Influence of carbon fiber reinforced polymers on upgrading shear behavior of RC coupling beams

Shear wall with coupling beam is a very effective means of providing lateral bracing for buildings subjected to earthquakes. The strength, stiffness and ductility of coupling beams considerably influence the behavior of coupled wall systems, since even the local failure of each coupling beam could lead to the global failure of the structure. In this paper, two common efficient strengthening methods for improving the behavior of RC coupling beams have been investigated. The nominal shear strength of an FRP-strengthened concrete member can be determined by adding the contribution of the FRP external shear reinforcement to the contributions from the reinforcing steel and the concrete. Numerical studies were conducted to analyze three groups of RC coupling beams, of which one was strengthened by externally bonded steel plates and the other two strengthened with FRP sheets. Fiber Reinforced Polymer (FRP) composites have found increasingly wide applications in structural engineering due to their high strength to weight ratio, high corrosion resistance and ease of installation. The FRP-strengthened groups differ on how the FRP is attached to the coupling beam. The material properties used for modeling the concrete, reinforcement and FRP were adopted due to experimental data. Based on the numerical results, strengthening using steel plates upgraded the lateral load bearing capacity up to 66%, while the improvement in deformation capacity was about 50%. Also, the FRP sheets could considerably enhance the strength and deformation capacity of coupling beams; as in the most effective procedure (wrapping) increased the shear force by 84% and chord rotation capacity by 77%.