Integrated foundation-structure seismic assessment through non-linear dynamic analyses

This paper aims at clarifying the role of dynamic soil-structure interaction in the seismic assessment of structure and foundation, when the non-linear coupling of both subsystems is accounted for. For this purpose, the seismic assessment of an ideal set of bridge piers on shallow foundations is considered. After an initial standard assessment, based on capacity design principles, the evaluation of the seismic response of the piers is carried out by dynamic simulations, where both the non-linear responses of the superstructure and of the foundation are accounted for, in the latter case through the macro-element modeling of the soil-foundation system. The results of the dynamic simulations point out the beneficial effects of the non-linear response of the foundation, which provides a substantial contribution to the overall energy dissipation during seismic excitation, thus allowing the structural ductility demand to decrease significantly with respect to a standard fixed-base or linear-elastic base assessment. Permanent deformations at the foundation level, such as rotation and settlement, turn out to be of limited amount. Therefore, an advanced assessment approach of the integrated non-linear system, consisting of the interacting foundation and superstructure, is expected to provide more rationale and economic results than the standard uncoupled approach, which, neglecting any energy dissipation at the foundation level, generally overestimates the ductility demand on the superstructure.