Seismic assessment of pile-supported bridges considering the rotational excitation of earthquake ground motion

The scope of this paper is to investigate the response of RC bridges, founded on pile groups in a liquefiable, layered soil, under simultaneous earthquake-induced translational and rocking excitation. The rocking excitation results from pile bending, under vertically propagating seismic S-waves, which, in turn, depends on the relative flexibility between the pile group and the surrounding soil, a phenomenon known as "kinematic interaction". Typically, the rotational component of the seismic excitation is not taken into consideration in the design, neither is it prescribed in any of the modern seismic codes. Based on the previous research of a pile-induced rocking in CIDH pile supported bridges [1], an effort is made to extend the above findings considering soil liquefaction and a pile group foundation. For this reason, the lateral response of a typical bridge in the Egnatia Highway Greece, is analytically studied for various acceleration scenarios. The response of the pile cap, in terms of displacement and rotation time histories, as a result of the kinematic interaction analysis of the foundation system, is the total foundation input motion (F.I.M.) of the superstructure. The resulting displacement demand of the coupled load is then compared to the displacements that would develop by ignoring the rotational component of the excitation. From the set of parametric analyses conducted, it is concluded that ignoring the rocking component of the input motion, transverse deck displacements may differ significantly, based on the dynamic characteristics of the foundation and the superstructure.