Prediction of collapse of structures under earthquake excitations

Abstract eng:
This paper presents a summary of the state of knowledge in structural component and system modeling for predicting the collapse potential of buildings structural systems. Collapse is defined here as the loss of ability of a structural system to resist gravity loads in the presence of seismic effects. In this context, collapse implies dynamic instability in a sidesway mode, usually triggered by large story drifts that are amplified by structure P- effects and deterioration in strength and stiffness of the components of the system. Realistic modeling of deterioration is found to be the most essential aspect of collapse prediction through nonlinear dynamic analysis. 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. Different ground motions will lead to different collapse capacities because of the inherent record-to-record (RTR) variability. A collapse fragility curve that incorporates aleatory uncertainty due to RTR 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 and variability in the parameters 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 corresponding hazard curve for the site of the structure.

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