Optimisation of reliability-based design for spiral FRP retrofitted RC beams

Fibre-reinforced polymers (FRPs) have been thoroughly researched for their effectiveness in repairing and enhancing the flexural capacity of reinforced concrete (RC) beams. This paper seeks to introduce an optimised reliability-based design of a strengthened RC beam with spiral FRP. The critical cross-section of the beam is analysed in accordance with British Standard 8110 to satisfy the strain compatibility conditions. Based on this analysis, the relationship between the moment capacity and beam curvature is established. Furthermore, the influence of the FRP wrapping angle on the beam curvature is determined for both the horizontal and vertical faces. A parametric study is executed, considering different design parameters for the strengthened RC beam. It is concluded that the best achievable wrapping angles on the vertical and horizontal faces of the beam within the feasible design domain are 50°, 48° and 12° and the best achievable thickness–width ratios within the feasible design domain for the FRP strip are 0.0042, 0.0022 and 0.0012 when the moduli of elasticity are 75 GPa, 138 GPa and 200 GPa, respectively.