Seismic verification of viaduct piers on piled raft foundations in soft soils

European critical infrastructures, including bridges and viaducts, play a vital role in transportation, emergency services, and economic activities; however, they are frequently exposed to seismic hazards. Traditional seismic assessments often employ pseudo-static approaches or consider dynamic analysis neglecting foundation system compliance (the base is assumed to be rigid). In this study, the authors introduce a conceptual model that captures the dynamic response of viaduct piers on piled foundations in soft soils by: (i) idealizing the deck as a concentrated mass, (ii) assuming the involved mass of the pier and the foundation system to be negligible, (iii) modeling the pier behavior with an in parallel spring-dashpot system, (iv) incorporating the translational and rotational displacements of the foundation system; (v) evaluating foundation stiffness by employing the macroelement approach and by considering Piles-Raft-Soil Interaction. The model has been applied to simulate the bridge response under 20 seismic records taken from the Italian database. Results indicate that considering SSI effects very often leads to a decrease in the actions on both the structure and the foundation system. The comparison with an existing elastic-plastic macroelement recently proposed by the authors suggests that for PGA < 2m/s2 the piled raft foundation can be reasonably schematized by means of elastic springs.