Comparative Experimental Investigation on Flexural Performance and Crack Evolution of RC Beams Strengthened with Varying Ply Numbers of GFRP and CFRP

Abstract

Existing studies on FRP strengthening have largely focused on a single material, with limited systematic comparison of GFRP and CFRP systems at varying ply numbers under consistent conditions. This study comparatively investigates the bearing performance of full-span stirrup-reinforced RC beams externally bonded with GFRP and CFRP sheets under three-point bending. Fourteen specimens across seven groups were tested, comprising one control and six strengthened groups with one, two, or three plies of GFRP or CFRP. Bearing capacity, load–deflection response, ductility, and crack evolution were systematically compared. The results indicate that FRP strengthening significantly enhances cracking, yield, and ultimate capacities, with CFRP exhibiting superior performance to GFRP: relative to control beams, CFRP outperforms GFRP by 7–24.6 and 10–17.2 percentage points in yield and ultimate load enhancements, respectively. Sectional stiffness retention increases with ply number; at equal ply count, CFRP provides 11–31 percentage points higher stiffness improvement than GFRP. However, GFRP exhibits superior ductility, with coefficients 12–69.1% higher at identical ply numbers. Both FRP types effectively suppress cracking, shifting the distribution from sparse, wide, localized cracks to dense, narrow, uniformly dispersed cracks, with CFRP achieving better crack width control.