EFFECTS OF SOIL-STRUCTURE INTERACTION ON INELASTIC SEISMIC RESPONSE OF BRIDGE PIERS

The investigation reported in the paper is an attempt to assess the re levance of soil-structure interaction (SSI) effects on the dynamic res ponse of bridge piers responding in the inelastic range and, in partic ular, on the maximum required ductilities in the critical regions of t he superstructure. The problem is dealt with reference to a simple str uctural configuration: a vertical cantilever carrying a mass at the to p, representing realistic cases of bridge piers of common geometry wit h spread footing foundations. A relatively large number of parameters has been considered in the analysis, with a total of 240 cases examine d, and with ductility demands on the piers ranging between 1.5 and 7. The results indicate that although in most cases SSI produces an incre ase of the maximum displacements, this effect is not very significant, and the inelastic demand in terms of curvature essentially remains un affected by soil-structure interaction, showing a tendency to decrease . Finally, the stability of these conclusions against rather extreme v ariations 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.