Effect of confinement using steel, FRC, or FRP on the bond stress-slip response of steel bars under cyclic loading

Abstract

The results of experimental investigation of the local bond stress-slip response of steel bars embedded in confined concrete and subjected to cyclic loading are presented. Different types of confinement and their effect on the bond stress-slip response were evaluated and compared. These included internal confinement by ordinary transverse steel ties or steel fiber reinforcement, and external confinement by fiber reinforced polymer (FRP) composites. Beam specimens with spliced reinforcement at midspan were tested. The test parameters included the size of the steel bars, the ratio of concrete cover to bar diameter, and the amount of confinement. Without confinement, the specimens suffered significant bond deterioration and loss in load resistance in the first or second load cycle after bond splitting. Confining the concrete with transverse steel, steel fiber reinforcement or FRP composites within the splice region increased the bond strength and reduced the bond degradation with the number of loading cycles, leading to significant improvement in seismic performance. The envelope curve of the cyclic bond stress-slip response showed very good agreement with earlier test results obtained under static load conditions and the results predicted using an analytical model of the local bond stress-slip response of steel bars embedded in confined concrete.