抄録
A survey conducted in Banda Aceh after the Great Sumatra Earthquake reveals that many bridges were severely damaged by tsunami water. Some of them are even completely washed away. Calculations have shown that water velocity as low as 11 kilometers per hour is capable of displacing a concrete bridge deck and girder. Meanwhile, an estimation by other researchers using video records shows that water-flow velocities in Banda Aceh were between 18 to 21 kilometers per hour. Therefore the water drag forces acting on the bridge should have been significantly large. Nevertheless, some bridges could survive just because the deck lateral movement was non-uniform so that the decks were locked to each other.
Unseating is the problem for a bridge suffering from water drag forces. Meanwhile, in earthquake engineering, unseating is also the problem for bridges under severe ground excitation. Therefore, it is expected that prevention system for the seismic unseating problem would be applicable for those by tsunami water force as well. For example, water drag force is around 1.2 times of the weight of the bridge, whereas a severe inter-plate earthquake produces maximum force of about 1.0 times of the bridge weight. Therefore, unseating prevention system for water drag force needs stronger piers and abutments in the lateral direction.
Debris floating with water is also potential in damaging a bridge. Calculations show that debris impact force is quite significant. Some kind of soft and dampening bumper systems would be helpful in reducing debris impact forces. There are also other factors advantageous for reducing water forces: stream-lined shape of the deck and girders, and weak railing of the bridge. The stream-lined shape will reduce water drag force, whereas weak railing will break when debris hit it so that the debris can flow freely over the bridge.
