Investigation of the dynamic response of rigid footings on tensionless Winkler foundation

The dynamic response of a rigid footing resting on an elastic tensionless Winkler foundation is examined. A parametric investigation, concerning the effect of the main parameters on the response, is performed for harmonic excitation. The parameters examined include the stiffness and the damping of the foundation, the excitation frequency and the superstructure characteristics and loads. The maximum rocking response, the minimum length of contact after uplift, the maximum stress developed at the soil and the factor of safety with respect to the bearing capacity of the soil are used to measure the effect of each dimensionless parameter. An example for earthquake excitation is also given for a plane frame. The results are compared to the ones of a simplified static approach based on the maximum values of the applied loads, similarly to the procedure that is usually applied in practice. The results show that the static approach can predict the response satisfactorily if resonance does not happen, if the stiffness of the foundation is not large compared to the stiffness of the superstructure and if the dynamic part of the axial force of the column is not large; in these cases, it may underestimate or overestimate the response significantly, depending on the sign of the dynamic axial force that is considered.