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Investigation of Shear Lag Effect in High-Rise Buildings with Diagrid System

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Investigation of Shear Lag Effect in High-Rise Buildings with Diagrid System Investigation of Shear Lag Effect in High-rise Buildings with Diagrid System by Johan Leonard B.S., Civil Engineering (2004) Illinois Institute of Technology Submitted to the Department of Civil and Environmental Engineering in Partial Fulfillment of the Requirements for the Degree of Master of Engineering in Civil and Environmental Engineering at the Massachusetts Institute of Technology June 2007 © 2007 Johan Leonard All rights reserved The author hereby grants MIT permission to reproduce and to distribute publicly paper and electronic copies of this thesis document in whole or in part in any medium now known or hereafter created Signature of Author .......................................................................................................... Department of Civil and Environmental Engineering May 21, 2007 Certified by ...................................................................................................................... Jerome J. Connor Professor of Civil and Environmental Engineering Thesis Supervisor Accepted by ..................................................................................................................... Daniele Veneziano Chairman, Departmental Committee for Graduate Students Investigation of Shear Lag Effect in High-rise Buildings with Diagrid System by Johan Leonard B.S., Civil Engineering (2004) Illinois Institute of Technology Submitted to the Department of Civil and Environmental Engineering in Partial Fulfillment of the Requirements for the Degree of Master of Engineering in Civil and Environmental Engineering ABSTRACT In the recent years, there have been many new skyscrapers built which soar into new heights. The most efficient building system for high-rises has been the framed tube system. However, the framed tube building suffers from shear lag effects which cause a nonlinear distribution of axial stresses along the face of the building. A particular structural system called a diagrid system has caught the attention of the public. The diagrid system is not a new invention. The idea had been around since 1960 and few buildings have been built with the diagrid system. However, the implementation in a larger scale of such tall building was not practical due to high cost related to the difficult node connections. It is only in recent years that the technology has allowed for more reasonable cost of making the diagrid node connections. Despite becoming the new trend in high-rise structures, there are not many technical publications related to diagrid building system. A recent thesis by Moon (2005) studied the various angles of the diagrid to find optimum angle. He has also reviewed the design considerations for diagrid building. This thesis attempts to build on the study by Moon related to the shear lag effect in diagrid building. Diagrid buildings of different configuration are modeled in SAP2000 and analyzed for shear lag effect and structural performance. Thesis Supervisor: Jerome J. Connor Professor of Civil and Environmental Engineering Acknowledgements I would like to thank my family for their unwavering support. Without their prayers and support I would not have the chance to study in United States. Because of their support I also have the chance to study in the best institute in the world at MIT. I would like to thank all the professors and TA that I have encountered in my study at MIT. They have made me a better engineer. Special thanks to Professor Jerome Connor for his guidance throughout my study at MIT. He was a great teacher both inside and outside the classroom. I also would like to thank all of my friends. To each one of the M.Eng/The Mafia. Thanks for a great year. Each one of you was a great company in tough times and fun times. It was a pleasure to study with all of you, and play basketball and softball together. Thanks to Keith Coleman for being my partner in studying and doing all of our schoolwork. I would like to also thank other friends who have supported me even though they were not present in person, those who kept me company in my late night studies. Table of Contents Chapter 1: Introduction....................................................................................................8 Chapter 2: Shear Lag Effect...........................................................................................10 2.1 Introduction to Shear Lag ....................................................................................10 2.2 Shear Lag in Framed Tube Structure....................................................................13 Chapter 3: Diagrid Building System ..............................................................................19 Chapter 4: Modeling and Analysis.................................................................................23 4.1 Analysis Method..................................................................................................23 4.2 Analysis and Results............................................................................................25 4.3 Parametric Study .................................................................................................27 4.3.1 Angle Variation.............................................................................................27 4.3.2 Diagrid Density Variation .............................................................................32 4.4 Discussions..........................................................................................................35 Chapter 5: Conclusion ...................................................................................................41 Appendix A...................................................................................................................45 Appendix B...................................................................................................................49 4 List of Figures Figure 2-1: Axial Stress Distribution in Beam Structure ................................................10 Figure 2-2: Negative Shear Lag.....................................................................................11 Figure 2-3: Top Flange Stresses for Concentrated Load at Midspan...............................12 Figure 2-4: Deformed Shape of Flange..........................................................................12 Figure 2-5: Linearly Distributed Load Divided into 2 Load Cases .................................13 Figure 2-6: Stress Resultant at Point of Load Separation................................................13 Figure 2-7: Shear Lag in Framed Tube Building............................................................14 Figure 2-8: Variation of (ΔF)1 and (ΔF)2 along Height of Building ................................16 Figure 2-9: Axial Forces in Flange of 40 Story Building................................................16 Figure 2-10: Mega Bracings in Framed Tube Buildings.................................................18 Figure 2-11: Belt Truss in Framed Tube Building..........................................................18 Figure 3-1: CCTV Headquarters, Beijing.......................................................................20 Figure 3-2: Swiss Re, London .......................................................................................20 Figure 3-3: Hearst Tower, New York ............................................................................21 Figure 3-4: Kaiserslautern Landmark, Germany ............................................................21 Figure 4-1: 71.6° Diagrid Model....................................................................................24 Figure 4-2: Diagrid Building Model ..............................................................................24 Figure 4-3: Axial Stress Distribution in Flange Panel ....................................................26 Figure 4-4: Axial Stress Distribution in Web Panel........................................................26 Figure 4-5: Deflection of Diagrid Models for Various Angles .......................................29 Figure 4-6: Shear Lag Ratio in Diagrid Structure for Various Angles ............................29 Figure 4-7: Lateral Structure Weight for Various Diagrid Angles ..................................30 Figure 4-8: Deflection of Diagrid Models vs. Lateral Structure Weight .........................31 Figure 4-9: Lateral Structure Weight for Various Diagrid Densities...............................33 Figure 4-10: Shear Lag Ratio in Diagrid Structure for Various Diagrid Densities ..........33 Figure 4-11: Lateral Structure Weight for Various Diagrid Densities.............................34 Figure 4-12: Deflection of Diagrid Models vs. Lateral Structure Weight........................35 Figure 4-13: Tension Flange Axial Stresses...................................................................36 5 Figure 4-14: Web Panel Axial Stresses ..........................................................................36 Figure 4-15: Top Half of the Tension Flange Panel........................................................37 Figure 4-16: Bottom Half of the Tension Flange Panel ..................................................37 Figure 4-17: Compression Member ...............................................................................38 Figure 4-18: Box Panels Unfolded Showing Only Compression Components................38 Figure 4-19: Number of Nodes in Diagrid Building for Various Angles.........................39 Figure 4-20: Number of Nodes for Various Diagrid Densities
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