Steel Fiber Ratio Research Articles

Pull-out behavior of single steel fiber from SIFCON matrix

Slurry Infiltrated Fiber Concrete (SIFCON) is a special type of steel fiber-reinforced cement composite which has superior mechanical properties such as compressive, tensile, shear and flexural strengths with extraordinary toughness values. In this experimental study, the effect of mix proportions of SIFCON matrix (slurry), curing conditions, aspect ratio of steel fiber, embedded length and fiber type on the single fiber pull-out behavior from SIFCON matrix was investigated. Test results indicated that fiber type, embedded length of fiber, curing conditions, fiber end condition, and matrix strength has a considerable effect on fiber–matrix bond. Increasing the diameter of the fiber and improving the curing conditions increased matrix–fiber bond. In addition, increasing bond strength was observed with increasing strength of SIFCON matrix. The pull-out toughness increased by increasing embedded length of fiber. It has been observed that hooked end fibers have shown better interface bond compared to the smooth fibers.

Experimental Study on Shear Behavior of Hybrid Fiber Reinforced High Performance Concrete Deep Beams

In order to investigate the effect of steel fiber and polypropylene fiber on shear behavior of HPC deep beams, the shear tests were conducted on 18 different groups of deep beams with steel fiber and polypropylene fiber and 2 groups of HPC deep beams without fiber according to the orthogonal experiment. 6 factors, including the shape of steel fiber, the volume fraction of steel fiber, the aspect ratio of steel fiber, the volume fraction of polypropylene fiber, the ratio of web horizontal reinforcement and the ratio of web vertical reinforcement, were compared by direct-viewing analysis. Results illuminate that hybrid fibers greatly increase the diagonal cracking strength and shear strength of HPC deep beams. The aspect ratio of steel fiber plays the most important role in diagonal cracking strength whereas the ratio of web vertical reinforcement has minimum effect. Meanwhile the ratio of web horizontal reinforcement plays the most important role in shear strength whereas the volume fraction of polypropylene fiber has minimum effect. An anti-cracking capacity for inclined section calculation formula and a shear bearing capacity calculation formula for hybrid fiber reinforced HPC deep beams are put forward based on current code. Meantime test verification is carried out and the calculated results are satisfied.

An Experimental Study on the Fire Resistance Performance and Spalling of 100MPa HSC Column Mixed with Fiber-Cocktail

As the fire-resistance performance of high-strength concrete has emerged as a social issue and Korean Ministry of Land, Transport & Maritime Affairs has announced the standard for the fire-resistance performance of the concrete, studies to improve its fire-resistance have been conducted actively. In this paper, the study to develop high-strength concrete mixed with fiber-cocktail, a hybrid of polypropylene fiber and steel fiber was conducted. The fire-resistance test of 100MPa high-strength concrete and the analysis of steel bar temperatures for finding the optimal cross-sectional condition showed that the larger the section size is, the lower the temperature of steel bars is. It was also shown that the concrete columns with section sizes of 600mm x 600mm and 800mm x 800mm secure fire-resistance performance and the former is the optimal section size in terms of economic efficiency. The analysis of steel bar temperatures of the column having section size of 600mm x 600mm showed that the polypropylene fiber to steel fiber ratio of 1.5 to 40 (㎏/㎥) is the optimal for the fiber cocktail.

반복하중을 받는 강섬유 보강 철근콘크리트 외부 접합부의 거동 특성

횡보강근이 적게 포함된 보통강도 철근콘크리트 보-기둥 접합부에서 강섬유의 보강효과에 관한 실험적 연구를 진행하였다. 이를 규명하기 위해 총 10개의 접합부 실험체를 제작하였으며, 접합부 횡보강근량과 강섬유 혼입률(Vf = 0%, 1%, 1.5%)을 주요변수로 실험하였다. 실험은 총 19싸이클의 반복주기하중의 형태로 가력되었으며 각 싸이클의 반복회수는 2싸이클씩 준정적 지진하중의 형태로 적용되었다. 실험 결과를 통해 보통 강도 철근콘크리트 보-기둥 접합부에 강섬유를 보강함으로써 횡보강근 감소에 따른 피해정도를 어느 정도 줄일 수 있다는 결론을 얻었고, 또한 강섬유 보강으로 접합부 전단강도를 증가시킬 수 있고 동시에 에너지소산능력을 향상시킬 수 있다는 결론을 도출하였다. 보다 정량적인 평가를 위해 이 연구의 시험체들과 기존의 보-기둥 접합부 RC 시험체들에서 측정된 최대 접합부 전단강도값과 ACI 352R-02의 설계기준식, Jiuru et al.의 제안식, 그리고 Kim et al.의 제안식을 비교·분석하였다. 이러한 분석 결과 Jiuru et al.의 전단강도 제안식이 실험 결과를 과대평가하는데 반해 Kim et al.의 전단강도 제안식은 모든 시험체에 대해 안정적인 결과와 적은 오차범위를 나타내었다. 따라서, 이 연구를 바탕으로 해서 적절한 접합부 배근상세와 함께 강섬유 보강 철근콘크리트 보-기둥 접합부에 대한 추가적인 연구가 진행된다면, 횡보강근의 감소를 통한 시공의 어려움 해소 및 내진성능의 향상이 가능할 것으로 판단된다.

Flexural Behavior of Steel Fibrous Reinforced Concrete Deep Beams

Experimental research was carried out regarding the flexural behavior of deep beams cast with plain and fibrous concrete with hooked steel fibers, and subjected to monotonic vertical loads. Four deep fiber-reinforced concrete beams were cast. Two of them were made of plain concrete with main and web steel reinforcements (RC), and two were made of hooked steel fiber-reinforced concrete (SFRC) with main steel reinforcements. The experimental results show the brittle behavior of reinforced deep RC members characterized by crushing of concrete struts and fracture of web steel bars. SFRC deep beams exhibit higher strength and, above all, ductility with respect to RC members due to the bridging actions of fibers across main and secondary cracks. From the analytical point of view, a softened strut-and-tie macromodel able to reproduce the flexural behavior (in terms of multilinear load-deflection curves) of deep beams in plain and fibrous concrete and with the presence of horizontal steel bars, including softening of compressed struts and yielding of steel bars, is presented. The model is able to take into account the tensile behavior of main bars embedded in the surrounding concrete and the softening of the compressed strut, the arrangement and percentage of the steel bars, and the percentage and aspect ratio of steel fibers. The experimental results obtained here and those available in the literature are compared with the results obtained through the proposed model and with the other models given in the literature, showing good agreement. Finally, a validation of the proposed model is made numerically by using a nonlinear finite-element program (ATENA-2D) able to analyze the flexural behavior of deep members.

Strength Development, Toughness and Fire Resistive Performance of 150 to 200N/mm2 Super-High Strength, High Performance Concrete

Super high strength concrete with compressive strength of 150 to 200N/mm2 using hybrid fiber reinforcement of organic and steel fiber was developed. Properties of fluidity of fresh concrete and effect of curing condition on strength development were studied. Viscosity of fresh concrete was significantly reduced by newly developed Maleate polycarboxylate-based superplasticizer. Strength development of high strength concrete was enhanced by high temperature steam curing. Hybrid fiber reinforcement was effective to improve toughness and fire resistance of super high strength concrete. The higher the aspect ratio and tensile strength of steel fiber, the higher the toughness of concrete became. Hybrid fiber reinforcement enables to reduce spalling and to maintain fire resistance for 3 hours in super high strength concrete columns.

Study on the Influence Factors of Bearing Capacity of the Fiber Reinforced High Strength Concrete Three-Pile Caps

Based on the experiments of 10 model specimens of fiber reinforced high strength concrete three-pile caps with the dimension of 831mm×831mm×831mm, the mechanical behavior and the important factors on the cracking load and ultimate bearing capacity of fiber reinforced high strength concrete three-pile caps were researched. The study indicates that with increasing of concrete strength, the volume fraction of steel fiber, the effective thickness and reinforcement ratio of pile cap, the bearing capacity of three-pile caps improves largely. At the same time the type of steel fiber and steel ratio have remarkable effects on the bearing capacity. The results are valuable for establishing bearing capacity calculation formulas of fiber reinforced high strength concrete three-pile caps and improving “the Technical Specification for fiber Reinforced Concrete Structure.”

Synergetic effect of steel fibers and shear-reinforcing bars on the shear-resistance mechanisms of RC linear members

Reinforced concrete with steel fibers (RSF) is one type of a hybrid structure that can improve the shear-load capacity of conventional reinforced concrete (RC) structures. This paper studies the synergetic effect of shear-reinforcing bars and steel fibers on the shear-resistance of RSF beams and columns, based on the shape and the distribution of diagonal cracks. A series of bending and lateral cyclic-loading tests were conducted to consider the effect of loading and support conditions on the shear-resistance mechanism. As a result, the optimum ratio of steel fibers to shear-reinforcing bars for the shear-load capacity is determined for the RSF linear members.

Cracking resistance performance of super vertical-distance pumped SFRC

The mix ratio of steel fiber reinforced concrete (SFRC) was optimized using the principles that workability must meet the pumping demand and anti-cracking performance should be optimal. The effect of SFRC on the initial cracking load, the ultimate load and the crack width of the reinforced concrete (RC) member were analyzed in this paper. It was found that the admixture had good preservation of moisture and adhesion and the fibers distributed homogeneously in one hour out of the machine. According to the pumping results, the SFRC could be pumped vertically up to 306 m. Based on the standard computation formula of cracks, the maximum crack width of an RC member with 0.8% steel fiber (by volume) is about 32% lower than that of standard RC member. Through an experimental research on full-scale model tests for the steel and concrete composite anchorage zone on a pylon, the SFRC not only remarkably increases the crack resistance and the ultimate load, but the initial load also improves 33%a pproximately. It is also indicated that plastic shrinkage cracking of SFRC in which volume fraction of steel fibers is 0.8% can be restrained obviously and the unrestrained drying shrinkage can be diminished by about 50% at early age. The results confirmed that the SFRC can lessen the shrinkage crack of concrete and enhance markedly the direct tensile strength. Therefore, the SFRC can solve the key question of crack resistance for the anchorage zone of a bridge tower.

Lateral load response of steel fiber reinforced concrete model piles in cohesionless soil

It has been long recognized that piles could be damaged under major lateral loading environments. Precautions such as increasing pile dimensions or reinforcement to avoid damages were often proved to be inadequate for satisfactory pile design especially against heavy lateral loads. This fact necessitated research for piles that are more resistant to lateral forces. Recent debate for better lateral load performance has been about the design and construction of ductile piles. In this respect, steel fiber reinforced concrete (SFRC) can be considered as a contemporary material being able to provide desired additional ductility to conventional reinforced concrete (RC) piles. The lateral load carrying mechanisms of SFRC piles and their interaction with surrounding soil have not been fully studied yet. In this study an investigation for lateral load carrying capacity of SFRC piles in cohesionless soils has been undertaken. A model study involving instrumented model piles, a testing pool and a monotonic loading mechanism has been planned and pursued. Three different steel fiber ratios by volume were utilized in the production of model piles. Performances of these piles were compared with that of the conventional concrete pile. The goal was to observe the influence of steel fibers on ductile pile behavior by isolating them from other reinforcement components (i.e. bending and shear reinforcement). It has been found that SFRC model piles with steel fiber reinforcement ratios of 1% and 1.5% are capable of providing more ductility and higher lateral load carrying capacity while taking lower bending moments compared with the concrete model pile.

The effects of stirrups and the extents of regions used SFRC in exterior beam-column joints

Seven full-scale exterior beam-column joints were produced and tested under reversible cyclic loads to determine. Two of these seven specimens were produced using ordinary reinforced concrete (RC). Steel Fiber Reinforced Concrete (SFRC) was placed in three different regions of the beams of the rest five specimens to determine the extent of the region where SFRC is the most effective. The extent of the region of SFRC was kept constant at the columns of all five specimens. Three of these five specimens which had one stirrup in the joint, were tested to evaluate the effect of the stirrup on the behavior of the beam-column joint together with SFRC. In production of the specimens with SFRC, all special requirements of the Turkish Earthquake Code related to the spacing of hoops were disregarded. Previous researches reported in the literature indicate that the fiber type, the volume content, and the aspect ratio of steel fibers affect the behavior of beam-column joints produced with SFRC. The results of the present investigation show that the behavior of exterior beam-column joints depends on the extent of the region where SFRC is used and the usage of stirrup in the joint, in addition to the parameters listed in the literature.

Behavior of high-strength fibrous concrete slab–column connections under gravity and lateral loads

Ten slab–column connections were tested under combinations of gravity and lateral loads to investigate the effect of adding steel fibers to concrete mix on the structural behavior of normal- and high-strength slab–column connections. The variables selected for this study were the strength of concrete, volumetric ratio of steel fibers, type of steel fibers, and moment to shear ratio. The test specimens consisted of two identical series. The first series constructed with normal-strength concrete with a cube compressive strength of about 28 MPa, and designated as NSC. The second series constructed with high-strength concrete with cube compressive strength of about 75 MPa were designated as HSC. Each series consisted of three specimens with steel fibers and were tested under gravity load and unbalanced moment, and two control specimens; one was tested under gravity load only, while the other was tested under pure moment. The addition of steel fibers does significantly enhance the performance of the tested slab; it improves the shear strength, increases the ductility due to deflection and rotation, yields greater stiffness, and smaller cracks widths. Further improvement was also obtained when larger aspect ratio was used. Test results showed that the high-strength concrete specimens had larger shear strength, displacement and rotation ductility ratios, and corresponding energy absorption, than the normal-strength specimens by about 7–21%, 11–64%, 106–123%, 48–150%, and 93–246%, respectively. Incorporating steel fibers with high-strength concrete improved the overall deformation characteristics of the tested specimens and resulted in less sudden and more gradual failure mode.

Thermo-mechanical properties of fiber reinforced raw perlite concrete

The effect of hooked steel, wavy steel and polypropylene fibers on the thermo-mechanical properties of raw perlite aggregate concrete was investigated. In order to determine the effect of fiber ratio on the thermo-mechanical properties of 100% raw perlite concrete, 0.25%, 0.75%, 1.25%, and 1.75% fiber ratios were used by volume of the sample and also, 350 kg/m 3 cement dosage and 3 ± 1 cm slump were used. When compared to the control sample that contains no fiber, (1) with the increase of steel fiber ratio in the mixtures thermal conductivity (TC), unit weight, splitting-tensile strength, and flexural strength of concretes increased, (2) with the increase of steel fiber ratio in the mixtures compressive strength of concretes decreased, and (3) with the increase of polypropylene fiber ratio in the mixtures TC, unit weight, compressive strength, splitting-tensile strength, and flexural strength of concretes decreased.

Seismic Behavior of 200 MPa Ultra-High-Strength Steel-Fiber Reinforced Concrete Columns under Varying Axial Load

Cyclic loading tests were carried out on ultra-high strength RC columns under high axial load conditions. Effective concrete strength of 200 MPa with high-strength steel fibers (SF) was used. The investigated parameters were: 1) volumetric ratio of steel fiber, 2) lateral reinforcement ratio, and 3) axial loading type. The main characteristics of the tested columns (maximum strength, deformation capacity and equivalent viscous damping factor) are presented and the influence of various parameters is discussed. The test results revealed the advantage of using SF in terms of strength and damage control. The maximum strength of the tested columns using SF, assessed using a number of different formulas, proved to be on the safe side. On the other hand, in the case of columns in which SF was not used, the estimated maximum strength was found to be larger than the tested value, except when using NZS3101 equation. This difference is probably due to early spalling off of the cover concrete.

Effect of aspect ratio and volume fraction of steel fiber on the mechanical properties of SFRC

In this study, effects of aspect ratio ( l/ d) and volume fraction ( V f) of steel fiber on the compressive strength, split tensile strength, flexural strength and ultrasonic pulse velocity of steel fiber reinforced concrete (SFRC) were investigated. For this purpose, hooked-end bundled steel fibers with three different l/ d ratios of 45, 65 and 80 were used. Three different fiber volumes were added to concrete mixes at 0.5%, 1.0% and 1.5% by volume of concrete. Ten different concrete mixes were prepared. After 28 days of curing, compressive, split and flexural strength as well as ultrasonic pulse velocity were determined. It was found that, inclusion of steel fibers significantly affect the split tensile and flexural strength of concrete accordance with l/ d ratio and V f. Besides, mathematical expressions were developed to estimate the compressive, flexural and split tensile strength of SFRCs regarding l/ d ratio and V f of steel fibers.

Effect of steel fibers on the mechanical properties of natural lightweight aggregate concrete

In this study, the effect of steel fibers on the mechanical properties of pumice aggregate concrete was investigated. In order to determine the effect of steel fiber ratio on the mechanical properties of concrete, (1) 25%, 50%, 75%, and 100% pumice ratios were used instead of natural aggregate by volume, (2) 0.5%, 1.0%, and 1.5% steel fiber ratios were used by volume of the sample and (3) also, 300 kg/m3 cement dosage and 3±0.5 cm slump were used. The test results showed that the increasing pumice aggregate ratio decreased the unit weight and the mechanical properties of the concretes. When compared to the control sample that contains no fiber, with the increase of steel fiber ratio in the mixtures unit weight, compressive strength, splitting-tensile strength and flexural strength of concretes increased up to 8.5%, 21.1%, 61.2% and 120.2%, respectively. Moduli of elasticity and deformation capability were decreased with increase of pumice aggregate and steel fiber ratio in the mixture.

Cracking behaviour of concrete beams reinforced with a combination of ordinary reinforcement and steel fibers

The paper presents an experimental and theoretical study on the cracking behaviour of concrete beams having longitudinal tension reinforcement and various combinations of volume and aspect ratio of steel fibers. Five full-scale beams with a concrete compressive strength of 42 MPa were tested. The mechanical properties of the steel fiber concrete under tension were determined by means of the four-point bending test specified in the Belgian standard NBN B15-238. The experimental results show that the addition of steel fibers decreases both the crack spacing and the crack width. A modification of the model of Nemegeeret al. to predict crack widths is suggested.

Production and Electromagnetic Shielding Effectiveness of the Knitted Stainless Steel/Polyester Fabrics

This paper describes a study on the development of stainless steel/polyester knitted fabrics for electromagnetic shielding applications. To facilitate knitting of stainless steel wires and to reduce the material cost, initially blended yarns of staple stainless steel and polyester fibers were fabricated by using the ring and open-end friction spinning methods. The stainless steel/polyester produced by ring and open-end friction spinning methods, and their knitted fabrics made from 14G flat knitting machine were developed successfully. Using a coaxial transmission line holder set-up, the electromagnetic shielding effectiveness (EMSE) of various knitted fabrics was carried out in the frequency range from 30kHz to 3000MHz. The variations of EMSE with the knitted structures, yarn type, and the blend ratio of stainless steel fiber and wire to the polyester fiber in the yarns are discussed. The results indicate that the proposed knitted fabric having higher EMSE can be used for the purpose of EMI shielding, as well as for some electronic and electrical applications.

Effect of silica fume and steel fibers on some properties of high-strength concrete

The main disadvantage of high-strength concrete is its highly brittle behavior and this can beovercome by adding fibers to the concrete. This would also improve some other mechanical properties of high-strength concrete such as tensile strength and compressive strength. These properties are not very well established for high-strength steel-fiber reinforced concrete (HSFRC) yet. In this study the influence of silica fume on the properties of HSFRC were investigated by using silica fume of two different percentages and three different hooked-end fibers namely, 30/0.50, 60/0.80 and 50/0.60 length/diameter (mm/mm). Fibers were added to concrete in three different volume percentages of 0.5, 1.0 and 2.0 by volume of concrete. The results indicated that there is a linear function between splitting tensile strength ( F splt) and volume percentage of fibers ( V f) [i.e. F plt = A( V f) + B, where A and B are correlation coefficients] as well as between splitting tensile strength ( F splt) and compressive strength ( F c) of plain series A concrete [i.e. F splt = C (√ F c) + D, where C and D are correlation coefficients]. These relations can describe the development of splitting tensile strength of HSFRC containing no silica fume, 5% silica fume and 10% silica fume by weight of cement. On the other hand, although silica fume has an effect on compressive strength, volume percentage and aspect ratio of steel fibers has little effect.

鋼繊維補強コンクリートの力学パラメータに及ぼす調合因子の相互作用の定量分析

For the purpose with apllying steel fiber reinforced concrete (SFRC) to structural components, it is an important subject to establish and connect each other designs of mix proportion, material characteristics and component section, respectively for good workability, necessary mechanical properties and required component performance of SFRC. In this paper, in order to establish a material design of SFRC, experimental investigations were conducted by compression, tension and fracture toughness testings for a sines of SFRC specimens with manufactured under various mix proportions. From the experimental results, quantitative analyses were performed concerning interactions among aspect ratio of steel fiber, fiber volume fraction and cement-water ratio on mechanical parameters of SFRC.