Size Effect in RC T-Beams Strengthened in Shear with Externally Bonded CFRP Sheets: Experimental Study

Numerous investigations have addressed the size effect on the shear behavior of conventional reinforced concrete (RC) beams. In contrast, very few studies have been dedicated to the size effect of RC beams strengthened in shear with externally bonded (EB) fiber-reinforced polymer (FRP) sheets. This paper presents the results of an experimental investigation conducted on 18 RC T-beam specimens of three different sizes to study the size effect on concrete shear strength at failure of RC beams strengthened in shear with EB carbon FRP (CFRP) sheets. The specimens were divided into two groups, with and without internal transverse steel, and six series, each consisting of small, medium, and large beams as follows: two series of control (unstrengthened) specimens, two series of specimens strengthened in shear with one-ply EB-CFRP sheets in a U-wrap configuration, and two series of specimens strengthened in shear with two plies of EB-CFRP sheets in a U-wrap configuration. The results clearly revealed the presence of a size effect on both the concrete and CFRP sheet contribution to shear resistance. For strengthened specimens without internal transverse steel, the size effect was found to be magnified as the CFRP sheet stiffness increased. This was not the case for beams strengthened with transverse steel, where the size effect behavior reduced considerably due to the interaction between internal transverse steel and EB-CFRP sheets.