Effect of the Failure Mode on the Macro-Response of Pile Groups

This paper contributes to the generalisation of existing models that describe the multiaxial response of pile groups. Most of these models, including a specific model proposed by the Authors, assume that the foundation piles are rigidly connected to the raft. In this study, the multiaxial conditions of deep foundations are analysed by assuming a frictional disconnection at the pile-raft level, aimed at limiting the shear forces transferred to the superstructure under seismic loading. This objective is accomplished through numerical-aided limit analysis and using advanced finite-element analysis. The modifications on the failure loads obtained for the dissipative configuration are incorporated into a hyperplastic macroelement of the piled founda-tion system to provide a calculation tool capable to account for a disconnection at the piles-raft interface. The macroelement is implemented in OpenSees and the effectiveness of the frictional disconnection is tested on a case study of a multi-span girder bridge in which both the piers foundations and the abutments are provided with this base isolation device.