The modified dynamic-based pushover analysis of steel moment resisting frames

A modified dynamic-based pushover (MDP) analysis is proposed to properly consider the effects of higher modes and the nonlinear behavior of the structural systems. For this purpose, first, a dynamic-based story force distribution (DSFD) load pattern is constructed using a linear dynamic analysis, either time history (THA) or response spectrum (RSA). Performing an initial pushover analysis with the DSFD load pattern, a nonlinearity modification factor (NMF) is calculated to modify the DSFD load pattern. The envelope of the peak responses of the structure obtained from 2 pushover analyses with the modified DSFD load pattern as well as the code suggested first mode load pattern are considered as the final demand parameters of the structural system. The efficiency of the proposed MDP procedure is investigated using the results of nonlinear THA besides some existing pushover procedures. For this purpose, the 2-dimensional 9-, 15-, and 20-story, SAC steel frame building models are considered for parametric studies using OpenSees program. The results indicate that the proposed MDP-THA and MDP-RSA methods can significantly improve the performance of the pushover analysis. Considering the accuracy and calculation efforts, the MDP-RSA method is strongly suggested as an efficient and applicable method to estimate the nonlinear response demands of steel moment resisting frames.