the structure so that the response of the plates to the loading can be easily observed after the analysis has been done. Preceding this, the analysis was run. The results of the analysis were plotted on section 3.3 of the report. From Figure 3.12, the deflection of the structure can be observed. The deflection of the columns, beams, purlins and truss members was not too obvious. There was only a slight displacement observed. The most obvious deflection was observed on the first storey floor. It was recorded to be 59 mm downwards (node 91, exactly at the centre of the plate) which was considered as a very large deflection. The reason why this plate deflected so much is because it was not supported by any beams at the side. As far as this plate is concerned, it was actually supported by the ground underneath it. Therefore, the deflection of the plate depends on the degree of compaction of the soil below it. If the soil is not well-compacted which has many voids and is not stable, a long-term loading on the floor might cause the plate to fail. However, the deflection was also observed on the second storey floor. But, for this plate, the deflection was not that much as compared to the first storey floor. From the result in Table 8, the maximum deflection observed was 22 mm downwards. This deflection can still be decreased by adding secondary beam in between the main beam, to support the centre part of the floor plate. On the other hand, axial stresses of the structure were analysed as well. For the column stresses, only one column was chosen from each storey for analysis by considering other three beams experiencing the same stresses and loading. From Figure 3.14, the stresses of the first storey column were observed. The maximum compression stress was determined to be 252.38 N/mm2 whereas the maximum tension stresses was determined to be 209.09 N/mm2 . Both maximum stresses were found near the top end of the column span. Moreover, from Figure 3.16, the stresses of the second storey column were observed. The maximum compression stress was determined to be 182.10 N/mm2 , whereas the maximum tension stress was determined to be 178.33 N/mm2 . Both maximum stresses were found near the bottom end of the column span. For the beam stresses, one 6 m beam and one 7 m beam was chosen for the analysis. The beam chosen was not the whole beam since mesh has been generated on the plate
  • 38. causing the beam to be separated by many nodes. Thus, the middle element of mesh beam was chosen, assuming the maximum stresses occurred there. 7 m beam which supports the longer side of the floor has the maximum compression stress of 193.47 N/mm2 at its top flange and 193.54 N/mm2 of maximum tension stress at its bottom flange (Figure 3.18). Besides, for the 6 m beam, it has the maximum compression stress of 85.09 N/mm2 and maximum tension stress of 84.85 N/mm2 at its top flange and bottom flange, respectively (Figure 3.20). From the analysis results, it can be explained that the loading caused the beam to bend downwards resulting in compression stress at the top flange and tension stress at the bottom flange. For the truss member stresses, only members that experienced the maximum tension and maximum compression axial stresses were taken into analysis (assuming other members will experience smaller stress). Those two members are located near to the support of the roof truss. For these two members, even though they are tension or compression member, they still experience the opposite stress within the member e.g. compression member experiences tension stress. For the tension member, the maximum tension stress was determined to be 77.65 N/mm2 while the maximum compression stress was determined to be 48.98 N/mm2 (Figure 3.22). For the compression member, only a small element of the truss member was taken since the mesh has been generated on the roof plate. The element chosen was the element having the largest stresses (element near the support of the truss). The maximum tension stress of the element was determined to be 58.14 N/mm2 , whereas the maximum compression stress was determined to be 155.93 N/mm2 . Lastly, the stresses on the purlins were observed as well. Same as beam, since the mesh has been generated on the roof plate, the purlin was separated by many nodes. Assuming the largest stress occurred at the middle of the purlin, the element at the middle of purlin was chosen. According to Figure 3.26, the maximum compression stress was determined to be 102.44 N/mm2 , while the maximum tension stress was determined to be 258.37 N/mm2 . From the STAAD.Pro analysis, although a significant plate deflection was detected on the first storey floor, it was found out that there were no failed structures (beams) which means all the sections assigned is adequate to support the loading. The STAAD.Pro simulation result was then verified by the hand calculation.
  • 39. For the hand calculation, the design was started from the purlin. There are two methods in designing purlin; Empirical Method and Beam Method. Empirical Method can only be used if the sloping angle of the roof is less than 30o , whereas Beam Method is used when the sloping angle is more than 30o . For this building design, sloping angle is 26.57o . Therefore, the purlin was designed by using Empirical Method. All the loadings imposed to the roof were changed to the slope loading and was totalled up to get unfactored load. Thereafter, the required elastic modulus, depth and breadth of the section were calculated. The section chosen must be larger than the required in order to not fail. Properties Required 80 x 60 x 7 L Elastic Modulus, Zx (cm3 ) 3.823 10.70 Depth, D (mm) 77.78 80.00 Breadth, B (mm) 58.33 60.00 Table 11. Purlin Properties Comparison Since all the properties from the section chosen are larger, the purlins were then designed by using 80 x 60 x 7 L single unequal angle section. Afterwards, the roof truss members were designed. Firstly, the internal forces at all members were determined and member that has maximum compressive and tensile force was taken to be analysed. Maximum compressive force and tensile force were calculated to be 18.46 kN and 16.51 kN, respectively. By assuming the connection between truss members is welded, the truss member was designed. First, the required area for the compression member was calculated. The section chosen must have a larger section area than the required area. After that, the section classification was done to check whether it falls under class 4 (slender). Thereafter, the critical slenderness was calculated to find the compressive resistance. At the same time, the required are for the tension member was calculated as well. It was then compared to the area of section chosen. Subsequently, the tensile capacity was determined. Properties Required 65 x 50 x 5 L Area, A (cm2 ) 3.356 5.540 Compressive Force (kN) 18.46 45.86 Table 12. Truss Member (Compressive) Properties Comparison
  • 40. Properties Required 65 x 50 x 5 L Area, A (cm2 ) 0.600 5.540 Tensile Force (kN) 16.51 133.457 Table 13. Truss Member (Tensile) Properties Comparison It was observed from Table 12 and Table 13 that the compressive resistance of the section chosen is much larger than the maximum compressive force experienced by the truss member. On the other hand, the tension capacity offered by the same section is much larger than the tensile force experienced by the truss member. Therefore, 65 x 50 x 5 L single unequal angle section was then adopted for all the truss members. After the section chosen for the truss was verified, the section for beam supporting the second storey floor was calculated. Firstly, all the loading imposed on the floor was calculated. Since the slab is a two-way slab ( ⁄ ), therefore the loading was distributed or supported by all four beams surrounding it. The required plastic modulus was then calculated. At the same time, the shear force and bending moment were calculated as well for the purpose of bearing and buckling checking. The section was chosen from the STAAD.Pro was then analysed. The shear buckling, shear capacity, moment capacity, deflection, bearing capacity and buckling resistance was needed to be checked to ensure the adequacy of the section. Properties Required 356 x 171 x 57 UB Plastic Modulus, Sx (cm3 ) 834.0 1010 Shear Buckling No need to check Shear Capacity (kN) 98.29 478.5 Moment Capacity (kNm) 229.4 277.8 Deflection (mm) 13.73 19.44 Bearing Capacity (kN) 98.29 145.2 Buckling Resistance (kN) 98.29 107.7 No stiffener is required at the support Table 14. 7 m Beam Properties Comparison
  • 41. Properties Required 356 x 171 x 57 UB Plastic Modulus, Sx (cm3 ) 711.3 1010 Shear Buckling No need to check Shear Capacity (kN) 97.80 478.5 Moment Capacity (kNm) 195.6 277.8 Deflection (mm) 8.643 16.67 Bearing Capacity (kN) 97.80 145.2 Buckling Resistance (kN) 97.80 107.7 No stiffener is required at the support Table 15. 6 m Beam Properties Comparison It was observed from Table 14 and Table 15 that all the properties of the beam chosen from STAAD.Pro are larger than the required value (shear, moment, deflection and plastic modulus). Hence, 356 x 171 x 57 UB was adopted for the beams. Lastly, the section chosen for the column was verified. There were two different loads that the columns on this building carry. Four columns at the second storey of the building will only carry the load from the roof, whereas the other four columns at the first storey will carry the load from second storey floor and the roof. The section for the columns can be different. But, in order to avoid confusion to the workers (having different sizes of beams), the columns were designed by using the same section even though the loads carried are different. The verification was then done on the column that carries the largest loading (first storey column). Initially, a table was constructed to calculate the loading transfer (Table 10). The load carried by the first storey column was determined to be 181.217 kN. The section chosen from STAAD.Pro was then verified for its adequacy. Properties Required 406 x 178 x 54 UB Compression Force, Fc (kN) 181.2 1134 Table 16. First Storey Column Properties Comparison Properties Required 406 x 178 x 54 UB Compression Force, Fc (kN) 32.45 1095 Table 17. Second Storey Column Properties Comparison From comparison on Table 16, the section chosen was able to support the compressive force applied on it, thus, this section is adequate for the first storey column
  • 42. design. Simultaneously, on Table 17, the same section was checked if it is able to support the second storey column. Since it has a much larger compressive resistance as compared of the compressive loading that the columns carry, 406 x 171 x 54 UB was adopted for the column design. The verification was done and all members were checked to be adequate for the building. Therefore, the building construction can be preceded. From this project, the concept of building design was understood. The design of the building has to be started from the top to the bottom as the bottom part will carry the load from the top. Therefore, the design must be started from the roof. Then, the roof and slab will transfer the loading to the column. Before designing the column, the beam needs to be designed first because it is the one that supports the slab. After the beam is designed, the loading from the slab and beam will be transferred to the column. Then only, the column design can be started. The loading carried by the column will ultimately go to the foundation. Therefore, the soil on which the building is built has to have a very good bearing capacity. Otherwise, the building will just collapse. Other than that, the advantages of steel structure as a building construction were learnt. Since this office building was needed to be finished urgently, hence, steel structure is the best choice. Unlike concrete, steel structure does not need time for curing or setting or hardening. Steel structure can just be welded or bolted to the foundation to start construction or to other steel structure for extension. After the connection is done, the structure is ready to be used. In addition, it has a good ductility property that it bends first before it breaks. Additionally, the software used for this project, STAAD.Pro 2007, was understood as well. It was studied that the software is able to perform simulation and show if there are fail members. There are many other things that the software can display. All the structural response to the applied loading can be shown after the analysis has been done. All information of the structural response can also be printed out for the design purpose. This software is very useful for the design or structural engineer. This will help the design or structural engineer in ensuring that his/her design is adequate and failure will not occur during the construction. This will literally cut off the costly maintenance cost, especially if the structure needs to be rebuilt because it is unable to be fixed anymore.
  • 43. During the design using the STAAD.Pro, it was found that there were no failed beams even though the section chosen was the very small. But, when the same section was verified by using the hand calculation, for instance the roof truss member, the section area was found out to be smaller than the required area. This means that the section chosen previously in the STAAD.Pro will most likely fail. In addition, the section chosen for beam and column was also smaller than the requirements. Therefore, during the design, it was needed to check for the first requirement such as required area (truss member), plastic modulus (beam), and elastic modulus (purlin) before assigning the section to the structure. This error might happen because of some factors. Many assumptions taken in the hand calculation that was not inputted onto the STAAD.Pro analysis such as the grade of the steel and the connection between members, might affect the result of the analysis. Other than that, it was observed from the rendered view, the structural arrangement for the angle section was not correct. The longer side of the angle is supposed to be vertical and the other part of the angle is supposed to be horizontal. But, on the rendered view, the angle of the section pointed upwards. This was totally different from what was assumed in the hand calculation part in which the angle was welded on its longer side to the gusset plate. Equally important, during hand calculation, only the members that carry the largest loading were taken into account. All members carrying smaller loading will have to follow the same design section in order to avoid confusion of having various sections. The section that was designed for the maximum force will be adequately able to support the smaller loading applied on it. For the truss members, only the members experiencing the maximum compression and maximum tension were designed and the rest of the members will follow that design. For the purlins, the middle purlin was chosen since that purlin will carry more loading compared to the end purlin. For the beam, a beam of 6 m length and a beam of 7 m length were chosen for calculation. Lastly, for the column, all four columns at each floor were assumed to carry the same loading (which in real case, does not, due to the wind loading, columns located at the leeward side of the building will have to carry more compressive force). Therefore, one of the columns was chosen and the other three columns will follow the design. The compressive resistance of section chosen for the columns was much bigger than the loading that it carries. Therefore, the assumption will not affect the results significantly.
  • 44. If the result from STAAD.Pro analysis is to be compared to the hand calculation results, there were many factors that need to be equated. Some assumptions taken during hand calculation were not put into the STAAD.Pro analysis. The results from both calculations would not be similar or close. As aforementioned before, the factors such as structure arrangement and the connection were the problems faced on the STAAD.Pro. Although the difference between the STAAD.Pro simulation result and the hand calculation result was detected, the factors affecting it were determined. However, the section chosen on this building was proven to be adequate by simulation and hand calculation. Therefore, the design project was successful.
  • 45. CONCLUSION At the end, the double storey steel building was designed successfully according to the BS 5950-1:2000. The section chosen for purlins, roof truss members, beams and columns are adequate to support the loading imposed on the building. The adequacy of the section has been checked and verified by STAAD.Pro simulation and hand calculation. From the results, the purlins will be constructed by using 80 x 60 x 7 L single unequal angle section, roof truss members will be constructed by using 65 x 50 x 5 L single unequal angle section, beams will be constructed by using 356 x 171 x 57 Universal Beam section and columns will be constructed by using 406 x 178 x 54 Universal Beam section. Those sections have been proven as safe sections to be used for this building. On the other hand, during the completion of this project, the concept of steel structure designing was obtained and understood. A building design has to be started from the top part since the top part will only carry the loading from that area. The loading is then transferred to the lower level. Thereafter, the design for the structure on the lower level can only be started. The parameters, such as shear capacity on beam, compressive resistance on column, are to be checked before the section is chosen are also understood. Additionally, the merits and limitations of the steel structure were understood as well. Despite of having many merits, there are still safety measures to the steel building itself. Steel structure is known for its good ductility and ease of construction. But at the same time, it is also susceptible to corrosion and loses its strength on high temperature. Therefore, good maintenance and care will keep the steel structure on its highest performance. To conclude, this design project was done successfully. The concept of designing steel structure was fully understood.
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