Generalized Pushover Analysis For Torsionally Coupled Systems

Generalized pushover analysis procedure that was previously formulated on 2D planar frames is extended to 3D systems with torsional coupling in the presented study. The instantaneous force distribution acting on the system when the interstory drift at a story reaches its maximum value during seismic response is defined as the generalized force distribution. This force distribution is then expressed in terms of combinations of modal forces. Modal contributions to the generalized force vectors are calculated by a modal scaling rule which is based on the complete quadratic combination. Generalized forces are applied to the mass centers of each story incrementally for producing nonlinear static response. Maximum response quantities are then obtained when the individual frames attain their own target interstory drift values in each story. Finally, internal forces and deformations of the structural members are compiled through an envelope algorithm; registered as the inelastic seismic response of the asymmetric-plan structure. The developed procedure is tested on a plan-asymmetric, torsionally coupled eight-story structure under a set of ground motion records which are employed without any modification. Performance of the procedure is assessed by comparing the results with those obtained from nonlinear time history analysis. Seismic response parameters such as interstory drifts and plastic rotations are presented for selected ground motions as well as mean results calculated for the ground motion set. The method is deemed successful in predicting the torsionally coupled inelastic response of 3D systems in terms of deformation and force demands