Comparison of the flexural and flexural-bond behaviour of beams reinforced with CFRP rods with different surfaces

Abstract

Carbon-fibre-reinforced polymer (CFRP) bars are available with diverse surfaces and with a wide range of tensile strengths compared with traditional rebars. However, CFRP rods in beams require a larger cross-section than steel rebars in order to meet the required anchorage length in current design standards. The goal of this work was to compare the flexural and flexural-bond behaviours of CFRP-reinforced beams and steel-reinforced beams using four-point flexural tests. CFRP rods with thread-wrapped and sand-coated surfaces, each with distinct characteristics, were used. Additionally, two shear span/depth ratios were considered (2.5 and 3.5). The results indicated pseudo-plastic behaviour in the load–deflection curves of the CFRP-reinforced beams. This behaviour was attributed to the slip due to the reduced bond strength between the concrete and reinforcement, leading to the final failure. Based on the surface type of the CFRP rods, a cross-sectional design with the maximum load exceeding the design load was realised, even when the CFRP-reinforced beam failed to satisfy the required anchorage length. These findings suggest that the current anchorage length equations may be overly conservative, indicating the need for appropriate adjustments to the design approach.