Transverse displacement capacity and stiffness of steel plate girder bridge superstructures for seismic loads

Ductile end cross frames have been shown to reduce the transverse seismic demand in composite steel plate girder bridge superstructures. However, the effectiveness of these cross frames is strongly influenced by the transverse flexibility of the superstructure and its capacity for potentially large relative transverse displacements between the deck slab and bearing supports. A simplified method is developed in this paper for the calculation of these displacements based on the elastic girder stresses and transverse girder stiffnesses, which are shown to compare well with results given by the finite element method. In addition the method is shown to give results that compare well with experimental data from a 0.4 scale model subject to shake table excitation. Parametric studies are then described that show typical II-girder superstructures are able to accommodate large transverse drifts (up to 17% of the girder height) while remaining in the elastic range. These large drifts are possible without distress to the slab-to-girder connection, by omitting shear studs over a short length of the girder at the support cross frame locations. Based on the above, a step-by-step procedure is proposed for evaluating the transverse displacement, stiffness and capacity of the steel girder superstructures in the region of the end and intermediate supports.