Tsunami Effects on Buildings and Coastal Structures

In 2011, the Heisei Tsunami (also known as the East Japan Tsunami) caused unprecedented damage to well-engineered buildings and coastal structures. We examine two reinforced concrete buildings that were exposed to similar tsunami loadings, but one collapsed and the other did not. It is shown that the contrast is partly resulted from the presence of a building foundation that could cause a time delay and attenuation of the buoyancy effect on the buildings. The surviving building must be stabilized by the weight of water that flooded the building interior. We also investigate failure patterns of concrete seawalls and coastal dykes. It is demonstrated that flow-induced suction pressures on the crown play a role in the failure of concrete panels that covered the dyke's infill. High-speed flows together with high compressing pressures can cause the formation of a scour at the leeside foot of the dyke. Considerations for the design guidelines for buildings and coastal structures to cope with the "beyond-thedesign-basis" extreme coastal hazards are proposed.