Resistance of interfacial debonding failure of GFRP bars embedded in concrete reinforced with structural fibers under cycling loads

GFRP rebars with different surface treatments such as helical wrapping and sand coating were evaluated under cyclic loads. The pull-out specimens were made from the addition of structural fibers (hooked end steel, PP, PVA fibers) with 1% of fiber volume fraction in a concrete matrix with expected change in interfacial bonding property as well as ductility improvement after first cracking. The experimental results were analyzed in terms of bond stress-slip curve, bond strength ratio, and energy dissipation. Severe failures in the interfacial layers of the GFRP rebars at the resin-bar fiber interface was observed as cycling loads increased. The addition of structural fibers to concrete generally showed significant changes for debonding failure mechanism since the strong bonding resulted in reduced energy dissipation as well as a sharp increase of load in the bond stress-slip curve. For the GFRP rebars, wedge effects from crushed or cracked particles due to repeated damage in the interfacial debonding zone affected the low dissipated energy. Abrupt pull-out bar failure was represented. The effect of fibers in the interfacial bonding layer confirmed that resistance of steel rebar to cycling debonding failures from rebar types showed the best performance. In particular, the addition of hooked steel fibers indicated the best performance regardless of rebar types.