The Effects of Multimode Load Pattern on Pushover Analysis to EstimateThe Seismic Demandsfor Symmetric Steel Building Frames

Abstract

To take into account higher-mode effects in pushover analysis for estimating the seismic demands of high-rise building structures, the multimode load pattern (MLP) procedure has been proposed. The multimode load pattern analyses were carried out with the force distributions using mode-shapes obtained from Eigen-analysis of linearly elastic structure and the pushover analysis were done consecutively, such that first mode pushover analysis has performed, the next mode begins with the initial structural stage (stress and deformation) which is the same as the condition at the end of previous stage. Predictions based on single mode and response spectrum analysis procedures were also presented for the sake of comparison to those obtained by the MLP procedure. The implication of using multimode and single mode in MLP analysis, the higher modes in the MLP analysis strongly affect the responses at the mid and upper storey of tall building structures, contrary to the lower storey thus gives better prediction of storey drift and plastic hinge for mid and upper storey. From the comparison to each capacity curves in term of analysis procedure performance, MLP gives better results to describe the structure performance in handling earthquake force.