Experimental study on high pre-cracked RC beams shear-strengthened with CFRP strips

Experimental studies on shear capacity of eighteen pre-cracked reinforced concrete (RC) beams shear-strengthened with carbon fiber reinforced polymer (CFRP) strips are carried out in this study. The effects of CFRP strips spacing, shear span ratio and pre-cracked degree on the failure mode, shear capacity, load-deflection curve and moment-curvature relationship of strengthened specimens are analyzed. Three failure modes related to the failure of CFRP strips, that is the bonding failure, the debond failure and the fracture failure of CFRP strips, are observed for specimens with different structural parameters. Moreover, with decrease of CFRP strips spacing, the shear capacity, the ultimate deflection and the bending stiffness of specimens increase. With increase of pre-cracked degree, the increment of shear capacity of RC beams shear-strengthened with CFRP strips is lower than that of non-cracked beams. The pre-cracked degree presents slight effect on the stiffness of CFRP strips-strengthened beams. Further, a revised model to determine the shear capacity of CFRP strips is proposed by accounting for the strain distribution of CFRP strips and the pre-cracked degree. Comparison between the experimental results and the calculated values indicates that the proposed formula can versatilely evaluate the shear capacity of CFRP strips strengthened RC beams.