Kinematic Bending Moments in Square Pile Groups

This paper describes kinematic seismic interaction analysis of square pile groups in homogeneous soil deposits, focusing on bending moments induced by the transient motion. Analyses were performed by means of a three-dimensional (3D) numerical procedure able to account for both pile–soil–pile interaction and radiation damping. The seismic motion was defined by an artificial accelerogram at the outcropping bedrock, and one-dimensional (1D) propagation analyses were performed to define the free-field motion within the deposits. An extensive parametric study was conducted to determine the effects of different variables, such as the soil properties, the bedrock location, the number of piles, and the pile spacing, on the dynamic response of pile-group foundations. Bending moments obtained from the analyses of the pile group, both at the pile head and at the interface separating soil layers, were normalized with respect to the single-pile bending moments, allowing for the proposal of a new design formula for the estimation of the kinematic bending moments in the most stressed pile of the group, starting from the knowledge of the single-pile response. The proposed formula was used, in conjunction with some simplified approaches that allow estimation of the single-pile response, to evaluate bending moments in the analyzed pile groups. The adequacy of the formula for design purposes is demonstrated.