Damage Assessment of Road Bridges Subjected to the 2011 Tohoku Pacific Earthquake Tsunami

The authors assessed the tsunami damage to a girder-type road bridge, focusing on a washed-away deck that failed during the 2011 Tohoku Pacific earthquake tsunami. The inundation depth, ratio of inundation depth to girder elevation, and flow velocity were used as the three indices of the tsunami wave load acting on a road bridge deck. A gently shaped tsunami waveform was selected at a wave-front with a water surface level increase rate of less than 2.0 m/min. The damage ratio was computed for the above three indices, as defined by the number of washed-away bridges divided by the total number of bridges exposed to the tsunami. Based on statistical analysis for the damage ratio data, damage functions using the three indices were proposed. In addition, the spatial distribution of physical wash-away damage to road bridges by the anticipated Nankai Trough earthquake tsunami was shown by applying the derived damage functions.