The paper presents a numerical procedure to evaluate kinematic and inertial interactions effect for pile groups by using a finite element approach. The method is used to calibrate Lumped Parameter Models (LPMs) which can be implemented in commercial finite elements programs to perform time domain analyses. The procedure is employed to study the spatial dynamic response of the railway bridge on the Tronto river (Marche region, Italy) that, due to the particular stiffness of substructures and deck, represents an interesting case study. The seismic analysis is carried out in the time domain considering several real accelerograms. The results are compared with those obtained from the fixed base model by showing the importance of Soil-Structure ...