Structural Performance of Bridges in the Tohoku‐Oki Earthquake

Including minor nonstructural damage, over 1,500 highway bridges and numerous rail bridges were damaged during the Tohoku‐oki earthquake of 11 March 2011. The causes of this damage can be broadly classified in two categories: ground shaking, including ground failure (liquefaction); and tsunami inundation. Damage included span unseating, column shear and flexural failures, approach fill erosion, liquefaction induced settlement, and failed steel and elastomeric bearings. Since many bridges in the north Miyagi‐ken and south Iwate‐ken suffered extensive damage during the 1978 Miyagi‐ken‐oki earthquake, bridge performance during the 2011 earthquake is of particular interest. Advances in design and retrofit may be assessed by looking at the performance of bridges designed to post‐1990 codes and those retrofitted since the Kobe earthquake in 1995. In both categories, bridge damage due to ground shaking was minor, thus validating the provisions in the post‐1990 codes and the Japan bridge retrofit program. Damage that did occur due to ground shaking was mainly to bridges not yet retrofitted or only partly so. Tsunami‐related damage included complete loss of span and erosion of backfills. However, many bridges survived, despite being totally submerged, and their performance gives insight into the potential design of tsunami‐resistant bridges.