Dynamic Response Verification of Simplified Bridge‐Foundation Model

A simplified method for finding rotational boundary stiffnesses, representing the foundations of a structure and its surrounding soil, is developed. This technique is applied to the Meloland Road overpass, for which records were obtained during the 1979 Imperial Valley earthquake. A system identification method was previously used to find the predominant modes of the structure. A very simple, finite element 3‐D beam model for the bridge is constructed, and the rotational stiffnesses are used to model the effect of the foundations. A dynamic analysis is performed, in which the recorded translational earthquake accelerations are used as input excitation to the structure, and the predominant modal frequencies of the model are shown to compare well with the results obtained through system identification, even though simplifying assumptions were made. A sensitivity analysis is also performed on the rotational boundary springs to study how much they affect the dynamic response of the structure. In further studies, these procedures could be used to gain more insight into the dynamic effects of soil‐structure interaction and should prove to be particularly useful for preliminary designs of structures.