Strengthening of reinforced concrete beams with externally bonded fiber-reinforced-plastic plates: design guidelines for shear and flexure

This paper presents a comprehensive design approach for reinforced concrete flexural beams and unidirectional slabs strengthened with externally bonded fiber-reinforced-plastic (FRP) plates. The approach complies with the Canadian Concrete Standard. The paper is divided into two parts, namely flexural strengthening and shear strengthening. In the first part, analytical models are presented for two families of failure modes: classical modes such as crushing of concrete in compression and tensile failure of the laminate, and premature modes such as debonding of the plate and ripping off of the concrete cover. These models are based on the common principles of compatibility of deformations and equilibrium of forces. They can be used to predict the ultimate strength in flexure that can be achieved by such elements, given the FRP cross-sectional area, or conversely, the required FRP cross-sectional area to achieve a targeted resisting moment for rehabilitated flexural elements. In the second part, design equations are derived to enable calculation of the required cross-sectional area of shear lateral FRP plates or strips for four plating patterns: vertical strips, inclined strips, wings, and U sheet jackets. A step by step procedure is also presented along with an easy to use flow chart. Finally, a numerical design example is provided to demonstrate the applicability of the approach. This study is believed to be timely and very useful for the practicing engineer.Key words: reinforced concrete, beams, slabs, strengthening, FRP, plates, design, flexure, shear, mode of failure, adhesive.