Flexural Behavior of Concrete Beam Using Glass Fiber Bars as Reinforcement

Reinforced concrete structures have been widely used in Thailand because of their strength, durability, and relatively low cost compared to other structural systems. However, a major problem commonly found in reinforced concrete structures is corrosion of the reinforcing steel, which reduces structural safety. At present, glass fiber–reinforced polymer (GFRP) bars are considered an alternative material to replace steel reinforcement, as they do not corrode. Nevertheless, concerns remain regarding the load-carrying capacity of structures using this material. The objective of this research project is to study the flexural behavior of concrete beams reinforced with GFRP bars and to compare the results with those of conventional steel-reinforced concrete beams. In addition, the flexural test results were analyzed and compared with design calculations based on ACI 440.1R-15. The concrete beam specimens had a cross-sectional dimension of 150 × 250 mm and a length of 1,900 mm. They were tested under three-point bending with a span length of 1,800 mm. A total of six beam specimens were tested, consisting of one control specimen reinforced with steel bars and five specimens reinforced with GFRP bars. The amount of reinforcement was varied to induce three different failure modes: rupture of GFRP bars, concrete crushing, and shear failure. The results indicate that GFRP-reinforced concrete beams generally fail in a sudden manner, predominantly due to concrete crushing. When considering serviceability deflection limits between L/360 and L/180, steel reinforced concrete beams can resist significantly higher bending moments than GFRP-reinforced concrete beams. However, at the ultimate bending state, GFRP-reinforced concrete beams can resist higher bending moments than steel-reinforced concrete beams, although the maximum bending capacity occurs at much larger deflections compared to steel-reinforced concrete beams. Finally, when comparing the experimentally obtained flexural capacities with those calculated according to ACI 440.1R-15, it was found that the GFRP-reinforced concrete beams tested in this study exhibited higher flexural capacities than those predicted by the design calculations.