Modal Pushover Analysis of SAC Buildings

The nonlinear static procedure (NSP) or pushover analysis in FEMA-273 [FEMA, 1997] has become a standard procedure in current structural engineering practice. Seismic demands are computed by nonlinear static analysis of the structure, which is subjected to monotonically increasing lateral forces with an invariant height-wise distribution until a target displacement is reached. None of the current invariant force distributions can account for the contribution of higher modes—higher than the fundamental mode—to the response or for redistribution of inertial forces because of structural yielding. To overcome these limitations several researchers have proposed adaptive force distributions that follow more closely the time-variant distributions of inertia forces (Fajfar and Fischinger, 1988; Bracci et al., 1997; Gupta and Kunnath, 2000). Others have tried to address this issue by considering more than the fundamental vibration mode in standard pushover analysis (Paret et al., 1996; Sasaki et al, 1998, Gupta and Kunnath, 2000; Kunnath and Gupta, 2000; Matsumori et al., 2000).