Time-dependent seismic reliability of isolated bridges considering ageing deterioration of lead rubber bearings

Seismic isolation is an effective technology for mitigating the seismic damage to bridges. However, rupture and large cracks of laminated rubber bearings, including lead rubber bearings, have occurred at several bridges during recent earthquakes. Preventing the rupture of seismic isolators by considering uncertainties and variations in the mechanical properties due to ageing deterioration can improve the ductility capacity of the bridge systems when subjected to extreme ground motions. This study presents a time-dependent seismic reliability assessment methodology for isolated bridges that considers long-term ageing deterioration of lead rubber bearings. The effects of capacity hierarchy between the isolator and the column, as well as the ageing deterioration of isolators on the seismic reliability and the predominant ultimate failure mode were clarified. It was found that the effect of ageing deterioration of lead rubber bearings on seismic reliability is relatively smaller than that of the difference in seismic hazards at different sites. Furthermore, the seismic safety of isolated bridges can be significantly improved by setting an adequate capacity hierarchy between the isolator and the column, as it can prevent the rupture of the isolator under extreme ground motions considering the ageing deterioration of the isolator.