Adaptive Spectra-Based Pushover Procedure for Seismic Evaluation of Structures

Abstract

The estimation of inelastic seismic demands using nonlinear static procedures, or pushover analyses, are inevitably going to be favored by practicing engineers over nonlinear time-history methods. While there has been some concern over the reliability of static procedures to predict inelastic seismic demands, improved procedures overcoming these drawbacks are still forthcoming. In this paper, the potential limitations of static procedures, such as those recommended in FEMA 273, are highlighted through an evaluation of the response of instrumented buildings that experienced strong ground shaking in the 1994 Northridge earthquake. A new enhanced adaptive “modal” site-specific spectra-based pushover analysis is proposed, which accounts for the effect of higher modes and overcomes the shortcomings of the FEMA procedure. Features of the proposed procedure include its similarity to traditional response spectrum-based analysis and the explicit consideration of ground motion characteristics during the analysis. It is demonstrated that the proposed procedure is able to reasonably capture important response attributes, such as interstory drift and failure mechanisms, even for structures with discontinuities in strength and/or stiffness that only a detailed nonlinear dynamic analysis could predict.