Behavior of reinforced concrete t-beams strengthened in shear using closed carbon fiber-reinforced polymer stirrups made of laminates and ropes

摘要

Shear-strengthening of reinforced concrete (RC) beams with externally bonded (EB) carbon fiber-reinforced polymer (CFRP) using L-shaped laminates is gaining popularity and is successfully used in practice. However, the technique may present some drawbacks related to FRP debonding at the FRP/concrete interface and lack of anchorage. This premature failure may inhibit the fiber-reinforced polymer (FRP) to reach its full strength, thereby limiting the cost-effectiveness of the strengthening material. This paper presents the results of an experimental investigation on RC T-beams shear-strengthened with new closed CFRP stirrup technology. The closed stirrup is made of prefabricated CFRP L-shaped laminates and a CFRP rope as a closure. The purpose of using such a technique is to inhibit premature debonding by reproducing the advantage of full-wrap strengthening configuration. This application method provides a durable and cost-effective solution because it requires less surface preparation and does not use mechanical anchors. This can also be practical in seismic regions where transverse reinforcement is required to be closed for confinement purposes. Laboratory tests were performed on full-size RC T-beams with three different ratios of internal transverse steel. The feasibility of the full-wrap shear strengthening using the closed CFRP stirrup technique and the influence of the internal steel stirrup ratio on the performance of EB CFRP composites were investigated. The results confirmed the effectiveness of using the closed CFRP stirrup technique in increasing the shear resistance of strengthened RC beams. The gain ranged between 20% and 140% for specimens with and without internal transverse steel reinforcement, respectively. The results also demonstrated the existence of an interaction between internal steel stirrups and EB CFRP.