• 한국구조물진단유지관리공학회 논문집
• /
• 제22권4호
• /
• pp.126-132
• /
• 2018

본 연구는 순환골재를 사용한 콘크리트의 활용증대 방안으로 철근콘크리트 구조물의 노후화와 내구성 저하 시 보수 보강으로 사용되는 FRP (AFRP, CFRP) 판으로 보강된 순환골재 고강도콘크리트(40MPa, 60MPa) 보를 제작하여 순환골재 철근콘크리트 보의 휨 보강에 대한 적용성을 평가하고자 한다 기존의 표면매입보강에 따른 에폭시와 FRP 판의 부착력을 고려하지 않기 위해 콘크리트 타설 전 FRP 보강판을 거푸집에 미리 설치하였으며, 순환골재 치환율(30%), 콘크리트 강도(40MPa, 60MPa), 이형철근(D10, D13), FRP 판의 종류(AFRP 판, CFRP 판)를 변수로 12개 실험체를 제작하여, FRP 판과 순환골재 치환율에 따른 휨 성능을 분석하였다. 그 결과 FRP 판으로 보강한 실험체는 무보강 실험체에 비해 최대 17% 증가하는 경향을 나타내었으며 AFRP 판에 비해 CFRP 판의 보강 성능이 우수한 것으로 나타났다. 또한 순환골재 치환율에 따른 보강 성능의 차이는 없는 것으로 나타났다. 실험에 의해 측정된 균열모멘트는 파괴계수를 이용한 결과 기준식과 비슷한 값을 나타났으며 휨 모멘트는 FRP 판을 보강한 일부 시험체가 KCI 2012와 ACI 440-2R에서 제시한 기준을 만족하지 못하는 것으로 나타났다.

• Structural Engineering and Mechanics
• /
• 제63권3호
• /
• pp.361-370
• /
• 2017

Through the use of finite element analysis and acoustic emission techniques we have evaluated the interfacial failure of a carbon fiber reinforced polymer (CFRP) repair patch on a notched aluminum substrate. The repair of cracks is a very common and widely used practice in the aeronautics field to extend the life of cracked sheet metal panels. The process consists of adhesively bonding a patch that encompasses the notched site to provide additional strength, thereby increasing life and avoiding costly replacements. The mechanical strength of the bonded joint relies mainly on the bonding of the adhesive to the plate and patch stiffness. Stress concentrations at crack tips promote disbonding of the composite patch from the substrate, consequently reducing the bonded area, which makes this a critical aspect of repair effectiveness. In this paper we examine patch disbonding by calculating the influence of notch tip stress on disbond area and verify computational results with acoustic emission (AE) measurements obtained from specimens subjected to uniaxial tension. The FE results showed that disbonding first occurs between the patch and the substrate close to free edge of the patch followed by failure around the tip of the notch, both highest stress regions. Experimental results revealed that cement adhesion at the aluminum interface was the limiting factor in patch performance. The patch did not appear to strengthen the aluminum substrate when measured by stress-strain due to early stage disbonding. Analysis of the AE signals provided insight to the disbond locations and progression at the metal-adhesive interface. Crack growth from the notch in the aluminum was not observed until the stress reached a critical level, an instant before final fracture, which was unaffected by the patch due to early stage disbonding. The FE model was further utilized to study the effects of patch fiber orientation and increased adhesive strength. The model revealed that the effectiveness of patch repairs is strongly dependent upon the combined interactions of adhesive bond strength and fiber orientation.

• 한국재난정보학회 논문집
• /
• 제12권1호
• /
• pp.54-61
• /
• 2016

구조물에 복합재료를 사용한 보강과 복구에 대한 사용이 증가하고 있는 상황에서 갑작스러운 강도저하로 발생되는 재난을 피하기 위하여 임시 보강하고자 탄소섬유 판을 이용하여 기존금속재와 접합(접착방식)을 통한 강도증진효과를 연구하였다. 특히 실험을 통하여 강-탄소섬유보강재로 이루어진 복합 재 거동을 파악하였으며 여기에 적절한 시험을 위한 새로운 형태의 시험편을 제작하였다. 접합재로 레진을 접착하는 부착 면을 달리하여 거동을 비교하기 위하여 표면처리가 다른 시험편을 각각 고려하여 시험한 결과 강성보강효과는 물론 일체거동의 특성이 잘 나타남을 알 수 있었다.

• Steel and Composite Structures
• /
• 제14권1호
• /
• pp.41-55
• /
• 2013

Fiber reinforced polymers (FRP) materials are increasingly being used for strengthening and repair of steel structures. An issue that concerns engineers in steel members which are retrofitted with FRP is stress experienced due to temperature changes. The changing temperature affects the interface bond between the FRP and Steel. This research focused on the effects of cyclical thermal loadings on the interface properties of FRP bounded to steel members. Over fifty tests were conducted to investigate the thermal effects on bonding between FRP and steel, which were cycled from temperature of $-11^{\circ}C$ ($12^{\circ}F$) to $60^{\circ}C$ ($140^{\circ}F$) for 21-36 days. This investigation consisted of two test protocols, 1) the tensile test of epoxy resin, tack coat, FRP and FRP-steel plate, 2) tensile test of each FRP compound and FRP with steel after going through thermal cyclic loading. This investigation reveals an extensive reduction in the composite's strength.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 1997년도 가을 학술발표회 논문집
• /
• pp.450-455
• /
• 1997

In recent years the research and development about the new material proceeds rapidly and actively in building industry. We are concerned with high-strength concrete as a new material. As the building structure becomes bigger, higher and more specialized, so does the demand of material and member with high strength for building expands greatly. In the future, we will quite need to research repair and rehabilitation to make high strength concrete structural building for our safe. So, I did an study on carbon fiber sheet rehabilitation(CFSR) of reinforced high strength concrete beams. The carbon fiber reinforced plastic(CFRP) bonding method is widely used for reinforcing the existing concrete structure among the various methods. The test results indicate that CFS is very effective for strengthening the damaged beams and controlling deflections of the repaired beams. When carbon fiber sheet rehabilitation of reinforced high strength concrete beams happened diagonal crack, the increase in the number of CFS layer didn't effect the increase in strength of beams. Also, by changing the CFS stick position gave diversified ultimate load in CFSR beams.

• 비파괴검사학회지
• /
• 제27권1호
• /
• pp.48-57
• /
• 2007

사용 중인 항공기 구조를 모사하여 리벳구멍 주위에 피로균열이 존재하는 AA2024-T3 박판을 CFRP 복합재 패치로 접합하여 보수한 후 피로균열 성장거동을 음향방출(AE)을 측정하면서 관찰하였다. 패칭의 효과로 균열성장속도의 뚜렷한 감소와 균열이 인접한 리벳 구멍으로 전파되는 시간을 지연시키는 효과가 있음을 확인하였다. 그리고 패칭 후 균열성장에 의해 탐지된 신호와 패치와 알루미늄 사이의 접합계면 분리에 의한 신호의 구별 가능성을 다변량 자료분석 기법인 주성분분석을 통해 알아보았다. 그 결과 균열성장에 따른 AE신호는 계면분리에 따른 AE신호에 비해 중심주파수가 높고 작은 에너지를 가지는 반면, 계면분리 신호는 균열성장 신호에 비해 상승시간이 길고 중심주파수가 상대적으로 낮으며 비교적 큰 에너지를 가진 것으로 나타났다. 따라서 AE신호의 유형인식 방법은 AE 발생원의 위치표정 결과와 결합할 경우 패치 접합으로 보수된 구조에서의 피로균열 성장거동을 예측하는 방법으로 충분히 활용될 수 있다.

• Advanced Composite Materials
• /
• 제17권3호
• /
• pp.277-299
• /
• 2008

High quality and expedient processing repair methods are necessary to enhance the service life of bridge structures. Deterioration of concrete can occur as a result of structural cracks, corrosion of reinforcement, and freeze.thaw cycles. Cost effective methods with potential for field implementation are necessary to address the issue of the vulnerability of bridge structures and how to repair them. Most infrastructure related applications of fiber-reinforced plastics (FRPs) use traditional hand lay-up technology. The hand lay-up is tedious, labor-intensive and relies upon personnel skill level. An alternative to traditional hand lay-up of FRP for infrastructure applications is Vacuum Assisted Resin Transfer Molding (VARTM). VARTM uses single sided molding technology to infuse resin over fabrics wrapping large structures, such as bridge girders and columns. There is no work currently available in understanding the interface developed, when VARTM processing is adopted to wrap fibers such as carbon and/or glass over concrete structures. This paper investigates the interface formed by carbon fiber processed on to a concrete surface using the VARTM technique. Various surface treatments, including sandblasting, were performed to study the pull-off tensile test to find a potential prepared surface. A single-lap shear test was used to study the bond strength of CFRP fabric/epoxy composite adhered to concrete. Carbon fiber wraps incorporating Sikadur HEX 103C and low viscosity epoxy resin Sikadur 300 were considered in VARTM processing of concrete specimens.

• International Journal of Concrete Structures and Materials
• /
• 제11권1호
• /
• pp.115-133
• /
• 2017

To investigate the effectiveness of using fiber reinforced polymer (FRP) sheets in confining heat-damaged columns, 15 circular RC column specimens were tested under axial compression. The effects of heating duration, stiffness and thickness of the FRP wrapping sheets were examined. Two specimen groups, six each, were subjected to elevated temperatures of $500^{\circ}C$ for 2 and 3 h, respectively. Eight of the heat-damaged specimens were wrapped with unidirectional carbon and glass FRP sheets. Test results confirmed that elevated temperatures adversely affect the axial load resistance and stiffness of the columns while increasing their ductility and toughness. Full wrapping with FRP sheets increased the axial load capacity and toughness of the damaged columns. A single layer of the carbon sheets managed to restore the original axial resistance of the columns heated for 2 h yet, two layers were needed to restore the axial resistance of columns heated for 3 h. Glass FRP sheets were found to be less effective; using two layers of glass sheets managed to restore the axial load carrying capacity of columns heated for 2 h only. Confining the heat-damaged columns with FRP circumferential wraps failed in recovering the original axial stiffness of the columns. Test results confirmed that FRP-confining models adopted by international design guidelines should address the increased confinement efficiency in heat-damaged circular RC columns.

• Steel and Composite Structures
• /
• 제11권4호
• /
• pp.307-324
• /
• 2011

With the increasing use of concrete-filled steel tubes (CFST) as structural members, there is a growing need to provide suitable measures for possible strengthening or repair of these kinds of structural elements. Fibre reinforced polymer (FRP) jacketing is a recent method and is particularly attractive in which it does not significantly increase the section size, and is relatively easy to install. Thus, it can be used to enhance strength and/or ductility of CFST members. Very little information is available on the performance of FRP-strengthened CFST members under fire conditions. This paper is an attempt to study the fire performance of CFST columns strengthened by FRP. The results of fire endurance tests on FRP-strengthened circular CFST columns are presented. Failure modes of the specimens after exposure to fire, temperatures in the cross section, axial deformation and fire resistance of the composite columns are analysed. It is demonstrated that the required fire endurance can be achieved if the strengthened composite columns are appropriately designed.

• Smart Structures and Systems
• /
• 제17권1호
• /
• pp.91-105
• /
• 2016

One of the most commonly used techniques to strengthen steel reinforced concrete structures is the application of externally bonded patches in the form of carbon fiber reinforced polymers (CFRP) or recently, textile reinforced cements (TRC). These external patches undertake the tensile stress of bending constraining concrete cracking. Development of full-field inspection methodologies for fracture monitoring are important since the reinforcing layers are not transparent, hindering visual observation of the material condition underneath. In the present study acoustic emission (AE) and digital image correlation (DIC) are applied during four-point bending tests of large beams to follow the damage accumulation. AE helps to determine the onset of fracture as well as the different damage mechanisms through the registered shifts in AE rate, location of active sources and change in waveform parameters. The effect of wave propagation distance, which in large components and in-situ can well mask the original information as emitted by the fracture incidents is also discussed. Simultaneously, crucial information is supplied by DIC concerning the moments of stress release of the patches due to debonding, benchmarking the trends monitored by AE. From the point of view of mechanics, conclusions on the reinforcing contribution of the different repair methodologies are also drawn.