Analysis of reinforced concrete beams strengthened with FRP laminates

A significant percentage of the bridges in North America were built after the Second World War. Most of them were originally designed for smaller vehicles, Lighter loads, and a lower traffic volume than commonly experienced today. A study reported by Klaiber et al. indicates that over 50% of all bridges in the United States were built before 1940, and approximately 42% of these bridges are considered to be structurally deficient. This alarming statistic underscores the importance of developing reliable and cost-effective repair and strengthening techniques for existing bridge structures. A particularly challenging problem in this area is the rehabilitation of reinforced concrete structures. In recent years, the repair of understrengthened or damaged reinforced concrete members by the external bonding of fiber-reinforced polymer (FRP) laminates has received considerable attention. This paper investigates the flexural behavior of reinforced concrete beams strengthened with externally bonded FRP laminates. A simple and direct analytical procedure for evaluating the ultimate flexural capacity of FRP strengthened reinforced concrete flexural members is presented. The procedure is derived from equilibrium equations and compatibility of strains and is applicable to both singly and doubly reinforced concrete rectangular sections, as well as hanged sections. The procedure is validated by comparisons with results of experimental data available in the Literature. Upper and lower Limits of FRP that may be bonded to a reinforced concrete cross section to ensure ductile behavior are established, and design nomographs to facilitate implementation of the procedure are presented.