CCEER-05-3: Seismic Load Path in Steel Girder Bridge Superstructures

Abstract

Past earthquakes have shown that the inherent strength assumed in a bridge superstructure does not always prevent damage to components of steel plate girder superstructures during moderate to large earthquake excitation. Cyclic and shake table experiments on a 2/5th scale model of a simply supported steel girder bridge superstructure, with two steel plate I-girders and a reinforced concrete deck slab, were performed to determine the effects of transverse seismic loading on this type of bridge superstructure in high seismic regions. From experiments it is shown the superstructure deforms in a flexural-torsional mode with transverse seismic forces distributed along the span and resisted at the supports. At the supports, the loads are transferred from the deck slab into the girders through the shear studs located near the girder supports or through a top chord connecting the deck slab to the end cross frames. The transverse loads are then distributed from the top into the base of the girders through the end cross frames and into the substructure through the bearings and transverse bearing restraints. Each of these critical components should be designed for transverse seismic loading.