Experimental Performance Assessment of Large-Scale Polyurethane-Enhanced Damage-Resistant Bridge Columns with Energy Dissipation Links. I: Overview and Damage Assessment

Abstract

This paper, which is the first of two companion papers, investigates the performance of a novel bridge column design, termed polyurethane (PU)-enhanced rocking column with energy dissipation (ED) links, through a large-scale testing program. The proposed column design offers explicit damage control via damage-resistant end segments made of PU, ED and flexural strength/stiffness through ED links, and self-centering through internal unbonded post-tensioning. The PU segments have high deformability, allowing large lateral column deformations with negligible damage. The ED links are in the form of buckling-restrained bars made of high-performance steel and offer hysteretic damping and flexural stiffness and strength to reduce the seismically induced displacement demands. The experimental program included cyclic testing, at various loading rates, of large-scale (approximately 1:2.5) PU-enhanced cantilever rocking columns with two designs for the PU segment: (1) solid PU segment, and (2) axisymmetrically bilayered segment with an exterior PU layer to withstand seismic loads and an internal reinforced concrete core to sustain long-term axial service loads and provide resistance against creep. The specimens are subjected to displacement-controlled lateral cyclic loading of increasing amplitude (exceeding a 10% drift ratio) at several drift ratio rates (up to 1/s). A tested column is repaired via ED link release and retightening to demonstrate their rapid reparability characteristics and are retested to demonstrate the recovery of the original column properties. While ED link release and retightening (i.e., ED link reuse) is adopted in this study, because the yielding of the ED links was small as verified in the second companion paper by the practically identical response of the original and retrofitted column, it can be deduced that ED link replacement (i.e., use of new/pristine ED links) would also restore the original column properties. A rocking-only precast concrete column is also tested under the same loading protocols to serve as reference for comparisons. This first companion paper outlines the experimental program, quantifies the observed damage of the proposed column design for a range of seismic hazard intensities and compares it with that of the rocking-only column, and validates the capability of ED link release and retightening (and, by extension, ED link replacement) as a repair method that recovers the damage resistance/avoidance properties of the original system. Compared to conventional RC rocking columns, the proposed column design demonstrated significantly higher resistance against damage in terms of concrete spalling and crushing.