Regional‐risk‐targeted seismic design: A novel approach for earthquake resistant design

Abstract Current seismic design codes define safety levels based on the seismic risk of individual structures, such as specifying a maximum probability of collapse in 50 years. The design remains the same whether the structure is located within a sparsely populated area or within a densely populated area provided that both areas have the same seismic hazard. A novel seismic design approach, referred to as regional‐risk‐targeted seismic design is proposed in which the design level is based on a target seismic risk at the regional scale, as opposed to at the individual structure level. The proposed approach, which is aimed at new constructions, allows local governments to define acceptable levels of regional seismic risk and modify the seismic design criteria contained in national standards to satisfy them. As the possible consequences of a seismic event increase at the regional level, the design level becomes more stringent to control the regional seismic risk to acceptable limits. A series of simplifications are considered to facilitate its application. We illustrate the application of the proposed regional‐risk‐targeted seismic design with three examples in the city of San Francisco, California. In these examples, we iteratively compute the modifications to the maximum seismic risk on individual structures required to comply with specific target levels of regional seismic risk. In the proposed approach, the maximum tolerable seismic risk in individual structures depends not only on the seismic hazard at the site, but also on the number of structures and density in the region of interest. It is concluded that the proposed seismic design approach provides a more rational tool for local government officials to set and calibrate seismic design criteria to comply with their locally‐defined acceptable levels of regional seismic risks within a probabilistic risk management framework.