Simplified assessment of pile-head kinematic demand in layered soil

Soil-pile kinematic interaction develops as a consequence of soil movements during seismic excitations. Severe bending strains exceeding the strain limits of the pile material can then develop. The highest kinematic bending moments occur at the interface of layered soil, characterized by consecutive layers with a high Vs2/Vs1 ratio between their shear wave velocities, or at the pile-head of fixed-head piles. Seismic design codes are generally worried about the kinematic bending developing at the interface of two layers with different stiffnesses and suggest evaluating kinematic effects on strategic buildings in seismic prone areas. Recent research has shown that the kinematic demand at the pile-head is important in the design of reinforced concrete piles in soft deposits, and relatively simple formulas exist for its assessment, both in homogenous and inhomogeneous soil conditions. However, there are no simplified solutions for the assessment of the kinematic demand at the pile-head in two-layered soil with a relatively shallow interface depth. In this study a recently developed BEM-based code (KIN SP) is used for this, and the relevance of the threshold values of the average shear wave velocity parameter suggested in seismic codes is discussed. The influence of pile and soil nonlinearities is also investigated with KIN SP, which has been enhanced to account for these nonlinearities.