Analysis of the importance coefficient of offshore bridges under earthquakes based on seismic fragility and incremental dynamic analysis

Focusing on the continuous damage and seismic-induced stability of offshore bridges, this paper presents an optimized quantification of the importance coefficient of bridges subjected to earthquakes. First, the timedepending durability analysis model of materials, probabilistic seismic demand model, damage indicator analysis, and input of earthquake ground motions are investigated. Subsequently, using incremental dynamic analysis, fragility, and reliability, a quantitative criterion of the importance coefficient for offshore bridges is proposed. Thereafter, a case of an offshore bridge is analyzed, including the description, finite-element modeling method, the efficient and refined simulation of materials, construction of the damage indicator, and classification of collapse scenarios, also, the collapse resistance of bridges under earthquakes. This study indicates that the importance coefficient increases with the extension of the service time, the time-depending durability damage effects have a significant influence on the importance coefficient. The mainshock-aftershock sequence is vital to the importance coefficient of a bridge during the whole life cycle, and the bridge will still have a certain service performance when it exceeds its design service life.