Three-Dimensional Modal Pushover Analysis of Unsymmetric-Plan Buildings Subjected to Two Components of Ground Motion

Abstract

The original modal pushover analysis (MPA) to estimate seismic demands due to one component of ground motion is extended to consider two horizontal components simultaneously in three-dimensional analysis of buildings and to estimate internal forces and plastic hinge rotations directly from pushover analyses. Subsequently, the accuracy of the three-dimensional modal pushover analysis (MPA) procedure in estimating engineering demand parameters (EDPs) is evaluated. Eight low- and medium-rise structures were considered. Four intended to represent older buildings were designed according to the 1985 Uniform Building Code, while four other designs intended to represent newer buildings were based on the 2006 International Building Code. Median EDP values for these buildings to 39 two-component ground motions, scaled to two intensity levels, were computed by MPA and nonlinear response history analysis (RHA) and then compared. Even for these ground motions that deform the buildings significantly into the inelastic range, the MPA offers sufficient degree of accuracy. It is demonstrated that the PMPA, a variant of the MPA procedure, for nonlinear systems is almost as accurate as the well-known standard response spectrum analysis procedure is for linear systems. Thus, for practical applications, the PMPA procedure offers an attractive alternative to nonlinear RHA, whereby seismic demands can be estimated directly from the (elastic) design spectrum. In contrast, the nonlinear static procedure specified in the ASCE/SEI 41-06 standard is demonstrated to grossly underestimate seismic demands for some of the unsymmetric-plan buildings considered.