콘크리트 구조의 인장 보강재로 주로 사용되는 철근은 높은 인장강도와 연성이 우수한 변형 특성에 도 불구하고 부식이 발생할 수 있다는 단점을 갖고 있다. 이러한 문제점을 개선하기 위하여 부식이 발 생하지 않는 다양한 재료 중 FRP(Fiber Reinforced Polymer)를 철근과 유사한 형태의 Rod로 제작하 여 철근을 대체하는 보강재로 사용하기 위한 연구가 진행되고 있다. 그중에서도 인장강도가 우수한 탄 소 및 유리섬유를 일방향으로 성형하고 Rod 표면을 굴곡 처리한 CFRP 및 GFRP 보강근을 중심으로 콘크리트 구조에 적용하기 위한 연구가 활발하게 진행되고 있다. 이 연구에서는 FRP Rod를 보강근으 로 하는 콘크리트 부재의 부착특성과 균열폭, 처짐과 같은 사용성 평가에 중요한 역할을 하는 인장강 화효과를 포함한 균열거동 특성을 파악하기 위하여 단변의 피복두께와 FRP 보강근 지름의 비를 1.0에 서 3.5 까지 0.5배씩 증가하는 직사각형 단면을 갖는 길이 1,000mm의 인장부재를 제작하여 만능재료 시험기(Universal Testing Machine)를 이용한 직접인장실험을 수행한 후, 피복두께와 FRP 보강근의 지름 비에 따른 균열거동(Cracking Behavior) 및 인장강화효과(Tension Stiffening Effect)를 분석하고 현행 설계기준의 규정과 비교하였다. 작용하중에 따라 발생하는 균열에 대해서 횡방향균열(Transverse Crack)과 쪼갬균열(Splitting Crack)로 각각 구분하고, DAQ(Data Acquisition) 시스템을 이용하여 콘 크리트 인장부재에 매입된 CFRP 및 GFRP 보강근의 변형량 및 작용하중을 측정하였으며, 그 결과로 부터 하중-변형률 관계로 대표되는 인장강화효과를 분석하였다. 균열거동 및 인장강화효과를 분석한 결과, CFRP 또는 GFRP Rod를 보강근으로 하는 콘크리트 인장부재는 FRP 보강근과 콘크리트의 부 착강도를 감소시키는 쪼갬균열이 발생하지 않도록 피복두께를 보강근 지름의 2.5배 이상 확보하였을 때, 각 보강근별로 극한강도 fu의 60-70%에 해당하는 하중이 작용하는 단계에서 인장강화효과는 우 수한 것으로 나타났으며, 철근을 보강근으로 하는 현행 설계기준의 규정으로 예측한 결과보다 우수한 인장강화효과를 얻을 수 있음을 확인하였다.

This paper presents experimental results for evaluating bond strength of FRP Hybrid Bars(HYB). In order to confirm the bond strength of HYB, direct bond strength tests were performed on 20 specimens. 20 specimens made of deformed steel bars were also tested for relative comparison. HYB and deformed steel bars were embedded in a concrete block with a size of 200 mm and different attachment lengths were applied depending on the diameter of the reinforcing bars. During the test, load and relative displacement(slip) were measured and the load-displacement behaviors of all specimens were analyzed from the measured results. The maximum bond strength of deformed steel bars were higher than that of HYB regardless of its diameter. However, after the maximum load, the deformed steel bars were more dominant than the HYB in the sudden load reduction tendency.

This paper presents experimental and analytical results for predicting tensile behavior of FRP Hybrid Bar(HYB). In order to confirm the tensile behavior of HYB wrapped with glass fiber reinforced polymer(GFRP) on deformed rebar, direct tensile tests were performed on 8 specimens. The diameter of the HYB was considered as a test variable and the tensile load, displacement, and tensile strain of each specimen were measured by tensile test. In order to predict the tensile behavior of HYB, numerical analysis based on tensile model of each material was performed. The tensile models of reinforcing bar, glass fiber, and resin, which are the constituent materials of HYB, are assumed to be simple shapes according to their material properties. The results of the numerical analysis through the strain compliance condition of each material were compared with the experimental results and both results showed consistent trends. The experimental and analytical ratios for yield and ultimate loads were 1.02 and 1.00, respectively, and the coefficient of variation were 3.61 and 2.54, respectively. However, a maximum of about 9 mm error occurred due to the slip generated by the direct tensile test in the comparison between the experimental results and the analytical results for the tensile displacement.

ber reinforced polymer (FRP) reinforcing bars for concrete structure have been extensively investigated and a number of FRP bars are commercially available. However, major shortcoming of the existing FRP bars is low elastic modulus compared to conventional steel bars. Because of these reasons, FRP Hybrid Bar which have the concept of material hybridization(synthetic resins, deformed bar, glass fiber etc) for concrete structures have been developed. One of main features of this bar is corrosion resistance and this is important to confirm this anti-corrosion capacity of FRP Hybrid Bar. In this study, galvanic corrosion current behavior of 3 types of specimens, including two types of FRP Hybrid Bars and one conventional steel rebar, was investigated under the 0%, 1.5%, 3% and 6% salt water ratio condition. The result of this study can be used to evaluate the applicability of FRP Hybrid Bar to concrete structures.

GFRP(Glass Fiber Reinforced Polymer Plastic) has a superior corrosion resistance, high specific strength/stiffness, etc. Therefore, such properties can be used to mitigate the problems associated with the use of conventional construction materials. In this study, the various rib and pitch distance of hybrid fiber GFRP bars were evaluated by experimental method. From the test result, thirty two types of FRP hybrid bars such as spiral type with the dimension of rib geometry were fabricated. To evaluate the bond properties of them, direct pull-out test was performed. All testing procedures including specimen preparation, set-up of test equipment and measuring devices were made in accordance with the recommendations of ASTM D 7913. From the test results, it was found that cross type hybrid GFRP reinforcing bars showed the highest bond strength than that of the others due to the higher relative rib area.

During the last two decades, fiber reinforced polymer (FRP) reinforcing bars for concrete structure have been extensively investigated and a number of FRP bars are commercially available. However, major shortcomings of the existing FRP bars are its high initial cost and low elastic modulus compared to conventional steel bars. Because of these reasons, Korea Institute of Civil Engineering and Building Technology (KICT) in Korea has developed the FRP Hybrid Bar which have the concept of material hybridization for concrete structures, especially for marine and waterfront concrete structures. This developed bar is new type material in construction field, verification of long term performance is very important for commercialization. In this paper, verification methodology on long term performance(corrosion, flexural behavior etc) of FRP Hybrid Bar is suggested.

To overcome shortcomings of fiber reinforced polymer (FRP), a hybridized FRP rebar was developed by the authors. This hybrid bar herein called “FRP Hybrid Bar” was fabricated by adopting advantages from two different materials, including glass fiber reinforced polymer (GFRP). Corrosion resistant characteristics of FRP Hybrid Bar were evaluated and the test results were explained in this paper. The use of the alternative reinforcement could allow concrete structures to extend life-span, to save maintenance and repair costs, etc. if the FRP Hybrid Bar was applied to RC structures located in a very corrosive environment, such as marina or harbor areas.

GFRP(Glass Fiber Reinforced Polymer Plastic) has a superior corrosion resistance, high specific strength/stiffness, etc. Therefore, such properties can be used to mitigate the problems associated with the use of conventional construction materials. In this study, the various rib and pitch distance of hybrid fiber GFRP bars were evaluated by experimental method. From the test result, thirty two types of FRP hybrid bars such as spiral and cross type with the dimension of rib geometry were fabricated. To evaluate the bond properties of them, direct pull-out test was performed. All testing procedures including specimen preparation, set-up of test equipment and measuring devices were made in accordance with the recommendations of ASTM D 7913. From the test results, it was found that cross type hybrid GFRP reinforcing bars showed the highest bond strength than that of the others due to the higher relative rib area.

FRP Hybrid Bar, composite structures composed of synthetic resins, deformed bar and glass fiber, was invented in order to solve corrosion of rebar in reinforced concrete structures. In order to bond deformed bar and glass fiber to FRP Hybrid Bar, synthetic resins is used. Curing time of the synthetic resins greatly affect productivity. If curing time of synthetic resins is short, cost of facilities is reduced and productivity is increased. Also, If this curing time is shorter or omitted, FRP Hybrid Bar can be commercialized. So, it can cause mass-production and substantial economic effect. Therefore, in this paper, optimum mix proportion is observed in order to increase economic efficiency of FRP Hybrid Bar and reduce curing time of synthetic resins. Total 9 variables are set, adjusting ratio of hardener ratio, and 3 resin moulds on each variables are fabricated. Optimum mix proportion is suggested based on data measured by temperature sensor.

철근 및 FRP Bar를 보강재로 사용한 콘크리트 보의 전단 거동을 실험적으로 평가하였다. 실험 변수는 특성이 다른 보강근을 휨 및 전단 보강한 것과 전단보강근비이다. 콘크리트 보의 전단강도 산정에 일반적으로 널리 이용되는 수정트러스 이론의 타당성을 실험 결과의 분석을 통하여 평가하였다. CFRP 및 GFRP를 휨 및 전단 보강한 콘크리트 보에 그대로 적용하는 것은 적절하지 않음을 알 수 있었다. 실험결과는 FRP Bar를 보강근으로 사용한 콘크리트 보의 전단 문제에 수정트러스 이론을 그대로 적용하는 것은 타당하지 않다는 것을 알 수 있었다.

콘크리트 포장의 다웰바는 교통하중을 줄눈 넘어 인접한 슬래브로 전달하는 하중전달장치이다. 현재 국내에서 사용되는 다웰바는 원형봉강으로 교통하중과 환경하중으로 인해 반복적으로 발생하는 전단응력과 휨응력에 대해 높은 내구성을 갖고 있다. 그러나, 강재 다웰바는 장기간 공용시 줄눈틈, 포장 하부 등으로 침투한 수분으로 인해 부식이 발생한다. 특히, 겨울철에 사용되는 제설용 염수와 접촉할 경우 부식은 급격히 진행된다. 다웰바에 부식이 발생하면 부피가 증가하여 줄눈의 거동을 방해하며 유효단면적의 감소로 하중전달효과가 떨어질 수 있다. 이와 함께 지속적인 원자재 가격의 상승으로 강재 다웰바의 가격 경쟁력이 크게 낮아지고 있다. 이러한 강재 다웰바의 문제점은 새로운 재료를 사용한 대체 다웰바의 개발로 이어지고 있다. 본 연구에서는 높은 인장강도, 높은 내부식성을 갖춘 FRP(fiber reinforced plastic)를 튜브 형태로 제작하고 그 속을 고강도 무수축 모르타르로 충진한 FRP 튜브 다웰바에 대한 역학적 두께 설계를 실시하였다. 역학적 두께 설계의 기준으로 다웰바와 콘크리트 면 사이에 발생하는 지압응력을 사용하였다. 지압응력의 산정을 위하여 다웰바에 전달되는 교통하중을 이론식과 유한요소해석을 통해 산출하고 실내시험을 통해 FRP 튜브 다웰바의 물성을 측정하였다. 그 결과, 직경 32mm, 40mm FRP 튜브 다웰바 모두 지압응력 기준을 만족하는 것으로 나타났다. 국내 콘크리트 포장은 콘크리트 슬래브 하부에 강성이 큰 린 콘크리트층을 사용하기 때문에 다웰바에 전달되는 교통하중이 적고 이로 인해 지압응력도 낮아져 상대적으로 적은 직경의 FRP 튜브 다웰바의 사용이 가능한 것으로 판단된다.

Six concrete beam specimens reinforced with multiple layers of reinforcement and combinations of different reinforcement types (steel, GFRP, and CFRP bars), and four FRP bar-reinforced concrete beams with fibers were constructed and tested. An investigation was performed on load-carrying capacity, post cracking stiffness, cracking pattern, and ductility for all specimens. Addition of fibers and hybrid reinforcing with steel bars can be possible methods to overcome the low stiffness and ductility of FRP bar-reinforced beams.

Concrete structure is a construction material with durability and cost-benefit, however the corrosion in embedded steel causes a critical problem in structural safety. This paper presents an evaluation of chloride resistance and pull-off performance with various corrosion level. For the work, OPC(Ordinary Portland Cement) concrete and GGBFS(Ground Granulated Blast Furnace Slag) concrete are prepared with normal steel. Artificially notch induced FRP Hybrid Bar is also prepared and embedded in OPC concrete and accelerated corrosion test is performed. Through the test, FRP Hybrid Bar with notch is evaluated to have insignificant effect on pull-off capacity when corroded steel shows only 21% level of pull-off capacity. Furthermore GGBFS concrete with normal steel shows over 70% level of pull-off capacity due to reduced corrosion currency.

RC(Reinforced Concrete) 부재는 인장영역에서 보강재가 하중을 지지해야 하므로, 철근부식은 내구성 뿐 아니라 안전성에서도 매 우 중요하다. 본 연구에서는 최근 개발된 FRP Hybrid Bar와 일반 철근을 매립한 RC 보부재를 제작하였으며, ICM(Impressed Current Method) 를 적용하여 철근부식을 촉진시켰다. 기존의 이론식인 Faraday 법칙을 이용하여 부식량을 평가하였으며, 일반설계강도를 가진 콘크리트 보부 재에 대하여 휨시험을 수행하였다. 일반 철근에서는 부식량이 4.9∼7.8% 수준으로 평가되었으며 이에 따른 휨 저항능력은 -25.4∼-50.8% 수준 으로 감소하였다. FRP Hybrid Bar를 매립한 RC 보에서는 부식과 휨 저항 감소가 평가되지 않았는데, 이는 에폭시 도료로 코팅된 철근의 우수 한 내부식성에 기인한다. 촉진 부식실험에서는 FRP Hybrid Bar의 우수한 내부식성 및 부착성능을 확인하였는데, 실용화를 위해서는 장기적인 침지를 통한 내구성 평가가 필요하다고 판단된다.

Tensile performance of the recently developed “FRP Hybrid Bar” at Korea Institute of Civil Engineering and Building Technology (KICT) is experimentally evaluated by the authors. FRP Hybrid Bar is introduced to overcome the low elastic modulus of the existing GFRP bars to be used as a structural member in reinforced concrete structures. The concept of material hybridization is adapted to increase elastic modulus of GFRP bars by using steel. This hybridized GFRP bar can be used in concrete structures as a flexural member with a sufficient level of elastic modulus. In order to verify the effect of material hybridization on tensile properties, tensile tests are conducted. The results for both FRP Hybrid Bar and the existing GFRP bars are compared. The results indicate that the elastic modulus of FRP Hybrid Bar can be enhanced by up to approximately 250 percent by the material hybridization with a reasonable tensile strength. To ensure the long-term durability of FRP Hybrid Bar to corrosion resistance, the individual and combined effects of environmental conditions on the bar itself as well as on the interface between rebar and concrete are currently under investigation.

During the last two decades, fiber reinforced polymer (FRP) reinforcing bars for concrete structure has been extensively investigated and a number of FRP bars are commercially available. However, major shortcomings of the existing FRP bars are its high initial cost and low elastic modulus compared to conventional steel bars. Because of these reasons, KICT in Korea have developed the FRP Hybrid Bar which have the concept of material hybridization for concrete structures, especially for marine and waterfront concrete structures. In this study, for the discussing the applicability of FRP Hybrid Bar to real concrete structures, life cycle cost analysis were performed on small bridge and discussed considering various kinds of maintenance cases.

In the paper, newly invented FRP Hybrid Bar and normal steel are embedded in RC beam member, and ICM(Impressed Current Method) is adopted for corrosion acceleration. Corrosion amount level of 4.9∼7.8% are measured in normal RC member and the related reduction of flexural capacity is measured to –25.4∼-50.8%. But, durability evaluation through long-term submerged condition is required for actual utilization.