Effects of soil-structure interaction on inelastic seismic response of bridge piers

The investigation reported in the paper is an attempt to assess the relevance of soil-structure interaction (SSI) effects on the dynamic response of bridge piers responding in the inelastic range and, in particular, on the maximum required ductilities in the critical regions of the superstructure. The problem is dealt with reference to a simple structural configuration: a vertical cantilever carrying a mass at the top, representing realistic cases of bridge piers of common geometry with spread footing foundations. A relatively large number of parameters has been considered in the analysis, with a total of 240 cases examined, and with ductility demands on the piers ranging between 1.5 and 7. The results indicate that although in most cases SSI produces an increase of the maximum displacements, this effect is not very significant, and the inelastic demand in terms of curvature essentially remains unaffected by soil-structure interaction, showing a tendency to decrease. Finally, the stability of these conclusions against rather extreme variations of the parameters is confirmed by the results of additional bounding analyses, characterized by unusually soft soil conditions and by a seismic excitation multiplied by a factor of two.