Effect of Flexural CFRP Sheets and Plates on Shear Resistance of Reinforced Concrete Beams

Abstract

Ageing of reinforced concrete (RC) structures has captured the attention of a number of researchers to find different materials and techniques to strengthen and retrofit deteriorated structures. Carbon Fiber Reinforced Polymer (CFRP) composite plates and sheets are widely used to externally strengthen RC beams in flexure and shear. The conventional method of strengthening RC beams in shear is by externally bonding CFRP laminates to the beam's vertical sides via epoxy adhesives. However, in certain applications, the sides of the beam might not be accessible for shear strengthening. This study aims at investigating the contribution of longitudinal CFRP reinforcement on the shear strength of shear deficient RC beams. To achieve this objective, nineteen beams were cast without transverse reinforcement in the shear span and tested under four-point bending. The specimens were divided into three groups with different longitudinal steel reinforcement ratios. Each group has one control un-strengthened beam and five beams strengthened at their soffit with CFRP plates or sheets. An equivalent longitudinal reinforcement ratio was computed based on the modular ratio of the CFRP and steel reinforcement and ranged from 0.14 to 2.29%. The load and mid-span displacement values, strain gauges readings at different discrete locations along the beams' shear and mid-spans were recorded until failure. The specimens failed in shear as a result of a diagonal-tension crack as expected. The strengthened specimens showed a significant increase in the load-carrying shear capacity over the control specimens. The increase in the concrete shear capacity for beams strengthened with sheets and plates ranged from 10 to 70% and 30 to 151%, respectively, over the control specimens. It was concluded that CFRP composite plates and sheets, when externally bonded to the soffit of simply supported beams, will enhance both the flexural and shear capacity of such beams. In addition, the concrete shear capacity of the tested specimens was predicted using the ACI 318-08 and CSA 2004 simplified and detailed shear design provisions. The results indicated that CSA 2004 shear design provisions, which are based on the modified compression field theory, yielded the closest agreement with the obtained experimental data.