Some of the bridges swept away by tsunami during the Great East Japan Earthquake had been pushed up by powerful flows--as opposed to being moved horizontally--before being wholly carried away, a university study found.
The new findings highlight the need to investigate the water force imposed vertically on bridges, which has not been fully scrutinized, according to a team conducting the research.
The team, led by Kazuhiko Kawashima, professor of civil engineering at the Tokyo Institute of Technology, examined the ruins of the tsunami-devastated Utatsu-ohashi bridge on Route 45 in Minami-Sanriku, Miyagi Prefecture.
"Because earthquake-resistant standards for bridges have been set uniformly nationwide, similar damage could be caused to other bridges in different areas if another huge tsunami strikes," Kawashima said. "Bridges need to be reinforced against the 'push-up' force of water."
The group particularly looked at large steel fittings designed to prevent the bridge girders detaching from the bridge columns vertically when an earthquake hits, as well as blocks intended to restrict horizontal movement between the two bridge components.
As a result, no destruction or deformation caused to the fittings by the water force horizontally loaded on the bridge has been found. Such destruction or deformation are typically detected in the wreckage of a bridge when the bridge is pushed sideways by a tsunami. The blocks on the upstream side, however, were damaged instead.
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