Effect of Fiber Addition on the Performance of Preloaded CFRP Strengthened Concrete Beams

Abstract

The aim of this study is to evaluate the effect of fiber addition on the performance of Reinforced Concrete (RC) beams that have been externally strengthened in flexure using Carbon Fiber Reinforced Polymer (CFRP) sheets. Steel, synthetic and hybrid fibers (mix of steel and synthetic fibers) with a volume fraction of 0.5 % were added to the concrete matrix to prepare 15 beams. The experimental program consisted of three groups; 1) control beams without strengthening, 2) beams strengthened without preloading, and 3) beams preloaded to a stress level corresponding to 0.67 of yield stress (fy) of the steel reinforcement before strengthening with CFRP. A steel reinforcement ratio of 0.55% was used for all beams. Eight beams were tested for groups one and two as control (with and without strengthening) and seven beams were pre-loaded before strengthening to simulate the RC beams behavior and conditions at the repair stage. Test results showed that the addition of fibers improved the flexural capacity, crack initiation and propagation, post cracking behavior and ductility of the beams. All beams strengthened after preloading also showed better performance than that of the control beams. Synthetic fiber was found to improve the ductility of the RC beams by 81% when compared to the control specimen without fibers. Additionally, steel fibers caused a strength increase of up to 64% when compared to the control beams. The hybrid mix of fibers provided a combination of benefits from steel and synthetic fiber contributions. Applicability of ACI 440 equations to predict the capacity of fiber reinforce concrete beams was also investigated. The predicted results were in good agreement with the obtained experimental data.