An Energy-Based Formulation for First-and Multiple-Mode Nonlinear Static (Pushover) Analyses

Existing nonlinear static (pushover) methods of analysis establish the capacity curve of a structure with respect to the roof displacement. Disproportionate increases in the roof displacement, and even outright reversals in the case of higher mode pushover analyses, can distort the capacity curve of the “equivalent” SDOF system. Rather than viewing pushover analyses from the perspective of roof displacement, this paper considers the energy absorbed (or the work done) in the pushover analysis. Simple relations establish an energy-based displacement that is equivalent to the spectral displacement obtained by conventional pushover analysis methods within the linear elastic domain. Extensions to the nonlinear domain allow pushover curves to be established that resemble tradi-tional first mode pushover curves and which correct anomalies observed in some higher mode pushover curves. An example illustrates the application of a modified Multimode Pushover Analysis procedure using Yield Point Spectra.