• Journal of the Korea Concrete Institute
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• v.23 no.3
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• pp.385-392
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• 2011

In this study, experimental research was carried out to evaluate and improve the seismic performance of reinforced concrete beam-column joint regions using strengthening materials (steel plate, carbon fiber sheet, and embedded carbon fiber rod) in existing reinforced concrete buildings. Six specimens of retrofitted beam-column joints are constructed using various retrofitting materials and tested for their retrofit performances. Specimens designed by retrofitting the beam-column joint regions (LBCJ series) of existing reinforced concrete building showed a stable mode of failure and an increase in load-carrying capacity due to the effect of crack control at the time of initial loading and confinement from retrofitting materials during testing. Specimens of LBCJ series, designed by the retrofitting of FRP in reinforecd beam-column joint regions increased its maximum load carrying capacity by 26~50% and its energy dissipation capacity by 13.0~14.4% when compared to standard specimen of LBCJC with a displacement ductility of 4.

• Proceedings of the Korean Society For Composite Materials Conference
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• 1999.11a
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• pp.177-182
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• 1999

사용한 보수.보강재, Rod, Fabric, Strand 형상을 콘크리트 구조물등에 보강재로 사용되어왔다. 이 재료는 해양환경하에서 내식성과 내구성을 갖는 철근및 철골대체용 복합소재와 초고층 경량 연속섬유보강 시멘트 복합재료는 탄소섬유, 아라미드섬유, 유리섬유등의 쉬트(sheet)형상을 신건재, 비자성, 비전도성, 전파차폐용 재료등에 사용할수있다. 그러나 FRP Rod를 내식성이 요구되는 철근 및 철골대체재로 사용할 경우에는 폴리머 매트릭스의 열화, 섬유와 폴리머간 계면 접착강도의 한계, 화재시 내화성, 보강재의 인발성등의 단점들을 갖고있다[1]. (중략)

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.84-87
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• 2004

Nominal flexural strength of RC members strengthened with FRP sheets is generally based on the tensile strength of composite materials obtained from coupon tests. This method is based on the assumption that bond failure does not occur until the FRP sheet reaches its rupture strength. According to the previous researches, however, bond failure often occurs before the FRP sheet reaches its rupture strength. Some attempts were made to control debonding failure by increasing the bonded length of sheet or wrapping the section around their side of the member(U-wrap). In this study, the flexural failure mechanism of RC beams strengthened with AFRP sheets with different bond lengths is investigated. Their strengthening details to prevent the premature debonding failure are also suggested and its effectiveness is verified.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.896-901
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• 2003

This paper describes a model on shear strength of RC columns strengthened with FRP sheets. In this study, we propose a confined concrete strength model of RC columns confined by transverse reinforcement as well as FRP sheet by introducing corresponding effective confinement coefficient for each confined concrete area. Then, a shear strength model of the confined RC columns is proposed by lower and upper bound limit analysis which are based on the truss-arch model theory and shear band failure theory, respectively. Along with shear test data obtained from strengthened column specimens, the developed analytical models are verified. The comparison shows that the proposed model can be used effectively for the prediction of both ultimate strength and required amount of strengthening in retrofit design for RC columns.

• Journal of the Korea Concrete Institute
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• v.14 no.6
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• pp.922-933
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• 2002

Since the deterioration of concrete bridge decks affect durability, safety, and function, structural rehabilitation of damaged concrete deck that was strengthened with Fiber Reinforced Polymer(FRP) is increasing the latest. But recent studies on the strengthened structures are focused on the static behavior, however only a few studies on the fatigue behavior are performed. In this study, static and fatigue behavior of strengthened deck were peformed on 11 deck specimens strengthened with sheet typed Glass Fiber Reinforced Polymer(GFRP) that were reinforced by two different strengthening methods for the static test. A amount of strengthening material in the each direction such as transverse and longitudinal was adopted experimental variables for the static test and also the stress level of the static maximum load are adopted for the fatigue test. By the results of the experimental study, with respect to the strengthened decks, the resistance effect of crack propagation and effect of stress distribution are improved. In addition, the rate of variation of compliance decreased.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.100-103
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• 2004

Bridges are deteriorating over service life due to over weight vehicles, environmental conditions and so on. In addition to that, those could be classified into low level bridges which are not fit for highway because of upgrade of the design load. Consequently, such reasons impel the bridges to be repaired or strengthened. Among the rehabilitating methods, FRP sheets and externally prestressing methods are preferred recently. This paper presents experimental results about the behavior of PSC beams strengthened by external tendons and CFRP sheets.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05a
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• pp.283-286
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• 2005

The effectiveness of shear strengthening with glass fiber sheets on normal or low strength RC beams have been investigated experimentally. A design compressive strength of concrete of 13.5MPa has been planned considering the degradation state of the existing structure to be strengthened in this study. Also, concrete surface reinforcing agent was applied to increase bond capacity between concrete and GFRP sheets in case of low strength RC beams. Comparing the test results of low and normal strength beams strengthened with GFRP sheets indicated that total shear capacity of beams was decreased with concrete strength decreased, but the shear strengthening capacity of GFRP sheets are hardly affected by concrete strength. In addition, shear strengthening effects of RC beams strengthened with GFRP sheets can be estimated by $\rho_w{\cdot}f_w$ based on the maximum effective strain of FRP sheet proposed by ACI 440.2R recommendation.

• Journal of the Korea Concrete Institute
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• v.15 no.5
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• pp.635-642
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• 2003

Although the strengthening effect of deteriorated concrete bridge decks has been studied by various authors, most researches are focused on the experimental works on the pulsating loading in laboratory in spite of deterioration of deck caused by moving vehicle loads. In this research, a theoretical live load model that was proposed to reflect an effect of moving vehicle loads is formulated from a statistical approach on the measurement of real traffic loads for various time periodsin Korea. Fatigue life and strengthening effect of strengthened bridge decks strengthened with either Carbon Fiber Sheet or Grid typed Carbon Fiber Polymer Plastic by the probabilistic and the reliability analyses are assessed. As a results, secondary bridge deck (DB18) strengthened with FRP ensures a sufficient fatigue resistance against the increased traffic loads as well as load carrying capacity in life cycle.

• Journal of the Korea Concrete Institute
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• v.28 no.5
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• pp.535-544
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• 2016

This paper aims at examining the effects of sustained load and elevated temperature on the time-dependent deformation of a carbon fiber reinforced polymer (CFRP) sheets bonded to concrete as well as the pull-off strength of single-lap shear specimens after the sustained loading period using digital images. Elevated temperature during the sustained loading period resulted in increased slip of the CFRP composites, whereas increased curing time of the polymer resin prior to the sustained loading period resulted in reduced slip. Pull-off tests conducted after sustained loading period showed that the presence of sustained load resulted in increased pull-off strength and interfacial fracture energy. This beneficial effect decreased with increased creep duration. Based on analysis of digital images, results on strain distributions and fracture surfaces indicated that stress relaxation of the epoxy occurred in the 30 mm closest to the loaded end of the CFRP composites during sustained loading, which increased the pull-off strength provided the failure locus remained mostly in the concrete. For longer sustained loading duration, the failure mode of concrete-CFRP bond region can change from a cohesive failure in the concrete to an interfacial failure along the concrete/epoxy interface, which diminished part of the strength increase due to the stress relaxation of the adhesive.