Winkler model for predicting the dynamic response of caisson foundations

The paper presents a Winkler-based numerical model for the analysis of the dynamic response of caisson foundations. The model allows the evaluation of the impedance functions and of the foundation input motion (FIM), which can be used in the framework of the substructure approach to compute inertial soil-foundation superstructure interaction analyses. In addition, kinematic stress resultants due to seismic shear waves propagating into the soil can be estimated. The caisson is modelled as a Timoshenko beam and the soil-caisson interaction forces are derived from the analyses of the plane-strain vibration problem of an annular rigid ring embedded into the soil. The problem solution is obtained in the frequency domain exploiting the finite element approach and generic soil stratigraphies can be considered in the applications. The model, which is characterised by a very low computational effort, is validated by performing a parametric investigation, comparing results with those obtained from more rigorous BEM-FEM models of the soil-caissons systems. Finally, some applications to real caisson foundations of offshore wind turbines (OWTs) are shown to demonstrate the model accuracy in capturing the seismic response of the foundations obtained from more rigorous models.