Post-peak response analysis of SFRC columns including spalling and buckling

Dhakal, Rajesh P. Techno-Press 2006 Structural Engineering and Mechanics, An Int'l Jou Vol.22 No.3

Standard compression tests of steel fiber reinforced concrete (SFRC) cylinders are conducted to formulate compressive stress versus compressive strain relationship of SFRC. Axial pullout tests of SFRC specimens are also conducted to explore its tensile stress strain relationship. Cover concrete spalling and reinforcement buckling models developed originally for normal reinforced concrete are modified to extend their application to SFRC. Thus obtained monotonic material models of concrete and reinforcing bars in SFRC members are combined with unloading/reloading loops used in the cyclic models of concrete and reinforcing bars in normal reinforced concrete. The resulting path-dependent cyclic material models are then incorporated in a finite-element based fiber analysis program. The applicability of these models at member level is verified by simulating cyclic lateral loading tests of SFRC columns under constant axial compression. The analysis using the proposed SFRC models yield results that are much closer to the experimental results than the analytical results obtained using the normal reinforced concrete models are.

Fracture property of steel fiber reinforced concrete at early age

Chuan-Qing Fu,Qin-yong Ma,Xianyu Jin,A.A. Shah,Ye Tian 사단법인 한국계산역학회 2014 Computers and Concrete, An International Journal Vol.13 No.1

This research is focused on obtaining the fracture property of steel fiber reinforced concrete(SFRC) specimens at early ages of 1, 2, 3 and 7-day, respectively. For this purpose, three point bending tests of nine groups of SFRC beams with notch of 40mm depth and different steel fiber ratios were conducted. The experimental results of early age specimens were compared with the 28-day hardened SFRC specimens. The test results indicated that the steel fiber ratios and curing age significantly influenced the fracture properties of SFRC. A reasonable addition of steel fiber improved the fracture toughness of SFRC, while the fracture energy of SFRC developed with curing age. Moreover, a quadratic relationship between splitting strength and fracture toughness was established based on the experiment results. Additionally, afinite element (FE) method was used to investigate the fracture properties of SFRC.A comparison between the FE analysis and experiment results was also made. The numerical analysis fitted well with the test results, and further details on the failure behaviors of SFRC could be revealed by the suggested numerical simulation method.

강섬유로 보강된 콘크리트 보의 전단강도에 관한 실험적 연구

갈경완,김강수,이득행,황진하,오영훈 한국구조물진단유지관리공학회 2010 한국구조물진단유지관리공학회 논문집 Vol.14 No.3

강섬유를 혼입한 콘크리트(Steel Fiber Reinforced Concrete, SFRC) 보는 강섬유의 우수한 인장강도로 인하여 일반 철근콘크리트 보에 비하여 높은 전단강도를 가진다. 이 연구에서는 강섬유 혼입율에 따른 SFRC 보의 전단거동을 규명하기 위하여 실험을 수행하였으며, 특히, 압축영역에서의 비균열 콘크리트 단면의 전단저항 분담율을 분석하였다. 또한, 이 연구의 실험결과 및 기존에 보고된 87개의 실험 데이터를 수집하여 SFRC보의 전단예측식들에 대한 정확도를 평가하였다. 강섬유의 혼입율이 증가할수록 전단강도는 증가하는 경향성을 나타내었다. 그러나, 강섬유 혼입율이 0.5%인 실험체는 사인장 균열 이후 갑작스럽게 파괴되었고, 강섬유의 혼입율이 2.0%인 실험체에서는 전단보강효율이 감소하는 것으로 관찰되어 최대 전단보강효율을 가질 수 있는 혼입율은 1~2% 사이에 있을 것으로 추정된다. 또한, 압축영역에서의 비균열 콘크리트 단면의 전단저항 분담율은 약 21% 이상으로 관찰되었으며, 이 연구에서 평가된 SFRC보의 전단강도에 대한 기존 제안식 중에서 오영훈 등이 제안한 식이 비교적 정확하게 전단강도를 예측하였다. Steel Fiber Reinforced Concrete (SFRC) beams has greater shear strength than typical reinforced concrete beams due to the high tensile strength of steel fibers. In this research, an experiment has been conducted to investigate the shear behavior of SFRC beams, and especially, the portion of shear resistance by uncracked compressive concrete section has been measured. Based on the test results in this study and 87 test data collected from literature, the accuracy of the existing equations for the estimation of shear strength has been evaluated. The shear strength of SFRC beams increased as more steel fibers were mixed. However, it is considered that the most efficient amount of steel fiber for enhancement of shear strength would be between 1% and 2% in that the specimen with 0.5% of steel fibers were abruptly failed after inclined cracking, and that the specimen with 2.0% of steel fibers showed a relatively low efficiency in increasing shear strength. The portion of shear resistance by the uncracked compressive concrete section was measured to be greater than 21%, and the equation proposed by Oh et al. provided the best accuracy on the estimation of shear strength of SFRC beams among the approaches evaluated in this study.

환경친화적인 SFRC상판 개발에 관한 기초적 연구

서성탁(Sung-Tag Seo) 한국환경관리학회 2009 環境管理學會誌 Vol.15 No.1

최근 사회간접자본의 유지비는 증가하고 있으며, 노화된 구조물의 개량과 내구성의 향상이 매우 필요하다. 특히, SFRC의 품질이나 내구성 뿐만아니라 SFRC에 발생하는 균열폭에 대한 검토를 실시하여 구조물의 특성에 부합하는 허용 균열폭의 범위내에 있는지 검토할 필요성이 있다. 본 연구에서는 번들형 강섬유의 최적의 혼입율에 따른 콘크리트 상판의 강도와 변형특성을 검토하였다. 이를 위하여 Shell 요소를 이용한 FEM해석과 RC단면을 대상으로 계산값과의 비교 검토를 실시하였다. 검토결과 강섬유 보강 SFRC상판은 종국하중은 RC상판의 약 1.2배 향상되었으며, 상판중앙지점의 단면 하부에서 발생되는 교축방향의 콘크리트 변형률은 교축직각방향(Ex)의 콘크리트가 항복에 도달하는 하중 797 kN시 교축방향의 콘크리트 변형률은 846 μ로 매우 작은 값을 나타낸다. 또한, 공시체를 RC단면으로서 전단면 유효와 중립축이하 콘크리트의 인장응력을 무시한 RC단면으로 계산한 계산치와는 탄성영역에서는 해석치와 거의 일치하고 있으며, 해석의 타당성을 확인할 수 있었다. Recently maintenance cost are increasing by aging social overhead capital and more efficient improvement is required. Normalization of improvement and performance of durability of structure is required. Also, durability improvement and normalization of performance of structure are required by development and practical use of new technology. For improvement of fatigue durability and punching shear ability of slab deck, concrete pavement construction that strengthen steel fiber in deck plate is examined. This study presented strength and deformation property of concrete deck slab considered optimum mixing rate of bundle style steel fiber. In order to investigate reinforcement effect, this paper did FEM analysis with shell element and compared the calculated value with analysis result. The result were as follows; SFRC deck plate did elastic behavior to 300 kN, reinforcement effect of steel fiber(SF) was less. But SFRC's perpendicular deflection occurred little about 23 ㎜ comparing with RC deck plate in load 870 kN at the ultimate strength of concrete. Stiffness was very improved by steel fiber reinforcement. Concrete strain of axis direction of bridge was 846 μ in ultimate strength.

누적손상을 고려한 강섬유보강 콘크리트의 피로파괴 특성

김동호 ( Kim Dong Ho ),홍창우 ( Hong Chang Woo ),이주형 ( Lee Ju Hyong ),이봉학 ( Lee Bong Hak ) 한국농공학회 2002 韓國農工學會誌 : 전원과 자원 Vol.44 No.2

Concrete containing discontinuous discrete steel fiber in a normal concrete is called steel fiber reinforced concrete(SFRC). Tensile as well as flexural strengths of concrete could be substantially increased by introducing closely spaced fibers which delay the onset of tension cracks and increase the tension strength of cracks. However, many properties of SFRC have not been investigated, especially properties on repeated loadings. Thus, the purposes of this dissertation is to study the flexural fatigue characteristics of SFRC considering cumulative damage. A series of experimental tests such as compressive strength, splitting tensile strength, flexural strength, flexural fatigue, and two steps stress level fatigue were conducted to clarify the basic properties and fatigue-related properties of SFRC. The main experimental variables were steel fiber fraction (0, 0.4, 0.7, 1, 1.5%), aspect ratio (60, 83). The principal results obtained through this study are as follows: The results of flexural fatigue tests showed that the flexural fatigue life of SFRC is approxmately 65% of ultimate strength, while that of plain is less than 58%. Especially, the behavior of flexural fatigue life shows excellent performance at 1.0% of steel-fiber volume fraction. The cumulative damage test of high-low two stress levels is within the value of 0.6 ∼ 1.1, while that of low-high stress steps is within the value of 2.4 ∼ 4.0.

Coupled Effect of Temperature and Strain Rate on Mechanical Properties of Steel Fiber‑Reinforced Concrete

Ruiyuan Huang,Shichao Li,Long Meng,Dong Jiang,Ping Li 한국콘크리트학회 2020 International Journal of Concrete Structures and M Vol.14 No.5

The dynamic mechanical properties of steel fiber-reinforced concrete (SFRC) under high temperature and high strain rate were studied using a split Hopkinson pressure bar (SHPB) of 74 mm in diameter. As it is difficult to achieve constant strain rate loading in SHPB experiments with high temperature and high strain rate, this paper first presents a method for determining the strain rate under non-constant strain rate loading conditions. This method is proposed to deal with experimental data under non-constant strain rate loading conditions. Then, the influences of temperature on the ultimate compressive strength, peak strain, and failure modes of SFRC under different strain rates were analyzed and the results show that SFRC has a strain rate hardening effect. This paper also points out that there is a strain rate threshold for SFRC. If the strain rate is less than the strain rate threshold, there is a temperature softening effect. Conversely, if the strain rate is greater than the strain rate threshold, there is a temperature hardening effect. Finally, the relationship between the ultimate compressive strength and fiber volume fraction, strain rate, and temperature is presented and the prediction results are consistent with the experimental data.

프리스트레스가 도입된 강섬유보강콘크리트의 균열면 전단거동

갈경완,황진하,이득행,김강수,최일섭 한국구조물진단유지관리공학회 2012 한국구조물진단유지관리공학회 논문집 Vol.16 No.1

일반적으로 콘크리트는 경제성이 뛰어나지만 낮은 인장강도로 인하여 구조성능상의 한계를 가지고 있기 때문에 콘크리트와 결합된 다양한 합성재료의 특성을 활용한 구조부재의 개발이 진행되고 있다. 강섬유 보강 콘크리트(SFRC)는 높은 인장강도로 인하여 콘크리트의 재료적 단점을 보완할 수 있는 우수한 합성재료로서 알려져 있고, 특히 고강도 콘크리트의 화재시 폭렬현상에 대한 대안으로 여겨지고 있다. 또한, 프리스트레스트콘크리트(PSC) 부재는 장경간 구조에 매우 유리하며 일반철근콘크리트(RC) 부재에 비해 높은 전단강도를 가진다. 따라서, 이 연구에서는 SFRC에 프리스트레스를 적용한 강섬유 보강 프리스트레스트 콘크리트(SFR-PSC)부재의 전단거동을 이해하기 위하여 총 22개의 직접전단실험체를 제작하여 실험을 수행하였다. 또한, 실험결과를 바탕으로 SFR-PSC부재의 균열면에서의 균열전달 구성방정식을 제안하였다. SFR-PSC의 거동특성을 반영하여 제안된 재료관계식은 실험결과와 잘 일치하는 것으로 나타났다. Although structural concrete is well known for its good economic efficiency, it has limits of structural performance due to the low tensile strength, for which new structural members utilizing various concrete composite materials have been developed. Steel Fiber-Reinforced Concrete(SFRC) has great tensile strength, which is the one of the excellent composite material to complement the weakness of concrete, and it is also considered as a good alternative to prevent the explosive failure of high strength concrete under fire. Also, prestressed concrete members are of great advantages to long span structures and have greater shear strength compared to conventional reinforced concrete members. In this research, thus, a total of 22 direct shear test specimens were fabricated and tested to understand the shear behavior of Steel Fiber-Reinforced Prestressed Concrete(SFR-PSC) members, in which SFRC members combined with prestressing method. Based on the test results, the constitutive equations of shear behavior at crack interfaces were proposed, which provided good estimation on the shear behavior of the SFR-PSC direct shear test specimens.

강섬유보강 콘크리트의 인장파괴메카니즘에 대한 이론연구

김규선,이차돈,심종성,최기봉,박제선 한국콘크리트학회 1993 콘크리트학회지 Vol.5 No.2

콘크리트내에 짧은 길이를 갖고 임의의 방향으로 배향된 강섬유는 콘크리트가 인장응력을 받을 때 일반콘크리트에 비하여 인장강도와 연성을 증가시키며 이는 콘크리트모체내 강섬유의 균열억제메카니즘에 기인한다. 본연구에서는 기존의 각기다른 spacing 개념들에 의하여 SFRC의 인장강도를 예측하고 정확한도를 실험치와 비교하여 평가하였는데 시험체의 경계조건 및 타설시의 진동으로 인한 콘크리트내 강섬유의 재향성을 고려한 단위면적당 섬유수(N1)개념이 실행결과와 가장 좋은 상관관계를 나타내었다. 또한 SFRC의 강도후 영역에 대한 이론적인 해석이 고려되었으며 본 해석은 시험체의 경계조건, 진동효과, 콘크리트모체와 강섬유의 강섬유의 접촉면의 비선형부착특성 고려 및 특히 위험단면에서 매입길이가 다른 각 강섬유의 적합조건을 고려하였다.

SFRC구조물의 휨거동에 관한 해석적 연구

서성탁(Seung-Tag Seo) 한국산업융합학회 2008 한국산업융합학회 논문집 Vol.11 No.1

Various characters of the concrete are greatly improved as the effect of the steel fiber. As the improvement effect of the steel fiber, the increment in flexural strength, shear strength, toughness, and impact strength are remarkable, and tenacious concrete is obtained. This paper presents model which can predict mechanical behavior of the structure according to aspect ratio and volume fraction of steel fiber. Experiments on compressive strength, elastic modulus and tensile strength were performed with self-made cylindrical specimens of variable aspect ratios. This paper presents an analytical study on the behavior of a beam specimen with steel fiber reinforced concrete(SFRC). The effect of the SFRC on the crack pattern, failure mode and the flexural behavior of the structure were investigated. The analysis model based on the nonlinear layered finite element method was successfully able to find the necessary amount of steel fibers, tensile steels and beam section which can best approximate flexural strength and ductility of a given conventionally reinforced concrete beam.

신경망 기법을 이용한 강섬유 혼입율, 형상비에 따른 압축강도 추정모형 개발

정태영,박주경 한국복합신소재구조학회 2018 복합신소재구조학회 학술발표회 Vol.2018 No.04

The contemporary high-tech structures have become enlarged and their functions more diversified. Steel concrete structure and composite material structures are not exceptions. Therefore, there have been on-going studies on fiber reinforcement materials to improve the characteristics of brittleness, bending and tension stress and others, the short-comings of existing concrete. In this study, the purpose is to develop the estimated model with dynamic characteristics following the steel fiber mixture rate and formation ration by using the nerve network in mixed steel fiber reinforced concrete (SFRC). This study took a look at the tendency of studies by collecting and analyzing the data of the advanced studies on SFRC, and facilitated it on the learning data required in the model development. In addition, by applying the diverse nerve network model and various algorithms to develop the optimal nerve network model appropriate to the dynamic characteristics. The accuracy of the developed nerve network model was compared with the experiment data value of other researchers not utilized as the learning data, the experiment data value undertaken in this study, and comparison made with the formulas proposed by the researchers. And, by analyzing the influence of learning data of nerve network model on the estimation result, the sensitivity of the forecasting system on the learning data of the nerve network is analyzed.