DESIGN OF SLENDER TOWERS FOR WIND LOADS

Abstract

Wind loads essentially cause a dynamic response in the structure. Although there are a number of wind structure mechanisms which are capable of giving rise, to dynamic excitation but the two most common forms are buffecting of structures by gusts or vortex induced excitation due to eddy shedding from downstream side . For the present study aeroelastic models of a tapered concrete, latticed steel and two composite towers have been tested in boundary layer wind tunnel. Concrete and latticed steel towers were modelled by brass and aluminium angles respectively. Composite towers are just the combination in different length ratio of these tower with latticed portion fixed atop the cylindric2 portion. The mean and rms values of along-wind displacements, rms values c across-wind displacement, along-wind total force and base bending roomer have been measured for a range of wind velocities. From these results correE ponding prototype values were predicted. The values of displacements hav been compared with the theoreti cal values and experimental values available from profile grid wind tunnel experiments.. The values of force and base bendin moment were compared with values obtained by the analysis using Indian Codes. From the results, it was observed that for the concrete tower the across-wind response is maximum hence the replacement of certain top portion by latticed appendage seems to be beneficial. Unlike the along-wind mean response, the prediction of along-wind gust response can not be done only by the simulation of velocity profile but it also requires the detailed simulation of atmospheric conditions ( e .g . turbulence intensity , etc.). The dynamic forces given in the I .S . Code appear to be on the conser-vative side.