Numerical Simulation of Hybrid Sliding-Rocking Columns Subjected to Earthquake Excitation

Abstract

This paper introduces a novel element formulation for the dynamic analysis of bridges incorporating posttensioned segmental columns with hybrid sliding-rocking (HSR) joints distributed over their height. These columns are termed HSR columns. Bridges with HSR columns combine construction rapidity with superior seismic performance through joint sliding and rocking, thereby offering large deformation capacity with low damage, energy dissipation and self-centering properties. Hybrid sliding-rocking columns are typically designed, under quasi-static (single-mode) conditions, to exhibit rocking at the end joints and sliding at the intermediate joints over the column height. However, when HSR columns are subjected to arbitrary dynamic loading, any joint can exhibit sliding or rocking or both, depending on the intensity and frequency content of the applied load. As a result, there is a need for models capable of predicting such complex responses. The proposed two-node HSR element formulation combines a gradient inelastic (GI) flexibility-based (FB) beam-column element formulation that accounts for member material deformations and joint rocking with a hysteretic friction model that accounts for joint sliding. Joint rocking is considered within the GI FB element via a joint cross section of zero tensile strength. The proposed HSR element addresses major deficiencies of existing modeling approaches, including strain localization and loss of objectivity (lack of convergence with mesh refinements) due to the cross section of zero tensile strength. The proposed HSR element formulation is utilized to simulate two past experiments: a quasi-static test on an HSR column and a shake table test on a single-span bridge with two single-column HSR piers. None of the computational simulations exhibit instabilities in the numerical solution, which are common in analyses with models including friction elements subjected to rapidly fluctuating contact loads, demonstrating the good stability properties of the proposed HSR element formulation. The analysis results match the test data reasonably well, particularly in terms of peak forces and displacements, demonstrating that the proposed formulation can be used to further investigate the design and performance of HSR systems.