Fatigue Assessment of Shear-Strengthened RC T-Beams with Externally Bonded CFRP Closed Stirrups

Abstract

Research studies on reinforced concrete T-beams shear strengthened with externally bonded carbon fiber reinforced polymer (EB-CFRP) have shown that debonding at the CFRP–concrete interface is still a major concern. It is well established that shear strengthening using a full-wrap configuration offers a better solution than side bonding and U-wrap configurations without anchorage systems in preventing premature FRP debonding. However, such a strengthening technique can only be used for rectangular beams for which the four faces are accessible. This is clearly not practical, since most RC beams are cast monolithically with slabs and therefore have a T-section. The objective of the present research was to experimentally assess the effectiveness of a new and innovative EB-CFRP closed-stirrup technology for fatigue upgrade by reproducing the advantages of a full-wrap configuration. The CFRP shear-strengthening system consisted of L-shaped laminates and anchoring ropes to form EB-CFRP closed stirrups. Laboratory tests were performed on full-size RC T-beams with different ratios of internal shear reinforcement under fatigue cyclic loading. The specifications of North American design codes and standards for fatigue limit state design of RC structures were also assessed in this investigation. The EB-CFRP closed stirrups resulted in a decrease in the levels of transverse steel strains and thereby enhanced the fatigue performance of shear-strengthened specimens. The results also demonstrated the existence of an interaction between internal transverse steel and EB-CFRP under fatigue loading. Finally, strengthening with CFRP L-shaped laminates led to a significant increase in the shear resistance of RC T-beams.