Parameters affecting the behaviour of RC beams strengthened in shear and flexure with various FRP systems

An experimental investigation was carried out on rectangular RC beams strengthened with FRP in different strengthening forms in shear and flexure. The parameters examined in this study are as follows: The shear span to effective depth ratio (a/d), the number of FRP layers in shear, strengthening form (completely wrapping, U-wrapping, and side-bonding), FRP types (Glass or Carbon), and FRP strips width to spacing ratios (w(f)/s(f)). The experimental results showed that strengthening with FRP enhanced the load-carrying capacity, deflection capacity, initial stiffness, and ductility capacity with respect to the reference beams. Increasing the number of FRP layers in shear did not provide a proportional increase in the contribution of FRP to shear strength. The FRP types, FRP strips width to spacing ratios (w(f)/s(f)), the number of FRP layers in shear, a/d, and strengthening form affect the cracking patterns and loads of tested beams compared to reference beams. In addition, strengthening with FRP could change the failure modes of RC beams from brittle shear failure to more ductile flexural failure. It was also found that the equations used to calculate FRP contribution to shear strength (ACI 440.2R (2017), Fib-TG 9.3 (2001), Khalifa (2002), Triantafillou (1998), Bukhari (2010)) overestimated the FRP contribution and gave unconservative results, especially for U-wrapped and side bonded beams compared to the experimental results.