Seismic retrofit of truss bridge for highway and railway

For the steel truss portion of the Hitsuishijima viaduct, seismic performance evaluation was conducted and it was found that some members were damaged. Although the replacement of all the road deck bearings by isolation bearings was initially planned, scaffolding installation over the rail lines was limited within only three hours at midnight and heavy protection was required. In order to minimize work over the rail lines, isolation of truss girder was studied, which is unprecedented method for the highway-railway combined bridges in Japan. For the truss girder isolation, i) structural feasibility, ii) constraining effect of long rail, and iii) the running safety of the train were studied. By this method, the retrofit became minimal and economical.