Soil-structure interaction for bridge abutments: two complementary macro-elements

In recent years, the designers of girder bridges in seismic areas have frequently opted for a continuous structural scheme, in which the abutments are called to carry large seismic forces engaging the dynamic response of the soil-abutment system. It follows that the abutment response assumes a central role in evaluating the seismic performance of a bridge as an effect of its strong interaction with both the soil and the superstructure. This consideration introduces the cardinal question pursued in the present research: how and to what extent can the dynamic response of the abutments alter the global behaviour of a bridge and vice versa? To this end, this study proposes a method of analysis based on two complementary macro-elements, which simulate the salient aspects of the dynamic soil-abutment-superstructure interaction in the structural and geotechnical analyses of the bridge, preserving a manageable computational demand of the numerical soil-structure models. The two models consist of a macro-element of the soil-abutment system, developed as a useful tool for the structural analysis, and a macro-element of the superstructure to be included in the local model of the abutment instead. The internal responses of the macro-elements define a link between the dynamic response of the soil-abutment system and the global response of the superstructure, representing a step forward to a semi-direct approach for the study of the dynamic soil-structure interaction. The macro-elements were coded in the open-source finite element analysis framework OpenSees and validated against the results obtained with advanced nonlinear dynamic analyses of fully coupled soil-structure interaction models implemented in OpenSees.