Influence of CFRP Strand Sheet on Flexural Strengthening of Reinforced Concrete Beam

Abstract

Fiber Reinforced Polymer (FRP) composites in the form of laminates and fabrics are installed on reinforced concrete members, using externally bonded (EB) techniques for strengthening. However, the utilisation of capacity of FRP composites is limited due to debonding observed in the strengthening system, due to FRP and concrete interfacial shear stress. Carbon fiber reinforced polymer (CFRP), in a new form of strand sheets were recently developed and have not been adequately investigated upon. These strands are less than 1.0 mm in diameter is woven with thread to obtain the desired width of the sheet. Such strand sheets are likely to have enhanced bond strengths due to the gaps between the strands that increase the surface available for bonding with the adhesive compared to laminates. This paper presents details of an experimental investigation of the influence of CFRP strand sheets on the flexural performance of CFRP strengthened reinforced concrete (RC) beams. In the experimental study, RC beams strengthened with CFRP strand sheets and lami-nates, were tested under four-point bending and compared with an un-strengthened specimen. The main parameter varied was the elastic modulus of the CFRP strand sheet and width ratio (w_f /b) of high strength CFRP strand sheets. The relative contribution of the CFRP strand sheets to the bending moment capacity was observed to be significantly higher than that in the case of the CFRP laminate. The failure mode was observed to change from debonding to concrete cover separation with an increase in width ratio. The rupture was observed as the failure mode in the specimens strengthened with high modulus CFRP strand sheets. As a result, an increase in the bending-moment capacity and ductility of the beams was also observed. Based on the observed failure modes, models for predicting the mechanical behaviour of various systems were assessed.