A single-run multi-mode pushover analysis to account for the effect of higher modes in estimating the seismic demands of tall buildings

In this paper, a simpler and more effective procedure, called the single-run multi-mode pushover (SMP) analysis, is proposed to account for the effect of higher modes in estimating the seismic demands of tall buildings. The main simplification of this procedure is that the effect of higher modes is concentrated into a single invariant lateral force distribution computed by algebraically adding the modal story forces whereby a single-run multi-mode pushover analysis is implemented. An important advantage of the proposed procedure is that the spectral pseudo-acceleration of ground motions (or design spectrum) as a weighting parameter as well as the effective modal mass ratio is incorporated into the modal story forces. Then, the effect of the frequency content of ground motions is considered in the modal lateral forces. Another advantage of the SMP procedure is that the reversal of sign in the story forces of higher modes is taken into account. In this procedure, the seismic demands are finally obtained by enveloping the results of single-run conventional and single-run multi-mode pushover analyses. To assess the accuracy of the proposed procedure, three special steel moment-resisting frames are considered. The seismic demands resulting from the SMP procedure are compared to those from the nonlinear response history analysis as a benchmark solution, as well as to those predicted from the modal pushover analysis and the consecutive modal pushover procedures. The results demonstrate that the SMP procedure can accurately estimate the seismic demands of tall buildings.