Bond behavior between GFRP rod and concrete subjected to high stress reversals

Twenty standard bond specimens of GFRP rod were tested under monotonic load and cyclic load to study the changes of bond strength, the slip at the loaded end, unloading stiffness and hysteretic energy dissipation. The results indicate that the GFRP rod does not exhibit steady bond behavior under constant stress reversals (Δτ=0.7 τ_τu), and the bond strength of the specimens subjected to variable stress reversals degrades significantly as cycles increase. The envelop curves and the common-point curves show basically the same profile as those τ-s curves from the monotonic static test. The ratios of the bond stresses in the common-point curves to those in the envelop curves at the same slip range from 0.50 to 0.75. More serious damage can be observed around the ribs of the GFRP rod in the specimens after stress reversals than those subjected to monotonic static test. No splitting cracks can be seen in the concrete. From the investigation of the slip at the loaded end, hysteretic energy dissipation and unloading stiffness as reversals increase, the load history and accumulative damage status were found to be the two key influencing factors.