FEASIBILITY OF USING COLD FORMED STEEL SECTIONS FOR MEDIUM SPAN PORTAL FRAMES IN SRI LANKA M.A.M. Ziyath Degree of Master of Engineering in Structural Engineering Design Department of Civil Engineering University of Moratuwa Sri Lanka January 2013 i Declaration “I declare that this is my own work and this thesis does not incorporate without acknowledgement any material previously submitted for a Degree or Diploma in any other University or institute of higher learning and to the best of my knowledge and belief it does not contain any material previously published or written by another person except where the acknowledgement is made in the text. Also, I hereby grant to University of Moratuwa the non-exclusive right to reproduce and distribute my thesis, in whole or in part in print, electronic or other medium. I retain the right to use this content in whole or part in future works (such as articles or books).” Signature: Date: The above candidate has carried out research for the Masters under my supervision. Signature of the supervisor: Date ii Abstract Cold formed and thin walled steel (CFS) sectional members are used in building industry in many fields around the world. CFS sectional members are combined and used as a primary load bearing members on medium span structures. However use of combined CFS members on medium span portal frames in Sri Lanka is limited due to lack of knowledge. This research is to design and analyze the feasibility of using back to back CFS lipped channels on industrial portal framed building. There were 16 nos. models selected with varying spans of 6m, 9m, 12m and 15m, heights 4m and 6m and bay distance 4m and 6m. The models were first analyzed with computer analysis software called PROKON and optimum sections of back to back combined CFS lipped channels were selected so that it’s serviceability conditions were satisfied. Further the selected section sizes were revised until it’s combined moment and compression overall buckling criteria ( ) ( ) is satisfied. The major feasibility was carried through cost analysis with compared to hot rolled sectional portal frames are being constructed in Sri Lanka’s western region. Therefore the wind speed kept as constant of 140 km/hr (Maximum wind speed in western region). Out of 16 nos. models 14 nos. models shows cost effective ad saving on cost varied from 14% to 21.5% and an average of 12.5%. 4m bay distance is economical than 6m bay distance. 12m span is found to be the most economical span in these models. iii ACKNOWLEDGEMENT I would like to express my deep and sincere gratitude to my supervisor, Dr. (Mrs.) M.T.P. Hettiarachchi. Her wide knowledge and logical way of thinking have been of great value for me. Her patience, understanding, encouraging and personal guidance have provided a good basis for the present thesis as well as in my past undergraduate research done on “use of tapered steel sections in pitched portal frames”. I am also grateful to the course coordinator Dr. (Mrs.) D. Nanayakkara, research coordinator Dr. K. Baskaran, teachers and head of Department of Civil Engineering at University of Moratuwa for all kind of support and help. I wish to express my warm and sincere thanks to Eng. M.A.R.M. Abdul Jabbar for his valuable advices and friendly help. The extensive discussions around my work and often very useful insights have been of great value in this research. My warm thanks are due to Mr. Sanjeev Jayasinghe and Mr. Asela Perera who are pioneers in steel construction in Sri Lanka for their encouragement to choose this subject, giving opportunity to express my knowledge in various types of steel structures in Sri Lanka and explore the structural steel world. My sincere thanks are due to Eng. Ravindra Meewaddana for his support in comparing with existing hot rolled steel frames and enable this research to end up with efficient results. Special thanks are due to my wife Fouzana Ziyath for the support and encouragement provided over the last three years since I first set my foot in M.Eng, Structural Design. I did not think it would end up here, but you surely did. I wish to express my gratitude to all those people who have not been mentioned but helped in the realization of the thesis in various ways. iv Contents Declaration i Abstract ii Acknowledgement iii Contents iv Notations viii List of Tables xi List of Figures xii Chapter 1 1.0 Introduction 1 1.1. Background 1 1.2. Scope of work 3 1.3. Methodology 4 Chapter 2 2.0 Field Survey 6 2.1.1. CFS members in Sri Lanka 6 2.1.2 Shapes and sizes of CFS 9 2.1.3 Available sizes of lipped channels in Sri Lanka 10 2.1.4 Materials in CFS 11 v 2.1.5 Combined and back to back members in CFS 12 2.2 Case Studies 12 2.2.1 Introduction 12 2.2.2 Objective of the case study 13 2.2.3 Case study-1 13 2.2.3.1 Cost analysis 14 2.2.3.2 Technical review 15 2.2.3.3 Conclusion and recommendations 18 2.2.4 Case study-2 19 2.2.4.1 Conclusion and recommendations 23 Chapter 3 3.0 Literature Review 24 3.1. Main Characteristics of Cold-formed Members 24 3.2. Mode of Design Failures of CFS Sections 25 3.2.1. Lateral Buckling (Lateral-torsional Buckling) 26 3.2.2 Distortional Buckling 26 3.2.3 Flexural Torsional Buckling 27 3.2.4 Local Buckling 27 3.3 Other Investigation Projects on CFS Sections as Primary Structural Members 28 vi 3.4 Applicable standards and design methods 30 3.5. Back to back design rules for CFS 31 Chapter 4 3.0 Modeling and Analysis of CFS portal frames 32 4.1 Determination of roof loads 32 4.2 Determination of roof design loads 32 4.3 Determination of wind forces 33 4.4. Tabulation of results 40 4.4.1 Member sizes and deflections 40 4.5 Wind bracing design 46 Chapter 5 5.0 Results 48 5.1. Cost variation of CFS frames 48 5.2. Cost variation of hot rolled frames and comparison with CFS 49 Chapter 6 6.0 Conclusions and Recommendations 57 References 59 Appendix A Costing of CFS frames 62 Appendix B Costing of HRS frames 78 Appendix C 94 vii C.1. Specimen calculation for section properties and design strength of back to back CFS lipped channel 94 C.2 Specimen calculation for bending design 96 C.3. Specimen calculation for compression design 97 viii NOTATIONS fyb - Yield strength of cold formed steel coils fu - Tensile strength of cold formed steel coils s - Spacing between two interconnections rcy - Radius of gyration of one channel Fs - Shear force on interconnections Q - 2.5% of design axial force plus any load due to self weight or wind load LE - Effective length of compound member r1 - Radius of gyration of compound section about the axis parallel to web Gk - Dead load Qk - Live load Wk - Wind Load W - Design load on frames V -Wind Speed Vs - Design Wind Speed S1 - Topography Factor S2 - Ground roughness and building size factor S3 - Statistical concept factor q - Wind pressure Ix, Iy - Second moment of area of single cross section about x and y axes respectively Ixx, Iyy - Second moment of area of combined cross section about x and y axes respectively Zx, Zy - Elastic modulus of single cross section about x and y axes respectively Zxx, Zyy - Elastic modulus of combined cross section about x and y axes respectively Zc - Compression modulus of section in bending x - Distance from the shear centre to centroid of the combined half section measured along axis of symmetry ix rx, ry - Radii of gyration of single section about the x and y axes respectively rxx, ryy - Radii of gyration of combined section about the x and y axes respectively rcy - Radius of gyration of a channel about its centroidal axis parallel to the web e - Distance between a load and a reaction LE - Effective length of a member Ys - Nominal yield strength of steel Ysa - Average yield strength of a cold formed section Ysac - Modified average Yield Strength N - - No. of full 90 bends with radius < 5t py - Design Strength of steel Us - Nominal ultimate tensile strength of steel p0 - Limiting compressive stress in a flat web Dw - Equivalent depth of a stiffened web Mc - Moment capacity of a cross-section Pv - Shear capacity or shear buckling resistance of a member ME - Elastic lateral buckling moment of a beam E - Modulus of elasticity of steel D - Overall web depth Cb - Coefficient defining the variation of moments on a beam t - Net material thickness MY - Yield moment of a section ∩ - Perry coefficient pcr - Local buckling stress of an element Pcs - Short strut capacity PE - Elastic flexural buckling load (Euler load) for a column A - Cross sectional area of section Aeff - Effective area xo -Distance from the shear centre to the centroid of a section measured along the x axis of symmetry x ro - Polar radius of gyration of a section about the shear centre  - Ratio of end moments in a beam or Constant PEX, PEY - Elastic flexural buckling load (Euler load) for a column about x and y axes respectively CW - Warping constant of a section d - Flat depth of a section bL - Lipped height Hp - Heated perimeter xi List of Tables Table 2.1 Available Sizes of Lipped Channels in Sri Lanka 10 Table 2.2 Materials used for cold form operation in Sri Lanka 11 Table 2.3 Costing of proposed factory building for Roofmart (pvt) ltd. 15 Table 4.1 Summary of wind forces 35 Table 4.2 PROKON input coordinates 37 Table 4.3 Member Forces from analysis models 40 Table 4.4 Design capacity calculation summary 41 Table 4.5 Moment and Compression Capacity of Columns with Overall Buckling Criteria 43 Table 4.6 Moment and Compression Capacity of Rafters with Overall Buckling Criteria 44 Table 4.7 Optimum Member sizes and deflection for bay distance = 4m 45 Table 4.8 Optimum Member sizes and deflection for bay distance = 6m 45 Table 5.1 Cost variation of CFS Frames 48 Table 5.2 Frame sizes of Hot rolled Portal frames for bay Distance 4m 50 Table 5.3 Frame sizes of Hot rolled Portal frames for bay Distance 6m 50 Table 5.4 Cost variation of Hot Rolled Frames 51 Table 5.5 Cost comparisons of HRS & CFS Frames 52 xii List of Figures Figure 2.1 Galvanized steel cold formed raw steel coils 7 Figure 2.2 Mild steel cold formed raw steel coils 7 Figure 2.3 Typical cold formers 8 Figure 2.4 Cold former in Sri Lanka 8 Figure 2.5 Basic shapes of CFS sections available in Sri Lanka 9 Figure 2.6 Cold formed lipped channels in Sri Lanka 9 Figure 2.7 Basic shapes of combined thin walled sections 12 Figure 2.8 A factory building constructed by CFS section in Sri Lanka 14 Figure 2.9 Proposed eave connections 16 Figure 2.10 Proposed ridge connections 16 Figure 2.11 Section X-X (Typical member) 16 Figure 2.12 Modified eave connections with additional props 17 Figure 2.13 Modified ridge connections with additional haunch 18 Figure 2.14 Proposed eave connections for research model 19 Figure 2.15 Proposed ridge connections for research model 19 Figure 2.16 Proposed mezzanine floor layouts 20 Figure 2.17 Proposed mezzanine decks 21 Figure 2.18 Lateral failures of lipped channels 22 Figure 2.19 Lateral restrains to floor joist 23 Figure 3.1 Lateral buckling failure modes 26 Figure 3.2 Lateral distortional buckling failure modes 26 Figure 3.3 Flexural tortional buckling failure modes 27 Figure 3.4 Local buckling failure modes 27 Figure 4.1 Wind force coefficients 34 xiii Figure 4.2 Deflected Shape of Analysis model for span=12m, Height=3m and Bay Distance=4m 38 Figure 4.3 Maximum Moment on Column for Load Combination-3 38 Figure 4.4: Maximum Moment on Rafters for Load Combination-1 39 Figure 4.5 Wind bracing arrangement 46 Figure 5.1 Graphical Representation of Cost variation of CFS frames 49 Figure 5.2 Cost comparisons of frames for 3m height 53 Figure 5.3 Cost comparisons of frames for 6m height 53 Figure 5.4 Moment variation on columns for 3m height 54 Figure 5.5 Moment variation on columns for 6m height 55 Figure 5.6 Moment variation on rafters for 3m height 55 Figure 5.7 Moment variation on rafters for 6m height 55 Figure 5.8 Utilization of steel per unit building area 56