Bidirectional pushover analysis of irregular structures

Pushover analysis is one of the most-used nonlinear static procedures for the seismic assessment of structures; therefore, nowadays it is extensively used by practicing engineers for the seismic analysis of virtually every type of building. This paper proposes a bidirectional pushover analysis (BPA) method to overcome the limitations of current pushover methods to assess the seismic response of irregular (both in plan and in elevation) buildings subjected to bidirectional ground motions. The extended N2 method and the proposed BPA method were applied to estimate the nonlinear response of six highly irregular reinforced concrete frame structures designed according to the requirements of Eurocode 8. Results in terms of interstory drifts and floor rotations are compared with those given by nonlinear response history analysis (NRHA). For the latter, a suite of twenty Italian bidirectional seismic ground motions was selected. It was found that results given by the proposed BPA method match those given by NRHA when the earthquake loadings are considered to act simultaneously in two principal orthogonal directions (X and Y) with load factors of 1 and 0.6, respectively. These load factors are different from the values of 1 and 0.3 indicated in the European seismic code for bidirectional linear analysis.