Repair and Retrofit of Concrete Bridge Girders Using Hybrid FRP Sheets

The use of carbon fibers (CF) and glass fibers (GF) were combined to strengthen potentially non-ductile flexural members. Based on tension tests of fiber-reinforced polymer (FRP) rovings and sheets, as well as theoretical research on hybrid FRP, a volume ratio of (GF/CF) was determined to be about (8.8/1) to produce synergistic hybrid effects and pseudo-ductility. The (8.8/1) ratio was used to fabricate hybrid carbon-glass FRP sheets, and this optimal combination was verified through four-point loading tests of plain and reinforced concrete beams strengthened with single or multiple plies of FRP sheets. The increased flexural strengths were evaluated using available design procedures in conjunction with a proposed force-strain relationship for hybrid carbon-glass FRP sheets. Additionally, data of tensile tests of 94 hybrid carbon-glass FRP sheets and 47 carbon and glass fiber rovings or sheets were thoroughly re-examined in terms of tensile behavior. Based on thorough comparisons between the rule of mixtures for fibrous composites and test data, positive hybrid effects were clearly identified for almost all (GF/CF) ratios. In contrast to the rule of mixtures, the hybrid sheets with relatively low (GF/CF) ratios also produced pseudo-ductility. From the calibrated results obtained from experiments, a novel analytical model for the stress-strain relationship of hybrid FRP sheets was proposed. The effect of various epoxy resins, impregnating degree and specimen grips on the tensile behavior was minimal.