Reliability-based design recommendations for FRP-reinforced concrete beams

In recent years, there has been a growing interest on high performance materials such as high-strength concrete and composite materials. These materials may offer higher mechanical resistance and greater durability, and, as a consequence, potential gains throughout the life-cycle of the structure. A major problem associated with the durability of reinforced concrete structures is the corrosion of reinforcing steel. In this context, fiber reinforced polymers (FRP) provide a promising prospect for use as reinforcement in concrete construction. Although the use of FRP as structural reinforcement can show great promise in terms of durability, the characteristics of these materials have led to new challenges in the design of FRP-reinforced concrete (FRP-RC) components. In conventional RC beam design, failure is dictated by yielding of steel, thus resulting in a ductile failure. In the case of FRP-RC beams, where two brittle materials are involved, a brittle failure is unavoidable; thus, a change in the RC beam design paradigm is necessary. Since most of the variables involved are random, reliability-based recommendations shall be developed for design of FRP-RC beams. In this study, a contribution to the development of semi-probabilistic design recommendations for FRP-RC beams is presented. To this end, safety levels implicit in the design recommendations of 81 FRP-RC beams designed according to ACI-440 (2006) are assessed. Monte Carlo simulation is used in the estimation of the probability of failure of the designed beams with respect to the ultimate flexural strength. Special attention is given to the deterministic procedure for the computation of FRP-RC beam resistance. The effects of various parameters in the implicit reliability levels are discussed. The procedures presented herein can be easily extended to the treatment of design recommendations for FRP-RC beams other than ACI 440.