Influence of Soffit Bonded CFRP Strips on Shear Capacity and Failure Type of RC Beams without Stirrups

Presented herein is an experimental investigation on the efficacy of soffit-bonded longitudinal CFRP strips in upgrading the load-carrying capacities of RC beams without steel stirrups, a necessary disposal when the wrapped or the side transverse CFRP strips bonding is impossible due to the inaccessibility of the beam sides. The program deals with testing eight RC beams destitute of web reinforcement and strengthened by various CFRP strips combinations of soffit-bonded strips frequently accompanied by longitudinal top-bonded ones, in addition to three unstrengthened beams one of which is provided by the minimum amount of steel stirrups. The purpose is to evaluate their prime performances (shear resistance and concrete fracture mechanism with CFRP failure modes) and complementary properties (stiffness, ductility and energy absorbability). Effects of the fiber orientation in the CFRP strips and the shear span-to-depth ratio are specially attended. Test results demonstrate the profitable role of the flat soffit-bonded CFRP strips in delaying shear failure, admitting additional deflection and elevating the energy absorbability by 22 %. They also manifest the effective role of the longitudinal full-length top CFRP strips in contributing the resistance to shear failure announced by its transverse rupture. The advantageous effect of the two narrow side “crooks” along the soffit-bonded CFRP strips appears in the substantial increase in the energy absorbability and ultimate resistance attributed to magnifications in the concrete fracture pattern and CFRP debonding.