Shear transfer of concrete strengthened with externally bonded CFRP strips inclined to shear plane

Concrete with steel reinforcement across a shear plane was externally bonded using carbon fiber-reinforced polymer (CFRP) strips with different inclination angles to find optimal strengthening effect of shear resistance. Thirty-five Z-type specimens were tested and classified into two groups, i.e., the shear transfer group and shear component group, to investigate shear resistance and shear transfer behavior based on a component model. In this model, the shear resistance was contributed by six shear components, i.e., friction, aggregate interlock, adhesion, shear dilation, dowel action, and resistance parallel to the shear plane provided by CFRP strips. Results found that inclination angles of about 70 and 45° were optimal and associated with the maximum shear resistance for specimens with CFRP reinforcement ratios of 0.298% and 0.149%, respectively. Compared to the cases of CFRP strips perpendicular to the shear plane, additional percentage increases of the maximum shear resistance in a range of 8-23% were obtained in the cases using CFRP strips with optimal inclination angles. These extra benefits were mainly attributed to the increases in the friction and aggregate interlock, shear dilation, and resistance parallel to the shear plane provided by CFRP strips. A best-fitting expression was also proposed to predict the ultimate shear transfer capacities of strengthened reinforced concrete using CFRP strips with optimal inclination angles.