• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.2A
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• pp.301-310
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• 2006

Carbon fiber reinforced polymer (CRFP) materials are well suited to the rehabilitation of civil engineering structures due to their corrosion resistance, high strength to weight ratio and high stiffness to weight ratio. Their application in the field of the rehabilitation of concrete structures is increased due to the vast number of bridges and buildings in need of strengthening. However, RC members, strengthened with externally bonded CFRP plates, happened to collapse before reaching the expected design failure load. Therefore, it is necessary to develop the new strengthening method to overcome the problems of previous bonded strengthening method. This problems can be solved by prestressing the CFRP plate before bonding to the concrete. In this study, a total of 21 specimens of 3.3 m length were tested by the four point bending method after strengthening them with externally bonded CFRP plates. The CFRP plates were bonded without prestress and with various prestress levels ranging from 0.4% to 0.8% of CFRP plate strain. All specimen with end anchorage failed by a plate fracture regardless of the prestress levels while the specimen without end anchorage failed by the separation of the plate from the beam due to premature debonding. The cracking loads was proportionally related to the prestress levels, but the maximum loads of specimens strengthened with prestressed CFRP plates were insignificantly affected by the prestress levels.

• Journal of the Korea Concrete Institute
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• v.19 no.1
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• pp.121-130
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• 2007

To investigate the enhancement in strength and deformation capacities of concrete confined by FRP composites, tests under axial loads were carried out on three groups of thirty six short columns in circular section with diverse GFRP confining reinforcement. The major test variables considered include fiber content or orientation, wrap or tube type by varying the end loading condition, and continuous or discontinuous confinement depending on the presence of vortical spices between its two halves. The circumferential FRP strains at failure for different types of confinements were also investigated with emphasis. Various analytical models capable of predicting the ultimate strength and strain of the confined concrete were examined by comparing to observed results. Tests results showed that FRP wraps or tubes provide the substantial increase in strength and deformation, while partial wraps comprising the vertical discontinuities fail in an explosive manner with less increase in strength, particularly in deformation. A bilinear stress-strain response was observed throughout all tests with some variations of strain hardening. The failure hoop strains measured on the FRP surface were less than those obtained from the tensile coupons in all tests with a high degree of variation. In overall, existing predictive equations overestimated ultimate strengths and strains observed in present tests, with a much larger scatter related to the latter. For more accuracy, two simple design- oriented equations correlated with present tests are proposed. The strength equation was derived using the Mohr-Coulomb failure criterion, whereas the strain equation was based on entirely fitting of test data including the unconfined concrete strength as one of governing factors.