Kinematic Seismic Response of Single Piles and Pile Groups

Results of a numerical study are presented on the kinematic response of groups of vertical floating piles connected through rigid massless caps and subjected to vertically propagating harmonic S‐waves. Pile‐soil and pile‐pile interaction effects are modeled rigorously. Parametric results for the “effective seismic pile‐cap motion,” normalized by the “free‐field” ground‐surface motion, are displayed in dimensionless form for a number of typical pile‐group configurations, in three idealized soil profiles: a homogeneous half‐space, a half‐space with modulus proportional to depth, and a two‐layered stratum. It is shown that, whereas the influence of the nature of the soil profile is profound at all frequencies, the effects of pile‐group configuration, number of piles in the group, and relative spacing between piles are usually insignificant for lateral displacements, but quite important for pile‐cap rotations. Pile‐head “fixity” conditions and the pile/soil modulus ratio are found to affect appreciably and in a similar way the seismic response of a single pile and of a pile group.