Advanced 3D finite element analysis of a bridge pier on a rocking pile group under seismic loading

抄録

Research on foundation response to seismic shaking has shown that full mobilisation of bearing capacity and the promotion of rocking foundation response may be beneficial for structural integrity – particularly in the case of seismic motions that exceed design limits. Full mobilisation of foundation bearing capacity acts as a safety valve, limiting the inertia loading on the structure. While most research has focused on rocking shallow or embedded foundations, a rocking pile group foundation has attracted much less attention. Today, the growing need for retrofit of existing structures, which were typically designed and constructed long before the adoption of modern seismic design provisions, makes such a rocking pile group design an appealing solution, as it allows optimisation (or even complete avoidance) of foundation retrofit, which can be a major operation, especially in dense urban environments. Compared to the bearing capacity of surface shallow or embedded foundations, the failure modes of a rocking pile group are more complex. They may involve structural damage below the ground level, which is perceived as something to avoid, as it is difficult to repair or even detect. To shed more light on the problem, the present study develops a finite element (FE) model of an idealised yet realistic single bridge pier supported by a rocking 2x2 pile group. The FE model employs a carefully calibrated and thoroughly validated kinematic hardening model for the soil, combined with the concrete damaged plasticity (CDP) model for the reinforced (RC) piles and pier. The FE model is subjected to pushover and preliminary dynamic time history analysis. It is shown that the rocking pile group exhibits a ductile response.