Seismic risk assessment methodology for large-span CFST arch bridges in near-fault areas based on fragility analysis

Abstract

Large-span concrete-filled steel tube (CFST) arch bridges are widely built in high-seismicity mountainous areas in China due to their low maintenance costs and high adaptability to the challenging construction environments. The dynamic response of such bridges under seismic loading is highly complex, and their seismic performance is a major concern for multiple stakeholders. This study proposes a seismic risk assessment method for large-span CFST arch bridges from a risk perspective, based on seismic fragility analysis. The method begins with seismic hazard analysis of the bridge site, followed by seismic risk scenario identification of the bridge through fragility analysis, then quantifies the seismic risk scenarios from the perspective of economic losses, and finally evaluates the quantified results of discrete risk scenarios based on tolerance theory. A CFST arch bridge located in a near-fault area is analyzed as a case study, with two design schemes and five annual earthquake frequencies considered to validate the feasibility of the proposed method. The research results show that the seismic risk assessment method effectively identifies risk scenarios and their characteristics across different design schemes and seismic frequencies. Additionally, as the method presents results through macro risk tolerance zone divisions, it offers more intuitive and stakeholder-friendly outputs compared to traditional engineering-technology-based assessments (e.g., seismic fragility curves). Overall, the proposed method serves as a robust decision-making tool for the design, operation, and maintenance of large-span CFST arch bridges and similar structures with complex seismic responses.