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Comparison of Three Widely-used Aerodynamic Modifications that Minimize the Impact of Wind Loads on Tall Buildings by Raymond Hoi-Kit Kwok Bachelor of Science in Civil and Environmental Engineering, University of Wisconsin-Madison, 2006 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 MASSACHUSETTS INS1ffE I OF TECHNOOGY 0 7 2007 JUNE 2007 JUN @2007 Raymond Hoi-Kit Kwok. All rights reserved. LIBRARIES The author hereby grants to 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 o Civii)n vironmental ngineering C MvyM1 , 2007 Certified by 4r i Jerome J. Connor Professor, CivilandEnvironmental Engineering hepisf,8uipervisor Accepted by Daniele Veneziano Chairman, Departmental Committee for Graduate Students BARKER Comparison of Three Widely-used Aerodynamic Modifications that Minimize the Impacts of Wind Loads on Tall Buildings By Raymond Hoi-kit Kwok Submitted to the Department of Civil and Environmental Engineering on May 11, 2007 in partial fulfillment of the requirements for the Degree of Master of Engineering in Civil and Environmental Engineering Abstract For tall buildings, motion caused by wind is usually the most damaging to the lateral support system. As a result, engineers have invented many different methods to limit the motion of the buildings, for example dampers, bracings and outriggers etc. Aerodynamic modification, which is a passive approach, can also be used to reduce the impacts of wind loads. In this thesis, three widely-used aerodynamics modifications are discussed: 1) Shaping the corners of buildings, 2) Addition of openings through buildings and 3) Optimizing cross-sectional shapes of buildings. Comparison based on five criteria related to economy, sustainability, appearance, ease of construction and effectiveness in suppressing response of buildings caused by wind, is performed. With the help of a comparison matrix, it is shown that for a building located in downtown Boston, the method based on optimizing cross-sectional shapes is the best option. Thesis Supervisor: Jerome J. Connor Professor, Civil and Environmental Engineering Acknowledgements I am not sure if it is only me. I spent the most amount of time writing this section than any other parts in this thesis. One of the reasons is that I know everyone is going to read this page to see if his/her name is mentioned below. Another reason is that it maybe the only page in this thesis that one knows what I am talking about. First, the first person I would like to thank is definitely Professor Connor. Thank you very much for your patience. Without your advice, there is no way that I could complete writing this thesis. Of course, I would also like to thank my family. I thank you for the continual support to my education. Also, thank you for paying for my bills. I hope you can continue to take care of them though when I go to work. Professor Bank of University of Wisconsin-Madison. You are the first one to introduce me to the field of structural engineering. Thank you very much for stimulating my interest in this field. The MEng buddies, also known as the Mafia. Thank you everyone for giving me an enjoyable year. It was an honor to meet you all. Wherever you are going, good luck and have fun. And yes, thank you Alice for showing her support all the time through the phone. Thank you for all your care and love. Finally, I would like to thank my loyal dog Bobo, who passed away in Hong Kong last October when I was here in MIT. Thank you for all the happiness you brought during the last fifteen years. 3 Table of Contents MIT M.Eng. Thesis 2007 Table of Contents L ist of F igures .......................................................................... 7 L ist of T ab les ............................................................................ 9 1 Introduction 1.1 O verview .......................................................... .... 10 1.2 N ature of W ind ...................................................... 12 1.3 Impacts of Wind on Tall Buildings ................................. 13 2 Aerodynamic Modifications: Shaping Corners of Buildings 2.1 Introduction to Corner-shaping .................................... 14 2.2 Examples of Buildings Designed with Corners Shaped ......... 15 2.3 Effects of Corner-shaping 2.3.1 Alongwind Response ...................................... 16 2.3.2 Crosswind Response ....................................... 18 2.3.3 Wake Spectrum ............................................. 19 2.3.4 Force Spectrum ............................................. 20 2.3.5 Rounded versus Chamfered Corner ...................... 21 2.4 Limitations 2.4.1 Angle of Wind Incidence ................................... 22 2.4.2 Dependent on Cross-sectional Shape .................... 23 3 Aerodynamic Modification: Addition of Openings through Buildings 3.1 Introduction to Openings through Buildings ..................... 24 3.2 Examples of Buildings ................................................ 25 3.3 Effects of Adding Openings through Buildings 4 Table of Contents MIT M.Eng. Thesis 2007 3.3.1 Effect on Crosswind Response ............................ 27 3.3.2 Effect on Strouhal No. & Vortex Shedding Freq.......... 28 3.3.3 Pow er Spectrum .............................................. 29 3.3.4 Disruption of Vortex Shedding ............................ 30 3.4 Limitations 3.4.1 Size of O pening .............................................. 31 3.4.2 Angle of Wind Incidence ................................... 32 4 Aerodynamic Modification: Optimizing the Cross-sectional Shape 4.1 Introduction ............................................................ 33 4.2 Examples of Buildings ................................................ 34 4.3 Optimizing Cross-sections by Selection of Different Shapes 4.3.1 Crosswind Response ......................................... 37 4.3.2 Strouhal Number of Various Cross-sections .............. 39 4.3.3 Optimizing Cross-sections by Selection of Different Shape: A C ase Study .................................................. 40 4.4 Optimizing Cross-sections by Tapering 4.4.1 Displacement Responses .................................... 43 4.4.2 Power Spectrum .............................................. 44 4.5 Optimizing Cross-sections by Adjusting the B/D Ratio 4.5.1 Pow er Spectrum ........ ..................................... 47 5 Comparison of the Three Aerodynamic Modifications 5.1 A B rief O verview ...................................................... 50 5.2 Comparison Based on Angle of Wind Incidence .................. 50 5.2.1 M ethodology .................................................. 51 5.3 Comparison Based on Economy, Appearance, Ease of Construction A nd Sustainability ................................................... 54 5.4 Comparison Matrix ................................................... 57 5 Table of Contents MIT M.Eng. Thesis 2007 R eferen ces ................................................................................. 59 A p p en d ix ............................................................................... 6 1 6 List of Figures MIT M.Eng. Thesis 2007 Listof Fgure MI M.Eg. Tesis200 List of Figures Figure 1-1 Computer rendering and actual construction photo of Burj Dubai.... 10 Figure 1-2 730-tons tuned mass damper in Taipei and an active mass damper in University of Notre Dam e .............................................. 11 Figure 2-1 Illustration of different corners' shapes ................................ 14 Figure 2-2 Heart Tower in New York City ........................................ 15 Figure 2-3 Jin Mao Building in Shanghai, China .................................... 15 Figure 2-4 Shun Hing Square in Shanghai, China ................................... 15 Figure 2-5 Standard deviations of alongwind responses with different corner shapes when wind is acting on the longer and shorter side of the m o d e l ......................................................................... 16 Figure 2-6 Standard deviations of crosswind responses with different corner shapes when wind is acting on the longer and shorter side of the m odel ................................................................... .. 18 Figure 2-7 Wake spectrum of model with plain and chamfered corner........... 19 Figure 2-8 Crosswind force spectrum of models with plain and cham fered corner......................................................... 20 Figure 2-9 Crosswind responses with different corner modifications when wind is acted on the longer side of the model ........................ 21 Figure 2-10 Effect of angle of attack of wind to a building with cham fered corners ....................................................... 22 Figure 3-1 Different methods to introduce openings through buildings ......... 24 Figure 3-2 Computer rendering of the Shanghai World Financial Center ....... 25 Figure 3-3 Computer rendering of the opening at the top of the building ....... 25 Figure 3-4 Computer rendering of the Pearl River Tower in Guangzhou ....... 26 Figure 3-5 Crosswind deflection at the top of the model against wind velocity of models with openings in both directions, in only alongwind direction and without any openings ................................... 27 Figure

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