Seismic performance of multispan simply supported slab-on-girder steel highway bridges

The seismic response of existing multispan simply supported slab-on-girder steel highway bridges, never designed to resist earthquakes, is studied. Elastic response spectrum analyses are conducted for bridges with different bearing stiffness, span length and number of spans. It is found that the response of two-span simply supported bridges is highly dependent on the stiffness of fixed bearings on the abutments, but this effect vanishes as the number of spans increases. The transverse direction seismic capacity of bridges having more than two spans is not a function of the number of spans. These bridges may be damaged by earthquakes having peak accelerations less than 0.20 g. However, bridges with identical end-to-end length but subdivided into a smaller number of spans are found to be more vulnerable to seismic excitations than those with larger number of spans. Increasing span length is also found to have a negative impact on the seismic capacity of these bridges. Additionally, analytical expressions to calculate the minimum required seat width are developed.