Effect of torsional component of earthquakes on response of symmetric/asymmetric buildings

Abstract

Although buildings are excited by translational and rotational earthquake components, only translational components are considered in seismic loads. The effects of earthquake torsional components on building responses were studied in this work. For this purpose, the torsional component of 14 earthquakes was extracted from their translational components. Symmetric and asymmetric idealised single-storey models were analysed by considering the torsional and translational components. The models considered five different values of the uncoupled torsional frequency to uncoupled translational frequency ratio (Ω = ωθ/ωx = 1·5, 1·25, 1, 0·75, 0·5), with their lateral period varying from 0·05 to 2 s. The displacements of the left-hand side, right-hand side and centre of the diaphragm, the diaphragm rotation about the centre of mass and the base shear were studied. The results indicated that the effect of the torsional component on the non-linear responses of the building was considerable, and ignoring this effect led to an underestimation of the responses. The increase in the building's responses due to the torsional component was found to depend significantly on the value of Ω and the stiffness eccentricity. The maximum growth of the displacement of torsionally stiff and torsionally flexible buildings was 51% and 155%, respectively. The diaphragm rotation can be increased to 154% in the asymmetric systems.