**4.2 Flexural performance of GFRP reinforced beams**

The mechanical behaviour of GFRP-RC beams in flexure is visibly different from steel-RC beams (**Figure 7**). Broadly, the behaviour of GFRP-RC beams exhibits a bilinear load-deflection response up to the failure without any yielding or ductility as experienced by steel reinforced beams. Initially, the load-deflection curve is perfectly linear and this zone is un-cracked elastic zone I. A noticeable decrease in the stiffness of the beam is observed with the formation of hairline cracks at a load (Pcr) of (7.89, *Crack Classification in Steel-RC and GFRP-RC Beams with Varying Reinforcement Ratio Using… DOI: http://dx.doi.org/10.5772/intechopen.101305*

**Figure 7.** *Load v/s deflection plot for GFRP reinforced beams (one beam per type).*

8.0 and 11.42) kN with a deflection (*δ*cr) of (1.31, 0.9, and 0.39) mm in G-0.33-1, G-0.52-1, and G-1.11-1 RC beams, respectively. These minor cracks progress along the sides of the beam at constant stiffness. With an increase in the reinforcement ratio, initial bending stiffness also increases. As the load further increases, the cracks initiate and become visible at a load of (15, 20, and 33) kN for G-0.33-1, G-0.52-1, and G-1.11-1 RC beam in the pure bending region. Further with the increase in loading, cracks progress towards the compression zone, and this zone II is named cracked-elastic zone. The GFRP beams exhibit elastic response in this zone with the progression of flexural cracks. This trend continues till a first drop in the load-carrying capacity is observed at (33.6, 45.72, and 57.18) kN with a deflection of (30.33, 32.01, and 16.37) mm with increasing reinforcement ratio, pointing towards initiation of concrete crushing in G-0.33-1, G-0.52-1, and G-1.11-1 RC beams.

The failure is a typical flexural failure in the form of vertical flexural cracks in the pure bending zone along with their simultaneous spreading towards the entire length of the beam. Further the crushing of concrete progress with a sharp increase in the load-carrying capacity in zone III (concrete crushing zone). The beam continuous to carry load linearly with an increase in deflection until the second drop in load is observed at (41.7, 47.63, and 73.99) kN with a deflection of (52.68, 40.74, and 28.41) mm in G-0.33-1, G-0.52-1, and G-1.11-1 RC beams, respectively. The effective concrete section is highly reduced due to cracking and ineffective in resisting the tensile load and the beam fail at peak load of (PPeak) (51.32, 60.47, and 83.71) kN for in G-0.33-1, G-0.52-1, and G-1.11-1 RC beam with the ultimate deflection (*δ*u) (68.68, 60.09, and 34.47) mm. All the GFRP reinforced beams fail typically by concrete crushing since they are designed as over-reinforced beams to prevent the failure by GFRP rupture as expected in under-reinforced GFRP beams.
