EFFECTS OF EDGE CONFIGURATION ON THE RESPONSE OF TALL BUILDINGS UNDER WIND LOADS

Abstract

Wind flow is horizontal motion of air column in atmosphere. The pressure gradient, Coriolis effect, and earth’s frictional resistance are three basic factors which influences wind speed and direction. In building engineering wind pressure is an important factor governing the natural ventilation, pedestrian comfort, safety from the failure of cladding units, and design of the buildings for structural resistance and stability. With increase in height of buildings and; the complex architectural shapes, analysis of wind loads has become an integral part for building serviceability requirements and comfort of users. As of now, wind load analysis is done with the help of wind codes and/or wind tunnel experiments. However, with increasing developments in computer facilities and precise software, Computational Fluid Dynamics (CFD) is, now-a-days, being commonly used for the purpose. Computational Fluid Dynamics (CFD) is a convenient, economic, and faster solution to access the behaviour and wind pressure on tall buildings of complex architectural shapes, especially during the preliminary stage of finalization of the geometry of the building and its orientation. Through CFD, wind response on tall buildings for structural variables like moments, loads, pressure, etc. can be calculated up to a level of acceptable accuracy. ANSYS (CFX) is one of the CFD tools used to analyse wind pressure on any bluff body. It is suitable for low Mack number fluid flows on sharp-edged bluff bodies. In ANSYS (CFX) complex geometry of buildings can be easily modelled and discretized into smaller elements for numerical analysis. Good quality meshing can be achieved with full control. Changes in geometry and meshing can also be easily done for parametric studies. The Present study is an approach to quantitatively find out the pressure developed by the wind on the facades of the building and; the force and moment (base shear, base moment, and torsional moment) generated on the building and qualitatively understand the wind flow pattern and its effects on various building plan models having the equal plan area and height. iv The building models have been tested in a boundary layer flow using power law corresponding to terrain category - II, as defined in IS: 875 (Part-3): 2015. Steady state flow with 5 % turbulence at a wind speed of 0.63 m/s at the model top for stand alone has been adopted. Verification and validation have been done with wind standard codes and previous experimental data on rectangular model. The results for varied wind incidence angles have been presented in the form of contour plots and graphs. Structural parameters (base shear force/drag and lift, base moments and twisting moments have also been taken from the study. The results of the study will be of great use to architects while planning the cross-sectional shapes and deciding their critical orientations for good ventilation. Structural designers will be able to design tall buildings having similar cross-sections under wind loads with greater confidence without going for wind tunnel tests.