Risk-targeted design spectra for uniform risk seismic design

The uniform hazard response spectrum only considers the seismic hazard of a site, without taking into account the seismic fragility of the structure. As a result, structures designed based on this spectrum may exhibit varying levels of collapse risk under earthquakes in different regions. To this end, first, various cases are employed to determine a first-order approximation of the seismic hazard function H(x), followed by a validation of its rationality. Subsequently, with the objective of achieving uniform collapse risk, considering both seismic hazard and structural fragility, single anchor point, double anchor points, and multiple anchor points methods are proposed to construct the risk-targeted seismic design spectra for frequent earthquake (FE), design basis earthquake (DBE), maximum considered earthquake (MCE), and very rare earthquake (VRE). Furthermore, a comprehensive study is conducted to analyze the risk-targeted seismic design spectra corresponding to different seismic design levels, site classes, and characteristic periods constructed using the multiple anchor points method. In addition, a comparative analysis is conducted on the risk-targeted seismic design spectra constructed using different methods. The study indicates that determining H(x) based on DBE and VRE is reasonable, and the relative difference between the risk-targeted ground motion (RTGM) derived from this case and the RTGM obtained by determining H(x) based on probabilistic seismic hazard analysis is within 4%. The risk-targeted seismic design spectra constructed using three different methods show overall similarity. The single anchor point method offers simplicity in calculations and ensures that the uniform risk seismic design spectrum aligns with the uniform hazard seismic design spectrum in terms of spectral shape. Although the multiple anchor points method involves increased computational effort, it allows for the consideration of seismic hazard at multiple periods.