Curved FRP as concrete reinforcement

Abstract

The increased use of fibre-reinforced polymers (FRPs) in reinforced concrete construction is largely driven by the requirement for improved durability, especially for those applications subjected to the most severe environmental conditions. However, the adoption of FRP as embedded reinforcement in new structures has been much slower than in repair and strengthening applications. This is owing to the limited availability of curved FRP reinforcing elements. In addition, the mechanical performance of the bent portions of FRP bars is significantly reduced under a multiaxial combination of stresses, and the tensile strength can be as low as 40% of the uniaxial tensile strength. This paper presents and discusses potential issues relating to the use of curved FRP bars as embedded reinforcement in concrete and uses as an example one of the case studies that was examined during the European funded project, CurvedNFR. A 6 m long concrete plank reinforced with thermosetting FRP bars as longitudinal reinforcement and thermoplastic FRP strips as shear reinforcement was manufactured and tested. The use of FRPs allowed the reduction in the required concrete cover without compromising durability. This study shows that current design recommendations for FRP concrete structures are effective in predicting deflections and crack widths at service load. It is also shown that in FRP concrete, serviceability limit state can control the design.