Lateral Cyclic Response of Large-Scale Bridge Piers with Single and Double Layers of Longitudinal and Transverse Steel Reinforcements: An Experimental Study

Abstract

A circular reinforced concrete (RC) bridge column with two layers of longitudinal and spiral reinforcements is becoming a common structural form in high-seismic regions because they are expected to have improved seismic performance compared to conventional bridge piers. In seismic hazard zones, a large amount of transverse reinforcement is commonly required to satisfy the so-called antibuckling requirements. Accordingly, the double-confined steel (DCS) RC bridge pier is a simple and effective way to achieve high ductility levels and postyield stiffness for bridge piers in seismic regions. In DCS, the longitudinal steel rebars are well distributed inside the cross section; at the same time, the two layers of transverse reinforcement outline different levels of confinement for concrete, including unconfined (cover), singly confined (positioned between two spiral layers), and doubly confined (found inside the inner spiral layer or the core). The adopted reinforcement details, layout, and scale were unprecedented for lateral testing of large-scale DCS. Therefore, this experimental program investigated the effectiveness of DCS as an alternative to typical RC bridge piers. The behavior of large-scale DCS was compared with the performance of conventional RC bridge pier. During the quasi-static cyclic lateral displacement-controlled loading, the onset of cracking, concrete cover spalling, damage progression, plastic hinge length development, lateral load–displacement relationship, and strain in the steel reinforcements were observed. Overall, the curvature, stiffness degradation, and energy dissipation capacity all revealed that the DCS could significantly enhance the seismic performance of a bridge pier. A fiber-based finite-element model was generated to predict the experimental response of the piers under cyclic loading. Charts depicting the relationship between the ratio of elastic stiffness and axial load were developed to serve as a valuable design resource for bridge piers. The charts were created by conducting moment–curvature (M−Φ) analyses on DCS sections. These analyses involved varying the longitudinal reinforcement ratios, reinforcement layouts, and other parameters while also considering different axial load ratios. Subsequently, the performance-based design (PBD) approach was employed to assess the extent of damage relative to engineering demand parameters. Furthermore, a comprehensive example was provided to showcase the design of DCS within the framework of PBD. The findings revealed that DCS successfully met the performance objectives outlined in the PBD guidelines, making it an attractive design option for conventional RC bridge piers.