AERODYNAMIC STUDY OF TALL BUILDINGS UNDER WIND LOAD

Abstract

In Design of high-rise structures, Wind is considered as one of the important horizontal forces that have significant impact on the response of building. Due to rise in population, the demand for tall buildings is increasing day by day. Wind Load on such structures are calculated using pressure coefficients and force coefficients which are available in various international codes and standards. However, these international codes and standards give information about regular shape buildings such as square, rectangle, circular or octagonal. With the technological advancement, composite plan shape buildings such as square and circular, circular and hexagonal and square and octagonal etc. have been considered by many architects keeping in view of aesthetics of Building. The wind flow around a tall building with composite plan shapes having different height ratio variation differs from what we get in regular shape analysis. Since, data is not available regarding such buildings, the need to carry wind tunnel testing or CFD become important for analyzing wind effect on such buildings. CFD (Computation Fluid Dynamics) for determining wind responses is becoming immensely popular. It has expanded as a tool to replace wind tunnel testing as it is quicker, less expansive and give more information and control to designers. In the present research study, two building plan shape triangle and circle has been considered with different height ratio. The building selected to carry out the numerical analysis are uniform and composite plan tall buildings. The length of equilateral triangle is taken as 40m and height being 200m. For composite plan shape building only height ratio is changed keeping the same dimensions. The prototype building is considered to be located in terrain category 2 as per IS 875 Part 3. Assumption is made that the variation for wind speed with height follows the power law with power law coefficient taken as 0.147. CFD analysis is carried out in ANSYS CFX taking 1:200 scaled down model of tall buildings. In total, 5 models have been considered and pressure is evaluated taking various points on the building. Each model is analyzed for different angle of wind incidence namely 0, 60, 120 and 180 degrees. The result obtained for the uniform shape cross section building has been compared with the wind tunnel testing results available in various literatures.