Seismic reinforcement of historical steel bridges in Japan

Both the Kiyosu and Eitai Bridges, registered as important cultural properties in 2007, are located in the lower reaches of the Sumida River in Tokyo. They were rebuilt in the latter half of the 1920s after the great Kanto earthquake of 1923 in the Japanese capital. By examining their anti-earthquake performance under the revised new standards based on the information obtained from the magnitude M7.3 great Hanshin Awaji earthquake of 1995, it was discovered that strengthening was required for both bridges. Strengthening design was considered and discussed from 2012 to 2014. It was concluded that with respect to the Kiyosu Bridge, the installation of dampers on both girder ends was required. With respect to the Eitai Bridge, the bearings on both piers were immobilised by placing additional horizontal bearings. Also, the addition of stiffeners to the arch ribs was deemed necessary to increase rigidity. The strengthening work was carried out from 2014 to 2015. This experience is expected to supply useful information for strengthening and repair/design work of historical bridges.