• Structural Engineering and Mechanics
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• 제5권4호
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• pp.339-353
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• 1997

Fiber reinforced plastic (FRP) rods provide certain benefits over steel as concrete reinforcement, such as corrosion resistance, magnetic and electrical insulation, light weight, and high strength. FRP composites can be combined with a steel core to form hybrid reinforcing rods that take advantage of properties of both materials. The objective of this study was to characterize the bond behavior of hybrid FRP rods made with braided epoxy-impregnated aramid or poly-vinyl alcohol FRP skins. Eleven rod types were tested using two concrete strengths. Specific topics examined were bond strength, slip, and type of failure in concentric pull-out tests from concrete cubes. From analysis of identical pull-out tests on both hybrid and steel rods, information on relative bond strength and behavior were obtained. It is concluded that strength is similar but slip in hybrid rods is much higher. Hybrid rods failed either by pull-out or splitting the concrete block (with or without yielding of the steel core). Experimental data showed consistency with similar test results presented in the literature.

• International Journal of Concrete Structures and Materials
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• 제10권sup3호
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• pp.53-63
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• 2016

Steel fiber-reinforced prestressed concrete (SFRPSC) members typically have high shear strength and deformation capability, compared to conventional prestressed concrete (PSC) members, due to the resistance provided by steel fibers at the crack surface after the onset of diagonal cracking. In this study, shear tests were conducted on the SFRPSC members with the test variables of concrete compressive strength, fiber volume fraction, and prestressing force level. Their localized behavior around the critical shear cracks was measured by a non-contact image-based displacement measurement system, and thus their shear deformation was thoroughly investigated. The tested SFRPSC members showed higher shear strengths as the concrete compressive strength or the level of prestress increased, and their stiffnesses did not change significantly, even after diagonal cracking due to the resistance of steel fibers. As the level of prestress increased, the shear deformation was contributed by the crack opening displacement more than the slip displacement. In addition, the local displacements around the shear crack progressed toward directions that differ from those expected by the principal strain angles that can be typically obtained from the average strains of the concrete element. Thus, this localized deformation characteristics around the shear cracks should be considered when measuring the local deformation of concrete elements near discrete cracks or when calculating the local stresses.

• 콘크리트학회논문집
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• 제20권3호
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• pp.383-391
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• 2008

이 연구에서는 콘크리트의 압축강도가 증가함에 따라서 변화하는 GFRP 보강근의 부착 특성을 조사하였다. 실험에서는 3종류의 콘크리트에 배근된 27개의 보강근의 부착응력-부착미끌림 관계를 측정하였다. 하중가력이 종료한 후에 실험체를 절단하여 고강도콘크리트가 GFRP 보강근의 부착에 미치는 영향을 살펴보았다. 실험 결과에 의하면 GFRP 보강근의 부착파괴면은 철근과 상이하게 2개의 면으로 구분되었다. 파괴면은 콘크리트와 외피 사이의 파괴면과 외피와 섬유보강근 사이의 파괴면으로 구분 할 수 있었다. 이와 같은 GFRP 보강근의 부착파괴면은 콘크리트의 압축강도가 증가함에 따라서 콘크리트의 접착력과 외피의 접착력의 상호관계에 따라서 달라졌다. GFRP 보강근의 부착강도는 콘크리트의 압축강도가 증가함에 따라서 증가하였지만, 증가 비율은 철근의 부착강도보다 낮았다.

• 콘크리트학회논문집
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• 제28권2호
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• pp.223-234
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• 2016

이 연구에서는 노치 도입 인장시편을 사용하여 직접인장강도 실험을 통해 UHPC의 파괴거동을 살펴보고, 강섬유 혼입률에 따른 UHPC의 초기균열강도와 인장강도를 제안하였다. 실험결과 UHPC와 초기균열강도와 인장강도, 그리고 파괴에너지 등은 강섬유 혼입률이 증가할수록 증가하는 것으로 나타났다. 균열선단에서의 응집응력은 Barenblatt의 가정을 사용하여 결정되었으며, 이를 토대로 변형경화 현상이 발생하는 강섬유 혼입률이 1% 이상인 UHPC의 최대응집응력을 예측할 수 있는 간편식을 제안하였다. 인장강도는 강섬유 혼입률과 압축강도의 함수로 제안되었으며, 파괴에너지는 인장강도의 함수로 제안되었다. 제안된 간편식들은 실험값과 비교적 잘 일치하였으며, 향후 압축강도가 140~170 MPa이고, 강섬유 혼입률이 2% 이하인 UHPC에 적용가능 할 것으로 판단된다.

• Computers and Concrete
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• 제21권6호
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• pp.681-695
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• 2018

This pioneer study investigates the size effect on the compressive and tensile strengths of fiber-reinforced self-compacting concrete (FR-SCC) with different specimens, before and after exposure to elevated temperatures. 432 self-compacting concrete (SCC) specimens with two concrete grades (50 and 80MPa) and three steel fiber ratios (0%, 0.5% and 1%) were prepared and tested. Moreover, based on the experimental results, new formulations were proposed to predict the residual strengths for different specimens. A parametric study was also carried out to investigate the accuracy of proposed formulations. Residual strength results showed that the cylinder specimen with dimensions of $100{\times}200mm$ was the most affected, while the cube with a size of 100 mm maintained a constant difference with the standard cylinder ($150{\times}300mm$). Temperature effect on the cube specimen (150 mm) was the least in comparison to other specimen sizes and types. In general, provision of steel fibers in SCC mixtures resulted in a reduction in temperature effect on the variance of a conversion factor. Parametric study results confirm that the proposed numerical models are safe to be used for all types of SCC specimens.

• Structural Engineering and Mechanics
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• 제64권2호
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• pp.155-171
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• 2017

This paper presents a proposed method for producing reinforced composite concrete columns reinforced with various types of metallic and non metallic mesh reinforcement. The experimental program includes casting and testing of twelve square columns having the dimensions of $100mm{\times}100mm{\times}1000mm$ under concentric compression loadings. The test samples comprise all designation specimens to make comparative study between conventionally reinforced concrete column and concrete columns reinforced with welded steel mesh, expanded steel mesh, fiber glass mesh and tensar mesh. The main variables are the type of innovative reinforcing materials, metallic or non metallic, the number of layers and volume fraction of reinforcement. The main objective is to evaluate the effectiveness of employing the new innovative materials in reinforcing the composite concrete columns. The results of an experimental investigation to examine the effectiveness of these produced columns are reported and discussed including strength, deformation, cracking, and ductility properties. Non-linear finite element analysis; (NLFEA) was carried out to simulate the behavior of the reinforced concrete composite columns. The numerical model could agree the behavior level of the test results. ANSYS-10.0 Software. Also, parametric study is presented to look at the variables that can mainly affect the mechanical behaviors of the model such as the change of column dimensions. The results proved that new reinforced concrete columns can be developed with high strength, crack resistance, and high ductility properties using the innovative composite materials.

• Advances in concrete construction
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• 제14권1호
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• pp.45-55
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• 2022

In this article, the flexural and shear capacity of ultra-high-performance fiber-reinforced concrete beams (UHPFRC) using two kinds of rebars, including GFRP and steel rebars, are experimentally investigated. For this purpose, six UHPFRC beams (250 × 300 × 1650 mm) with three reinforcement ratios (ρ) of 0.64, 1.05, and 1.45 were constructed using 2% steel fibers by volume. Half of the specimens were made of UHPFRC reinforced with GFRP rebars, while the other half were reinforced with conventional steel rebars. All specimens were tested to failure in four-point bending. Both the load-deformation at mid-span and the failure pattern were studied. The results showed that utilizing GFRP bars increases the flexural strength of UHPFRC beams in comparison to those made of steel bars, but at the same time, it reduces the post-cracking strain hardening. Furthermore, by increasing the percentage of longitudinal bars, both the post-cracking strain hardening and load-bearing capacity increase. Comparing the experiment results with some of the available equations and provisions cited in the valid design codes reveals that some of the equations to predict the flexural strength of UHPFRC beams reinforced with conventional steel and GFRP bars are reasonably conservative, while Khalil and Tayfur model is un-conservative. This issue makes it essential to modify the presented equations in this research for predicting the flexural strength of UHPFRC beams using GFRP bars.

• Advances in concrete construction
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• 제13권1호
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• pp.35-43
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• 2022

The experimental investigations into hooked-end round steel fibers (HSF) effect on the age-dependent strengths of high volume fly ash (HVFA) concrete is studied. The concrete was prepared with class F fly ash used as partial cement replacement varied from 0% to 70% on an equal weight basis. Two percentages of HSF (i.e., 0.5% and 1.5% by volume fraction) of 50 mm length were added in plain, and 50% fly ash concrete mixes. The compressive and flexural tensile strength was determined at 7, 28, 56, and 90 days. The strength results of fly ash concrete mixes with and without steel fibers were compared with the plain concrete strength. The test results indicated that the strength of fly ash concrete is comparable with the plain concrete strength and further increases with an increase in the percentage of steel fibers. The maximum flexure strength of HVFA concrete is found with 0.5% steel fibers. It is concluded that the HVFA concrete with steel fibers of 50 mm length can effectively be used in concrete construction. The analytical models are proposed to predict the age-dependent compressive and flexural tensile strength of HVFA concrete with and without HSF. The compressive and tensile strength of HVFA concrete with HSF can be predicted using these models when the 28-day compressive strength of plain concrete is known. The present study will be helpful in the design and construction of reinforced and pre-stressed concrete structures made with HVFA and HSF.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 춘계 학술발표회 논문집(II)
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• pp.377-380
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• 2006

HPFRCCs(High performance fiber reinforced cementitious composites) is a class of FRCCs(Fiber reinforced cementitious composites) exhibit multiple crack. Multiple crack lead to improvement in ductility, toughness, and deformation capacity under compressive and tensile stress. These properties of HPFRCCs are affected by type of fiber, water cement ratio, type of admixture and rate of substitution. Furthermore these influence dispersion of fiber, mixing performance and fluidity of mixture. In this paper, HPFRCCs made of steel cord and carbon fiber were tested with water cement ratio, type of admixture and rate of substitution to evaluate characteristics of mixing and flexural strength.

• 한국구조물진단유지관리공학회 논문집
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• 제23권2호
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• pp.92-98
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• 2019

일반적인 고인성 고성능 시멘트 복합재료의 경우 균질한 재료분포를 위하여 기본적으로 굵은 골재를 배재하는 경향이 있다. 그러나, 굵은 골재를 배재한 섬유 복합 시멘트 모르타르의 경우 재료의 탄성계수가 낮으며 단위시멘트량이 높아 경제성과 효율이 낮은 배합이기 때문에 대량으로 신규 구조물에 적용하기 힘들다. 따라서, 본 연구에서는 적절한 수준의 굵은 골재를 혼입하였지만 여전히 휨인성과 휨강도는 확보하고 있는 동시에, 균열 분산성능도 보유하고 있는 고인성 섬유보강 콘크리트에 대한 개발 연구를 수행하였다. 굵은 골재의 혼입량을 실험 변수로 실험 연구를 수행하였고, 결과에 따르면 고인성 모르타르의 기본 배합에 굵은골재를 잔골재의 25%중량비로 추가한 경우에서 가장 좋은 휨인성 그리고 균열분산 특성을 나타내었다. PVA섬유는 균열분산과 연성 증진에 효과적이었고, 강섬유 섬유의 경우 균열분산보다는 강도증진에 효과적이었다.