• Structural Monitoring and Maintenance
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• v.9 no.4
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• pp.373-388
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• 2022

A USW based diagnostic procedure is presented for estimating the depth of surface-breaking cracks. The diagnosis is demonstrated on seven lab-scale SFRC beam specimens, which are subjected to the CMOD controlled three-point bending test to create real bending cracks. Then, the recorded multiple ultrasonic signals are examined with the signal processing techniques, including wavelet transform and two-dimensional Fourier transform, to investigate the relationships between the crack depth and two diagnostic indices, namely the attenuation coefficient and dispersion index (DI). Finally, the reliabilities of these indices for depth estimation are verified with the visually measured crack depths as well as the crack features obtained with a digital image processing algorithm. It is found that the DI outperforms the attenuation coefficient in depth estimation, where this index displays good agreement with the visual inspection for 86% of the inspected specimens.

• Magazine of the Korea Concrete Institute
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• v.2 no.3
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• pp.65-72
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• 1990

Theoretical expressions were dcrived for the numher of fibers per unit cross-sectional area in fiber reinforced concrete, with due consideration given to the effects of the surrounding boundaries. The number of fibers per unit cross-sectional area in steel fiber reinforced concrete was also measured experimentally for the specimens incorporating various volume fractions of fibers of different types. Statistical evaluation of the measured value was then performed in order to assess the differences in fiber concentration at different location on tbe cross section. Degree of reorientation of steel fibers in concrete occuring during vibration was examined by com¬paring the differences in the computed and measur'ed values of the number of fibers per unit cross-sectional area.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.04a
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• pp.285-291
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• 1998

During recent years, the durability of concrete structures has been considered in concret practice and material research. To preserve the brittleness of concrete as well as energy absorption and impact resistance, amount of fiber usage has greatly increased in the field of public works. Ultra fine powder, silica fume, mixed into concrete, it reduce void of concrete structure. Especially, there's a great effect for strength improvement of concrete by initial pozzolanic reactions. For these reasons, if silica fume mixed into concrete, it decrease the total void by microfilter effect . Pozzolan reaction, between cement particle and silica powder, can elaborate the micro structure of matrix. And so, in this paper, we deal SFRC for the purpose of efficiently using of industrial by-products(silica fume). Also we performed the test for durability such as freeze-thaw resistance and accelerated carbonation of SFRC using silica fume.

• Journal of the Korea Concrete Institute
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• v.27 no.3
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• pp.215-227
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• 2015

In this study, twenty four steel-fiber reinforced concrete (SFRC) beams using recycled coarse aggregates (RCA) were manufactured to examine the shear behavior of SFRC and to determine the beams' ultimate shear strengths. The RCA replacement ratio was fixed at 30%. The variables studied in this investigation are: (1) shear span-to-depth ratios (a/d) of 2, 3 and 4; (2) longitudinal reinforcement ratio (${\rho}$) of 0.008 and 0.0127; and (3) steel fiber volume fractions ($V_f$) of 0, 0.5, 0.75 and 1%. Test results were analyzed and then compared with the findings and proposals of various other researchers. Based on the test results, the more steel fiber volume fraction is increased, the large crack resistance and shear strength are exhibited. Most of the experimental data is higher than the theoretical value. Therefore, steel-fiber reinforced concrete beams using recycled coarse aggregates are suggested to be applied for building structures.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.4
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• pp.155-164
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• 2011

In the case of impact loading test, measurement of the test data has difficulties due to fast loading velocity. In addition, the dynamic behaviors of specimens are distorted by ignoring local fracture. In this study, therefore, finite element analysis which considers local fracture and strain rate effect on impact load was performed by using LS-DYNA, an explicit analysis program. The one-way and two-way specimens strengthened with FRP Sheets and steel fibers were considered as analysis models. The results showed that the impact resistance of steel fiber reinforced concrete (SFRC) and ultra high performance concrete (UHPC) was enhanced. In the case of specimens strengthened with FRP Sheets, GFRP was superior to CFRP in the performance of impact resistance, and there was little effect of the FRP Sheet orientation. The reliability of this analysis model was verified by comparing with previous experimental results.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.6
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• pp.209-217
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• 2021

This paper investigates the effect of high strength hooked-end steel fiber content and aspect ratio on the compressive and flexural performance of concrete. A total of ten mixtures were prepared and tested. Concretes with specific compressive strength of 30 MPa were reinforced with three different aspect ratios (l/d) of steel fibers 64, 67, and 80 and three different percentages of steel fibers 0.25, 0.50, and 0.75% by volume of concrete. Tensile strengths of steel fibers with l/d of 64, 67, and 80 are 2,000, 2,400, and 2,100 MPa, respectively. The compressive and flexural properties of plain and steel fiber-reinforced concrete (SFRC) mixtures were evaluated and compared. The experimental results indicated that the incorporation of high-strength hooked-end steel fibers had significant effects on the compressive and flexural performance of concrete. With the increase of steel fiber content, compressive performances, such as Poisson's ratio and toughness, of concrete were improved. The steel fibers with the least l/d of 67 resulted in a larger enhancement of compressive performances. The residual flexural strength, that is, post-cracking flexural resistance and toughness, of concrete is mainly depended on the dosage and aspect ratio of steel fibers. The residual flexural strength at serviceability (SLS) and ultimate limit state (ULS) defined in fib Model Code 2010 (MC2010) is increased as the fiber content and aspect ratio increase.

• Computers and Concrete
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• v.8 no.1
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• pp.1-22
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• 2011

A numerical model that can simulate the nonlinear behavior of ultra high strength fiber-reinforced concrete (UHSFRC) structures subject to monotonic loadings is introduced. Since engineering material properties of UHSFRC are remarkably different from those of normal strength concrete and engineered cementitious composite, classification of the mechanical characteristics related to the biaxial behavior of UHSFRC, from the designation of the basic material properties such as the uniaxial stress-strain relationship of UHSFRC to consideration of the bond stress-slip between the reinforcement and surrounding concrete with fiber, is conducted in this paper in order to make possible accurate simulation of the cracking behavior in UHSFRC structures. Based on the concept of the equivalent uniaxial strain, constitutive relationships of UHSFRC are presented in the axes of orthotropy which coincide with the principal axes of the total strain and rotate according to the loading history. This paper introduces a criterion to simulate the tension-stiffening effect on the basis of the force equilibriums, compatibility conditions, and bond stress-slip relationship in an idealized axial member and its efficiency is validated by comparison with available experimental data. Finally, the applicability of the proposed numerical model is established through correlation studies between analytical and experimental results for idealized UHSFRC beams.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.6
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• pp.47-54
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• 2023

In this study, the tensile behavior of concrete specimens reinforced with GFRP (Glass Fiber Reinforced Polymer), BFRP (Basalt Fiber Reinforced Polymer), and CFRP (Carbon Fiber Reinforced Polymer) bars was experimentally analyzed. The tensile strength of the FRP bars is appeared to be similar to the design strength, but the elastic modulus was somewhat lower. Additionally, the specimens for tension stiffening effect were manufacured using OPC (Ordinary Portland Cement) and SFRC (Steel Fiber Reinforced Concrete), with dimensions of 150(W)×150(B)×1000(H) mm. The crack spacing of specimens was most significant for GFRP reinforcement bars, which have a lower elastic modulus and a smoother surface, while BFRP and CFRP bars, with somewhat rougher surfaces and higher elastic moduli, showed similar crack spacings. In the load-strain relationship, GFRP bars exhibited a relatively abrupt behavior after cracking, whereas BFRP and CFRP bars showed a more stable behavior after the cracking phase, maintaining a certain level of tension stiffening effect. The tension stiffening index was somewhat smaller as the diameter increased, and GFRP, compared to BFRP, showed a higher tension stiffening index.

• Structural Monitoring and Maintenance
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• v.7 no.3
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• pp.167-193
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• 2020

In this paper, the behavior of interior steel fiber reinforced concrete beam - column joints (BCJs) under cyclic loading is investigated. An experimental program including tests on twelve reinforced concrete (BCJs) specimens under cyclic loading was carried out. The test specimens are divided into two groups having different geometry: group (G1) (symmetrical BCJs specimens) and group (G2) (nonsymmetrical BCJs specimens). The parameters considered in this study are the steel fibers (SFs) content by volume of concrete (V_f), the spacing of shear reinforcement at the joint region, and the area of longitudinal flexural reinforcement. Test results show that the addition of 0.5% SFs with stirrups spacing S=S_max has effectively enhanced the overall performance of BCJs with respect to energy dissipation, ductility ratio, spreading and width of cracks. The failure of specimens is governed mainly by the formation of a plastic hinge at the face column and outside the beam-column junction. Secondary shear cracks were also observed in the beam-column junctions.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.5
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• pp.110-118
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• 2010

This research dealt with the effect of steel-fiber reinforcement on the compressive strength of ultra high performance cementitious composites (UHPCC) and compared with that in normal steel-fiber reinforced concrete(SFRC). With wide range of compressive strength of UHPCC, experiments on the fiber reinforcement effect confirmed that the compressive strength in UHPCC is also improved by adding fibers as in normal SFRC. The experimental results were compared with previous researches about reinforcement effect by adding fibers, which are limited within 100MPa compressive strength. The comparison revealed the linear relationship between $f'_{cf}-f'_c$ and RI regardless of the magnitude of compressive strength, from which a general equation to express the effect of fiber reinforcement, applicable to various SFRC's with wide range of compressive strength including UHPCC.