Flexural strengthening of RC beams with longitudinal openings: Experimental and numerical evaluation of CFRP strip and ring configurations

This study investigates the flexural performance of reinforced concrete (RC) beams with longitudinal openings (holes) of different shapes and sizes, strengthened using carbon fiber-reinforced polymer (CFRP) sheets. Openings were circular, square, or rectangular and placed at different heights along the beam depth. These openings reduced the beam’s load capacity by 1% to 22%, depending on their size, shape, and location. Two CFRP strengthening techniques were used: bottom longitudinal strips and transverse ring strips. The study was performed using both experimental tests and nonlinear finite element analysis (NLFEA). The NLFEA models, created in ABAQUS, showed strong agreement with the test results with close prediction of the ultimate loads, deflections, and failure modes. A parametric study was then developed using the model to investigate the effect of varying concrete grades, tensile and compression reinforcement ratios, and using a steel anchor system on the beam’s strength. The results show that the use of longitudinal CFRP succeeded in restoring the solid beam capacity with an additional increment range between 2 and 16%. Beams having square holes strengthened with ring strips achieved the ultimate capacity of the solid beams with an increment of 4%. The different concrete grades, tensile and compression steel ratios, CFRP thickness, and anchoring system are critical factors in designing hollow beams. Furthermore, the addition of steel anchors has a significant contribution in delaying debonding and enhancing the bond between CFRP and concrete. Overall, the results confirm that CFRP sheets are effective in improving the structural performance of RC beams with openings.