Shear and flexural strengthening of reinforced concrete beams with variable compressive strength values using externally bonded carbon fiber plates

Abstract

This paper presents experimental and analytical research to study the shear and flexural performance of Reinforced Concrete (RC) beams strengthened using two types of externally bonded Carbon Fiber Reinforced Polymer (CFRP) composites; including laminates and sheets. A total of 24 full-scale RC beams were tested up to failure. Concrete compressive strengths of 17, 32, and 47 MPa were used, with CFRP composites attached in six different configurations in an effort to optimize the flexural and shear load-carrying capacities of the specimens tested. Results showed that externally bonded CFRP composites considerably improved both the shear and flexural strengths of the beams. Notably speaking, the effectiveness of the CFRP composite material was inversely proportional to the concrete compressive strength. Significant improvement of the shear strength ranging from 28.9% to 29.6% was observed for beams with CFRP U-wraps compared to beams with laminate strips which ranged between 14.4% and 23.8% when the compressive strength was increased from 17 to 47 MPa. Meanwhile, those strengthened with half U-wraps had a notable improvement in their flexural strength (i.e., ultimate load carrying capacity) by a range of 22.4%–46.2%, as opposed to laminate strengthened beams that varied between 17.8% and 38.4% with increased compressive strength of the concrete mix. Finally, theoretical predictions using the ACI 440.2R-14 guidelines were compared to experimental results; however, the differences turned out to be relatively large due to the intrinsic empirical nature of the Code predicted equations.