• Computers and Concrete
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• 제26권3호
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• pp.275-283
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• 2020

Reinforced concrete (RC) does not provide sufficient resistance against impacts and blast loads, and the brittle structure of RC fails to protect against fractures due to the lack of shock absorption. Investigations on improving its resistance against explosion and impact have been actively conducted on high-performance fiber-reinforced cementitious composites (HPFRCCs), such as fiber-reinforced concrete and ultra-high-performance concrete. For these HPFRCCs, however, tensile strength and toughness are still significantly lower compared to compressive strength due to their limited fiber volume fraction. Therefore, in this study, the tensile behavior of slurry-infiltrated fiber-reinforced cementitious composites (SIFRCCs), which can accommodate a large number of steel fibers, was analyzed under static and dynamic loading to improve the shortcomings of RC and to enhance its explosion and impact resistance. The fiber volume fractions of SIFRCCs were set to 4%, 5%, and 6%, and three strain rate levels (maximum strain rate: 250 s^-1) were applied. As a result, the tensile strength exceeded 15 MPa under static load, and the dynamic tensile strength reached a maximum of 40 MPa. In addition, tensile characteristics, such as tensile strength, deformation capacity, and energy absorption capacity, were improved as the fiber volume fraction and strain rate increased.

• Structural Engineering and Mechanics
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• 제90권5호
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• pp.481-492
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• 2024

This research examined the mechanical behavior of fiber-reinforced concrete at unstable environmental conditions. Concrete composites with varying percentages of steel and glass fibers were analyzed. Compressive, indirect tensile, and fracture toughness properties were evaluated using the Edge Notched Disc Bend (ENDB) test under freezing-thawing and acidic environments and the results were compared with normal conditions. Steel fibers decreased the strength in the specified cycles, while glass fibers showed a normal strength trend. The compressive, tensile and fracture toughness of the samples containing 1.5 vol.% fibers showed a 1.28-, 2.13- and 4.5-fold enhancement compared to samples without fibers, after 300 freezing-thawing cycles, respectively.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 추계 학술발표회 제16권2호
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• pp.441-444
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• 2004

This paper presnets the tensile behavior of 8 high performance fiber-reinforced cementitious composites (HPFRCCs) members, each reinforced with one deformed bar 16mm in diameter. The variables included HPFRCC(Ductal, steel cord and polyethylene hybrid fiber, PE fiber) versus normal concrete. Fibers used in HPFRCC significantly increased tensile strength, ductility, and tension stiffening of cementitious materials. For HPFRCC, after first cracking, tensile load continue to rise without fracture localization. Sequentially developed parallel cracks contributed to the inelastic strain at increasing stress level. After yielding of the reinforcing bars, HPFRCC showed increases in loads with increasing strains.

• 콘크리트학회논문집
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• 제17권6호
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• pp.983-992
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• 2005

섬유에 의하여 보강된 철근콘크리트 보의 파괴모드는 섬유가 파단하여 전단강도에 도달하는 경우와 섬유가 파단하기 이전에 전단강도에 도달하는 경우로 나누어진다. 이와 같이 섬유가 파단강도에 도달하지 않는 경우에 두 파괴모드의 전단강도는 상이하다. 섬유가 파단하지 않고 전단강도에 도달할 경우에 보의 전단강도를 예측하기 위하여 섬유의 파단강도를 사용할 수 없으므로 기존의 제안식에서는 섬유강도저감계수를 사용하여 섬유보강 보의 전단강도를 예측하였다. 그러나 기존 제안식의 대부분은 실험결과에 근거한 회귀분석을 통하여 일정한 상수 값에 의하여 섬유강도저감계수를 평가하였으며, 섬유의 도달강도와 밀접한 관계가 있는 콘크리트의 압축강도를 고려하지 않고 있다. 이 연구에서는 변형률의 적합조건을 이용한 트러스모델에 근거하여 섬유보강 보의 파괴모드의 경계점을 구별하고, 이를 이용하여 섬유보강 보의 전단강도를 예측하였다.

• Computers and Concrete
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• 제16권3호
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• pp.399-414
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• 2015

Nowadays, fiber reinforced polymer (FRP) composites are widely used for rehabilitation, repair and strengthening of reinforced concrete (RC) structures. Also, recent advances in concrete technology have led to the production of high strength concrete, HSC. Such concrete due to its very high compression strength is less ductile; so in seismic areas, ductility is an important factor in design of HSC members (especially FRP strengthened members) under flexure. In this study, the Adaptive Neuro-Fuzzy Inference System (ANFIS) and multiple regression analysis are used to predict the curvature ductility factor of FRP strengthened reinforced HSC (RHSC) beams. Also, the effects of concrete strength, steel reinforcement ratio and externally reinforcement (FRP) stiffness on the complete moment-curvature behavior and the curvature ductility factor of the FRP strengthened RHSC beams are evaluated using the analytical approach. Results indicate that the predictions of ANFIS and multiple regression models for the curvature ductility factor are accurate to within -0.22% and 1.87% error for practical applications respectively. Finally, the effects of height to wide ratio (h/b) of the cross section on the proposed models are investigated.

• Structural Engineering and Mechanics
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• 제56권6호
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• pp.899-916
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• 2015

Upgrading or strengthening of existing reinforced concrete (RC) infrastructure is an emerging demand nowadays. Near Surface Mounted (NSM) technique is very promising approach for flexural strengthening of RC members. However, premature failure such as concrete cover separation failure have been a main concern in utilizing this technique. In this study, U-wrap end anchorage with carbon fiber reinforced polymer (CFRP) fabrics is proposed to eliminate the concrete cover separation failure. Experimental programs were conducted to the consequence of U-wrap end anchorage on the flexurally strengthened RC beams with NSM-steel. A total of eight RC rectangular beam specimens were tested. One specimen was kept unstrengthened as a reference; three specimens were strengthened with NSM-steel bars and the remaining four specimens were strengthened with NSM-steel bars and U-wrap end anchorage using CFRP fabrics. A 3D non-linear finite element model (FEM) was developed to simulate the flexural response of the tested specimens. It is revealed that NSM-steel (with and without end-anchors) significantly improved the flexural strength; moreover decreased deflection and strains compared with reference specimen. Furthermore, NSM-steel with end anchorage strengthened specimens revealed the greater flexural strength and improve failure modes (premature to flexure) compared with the NSM-steel without end anchorage specimens. The results also ensured that the U-wrap end anchorage completely eliminate the concrete cover separation failure.

• Advances in concrete construction
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• 제14권5호
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• pp.299-307
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• 2022

Cement-based matrixes have low tensile strength and negligible ductility. Adding fibres to these matrixes will improve their mechanical properties and make these composites suitable for structural applications. Post-cracking tensile strength of steel fibers-reinforced cementitious composite materials is directly related to the number of transverse fibers passing through the crack width and the pulling-out behavior of each of the fibers. Therefore, the exact recognition of the pullout behavior of single fibers is necessary to understand the uniaxial tensile and bending behavior of steel fiber-reinforced concrete. In this paper, an experimental study has been carried out on the pullout behavior of 3D (steel fibers with totally two hooks at both ends), 4D (steel fibers with a total of four hooks at both ends), and 5D (steel fibers with totally six hooks at both ends) in which the fibers have been located either perpendicular to the crack width or in an inclined manner. The pullout behavior of the mentioned steel fibers at an inclination angle of 0, 15, 30, 45, and 60 degrees and with embedded lengths of 10, 15, 20, 25, and 30 millimetres is studied in order to explore the simultaneous effect of the inclination angle of the fibers relative to the alongside loading and the embedded length of fibers on the pullout response in each case, including the maximal pullout force, the slip of the maximum point of pullout force, pullout energy, fiber rupture, and concrete matrix spalling. The results showed that the maximum pullout energy in 3D, 4D, and 5D steel fibers with different embedded lengths occurs at 0 to 30° inclination angles. In 5D fibers, maximum pullout energy occurs at a 30° angle with a 25 mm embedded length.

• Advances in concrete construction
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• 제12권6호
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• pp.451-459
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• 2021

The mechanical behaviors and chloride resistance performance of fiber reinforced cementitious composites (FRCC) with hybrid polyethylene (PE) and steel fiber (in total 2% by volume) were investigated. Based on micro-mechanics and fracture mechanics, the reason why the tensile strain capacity of FRCC changed obviously was obtained. Besides, the effects of the total surface area of fiber in FRCC on compressive strength and chloride content were clarified. It is found that the improvement of the tensile strain capacity of FRCC with hybrid fiber is attributed to the growth of strain-hardening performance index (the ratio of complementary energy to crack tip toughness). As the total surface area of fiber related with the interfacial transition zone (ITZ) between fiber and matrix increases, compressive strength decreases obviously. Since the total surface area of fiber is small, the chloride resistance performance of FRCC with hybrid PE and steel fiber is better than that of FRCC containing only PE fiber.

• 콘크리트학회논문집
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• 제19권2호
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• pp.145-151
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• 2007

섬유에 의하여 보강된 철근콘크리트 보는 철근만에 의하여 보강된 보와 다른 파괴 모드를 나타낸다. 섬유 보강 보는 섬유의 양, 내부 전단 보강 철근의 양 및 콘크리트의 압축강도에 따라서 전단 보강 철근이 항복하고 콘크리트가 압축 파괴하는 경우(섬유는 탄성 상태)와 콘크리트가 압축파괴하기 이전에 섬유가 파단하는 경우로 구별할 수 있다. 대부부의 섬유 보강 철근콘크리트 보는 전자의 파괴 모드를 나타내며 이 경우에 전단파괴 시의 섬유의 유효변형률을 정확하게 예측하여야 한다. 이 연구에서는 11개의 섬유 보강 철근콘크리트 보 실험을 통하여 섬유의 유효변형률을 측정하였다 실험의 주요 변수는 섬유의 양, 섬유의 종류(탄소 섬유, 유리 섬유), 부착 형상 (전단면 감싸기, 스트립형 부착)이었다. 실험에 의하여 측정된 섬유의 유효변형률은 제안된 유효변형률 예측법과 비교되었다.

• Structural Engineering and Mechanics
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• 제5권4호
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• pp.355-368
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• 1997

Fiber reinforced plastic (FRP) rods are used as reinforcement (prestressed or not) to concrete. FRP composites can also be combined with steel to form hybrid reinforcing rods that take advantage of the properties of both materials. In order to effectively utilize these rods, their bond behavior with concrete must be understood. The objective of this study is to characterize and model the bond behavior of hybrid FRP rods made with epoxy-impregnated aramid or poly-vinyl alcohol FRP skins directly braided onto a steel core. The model closely examines the split failure of the concrete by quantifying the relationship between slip of the rods resulting transverse stress field in concrete. The model is used to derive coefficients of friction for these rods and, from these, their development length requirements. More testing is needed to confirm this model, but in the interim, it may serve as a design aide, allowing intelligent decisions regarding concrete cover and development length. As such, this model has helped to explain and predict some experimental data from concentric pull-out tests of hybrid FRP rods.