In order to investigate the strengthening effects of aramid fiber reinforced polymer (AFRP) sheets on the flexural performance of the corroded beams, the flexural behaviors of corroded RC beams strengthened with AFRP sheets under different degrees of corrosion (minor: reinforcement mass loss is 2.0%, medium: reinforcement mass loss is 6.0%) are researched experimentally in this paper, and compared with that of the control beams (un-corroded) and un-strengthened corroded beams. The results show that,compared with un-strengthened corroded beams under same degrees of corrosion, the cracking load, yield load and ultimate load of minor corroded RC beam strengthened with AFRP sheets is respectively increased by 20%, 27% and 60%, and increased by 15%, 36% and 83% for medium corroded RC beam strengthened with AFRP sheets respectively; The ultimate deflection of the medium corroded beam strengthened with AFRP sheets is 166% larger than that of corroded un-strengthened beam. AFRP sheets can improve significantly the bearing capacity and deformation for corroded RC beams.
This paper presents the results of an experimental investigation to determine the flexural fatigue strength and fatigue life of concrete beams reinforced with monofilament polyacrylonitrile fibers (PAN fiber for short). The performance of fresh concrete and the elastic and mechanical properties of hardened concrete are compared by samples with and without fibers. The toughness calculated according to both ASTM and JCI methods increased with the addition of fibers. The toughness indexes I5 was 3.8-4.2 times,I10 was 5.8—6.8 times that of the plain concrete. The equivalent strength was 0.63-0.87 MPa for PAN fiber reinforced concrete. When compared to plain concrete, the endurance limit of concrete beams only reinforced with PAN fiber is increased by 12 percent.
In order to research the seismic performance of strengthening corroded RC circular columns with hybrid Fiber Reinforced Polymer (FRP) sheets, ten RC columns were tested under cyclic load and constant axial. Test phenomena are described, experimental data are analyzed and compared, and the effect of the axial compression ratio and stirrup reinforcement ratio on the seismic behavior is studied. Results show that the corrosion of steel bars may introduce the brittle failure for RC columns in some extent, and the seismic performance can be enhanced effectively for RC columns strengthened with hybrid FRP. Ductility and energy dissipation are improved significantly, but the bearing capacity can be only increased within limits. When the degree of rebar corrosion is 5.1%, the maximum displacement ductility factor and accumulated energy dissipation of the strengthened corroded columns are 123% and 12.5 times larger respectively than that of the un-strengthened corroded columns.
Right evaluation of the bond behavior between corroded reinforcing bar and concrete wrapped with fiber reinforced polymers (FRPs) is a chief problem to confirm the effect of FRP confinement. the pullout tests on 96 test specimens were conducted to study the effect of Carbon FRP (CFRP) confinement on the bond behavior between corroded reinforcing bar and concrete, test variables included reinforcing bar types, concrete covers, degrees of corrosion and CFRP confinements. The test results show that CFRP confinements can make the failure mode of deformed reinforcing bar specimens change from concrete splitting to bar pullout. When the degree of corrosion is less than 5%, the ultimate bond strength of corroded specimens increases by 5%~7%; and the CFRP confinement has less contribution on the ultimate bond strength, but it is effective on slowing down the bond stress descending speed and maintaining the bond strength. When the degree of corrosion is higher than 5%, the ultimate bond strength of corroded specimens drops gradually with the increase of degree of corrosion.
Corroded RC columns do not possess necessary ductility to dissipate seismic energy during a major earthquake, the study investigates the use of hybrid fiber reinforced polymer (FRP) wrapping as a method of retrofitting non-ductile corroded RC columns, and a model to determine the envelope response of RC corroded columns strengthened with hybrid FRP are presented based on cross-section analysis for undamaged RC element. The results show that the technique of strengthening corroded RC column with hybrid FRP is quite effective, the envelope curve estimated using the linear plane assumption with modification by reinforcement slip model, may still be used as the envelope curve of RC corroded columns strengthened with hybrid FRP, a good agreement between analytical and experimental results is observed.
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