CIVIL 3811 Week 8 Lecture Slides PDF

Wind Loading on High- Rise Buildings CIVL3811 Engineering Design and Construction School of Civil Engineering | Faculty of Engineering THE UNIVERSITY OF SYDNEY The University of Sydney Page 1 Wind loading on high-rise buildings The wind is a phenomenon of great com...

Wind Loading on High- Rise Buildings CIVL3811 Engineering Design and Construction School of Civil Engineering | Faculty of Engineering THE UNIVERSITY OF SYDNEY The University of Sydney Page 1 Wind loading on high-rise buildings The wind is a phenomenon of great complexity because of the many flow situations arising from the interaction of wind with structures. The wind is composed of a multitude of eddies of varying sizes and rotational characteristics carried along in a general stream of air moving relative to the earth’s surface. These eddies give wind its gusty or turbulent character. The gustiness of strong winds in the lower levels of the atmosphere largely arises from interaction with surface features. (Mendis et al., 2007). The University of Sydney Page 2 Wind loading on high-rise buildings https://www.enr.com/articles/54334-paradigm-shift-in-tall-building-wind-design-cuts-material-cost-and-carbon The University of Sydney Page 3 DESIGN WIND LOADS The characteristics of wind pressures on a structure are a function of the characteristics of the approaching wind, the geometry of the structure under consideration, and the geometry and proximity of the structures upwind. The fluctuating pressures can result in fatigue damage to structures, and in dynamic excitation, if the structure happens to dynamically wind sensitive. The pressures are also not uniformly distributed over the surface of the structure, but vary with position (Mendis et al., 2007). The University of Sydney Page 4 https://www.simscale.com/blog/wind-loads-buildings/ Environmental wind studies This section Investigates the wind effects on the surrounding environment caused by erection of the structure (e.g. tall building). This study is particularly important to assess the impact of wind on pedestrians, motor vehicles and architectural features such as fountains, etc, which utilise public domain within the vicinity of the proposed structure (Mendis et al., 2007). https://www.constructionexec.com/article/how-famous-buildings-around-the-world-consider-wind-loads The University of Sydney Page 5 Skyscrapers and Sustainability https://buildingtheskyline.org/wind-turbines/ Skyscrapers with Wind Turbines. From Left to Right: The Strata SE1 (London), Bahrain World Trade Centre, Pearl River Tower (Guangzhou), Hess The University of Sydney (Discovery) Tower (Houston). Page 6 Wind loads for façade In order to assess design wind pressures throughout the surface area of the structure for designing the cladding system. Due to the significant cost of typical façade systems in proportion to the overall cost of very tall buildings, engineers cannot afford the luxury of conservatism in assessing design wind loads. With due consideration to the complexity of building shapes and dynamic characteristics of the wind and building structures, even the most advanced wind codes generally cannot accurately assess design loads (Mendis et al., 2007). The University of Sydney Page 7  WIND TUNNEL TESTS There are many situations where analytical methods cannot be used to estimate certain types of wind loads and associated structural response. For example, when the aerodynamic shape of the building is rather uncommon or the building is very flexible so that its motion affects the aerodynamic forces acting on it. In such situations, more accurate estimates of wind effects on buildings can be obtained through aeroelastic model testing in a boundary-layer wind tunnel. The University of Sydney Page 8 Wind tunnel testing is a powerful tool that allows engineers to determine the nature and intensity of wind forces acting on complex structures. Wind tunnel testing is particularly useful when the complexity of the structure and the surrounding terrain, resulting in complex wind flows, does not allow the determination of wind forces using simplified code provisions. (Mendis et al., 2007). Tested models in wind tunnel (Li et al, 2019) The University of Sydney Page 9  COMPUTATIONAL FLUID DYNAMICS TECHNIQUES In a number of fields, numerical simulation by means of CFD (Computational Fluid Dynamics) is becoming a promising and powerful tool for predicting the behaviour of structures in practical engineering cases. This includes applications involving fluid structure interaction. CFD techniques may be used for determination of wind effects where Standards are sometimes not directly or as easily applicable, for instance when designing tall buildings and non conventional structures. The University of Sydney Page 10  Stream line of a flow over a building model – Vertical view & Pressure distribution (Mendis et al., 2007). The University of Sydney Page 11  Structural systems to resist lateral loads http://www.sturdystructural.com/lateral-resisting-systems.html The University of Sydney Page 12  Reinforce concrete shear walls – In structural engineering, shear walls are walls made of different components, with the task of suppressing the effect of lateral loads on the structure. Shear walls are designed to resist lateral loads such as wind and earthquake. Shear walls significantly increase the stiffness, resistance and ductility of the structure, and improves the behaviour of structure against earthquakes. The University of Sydney Page 13  Reinforced Concrete Shear Walls https://theconstructor.org/structural-engg/shear-wall-types-efficiency/6820/ The University of Sydney https://theconstructor.org/structural-engg/shear-walls-structural-forms-positioning/6235/Page 14  (Babaei and Taherkhani, 2005) The University of Sydney Page 15 Actual damage and crack patterns from wall models (Henry et al., University of Auckland, 2015) The University of Sydney Page 16  Reinforced Concrete Shear Core The University of Sydney Page 17  Wind Loads on Temporary Structures https://www.civilengineeringforum.me/type-of-loads-acting-on-structures/wind-loads-engineersdaily/ https://www.indiamart.com/proddetail/structural-analysis-and-design-services-17833697855.html The University of Sydney Page 18  Case Study Steps to assembling a crane – Steps to assembling a crane 1. Creating the crane base. About two weeks before assembly, construction workers create a solid foundation to support the crane. 2. Transporting pieces of the crane. 3. Adding the mast. 4. Attaching the operator's cab and slewing ring 5. Adding the tower top. 6. Attaching the counter jib. 7. Attaching the front jib. The University of Sydney Page 19  Steps to assembling a crane https://www.westpark.org/en/CampusDevelopment/NewsRoom/FeaturedStories/LWLW_20200608 The University of Sydney Page 20 Transporting pieces of the crane The University of Sydney Page 21  Adding the mast The University of Sydney Page 22  Attaching the operator's cab and slewing ring The University of Sydney Page 23 Case study – The Burj Khalifa- Tallest building in the world- 828 meters and 163 storeys. – “Y” shaped in plan – to reduce the wind forces on the tower and known as buttressed core – Each wing, with its own high- performance concrete core and perimeter columns, buttresses the others via a six-sided central core, or hexagonal hub. – The core walls vary in thickness from 1300mm to 500mm. The University of Sydney Page 24 Finite Element Analysis Steel Spire (fy = 500 MPa) Concrete Core (fc’= 80 MPa) The University of Sydney Page 25  Load Cases Load Wind Load Wind Hazard Wind Duration Wind Cases Direction Function Level Speed Pressure AC1 Frequent 50 m/s 4.5 s 5 kPa 𝑃𝑃 cos 𝜔𝜔𝑛𝑛 AC2 Rare 90 m/s 4.5 s 15 kPa AC3 A Very Rare 170 m/s 4.5 s 50 kPa AS1 Frequent 50 m/s 4.5 s 5 kPa 𝑃𝑃 sin 𝜔𝜔𝑛𝑛 AS2 Rare 90 m/s 4.5 s 15 kPa AS3 Very Rare 170 m/s 4.5 s 50 kPa BC1 Frequent 50 m/s 4.5 s 5 kPa 𝑃𝑃 cos 𝜔𝜔𝑛𝑛 BC2 Rare 90 m/s 4.5 s 15 kPa BC3 B Very Rare 170 m/s 4.5 s 50 kPa BS1 Frequent 50 m/s 4.5 s 5 kPa 𝑃𝑃 sin 𝜔𝜔𝑛𝑛 BS2 Rare 90 m/s 4.5 s 15 kPa BS3 Very Rare 170 m/s 4.5 s 50 kPa DIRECTION A CC1 Frequent 50 m/s 4.5 s 5 kPa DIRECTION B 𝑃𝑃 cos 𝜔𝜔𝑛𝑛 CC2 Rare 90 m/s 4.5 s 15 kPa DIRECTION C C CC3 Very Rare 170 m/s 4.5 s 50 kPa CS1 Frequent 50 m/s 4.5 s 5 kPa 𝑃𝑃 sin 𝜔𝜔𝑛𝑛 CS2 Rare 90 m/s 4.5 s 15 kPa CS3 Very Rare 170 m/s 4.5 s 50 kPa The University of Sydney Page 26 27 Wind Loading Direction The University of Sydney Page 27  Dynamic Characteristics Natural Frequency (Hz) Mode ABAQUS ABAQUS ETABS (this project) (Bhavik et al., 2011) (Baker et al., 2008) 1 0.285 0.14 0.088 2 0.37 0.146 0.098 3 1.05 0.431 0.232 Mode 1 Mode 2 Mode 3 Mode 4 Mode 5 Mode 6 𝑇𝑇1 = 3.5𝑠𝑠 𝑇𝑇1 = 2.7𝑠𝑠 𝑇𝑇1 = 0.95𝑠𝑠 𝑇𝑇1 = 0.78𝑠𝑠 𝑇𝑇1 = 0.44𝑠𝑠 𝑇𝑇1 = 0.38𝑠𝑠 The University of Sydney Page 28  Critical Load Case Assessment AC3 AS3 BC3 BS3 CC3 CS3 12 10 Load Case Displacement Base Shear Overturning Max. Principal Moment Stress AC3 2.7 m 7.51 x 104 kN 1.98 x 106 kNm 1.7 MPa 8 AS3 8m 5.7 x 104 Kn 1.93 x 106 kNm 1.6 Mpa 6 BC3 2.82 m 6.7 x 104 kN 1.77 x 106 kNm 1.4 Mpa BS3 8m 6.9 x 104 kN 1.56 x 106 kNm 1.93 Mpa 4 CC3 2.87 m 7.2 x 104 kN 1.97 x 106 kNm 1.46 Mpa CS3 10 m 7.5 x 104 kN 2.1 x 106 kNm 2.57 MPa 2 0 Displacement Base Shear Overturning Maximum Moment Principal Stress The University of Sydney Page 29  Displacement – CS3 Wind Hazard levels Top Displacement Maximum Displacement Limit Status Frequent 0.45 H/500 Satisfied Rare 2.9 Exceeded H/100 Very Rare 10 Exceeded Top Displacement (m) 12 10 10 8 Top Displacement (m) 6 4 2.9 2 0.45 0 50 m/s 90 m/s 170 m/s Wind Speed The University of Sydney Page 30  This Week Tutorial Question Colour Type of Materials Type of Members Elements Core Wall 50 Mpa Concrete Shell Core Wall 40 Mpa Concrete Shell Core Wall 32 Mpa Concrete Shell Mega-Columns 50 Mpa Concrete Beams Mega-Frame Grade 350 Steel Beams The University of Sydney Page 31  References 1) Mendis, P., Ngo, T., Haritos, N., Hira, A., Samali, B., & Cheung, J. (2007). Wind loading on tall buildings. EJSE International, 41–53. 2) National Building Code of Canada National Building Code of Canada, Volume 1, Division B. (2005). 3) Reiter, S. (2008). Validation process for CFD simulations of wind around buildings. European Built Environment CAE Conference. 4) Sanaei E., & Babaei M., (2012). Topology Optimization of Structures using Cellular Automata with Constant Strain Triangles. International Journal of Civil Engineering, 10(3), 179-188. 5) Y. G. Li, M. Y. Zhang, Y. Li, Q. S. Li, and S. J. Liu, “Experimental study on wind load characteristics of high-rise buildings with opening,” The Structural Design of Tall and Special Buildings, Wiley, Hoboken, NJ, USA, 2020. The University of Sydney Page 32