Seismic Retrofit using the Largest Viscous Damper in Japan

The Tatara Bridge is a cable-stayed bridge with a center span 890m. The seismic verification analyses of the existing conditions were carried out with the aim of further improving the seismic performance of this bridge. The results of the analyses for the bridge revealed the considerable sway-mode vibration in longitudinal direction was dominant during large-scale earthquakes, and so seismic devices such as eight viscous dampers and stoppers were found to be necessary to mitigate the vibration. It was decided to install the largest viscous dampers in Japan with a damping resistance force of 2,000kN and a stroke of ±950mm at two towers. Before the installation, the performance tests assuming actual bridge conditions during earthquakes were conducted on one representative damper using a vibration table (length 20m × width 15m, maximum displacement ±1,000mm) owned by the National Research Institute for Earth Science and Disaster Resilience. Since the tests showed that one representative damper had the required performance, it was determined that the performance test was not necessary for the remaining seven dampers by considering a method of the performance verification. This paper describes the performance test of the representative damper and the performance verification method of the remaining seven dampers.