Seismic performance of bridge piers: caisson vs pile foundations

This work investigates the role of foundation type and layout on the seismic response of a bridge pier. Reference is made to an Italian case study of a bridge pier to be founded on a well-characterized subsoil. Both a caisson and a 3x3 pile foundation are considered as suitable design options. For each foundation type, three different geometrical layouts satisfying Ultimate Limit State (ULS) checks are analysed. Equivalent-linear ground response analyses are preliminary performed to derive the mobilized soil stiffness and damping ratio. FE analyses of the complete soil-foundation-bridge pier model are then carried out. Results indicate that consideration of Soil-Structure Interaction effects strongly reduces the pier acceleration, especially for pile foundations, which allow for a higher dissipation of energy due to radiation damping. Further, the role of foundation type and layout is discussed by separating the kinematic and inertial components of interaction, with reference to both frequency and time domain response. Some considerations about possible simplifying assumptions to account for these effects in routine engineering are finally reported.