Failure study of a bridge subjected to pounding and sliding under severe ground motions

Under strong ground excitations, highway bridge structures may experience severe nonlinear behaviors including the yielding and plastic deformation of pier members, and sometimes the pounding between adjacent decks induced by the local failure of hinge bearings necessary for restraining the girders. A kind of hinge bearing requires the use of steel dowels and is typical in many existing bridges. The objective of this study is to investigate why such hinge bearing did not function and how it contributed to the deck-falling failure of one particular highway bridge stricken by the 1999 Chi–Chi earthquake (magnitude 7.3) in Taiwan. To achieve this, incremental time history analyses for discrete dynamic systems are conducted on a group of models that incorporate sliding and impacting elements, to address nonlinear behaviors as a result of the failed bearing. Causes for discrepancy in bridge responses to seismic motions between the designed and the observed are disclosed by means of comparative study of models based on different scenarios. The study demonstrates that details of the bearing can significantly change overall behaviors of a bridge. In order to ensure the expected performance of a bridge during severe earthquakes, both designer and constructor should exercise caution.