Bridge Modal Properties Using Simplified Finite Element Analysis

Abstract

A simplified approach to the dynamic finite element modeling of composite girder-slab bridges is presented using the limiting case of a single beam element to represent the girder-slab cross section. Dynamic properties calculated with this simplified model are compared with experimental results obtained from an in situ composite girder bridge and with more detailed shell element model predictions. The simplified beam element model accurately calculates the mode shapes of the structure. This agreement, however, is dependent on accurate modeling of the piers and kinematic constraints between the bridge and piers and the appropriate representation of the bridge's torsional properties. The calculated resonant frequencies associated with these modes show some discrepancy when compared with the experimental results. This discrepancy is attributed to the inability of the single beam element model to simulate the three-dimensional boundary conditions found in the actual structure. The simple models provide approximations to the dynamic properties that are accurate enough to be useful in preliminary seismic scoping studies and in the simplified modeling of long, multispan bridges.