A Computational Framework for the Assessment of Earthquake-Induced Rocking in CIDH Pile Supported Bridges

Abstract eng:
The scope of this study is to investigate the response of RC bridges, founded on single castin-drilled-hole (CIDH) piles, under simultaneous earthquake-induced translational and rocking excitation. This rotational excitation results from pile bending under vertically propagating S-waves which, in turn, is dependent on pile’s relative flexibility with respect to the surrounding soil, a phenomenon known as “kinematic interaction”. Typically, the rotational component of seismic excitation of the superstructure is not taken into consideration; neither is it prescribed in any of the modern seismic codes, despite the fact that analytical solutions have been proposed in the literature. Moreover, the potential impact of such a pile-induced rocking of CIDH supported bridges has also not been quantified yet. Along these lines, an effort is made in this paper to present an analytical and computational framework for parametrically studying both: (a) the nature of the rotational excitation component and: (b) the additional displacement demand imposed to the superstructure. For this reason, a Matlabbased program is developed and the lateral response of multiple 4-DOF oscillators representing typical bridge structures is analytically studied, for various scenarios of excitation frequencies, superstructure height and soil stiffness. The resulting displacement demand is then compared to the displacements that would develop by ignoring the rotational component of ground excitation). From the set of parametric analyses conducted, it is concluded that ignoring kinematically induced rocking, transverse deck displacements may be significantly increased, especially in frequencies associated with the dynamic characteristics of the soil and the superstructure. 1

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