Experimental Performance Assessment of Nearly Full-Scale Reinforced Concrete Columns with Partially Debonded Longitudinal Reinforcement

Abstract

This paper presents an experimental study investigating the effect of partial debonding of longitudinal reinforcement at the location of the plastic hinge on the performance of reinforced concrete columns in special moment-resisting frames designed for seismic regions as per standard guidelines. Partial debonding is investigated as a means of spreading locally induced deformations over larger rebar lengths, thereby preventing early rebar yielding and fracture and improving the seismic performance of the columns. The experimental program, which was conducted at the University of Colorado Boulder, included quasi-static cyclic testing of three nearly full-scale (∼1∶1.14 or ∼88%) cantilever columns with various debonded reinforcement lengths. The experimental findings showed that reinforcement debonding resulted in early onset of concrete cracking and delayed reinforcement yielding. Spreading of concrete damage decreased with the debonded length, not exceeding half of the plastic hinge length (as opposed to the full plastic hinge length for bonded reinforcement). Debonding alleviated strain localizations in the steel reinforcement, at least, for drift ratios below 2%. The peak strength and initial elastic stiffness decreased with the debonded length. Energy dissipation and equivalent viscous damping ratio increased with the debonded length for drift ratios below 2%, and decreased with the debonded length for drift ratios exceeding 3%. Self-centering improved with the debonded length.