Strength reduction factor for flexural RC members strengthened with near-surface-mounted bars

Current American Concrete Institute (ACI) guidelines for the design of flexural RC members strengthened with externally bonded fiber-reinforced polymer (FRP) systems assign an additional partial strength reduction factor to the contribution of FRP, marking a deviation from ACI's approach in building codes. This conservative method finds its rationale in the novelty and the higher variability of FRP, because of its nature as a material (compared to steel) and the conditions of its installation (externally bonded). Using the case of near-surface-mounted (NSM) FRP bars, this paper demonstrates that a single strength reduction factor can be formulated, while maintaining the same reliability and safety required in conventional RC members. Using a comprehensive test matrix of flexural members processed with a computerized Monte Carlo simulation technique, the probabilistic implications of strengthening RC beams and slabs with NSM FRP bars are investigated. The generated statistical data are employed to recommend revised strength reduction factors for flexural RC members strengthened with NSM FRP bars that eliminate the partial factor, and yet, provide a safety level equal to ordinary steel RC members.