Seismic Collapse Risk Assessment of Buildings: Effects of Intensity Measure Selection and Computational Approach

Life safety and collapse prevention have always been primary goals of earthquake engineering, but the collapse risk of structures has not been explicitly quantified until recently. Advances in computational power and the development of models that can more accurately reproduce the behavior of structural components through failure have made collapse risk assessment possible. Interest in quantifying the collapse risk has risen significantly with the advent of performance-based earthquake engineering (PBEE), which considers uncertainties in the seismic hazard and structural response and seeks to engineer structures so that they achieve a desired level of performance in terms of expected monetary losses, downtime and casualties. In fact, collapse risk assessment is a necessary part of the PBEE process as collapse contributes to the expected economic losses, downtime and casualties resulting from a seismic event.

Collapse risk assessment of a structure involves combining information about the seismic hazard at the site with the behavior of the structure. Typically an intensity measure (IM) is used to describe the level of ground motion shaking and quantify the seismic hazard. The behavior of the structure is then characterized through nonlinear response history analysis (RHA) by subjecting the structure to many different ground motions at various intensity levels. A collapse fragility curve, which describes how the probability of collapse increases as a function of the ground motion intensity, is constructed based on analysis results and combined with the seismic hazard curve to compute the mean annual frequency of collapse (λc), a powerful collapse risk metric that describes the structure’s expected frequency of collapse in a year.