Flexural behavior of bonded post-tensioned concrete beams with steel or GFRP bars

Post-tensioned concrete beams with GFRP reinforcement have gained attention in recent years due to their unique flexural behavior and potential cost benefits. Because of the absence of comprehensive guidelines in international codes and limited application in constructions, this hybrid system is adopted in the current paper as a pioneering solution for sustainable and eco-friendly construction practices. Particularly noteworthy is the corrosion resistance of GFRP bars, which significantly enhances the durability of structures. The influence of using GFRP with bonded post-tension concrete beam is experimentally investigated compared to concrete beams with prestressing and non-prestressing reinforcement. Eight concrete beams with different reinforcement types and ratios were cast and tested under three-point load. Flexural resistance, crack pattern, deflections, and strains of the beams were compared with a reference beam with prestressing and non-prestressing reinforcement. Experimental load capacities of the tested beams were compared to those obtained from various international codes. The experimental results revealed that the beams with GFRP bars had smaller failure load and larger deflection compared to those with non-prestressing steel by up to 25 % and 37 %, respectively. A 3D finite element model (FEM) was developed and validated by comparing the numerical results with those obtained from the experiments. A sensitivity analysis was performed, using the validated FEM, by changing the concrete strength, steel yield stress, and GFRP ultimate strength by ± 20 %. The sensitivity analysis included seventy-two beams which had the same dimensions, loading, and boundary conditions of the tested beams. Changing the concrete strength only led to varying the beam capacities by −7 % ∼ + 4 %. Changing the steel yield stress only led to changing of the beam capacities by −13 % ∼ + 11 %. No change was observed when the GFRP ultimate stress was varied by 20 %. © 2024 Institution of Structural Engineers