Implications of Seismic Design Values for Economic Losses

Abstract

In the U.S., seismic design values are determined mostly through a risk-targeting process, which combines information about the expected collapse fragility of code-designed structures with seismic hazard at a site. However, this target only applies where the risk-targeted ground motions govern the design. In other areas, primarily close to active faults, seismic design values are reduced to values calculated from deterministic seismic hazard analysis, increasing seismic risk for near-fault sites by an unknown quantity. This study investigates the implications of designing buildings using deterministic and probabilistic design values in terms of earthquake-induced economic consequences. This investigation is carried out using a performance-based seismic risk assessment of modern code-designed buildings with various structural systems, following the FEMA P-58 framework. Specifically, structural responses and losses associated with code-designed systems (i.e., reinforced concrete, steel, wood light frame, and precast tilt-up buildings) considering different design values (i.e., risk-targeted, deterministic, and uniform-hazard) are assessed. This study finds that, while risk-targeted design maps specify a uniform collapse risk, they do not provide uniform risk of economic losses to modern buildings across the U.S. and are instead dependent on building type and site properties. Also, for the sites in this study governed by deterministic capping, design values in the current code may be up to 30% lower than design values derived from risk-targeted design maps, resulting in up to 40% higher expected seismic losses.