Effect of steel stirrups on shear resistance gain due to externally bonded fiber-reinforced polymer strips and sheets

Abstract

This paper presents the results of an experimental investigation of reinforced concrete (RC) T-beams strengthened in shear with externally bonded (EB) carbon fiber-reinforced polymer (CFRP) strips and sheets. The main objective of this study was to gain insight, by varying the test parameters, into the interaction between the internal transverse steel reinforcement and the externally bonded CFRP used for strengthening of RC beams in shear. The test parameters of this study were: 1) the CFRP ratio (that is, the spacing of the CFRP strips); 2) the presence or absence of transverse steel; 3) the transverse steel ratio (that is, the spacing of the stirrups); and 4) the use of CFRP strips versus CFRP sheets. In total, 10 tests were performed on 4520 mm (14 ft, 10 in.) long T-beams. The study showed that the presence of internal transverse steel reinforcement resulted in a significant decrease in the gain due to CFRP for all strengthened specimens. It also showed that the steel yielded before failure for all test specimens with transverse steel. Finally, the presence of CFRP did not result in a significant decrease in transverse steel strain. It can be concluded that the contribution of transverse steel to shear resistance is not affected by the addition of EB CFRP. These results are in good agreement with the assumptions made by existing codes and design guidelines, which are based on the yielding of transverse steel at ultimate strain for RC beams strengthened in shear with EB CFRP. Copyright © 2014, American Concrete Institute.