Predicting Collapse of Frame and Wall Structures

Abstract eng:
This paper summarizes the state of knowledge in structural system modeling and tool development for predicting the collapse potential of buildings whose lateral load resisting system consists of moment-resisting frames or reinforced-concrete shear walls. In this context, collapse implies dynamic instability in a sidesway mode, triggered by large story drifts that are amplified by structure P-Δ effects and deterioration in strength and stiffness of the components of the system. The collapse capacity of a building is defined as the maximum ground motion intensity (often represented by the spectral acceleration at the first mode period) at which the structural system still maintains dynamic stability. A collapse fragility curve that incorporates aleatory dispersion due to record-to-record variability is obtained by ordering the collapse capacities for a representative set of ground motions. Additional dispersion of the collapse fragility curve is caused by epistemic uncertainties due to modeling assumptions on which analytical predictions are based. The collapse potential of a building can be expressed as the probability of collapse at a discrete hazard level or the mean annual frequency of collapse, both of which can be computed from the collapse fragility curve and the hazard curve for the site of the structure. Collapse fragility curves and estimates of the collapse potential for generic structures are discussed, together with the effects of different levels of detailing in modeling for nonlinear analysis. Results for generic structures are compared to assess the merits of different structural systems for controlling the collapse potential.

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