Influence of c-CFRP Plate Length Variation on the Performance of Plain Concrete Beams under Four-Point Bending Test

Abstract

The use of externally bonded carbon fibre-reinforced polymer (CFRP) plates for flexural strengthening of concrete beams has been well established; however, limited studies have explicitly focused on co-cured CFRP (cCFRP) plates applied to plain concrete beams without internal reinforcement. Crack control and interface bonding become critical in such systems, yet the optimal c-CFRP plate length for effective stress transfer and energy absorption remains unclear. This study addresses this gap using a four-point bending test setup to investigate the flexural behaviour of plain concrete beams strengthened with two-layer c-CFRP plates of varying lengths (100 mm to 250 mm). The results show that increasing the plate length improves ultimate load, energy absorption, and deflection capacity. The 200 mm c-CFRP length achieved the most balanced performance, reaching an ultimate load of 15.61 kN and an energy absorption of 21.66 kN·mm. The 250 mm plate provided the highest overall capacity (18.94 kN) but exhibited signs of controlled delamination. In contrast, shorter plates led to shear cracks at the plate tip due to inadequate anchorage. These findings highlight the critical role of plate length in governing failure modes and stress distribution, offering practical guidance for optimising c-CFRP retrofit strategies. Future studies are recommended to investigate bond quality, multi-layer configurations, and environmental durability for long-term applications.