Performance-based seismic fortification criteria for offshore isolated bridge

Aiming at the present situation of china's earthquake fortification level for offshore isolated bridges, and introducing the performance-based seismic design criteria, a new earthquake fortification level for offshore isolated bridges was established in this paper. The offshore isolated brides' fortification levels were categorized into three grades according to bridges' function and the impact on the economy and the politics, and by defining three fortification levels the multilevel fortification idea was applied to practice. The bridge structures were classified into five behavior levels, and combining with the corresponding ground motion levels of various kinds of bridges, 12 lowest behavior objectives were established, three earthquake performance objectives methods were adopted for Level 1 isolated bridge, and two earthquake performance objectives methods were adopted for Level 2 and Level 3 isolated bridges. The seismic design categories are determined according to the importance of the three-level isolated bridges. The results indicate that using the performance-based seismic fortification criteria is feasible to set the earthquake resistance level for offshore isolated brides.