Enhancement of Flexural Strength Capacity of RC-Beams using LC-GFRP Plates with Effective Debonding Techniques

Abstract

Strengthening of reinforced concrete (RC) beams by externally bonded Carbon Fiber Reinforced Polymer (CFRP) is found to be a very effective method to increase their flexural strength capacity. However, the strengthening cost of the CFRP technique is very high and clients tend to avoid such expensive retrofitting methods. An alternative strengthening material, such as Glass Fiber Reinforced Polymer (GFRP), is a much less expensive material compared to CFRP. The GFRP strengthening method can achieve comparable strength gain and is an effective solution for strengthening RC beams. However, due to the lower strength and stiffness, a larger thickness of GFRP is required to obtain the target tensile strength. This increase in fiber thickness results in the commonly observed debonding failure of the GFRP-plated RC beams. Therefore, this study investigates the end anchoring technique by testing five beams under three-point bending. The first beam served as a controlled beam, while the second and the third beams were strengthened with one and three layers of GFRP to investigate the effect of the number of GFRP layers on debonding behavior. Anchored bolts were used to prevent debonding in the fourth specimen. The innovative W-shape inclined jacket technique was used for the last specimen. The test results revealed that the GFRP could effectively increase the beam's flexural strength. Nevertheless, when a larger number of GFRP layers was used, the debonding of GFRP occurred at an early loading stage. With the anchored bolted technique, the flexural strength of the RC beam was found to increase twice compared to the controlled specimen before failure due to the pulling off of the anchored bolts. Widespread shear cracks were observed near the failure stage. For the W-shape inclined jacket strengthening technique, the flexural strength was increased to a similar order as the anchored bolted technique, but the failure mode was due to slippage of the GFRP against the W-shape inclined jacket. Due to the use of a W-shape inclined jacket, the shear strength of the beam increased significantly. Therefore, the crack patterns near the final stage were controlled by flexure. The test results revealed that both techniques are effective methods to enhance the flexural strength of the GFRP-strengthened beam by achieving a similar magnitude of strength gain but failing in different failure mechanisms.