Effect of Modeling Assumptions on the Earthquake-Induced Losses and Collapse Risk of Steel-Frame Buildings with Special Concentrically Braced Frames

Abstract

This paper quantifies the collapse risk and earthquake-induced economic losses of steel-frame buildings with special concentrically braced frames designed in urban California. A probabilistic building-specific loss estimation methodology that can explicitly account for the main sources of variability related to seismic hazards and structural response is used for this purpose. It is shown that, depending on the choice of the loss metric, at seismic events with low probability of occurrence (i.e., 2% probability of occurrence in 50 years), losses because of demolition and structural collapse in steel-frame buildings with special concentrically braced frames designed in highly seismic zones may be significantly overestimated when ignoring the contribution of the composite floor and gravity framing system to the analytical model building representation. For frequent and moderately frequent seismic events (i.e., 50 and 10% probability of exceedance over 50 years of building life expectancy), acceleration-sensitive nonstructural component repairs govern building losses regardless of the analytical model representation used. For the same seismic events, an appreciable contributor to total losses in steel-frame buildings with special concentrically braced frames is structural repairs because of steel brace flexural buckling. It is suggested that dual-parameter rather than drift-based steel brace fragility curves should be used in loss computations conditioned on a single seismic intensity. Otherwise, the expected annual losses should be used as a metric for building-specific loss assessment of steel-frame buildings with special concentrically braced frames.