Bridge Abutments: Assessing Their Influence on Earthquake Response of Meloland Road Overpass

Strong‐motion earthquake data obtained on the Meloland Road Overpass during the 1979 Imperial Valley earthquake are used to examine the suitability of simple models for representing the transverse and vertical stiffnesses of the abutment‐embankment systems on highway bridges. Information on the seismic responses of both the abutment‐embankment systems and the bridge superstructure is obtained by applying techniques of system identification to the strong‐motion records. Analytic models, as developed in a companion paper, that account for the transverse and vertical stiffness characteristics of the bridge abutment systems are used to calculate equivalent abutment stiffnesses for incorporation into finite element models of the Meloland bridge. Predicted earthquake responses of these models are compared to the measured seismic responses and to optimal modal parameters obtained from the system identifications. Results of the various analyses show that the simplified models work quite well in simulating the stiffnesses of the abutments and are able to predict with good accuracy the frequencies and mode shapes of the first symmetric transverse and first symmetric vertical modes of the bridge. These two modes are the major contributors to the seismic response of this bridge. Use of the abutment stiffness models also provides insight into the damping ratios that have been observed for the bridge response.