Seismic Soil-Structures Interaction in Large-Diameter Shaft Foundations

FUORI CATALOGO

Aim of this work is to illustrate an analytical model for the assessment of kinematic interaction of large-diameter shaft foundations. The model is derived using recently obtained solutions of soil structure interaction problems of rigid walls and fixed base cylinders subjected to a dynamic excitation. The proposed model constitutes an extension to a deformable base of the elastodynamic solution of a rigid, fixed-base cylinder imbedded in a homogeneous or inhomogeneous soil stratum with different lateral boundary conditions. The analytical model has been validated by means of a finite elements code and it has been implemented in a consistent seismic soil-structure interaction analysis procedure. An application of the model to a long, multi-span continuous prestressed concrete viaduct with tall piers has been carried out focusing the attention on assessing the importance of kinematic interaction. The main finding of the study is that the foundation input motion is characterized not only by a translational horizontal component which is usually of a reduced amplitude if compared with the freefield ground motion, but also by a rotational component that is responsible of a large seismic demand in the viaduct’s superstructure. The proposed model represents an effective tool to be used in the engineering practice to assess both the seismic actions induced by the ground shaking on the foundation system and the effective input motion of a superstructure founded on massive, large diameter shafts.