Experimental and Analytical Study on Structural Behaviour of RC Beams Retrofitted with a Hybrid System of CFRP, GFRP, Mas Plates, and Concrete Jacketing
Michael Nii Sarbah Okine *
Department of Civil Engineering, Koforidua Technical University, Koforidua, Ghana and Department of Civil Engineering, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana.
Charles Kwame Kankam
Department of Civil Engineering, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana.
Fredrick Ali Issifu
Department of Civil Engineering, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana.
*Author to whom correspondence should be addressed.
Abstract
This study examines the flexural performance of reinforced concrete (RC) beams retrofitted with a first-time hybrid system comprising CFRP laminates, GFRP bars, mechanical anchorage plates, and concrete jacketing. Although similar retrofitting methods are increasingly adopted, detailed analyses in line with BS code provisions remain limited. The research addresses this gap through four-point bending tests, examining crack behaviour, failure modes, load–deflection behaviour, and comparisons between experimental results and analytical predictions based on BS code provisions. Five beams were used as controls and five beams used as the retrofitted beams. Beams A, B, C, and D shared a concrete compressive strength of 37.03 MPa, whereas beam E has a strength of 26.77 MPa. Tension reinforcement was varied between two 12 mm diameter bottom bars and three 12 mm bars. The ratio of the retrofitted beam to the unretrofitted beam ultimate loads were recorded as 140 %, 158 %, 154 %, 144 %, and 146 % for the beams A, B, C, D, and E respectively, indicating a significant increase as a result of the strengthening. A novel formula for estimating the flexural moment capacity of this first-time hybrid retrofitted beam is proposed and validated against experimental and analytical results. This novel combination of the hybrid retrofitting system significantly increased the flexural moment of the RC beam. The mean ratio of experimental to analytical moments is 0.94, with a variance of 0.00541, indicating strong agreement. The proposed novel hybrid retrofitting system and novel formula demonstrate high accuracy to the experimental results which helps to pre-empt the experimental moments before they are conducted. Also, the novel formula is suitable for application to beams with similar hybrid retrofitting configurations to significantly strengthen the flexural moment capacity of the RC beams.
Keywords: Carbon fibre reinforced polymer (CFRP), glass fibre reinforced polymer (GFRP), mechanical anchorage system (MAS) plates, Numerical analysis, Concrete jacketing