Effects of soil-structure interaction on the seismic damageability of coupled wall-frame systems on pile foundations

The paper presents a study on the seismic damageability of coupled wall-frame structures founded on piles. A complete soil-structure interaction analysis is carried out with reference to a case study. Three different soils and seven real accelerograms are considered. Local site response analyses are performed in order to evaluate the incoming free-field motion at different depths and the ground motion amplifications. A numerical model, accounting for the pile-soil-pile interaction and for material and radiation damping, is used to evaluate the impedance matrix and the foundation input motion. Dynamic analyses are then performed in the time domain by considering fixed and deformable base models. In the second case, the effects of the soil-foundation system deformability are taken into account with Lumped Parameter Models calibrated on the impedance functions previously evaluated. Rocking phenomena affect the behaviour of the structure by increasing the interstorey drifts. Evaluation of the return period of damaging events shows how for soft soils the usual design procedure may be not effective in protecting the building against seismic damages