Effect of torsional ground motion on the seismic response of multistorey buildings on different soil mediums

Abstract

The spatial variation of ground motion due to phase lag and coherency loss effect gives rise to rotational/torsional ground motions thereby inducing additional torsional deformations. For multistorey buildings, a systematic study is reported on the effect of torsional ground motion resulting from the propagation of motion through different soil mediums: firm soil and medium-firm soil. For these soil mediums, two cases of ground motion: (i) translation ground motion only and (ii) combined translation and torsional ground motion are considered. For torsional ground motion two sets of the angle of incidence of propagating waves with vertical, 10° and 20° based on recorded values at sites, are considered. A set of twelve multistorey buildings comprising of frames or frames and shear walls is considered. These chosen buildings cover practically the entire spectrum of torsionally flexible and torsionally stiff low rise buildings. Variation of increase in storey shears along the height is studied and it is found that this variation due to torsional ground motion for some frame shear wall buildings is non-uniform along the height. Further, it is found that the increase in the response is significant for buildings, having low fundamental translational periods of vibration and that are torsionally flexible.