Reliability-Based Design Recommendations for Deflection Control of Fiber-Reinforced Polymer-Reinforced Concrete Beams

Fiber-reinforced polymers (FRPs), as noncorrosive materials, offer agreat potential for use as reinforcement in concrete construction. Nevertheless, the characteristics of these materials have led to new challenges in the design of FRP-reinforced concrete (RC) components. Design of steel-RC beams usually results in under-reinforced beams, with failure governed by the yielding of steel, while in the FRP-RC counterparts, concrete crushing is the most desirable failure mode. Compared to steel bars, FRP displays higher strength and lower Young s modulus, thus indicating that the design of FRP-RC elements will be largely influenced by the serviceability limitstate of excessive deflections. A significant body of knowledge has been accrued towards the safety of FRP-RC components withrespect to ultimate limit states; on the contrary, the probabilistic assessment of the serviceability of FRP-RC beams is almost nonexistent. This study presents a contribution to the development of reliability-based design recommendations for deflection control of FRP-RC beams. A framework for the probabilistic assessment of the deflections of FRP-RC beams designed according to ACI 440is described. Monte Carlo simulation is used in the probabilistic description of beam deflections and in the computation of the probabilities of excessive deflections (and attendant reliability indexes) of 81 representative beams. The results indicate a wide rangeof values for the reliability indexes (from positive up to negative ones); additionally, all parameters (load ratio, FRP strength, concretecompressive strength, and failure mode) have a considerable impact on the resulting reliability levels. The use of a smaller strength-reduction factor led to a significant improvement in the resulting reliability levels for FRP-RC beams. Keywords: beams; deflections; design codes; fiber-reinforced polymer (FRP); Monte Carlo simulation; reinforced concrete (RC); reliability; serviceability limit state.