ABSTRACT
In the present paper the increase in the response of buildings under seismic excitation due to the torsional component of the ground motion is studied. In order to study the increase in the response a torsional response spectrum is defined at first, which is obtained from the translational response spectrum that is used, through a simple relationship. For the calculation of the structural response the response spectrum method of dynamic analysis is used and proper modifications of the computer program SUPER-ETABS are made for the numerical analyses. The parameters of the problem are obtained from the equations of motion of the single-storey structure and an important parameter: the relative torsional stiffness μ is defined whose value governs the increase of the response of a structure due to torsional ground motion. For symmetric single-storey structures an analytic expression gives the increase of the displacements due to torsional excitation at any point of the slab. Numerical analyses of many different symmetric and unsymmetric single-storey and multi-storey structures lead to specific conclusions.
