Computation of pile kinematic bending moments in non-homogeneous soil profiles. Testing the validity of a simplified Vs30-equivalent homogeneous medium

Abstract

The influence of the soil profile on the maximum kinematic bending moments of pile foundations is investigated in this work. For this purpose, power-law, linear and equivalent homogeneous profiles based on real boreholes are selected together with characteristic dimensions of pile foundations. The equivalence between the homogeneous and variable profiles is established in terms of the average shear wave velocity Vs,30 suggested by the codes for site classification. Envelopes of maximum kinematic bending moments are computed through the application of the standard frequency-domain method and accelerograms corresponding to real earthquake events. The pile harmonic response is computed through an efficient linear-elastic numerical model based on the reciprocity theorem in elastodynamics and the use of Green's functions for the layered half space. In this model, piles are considered as Timoshenko's beam elements and treated as load lines within the soil formulation. The obtained results show a large influence of the variability of the soil profile on the pile maximum kinematic bending moments both for single pile and pile groups. At the pile head, the homogeneous assumption underestimates the pile response, while the opposite effect is found along the pile shaft.