## 1 Introduction  
Bridges a vital component of road engineering infrastructure, and undertake such important functions as traffic and transportation. With the growing economic prosperity of coastal areas, offshore bridge construction has entered a period of rapid development. However, when offshore bridges have been in the marine environment for a long time, the chloride ion corrosion phenomenon can become severe. Corrosion of the reinforced concrete structure can have a wide range of adverse effects on the seismic performance of both single components and the entire bridge [1; 2; 3]. In addition, bridges can suffer large dynamic vibrations when ground motion occurs; in such cases, the seismic damage to single components and the entire bridge can be considerable, resulting in significant social and economic loss [3]. Therefore, it is critical to thoroughly conduct extensive seismic disaster risk research on offshore bridges and to ensure that rational seismic performance assessment considers chloride ion erosion. Seismic risk analysis is mainly used to quantitatively analyze and evaluate the possibility of ground motions of varying intensities, as well as the potential loss caused by engineering buildings in potential risk areas. Seismic risk analysis of bridge engineering first began in the 1980s. With the introduction of performance seismic design concepts in recent years [4], domestic and foreign scholars have performed related research work on site hazard analysis, structural fragility analysis, and seismic loss analysis, yielding a great number of research findings. [PERSON] and [PERSON] directly defined the bridge structure's damage level with the damage state of the pier while taking into account the uncertainty of seismic demand, and performed seismic risk analysis for an example bridge [5]. [PERSON] et al. conducted seismic risk and economic loss estimates for 375 bridges in South Carolina, United States, while accounting for uncertainty, providing a specific reference basis for determining bridge reinforcement plans and emergency response [6]. [PERSON] et al. proposed a multi-hazard risk assessment method based on parametric vulnerability, which is primarily applicable to highway bridge risk assessment under hurricane and earthquake actions [7]. Based on the IDA method, [PERSON] et al. converted the seismic intensity at the bridge site into the corresponding peak ground acceleration using Monte Carlo sampling; a cable-stayed bridge was chosen as the research object to validate the accuracy of above-mentioned method, then seismic risk analysis was performed on it [8]. [PERSON] et al. took a high-speed railway continuous beam bridge as an example to establish a seismic demand model for bridge components using the strip method, followed by the development of a seismic vulnerability function for bridge components [9]. Combining the geological structural conditions of the project site and historical earthquake damage data, they conducted seismic risk assessment for an example bridge. Employing a high-speed railway continuous beam bridge as an example, [PERSON] et al. investigated the influence of bond slip and chloride ion erosion on the seismic fragility of the bridge; their results revealed that the seismic damage risk of components increased with the increase in the reinforcement corrosion rate [10]. [PERSON] took a three-span continuous beam bridge as an example to calculate the seismic risk probability of an example bridge without taking into account time-varying characteristics [11]. The above excellent papers have greatly aided the research process of seismic risk analysis for bridge engineering. Furthermore, [PERSON] and [PERSON] have proposed that the accurate seismic fragility analysis of the entire bridge, rather than of single components, is the essential premise of seismic risk analysis [12].