The response of bridges when subjected to seismic excitation may be significantly influenced by the dynamic properties of their foundations. With current design practice, foundation elements are typically considered as elastic springs without consideration of material and radiation damping.
The objectives of this research were to identify general foundation models that are suitable for modeling soil-structure interaction in seismic bridge analysis, to modify an existing nonlinear seismic bridge analysis computer program to include a new element capable of representing such models, and to conduct a parametric study to assess the effect of the increased energy dissipation mechanisms on the response of bridge substructures.
For spread footing foundations, three different models were identified and applied to a typical two-column bridge bent. For pile foundations, four models were derived and applied to a five-column bent. The seismic response for each model was compared with conventional elastic and fixed-base models. Several soil stiffness values and earthquake records are considered for analysis. Maximum values of displacement, plastic hinge rotation, and cumulative plastic hinge rotations were noted and compared.
It was concluded that the use of the foundation models can produce an important change in the bridge response when compared to that of the fixed-base model, depending on the frequency content of the earthquake and the stiffness of the soil. The effects of radiation damping were observed to be insignificant for foundations on stiff soil, but important for those on soft soil. In addition, the performance of the simpler damped foundation models was found to be quite similar to that of the more complex models.