A study of flexural behavior of reinforced concrete beam strengthened with carbon fiber-reinforced plastic (CFRP)

This paper presents an analytical study on the flexural behavior of reinforced concrete beams strengthened with externally bonded carbon fiber-reinforced plastic (CFRP) laminates. Different failure modes of these strengthened reinforced beams have been reported and these failure modes are generally referred to as brittle failure or ductile failure involving the compression crushing of the concrete, debonding or rupture of the composite laminate and yielding of the steel reinforcement. For the analysis, the stresses and strains of all the components of the beam are related by the material properties, including the stress-strain curves for the concrete, steel and CFRP laminate. The strain distribution is assumed to be compatible within the distorted shape of the cross-section of the concrete beam. The resultant forces on the cross section are balanced with the applied loads for static equilibrium. The analytical solution is derived from the equilibrium equations and the compatibility of the strains, and it is applicable to both singly and doubly reinforced concrete beams strengthened with multi-layers of CFRP laminates. In this study, a simple and direct analytical procedure has been developed to evaluate the flexural capacity of concrete beams strengthened with CFRP and to predict their failure modes. An example is presented to illustrate the computational procedures. For design purposes, the upper and lower limits of CFRP cross-section areas are established to ensure that reinforced concrete beam strengthened with advanced composite materials will fail in a ductile manner. A comparison between the analytical results and the data obtained from the literature has been made and the agreement is very good.