Performance study of a bridge involving sliding decks and pounded abutment during a violent earthquake

This paper presents a case study on the sliding of bridge decks and pounding at abutment-backfill. It involves a multi-span concrete bridge supported on simple rubber bearings, subjected to longitudinal as well as vertical ground motions from the 1999 Chi-Chi earthquake. To account for soil–structure interaction, the stiffness and strength constants of backfill soils are determined by relating the tilting movement of the abutment to the bearing pressure of backfill soils. In order to evaluate the performance of the bridge, incremental time history analyses are conducted on a number of discrete mass-spring models to simulate various nonlinear behaviors of the bridge including frictional sliding at bearings, pounding among decks/abutments and elasto-plastic compression of backfill soils. Major parameters in the models are varied in ranges, which include gaps at expansion joints, friction coefficients at bearings, and strength limits in soils. Simulation results demonstrate that frictional sliding on bearing pads together with plastic deformation in backfill soils are essential to preventing deck fall-off disaster during large earthquakes. In the case the friction coefficient at bearings rises from 0.1 to 0.2, the maximum abutment tilting by pounding is reduced by ten times. Even if the soil strength were down by half, the maximum deck movement would be less than doubled. In any case, deck fall-off is very unlikely.