Experimental study on the interfacial shear stress of RC beams strengthened with prestressed BFRP rod

On the strengthening of concrete structures by externally bonding prestressed BFRP (basalt fiber reinforced polymer) rod, the release of the prestress may cause an interfacial shear stress concentrated at the prestressed BFRP ends which may cause BFRP prematurely debonding. In order to avoid this problem, the shear stress caused by BFRP prestress should not exceed the interfacial adhesive strength. In this study, the mechanical properties of the adhesive interface at the ends of the BFRP rod which is bonded to the concrete beams are evaluated by experimental studies considering different test methods such as the stretch adhesion test at both ends (double pull-pull test) and prestressed import test (single push-push test). Based on the existing research results, a modified formula is derived to predict the interfacial shear stresses, BFRP stresses and maximum achievable prestress level. The accuracy and validity of the proposed theoretical formula are confirmed by the experimental results. Moreover, an effective method of decreasing the interfacial shear stress is proposed for avoiding the possible premature failure near the BFRP ends caused by the shear stress concentration.