The trilinear moment vs. curvature relationship of concrete beams reinforced with fiber reinforced polymer (FRP) rebars

The properties of fiber reinforced polymer (FRP) rebars are different from those of conventional building materials. And the concrete beams reinforced with these rebars also exhibit different mechanical behavior during the whole testing regime. Due to the low modulus of elasticity of FRP rebars, the results from both testing and complete nonlinear sectional analysis in this paper demonstrate a distinct unloading process as a result of a sudden change of flexural stiffness caused by cracks. After beams have restored their strength, they behaved almost linearly until failure. Based on these observations, a simplified trilinear relationship between moment and curvature has been developed. The analysis results from this relationship have been compared with the test data from five concrete beams reinforced with glass fiber reinforced polymer (GFRP) rebars tested under two-thirds-point flexure until failure. The comparisons have indicated that the suggested relationship yields good predictions of flexural capacity of all beams and acceptable distributions of strains at three different levels as load increases, especially S₁ and S₂.