Una formulazione approssimata delle impedenze e del moto di fondazione per l’analisi inerziale di strutture fondate su pali

The paper presents a simple procedure for the time domain soil-structure interaction analysis of piled structures. The procedure is based on the use of a lumped parameter model for the approximation of the frequency-dependent dynamic stiffness of foundations. The lumped model can be easily implemented in commercial software to perform linear or nonlinear dynamic analyses of structures taking into account the translational, rotational and coupled rototranslational behaviour of the deep foundation system depending on the frequency of excitation and the characteristics of the deposit. In order to estimate the model parameters, closed-form formulas have been calibrated through a nonlinear least square regression procedure starting from results of a wide non-dimensional parametric analysis set performed with a model previously developed by the authors. Formulas can define lumped parameter models reproducing pile groups with square layout and different number of piles embedded in soft and stiff soils; in addition, they can be directly adopted to perform inertial structural analyses to account for the dynamic behaviour of the soil-foundation system. Some applications on typical bridge piers are finally presented to show examples of practical use of the proposed procedure. Results demonstrate the capability of the approach in capturing the actual dynamic response of soil-foundation systems, that is evaluated through a more rigorous soil-structure interaction analysis.