Seismic retrofit design of highway-railway combined suspension bridges

摘要

The seismic retrofit of the Seto-Ohashi Bridges (a group of long span bridges crossing Seto-Inland Sea) was started in 2013 and will be completed by 2020. The seismic performance verification of three suspension bridges (Shimotsui-Seto, Kita Bisan-Seto, and Minami Bisan-Seto Bridges) of the Seto-Ohashi Bridges was started in 2014. These bridges are one of the longest highway-railway combined suspension bridges. Recently, large-scale earthquakes that were stronger than considered in the original design occurred in Japan. Therefore, two types of large-scale earthquake motions coming from plate boundary and inland active faults, expected to occur in the future, were used in the seismic performance verification. All truss members of the stiffening girders were modeled in the analysis to see precise behaviors during earthquakes. As the result of the seismic performance verification, in all three bridges, it is found that main members (such as main towers, stiffening girders, and substructures) will not suffer severe damage and the total number of damaged portions is small. Although some members are damaged, the damage level is found to remain below acceptable level by the supplemental in-depth analysis. As members to be retrofitted are deck bearings only, a retrofit method for road deck bearings was selected from various candidates considering workability and efficiency.