Pile-Head Kinematic Bending of Fixed-Head Long Piles in Homogeneous and Layered Soils Considering Pile and Soil Material Nonlinearities in Case of Moderate to Strong Earthquake Motions

Abstract

The knowledge of fixed-head long piles response mechanism under harmonic excitations and earthquakes significantly increased in the last decades. Most of seismic codes suggest considering kinematic interaction for specific structures, in layered soil with high stiffness contrast and in case of high seismic input. More recently has been shown the importance of kinematic interaction in the design of concrete piles, especially when embedded in soft soil. Above all, the existence of a maximum allowable diameter ruled by kinematic interaction, affecting detrimentally the design in seismic conditions, has been identified. These findings are based on the main assumption that the soil is a linear viscoelastic material and the concrete remain in the uncracked stage. Here a recently developed BEM based code, called KIN SP, is used to provide new insights on pile-soil interaction during earthquakes. KIN SP models the nonlinear soil behavior with the Ramberg-Osgood law and the influence of concrete cracking is accounted, allowing to consider the cyclic variation of the pile flexural rigidity. The influence of pile and soil material nonlinearities in the assessment of pile-head kinematic bending both in homogenous and in layered soils will be discussed in case of moderate to strong earthquake motions. KIN SP results will be compared with commonly used simplified formulations available in literature. The results obtained show that material nonlinearities are relevant in the assessment of pile-head kinematic bending. The use of simplified solutions may lead to overestimate or underestimate pile-head bending moment.