DAMAGE OF ROAD BRIDGES BY 2018 HOKKAIDO IBURI TOBU EARTHQUAKE

Abstract

 33 road bridges have suffered structural damages by the 2018 Hokkaido Iburi Tobu Earthquake which was the most severe earthquake in Hokkaido, Japan. These damaged bridges were located in the western part of the epicenter which area exceeded JMA seismic intensity scale 6-. We have conducted both on-site and documentary surveys and also had interviews with road authorities.

 From these investigations, there is no severe damage that brought to long term traffic disruption and all damage cases have been known in previous earthquakes. Some bridges had damages on the side blocks and concrete blocks of rubber bearings. During the earthquake, a large inertial force that equivalents to Level 2 earthquake in the Japanese seismic design code for highway bridges acted to these structural members and therefore these damages were expected in the bridge seismic design. A short span concrete bridge had pile bent foundation under small abutments and 9 of 10 piles ruptured during the earthquake. This type of foundation was already warned by low seismic performance. Rotational movements of a concrete bridge span, a horizontal gap in steel bearing and clacks on concrete abutments were also observed in the investigation. In the out of structurally damaged bridges, level difference or subsidence between bridge joints and backfill have emerged. These defects prevented local traffic although road authorities repaired in the short term.

 There was a grope of intact bridges near the epicenter. Therefore further investigations need about dynamic responses of bridge, input excitation force and the applied design code of existent bridges for the better seismic design of highway bridges.