Steel Fiber Volume Fraction Research Articles

Enhancing the flexural load capacity of the reinforced concrete beams using Dramix 3D 80/60 BG steel fibres

The purpose of this study was to investigate the effect of adding Dramix 3D 80/60 BG steel fibres to the reinforced concrete beams experimentally. The main specimens were 6 reinforced concrete beams (dimension of 150 x 180 x 1700 mm) with a variety of the flexural reinforcement (i.e. 2D6, 2D10 and 3D10) and the fibre volume fraction (i.e. 0%, 0.5%, 1% and 1.5%). The concrete compressive strength was 25 MPa, no superplasticizer was added in the concrete mix. The test set-up of the beam specimen is, the beam was simply supports at the distance of 1500mm, 2 concentrated loads gradually were applied until it collapses. During applying the loads, measurements were taken including the deflection in the mid-span of the beam, the crack propagation and crack width. The results showed that the increase of fibre content will increase the load capacity and stiffness without reducing the ductility of the reinforced concrete beams. The steel fibre volume fraction of 1% is the maximum content that can be used without using superplasticizer to maintain the workability of the fresh concrete. The addition of 0.5% steel fibre provides a similar flexural performance to the addition of one D10 (flexural reinforcement) in a reinforced concrete beam.

Mechanical properties and constitutive model of steel fiber-reinforced rubberized concrete

This study aims to assess the mechanical behavior of steel fiber-reinforced rubberized concrete (SFR-RuC) with and without mix optimization through experimental investigations, and eighteen concrete mixtures were manufactured for test specimens. Through mix optimization, SFR-RuC with a steel fiber volume fraction no more than 1.5% and a rubber particle volume substitution as high as 20% could successfully achieve a compressive strength of 49 MPa-56 MPa. Cubic and uniaxial compressive tests, direct shear tests and four-point flexure tests were conducted on all specimens. The results showed that optimized SFR-RuC had overall improved mechanical properties and more ductile failure than nature concrete, and the elastic modulus and compressive, flexural and shear strength were enhanced by 13%, 16%, 25% and 50% respectively, when 10% rubber particles and 1.5% steel fibers were added. The peak strain, toughness and post-peak deformation of optimized SFR-RuC under compression increased with the steel fiber volume fraction as well as the rubber particle volume substitution, while the peak deflection, toughness and ductility under flexure and shear increased mainly with the steel fiber volume fraction. An obvious synergistic action was shown between the rubber particles and the steel fibers, through Scanning Electron Microscope (SEM) analyses on the microstructure, as well as test observations on the failure mechanism of specimens. Based on uniaxial compressive test results, formulas were proposed for the compressive strength, elastic modulus and peak strain of optimized SFR-RuC, and a modified stress–strain model was developed based on the classical concrete stress–strain model in the Chinese code (GB50010-2010), for a detailed assessment of the complete stress–strain response.

Investigation on mechanical behaviors of a new sustainable composite material for fiber-reinforced recycled aggregate concrete under compressive low-cycle loadings

Recycled aggregate concrete (RAC) has been attracting worldwide research and development interests due to its ecological and economic significance. In this investigation, the steel fiber (SF) and polypropylene fiber (PPF) were mixed into the recycled aggregate concrete (RAC) to improve the mechanical properties. Based on the cyclic compressive loading tests, the variation of the strength and deformation of fiber-reinforced recycled aggregate concrete (FRAC) was explored, and the optimum design method of fiber content for FRAC was proposed. The calculation models for fiber influence factors (FIFs) of the peak stress, peak strain, ultimate strain, and the post-peak modulus were put forward, respectively. The optimum volume fractions of SF and PPF for RAC were recommended, which are 1.7% and 2.27%, respectively. This study provides technical support and a theoretical basis for the promotion of recycled aggregate concrete material and structure.

Impact resistance of porosity-free fiber-reinforced concrete (PFFRC) beams under low-velocity impact loading

Ultrahigh-performance fiber-reinforced concrete (UHPFRC) is an advanced cement-based composite material. Its ultrahigh compressive strength and high ductility can enable the downsizing of structural members, with special application to high-rise buildings. These excellent mechanical properties also allow its application in protective structures to resist high-speed penetration, low-velocity impact, and blast loading. UHPFRC with a compressive strength of approximately 150–200 MPa has traditionally been used to investigate the impact resistance of structural members under low-velocity impact loading. Recently, however, porosity-free concrete of the 400 MPa class of compressive strength has been developed. In this paper, to investigate the effects of the concrete strength and the steel fiber volume fraction on the impact resistance of porosity-free fiber-reinforced concrete (PFFRC) members, static and drop-weight impact loading tests were conducted on PFFRC beams by varying the volume fraction of steel fiber from 1 to 3.5%. As reference beams, 90 MPa high-strength fiber-reinforced concrete (HSFRC) beams with a 2% fiber volume fraction and normal-strength concrete (NSC) beams without stirrups and steel fibers were also tested. The results obtained from this study were as follows: (1) the static load-carrying capacity of a PFFRC beam can be enhanced by more than two and three times that of an NSC beam by adding 1 and 3.5% volume fractions of steel fiber, respectively; (2) a PFFRC beam with 3.5% fiber had the greatest impact resistance of all the beams considered in this study, and the beam with 2% fiber volume had the second-greatest performance, but the difference was small; (3) even though an HSFRC beam with 2% fiber had a smaller static load-carrying capacity than a PFFRC beam with 1% fiber, the former exhibited a slightly greater impact resistance than the latter because the bridging effect of the steel fibers has a greater influence under impact loading than under static loading.

Shear strength of steel fibrous concrete beams strengthened by CFRP using various techniques

In recent years, carbon fiber-reinforced polymers (CFRP) have been widely used as the strengtheners in reinforced concrete members. This paper is an experimental study on steel fiber-reinforced concrete (SFRC) beam specimens strengthened by CFRP against shear than using externally bound reinforcement (EBR) and externally bound reinforcement on grooves (EBROG). Sixteen concrete beams with dimensions of 110 mm width, 150 mm depth, and 1300 mm length were tested to assess the effect of steel fibers and to evaluate the effects of grooving techniques in terms of improving the shear capacities of SFRC beams strengthened by CFRP. The beams were designed to fail via a shear failure mode. Five volume fractions of steel fibers were used: 0.0%, 0.8%, 1.5%, 1.5%* and 2%. The beams are tested under four-point loading with two values of shear span-to-depth (a/d) ratios, which were 2.2 and 2.85. The results show that the shear strength and the ductility increase with increasing fiber volume fraction, and that the load-carrying capacity of SFRC beams increased by 33% to 68% compared to the load-carrying capacity of the control beam (without steel fibers). Also, the test results show that strengthening beams using CFRP sheets enhanced the strength and stiffness of the tested beam specimens. The increase in the load-carrying capacity of SFRC beam strengthened by CFRP sheet using the EBR method was 79%, while the increase in the load-carrying capacity of SFRC beams strengthened by CFRP sheet using the EBROG method ranged from 89% to 110% compared to the control beam. Furthermore, the results show that the shape of the grooves influenced the capacity and the failure mode of the tested beams. Finally, it may be noted that the grooving method has a significant effect on the load-carrying capacity and failure mode in comparison with the EBR method.

Tension-softening behavior of UHPFRC based on fracture energy

In this study, a three-point bending test is performed on an ultra-high-performance fiber-reinforced concrete (UHPFRC) to determine its tensile performance based on the volume fraction of steel fibers (vf) and member depth as test variables. Based on the bending test results, the overall tensile behavior (σ-ε relationship) of each specimen is derived from an inverse analysis and optimization using a genetic algorithm, and changes in the behavior are analyzed comprehensively based on key variables. In addition, evaluation factors (η1 and η2) that can quantitatively represent the contribution of steel fibers on the fracture energy of the UHPFRC are proposed based on a comparative analysis between fracture energies calculated using the σ-ε relationship and conventional fracture energies. For specimens in which vf is less than 2%, the fracture energy enhanced by steel fibers decreases as the member depth increases, and the values of the evaluation factors (η1 and η2) are maximum at vf 2.0%

Shear strength prediction method of the UHPC keyed dry joint considering the bridging effect of steel fibers

The joints between segments of the precast ultra-high performance concrete (UHPC) segmental bridge (PUSB), which transmit compressive and shear stresses, require special attention in design. The shear strength of these joints is significantly improved in comparison with that of normal strength concrete (NSC) joints due to the excellent mechanical properties of UHPC. Nevertheless, little attention has been paid to predict the shear capacity of UHPC joints directly considering the shear contribution of steel fibers. This paper develops a new shear strength model for UHPC-keyed dry joints incorporating transferring mechanisms of three primary shear component based on previous experimental results and numerical simulation. Based on the modified compression-field theory, the shear contribution by the matrix in UHPC keys is mainly influenced by normal compressive stress and area of all bases of keys. Based on the mesoscale fiber–matrix discrete model, the shear contribution by steel fibers was affected by the steel fiber length, diameter, type, and volume fraction. To obtain more accurate prediction results, a reduction coefficient was utilized for UHPC multi-keyed dry joints in the proposed shear strength formula on grounds of regression analysis. The reliability and accuracy of these results were then verified by experimental results of 27 push-off tests available, with mean and standard deviations between the predicted and experimental shear strength of 0.98 and 0.27, respectively. Thus, the proposed formula can be used to predict the shear strength of UHPC dry joints with single and multiple shear keys.

Flexural behavior analysis and strength prediction of steel fiber-and-nanosilica reinforced rubber concrete

In this study, a series of experiments were conducted to investigate the effects of the hook-shaped steel fiber (SF) and nanosilica (NS) on the flexural properties of the rubber concrete (RC), and the modification mechanisms of the NS on the flexural properties of steel fiber-and-nanosilica reinforced rubber concrete (SFNS-RC) were also revealed by using the X-ray diffraction (XRD) and scanning electron microscope. Based on the RC specimen with a rubber content of 5%, the experimental variables included the SF volume fractions (0%, 0.5%, 1.0%, and 1.5%) and NS replacement ratios (0%, 1%, and 2%). The results indicated that the NS could improve the microstructure of the RC, the peaks of Ca(OH)2, C3S, and C2S steadily reduced as the NS replacement ratio increased, respectively, and the microstructure of SFNS-RC became more compact and uniform because the NS could produce pozzolanic activity to fill the pores of the matrix and strengthen the bond behavior between the SF and matrix. In addition, the RC specimens containing the SF and NS displayed the excellent flexural behaviors, including the ductility and energy dissipation characteristics. Finally, the empirical formulae for predicting the first-peak flexural strength and peak flexural strength of SFNS-RC were proposed through the analysis of experimental data, respectively.

Shear Response of Recycled Aggregates Concrete Deep Beams Containing Steel Fibers and Web Openings

Replacement of natural aggregates (NAs) with recycled concrete aggregates (RCAs) in complex reinforced concrete (RC) structural elements, such as deep beams with openings, supports environmental sustainability in the construction industry. This research investigates the shear response of RC deep beams with openings made with 100% RCAs. It also examines the effectiveness of using steel fibers as a replacement to the minimum conventional steel stirrups in RCA-based deep beams with web openings. A total of seven RC deep beams with a shear span-to-depth ratio (a/h) of 0.8 were constructed and tested. A circular opening with an opening height-to-depth ratio (h0/h) of 0.3 was placed in the middle of each shear span. Test parameters included the type of the coarse aggregate (NAs and RCAs), steel fiber volume fraction (vf = 1, 2, and 3%), and presence of the minimum conventional steel stirrups. The deep beam specimens with web openings made with 100% RCAs exhibited 13 to 18% reductions in the shear capacity relative to those of their counterparts made with NAs. The inclusion of conventional steel stirrups in RC deep beams with openings was less effective in improving the shear response when 100% RCAs was used. The addition of steel fibers remarkably improved the shear response of the tested RCA-based beams. The gain in the shear capacity of the RCA-based beams caused by the inclusion of steel fibers was in the range of 39 to 84%, whereas the use of conventional steel stirrups resulted in 18% strength gain. The use of 1% steel fiber volume fraction in the RCA-based beam with openings without steel stirrups was sufficient to restore 96% of the original shear capacity of the NA-based beam with conventional steel stirrups. The shear capacities obtained from the tests were compared with predictions of published analytical models. The predicted-to-measured shear capacity was in the range of 0.71 to 1.49.

Shear behavior analysis and capacity prediction for the steel fiber reinforced concrete beam with recycled fine aggregate and recycled coarse aggregate

This paper mainly studies the shear behavior of steel fiber reinforced concrete beams with recycled fine aggregate and recycled coarse aggregate. A total of thirteen beams with 150 mm width, 300 mm height, and 3000 mm length were tested under four-point bending. The shear span-to-depth ratio was kept the constant of 2. The spacing of stirrups was 150 mm, 200 mm, and 250 mm, respectively. The recycled fine aggregate and recycled coarse aggregate obtained from building demolition waste were introduced in the concrete mixes with the replacement ratio of 0%, 50%, and 100%, the steel fiber volume fractions in the beams were 0%, 0.5%, 1.0%, and 1.5%, respectively. The shear capacity, the mid-span deflection, and the stirrups strain were measured in this test. The results indicated that the shear capacity of the concrete beam with recycled aggregate and steel fibers decreased with the increase in the replacement ratio of recycled coarse aggregate, and gradually improved as the increase in steel fiber volume fractions, respectively. The steel fiber volume fraction of 1.0% in concrete was almost sufficient to offset the shear capacity degradation induced by 100% recycled fine aggregate replacement ratio and 100% recycled coarse aggregate replacement ratio. Finally, the effects of recycled fine aggregate, recycled coarse aggregate, and steel fibers on the shear behavior of the concrete beams were severally quantified by the linear equations, and a model for predicting the shear capacity of concrete beams with recycled fine aggregate, recycled coarse aggregate, and steel fibers was proposed and verified.

EFFECT OF STEEL FIBER PROPORTION ON SIFCON MECHANICAL PROPERTIES

Slurry Infiltrated Fiber Concrete (SIFCON) is a relatively new high-performance material that may be thought of as a high-fiber content version of fiber reinforced concrete. This matrix is comprised of flowing mortar that must penetrate the fiber network implanted in the molds sufficiently. SIFCON combines excellent mechanical properties with a high ductility and toughness grade. SIFCON is utilized in applications that demand a high degree of ductility and energy absorption, most notably seismic-resistant reinforced concrete structures and structures exposed to abnormal or explosive loads. Additionally, pavement overlays, prestressed beam repair, and structural reinforced concrete element restoration have all been effective. The main aim of this study is to determine the effect of hooked-end steel fiber and micro-steel fiber on the strength of SIFCON specimens exposed to flexural and splitting loading. Three volume fractions of steel fiber (8,10, and12) % were used in this investigation. By weight of cement in SIFCON slurry, the proportion of Silica Fume SF substitution was 10%. Flexural strength was determined by testing specimens of (100×100×500) mm, and splitting tensile strength was determined at 7 and 28 days using cylindrical specimens with dimensions (150mm × 300m).. The results obtained from these tests were compared with SIFCON containing micro steel fiber. The test results show superior characteristics of SIFCON containing hooked-end steel fiber, as compared with micro steel fiber. For example, the flexural strength and splitting strength are 24.89 MPa and 10.14 MPa, respectively for SIFCON with 8% hooked-end steel fiber and 17.51 MPa and 9.1 MPa for control specimens with micro steel fiber.

Behavior of Steel‐Fiber‐Reinforced Concrete (SFRC) Slab‐on‐Grade under Impact Loading

Structures such as industrial pavements, roads, parking areas, and airport runways are often slab‐on‐grade where steel‐fiber reinforcement can substitute conventional steel reinforcement. Due to the dynamic nature of loading while in service, these structures are exposed to the damaging effects of impact loading, such as strength and stiffness deterioration in materials or structural elements. In this study, the behavior of concrete slab‐on‐grade with steel‐fiber‐reinforced concrete under impact load has been investigated by considering different parameters. Nonlinear finite element software ABAQUS/Explicit is used to simulate the system. The accuracy of the nonlinear finite element models is verified using experimental work available in the literature. A total of 108 specimens are simulated by varying the volume fraction of steel fiber by 0.5%, 1%, and 1.5% coupling with the impact mass and velocity from the control specimen and variation of load location, thickness, and aspect ratio. The analysis results revealed that the addition of 0.5%, 1%, and 1.5% volume fraction of steel fiber in concrete could effectively accommodate up to 0%, 10%, and 26% reduction of thickness, respectively. These results confirmed that the appropriate use of steel fiber in concrete can be a feasible solution to improve the overall performance of slab‐on‐grade. Moreover, an increase in the aspect ratio of steel fiber improves the crack resistance of steel‐fiber‐reinforced concrete slab‐on‐grade, but a further increase in aspect ratio reduces the performance due to local crushing of concrete.

Static Mechanical Properties and Microscopic Analysis of Hybrid Fiber Reinforced Ultra‐High Performance Concrete with Coarse Aggregate

An orthogonal test was conducted to investigate the effect of hybrid fiber on the mechanical properties of ultra‐high performance concrete (UHPC‐CA) with coarse aggregate . It was used to design and manufacture 144 test specimens for compressive strength, flexural tensile strength, static compressive elastic modulus test, and SEM microscopic test. Considering the mass replacement rate of coarse aggregate (10%, 15%, 20%, and 30%), the steel fiber volume rate (0%, 0.5%, 1.0%, and 1.5%), and the polypropylene fiber volume rate (0%, 0.05%, 0.10%, and 0.15%). The results show that the volume fraction of steel fiber has the greatest impact on compressive strength and flexural tensile strength, followed by the mass substitution rate of coarse aggregate, and the volume fraction of polypropylene fiber has the smallest impact. For the elastic modulus under static compression, the mass substitution rate of coarse aggregate has the greatest impact, followed by the volume fraction of steel fiber and polypropylene fiber. Based on the analysis of compressive properties, flexural tensile properties, and elastic modulus, the optimal mix ratio is recommended as follows: coarse aggregate 15%, steel fiber 1.5%, and polypropylene fiber 0.10%. Finally, three kinds of strength parameters are predicted based on the back propagation (BP) neural network system. The absolute value of the relative error between the predicted strength and the experimental value is less than 5%, which indicates that the prediction model proposed in this paper can provide a reference for the multiobjective optimization of the mix proportion of hybrid fiber ultra‐high performance concrete.

Nonlinear Numerical and Analytical Assessment of the Shear Strength of RC and SFRC Beams Externally Strengthened with CFRP Sheets

This study investigates numerically utilizing nonlinear finite element (ANSYS software) and analytically the shear response of the Reinforced Concrete (RC) beams. Different beams are considered in the current study, such as RC, steel fibre reinforced concrete (SFRC) without web reinforcement, and RC externally reinforced in the shear zone with carbon fibre reinforced polymer (CFRP) sheets. Nonlinear finite element model (FEM) is designed to simulate the performance of the designed beams. The results of FEM are compared to experimental measurements and standard design codes (ACI 440.2R‐17, FIB 14, CNR‐DT200, and ACI 318‐19). According to the experimental approach and nonlinear finite element, the enhancement in the load carrying capacity of SFRC beam due to CFRP strengthening decreases with a volume fraction of steel fibres of 2%. However, the effect of CFRP strengthening on the shear behaviour of RC beams was observed in increased load carrying and ultimate deflection capacities as a result of the CFRP strengthening. The results show that CFRP has a significant contribution to shear strength. At each load increment, the created model accurately reproduced the initial and progressive crack patterns. A comparison of nonlinear finite element and analytical models was conducted using the codes ACI 440.2R‐17, FIB 14, CNR‐DT200, and ACI 318‐19. Numerically, the FEM results showed a high agreement with ACI 440.2R‐17 standard code, with correlation approach to 99%. The comparison experimental load capacity of beams to FEM and ACI 440.2R‐17 shows that the FEM can be significantly used to estimate the shear strength of beams in the X‐Y directions with simulating different scenarios of CFRP and SFRC characteristics. The discrepancy between the nonlinear FEA and the theoretical predictions from the ACI 440.2R‐17 code is less than 1%, from the FIB14 code is less than 2%, from the CNR‐DT200 code is less than 15%, and from the ACI 318‐19 code is less than 30%. The ultimate load capacity evaluated based on ACI 440.2R‐17 code provision shows a good agreement with the experimental data as compared to the others’ code provision. The results of the finite element analysis and analytical models were in good agreement with the experimental results. The most significant advantage of finite element analysis over experimental approaches was that it can aid in the investigation of different output results that cannot be measured experimentally, such as shear stress in the XY direction throughout the beam strengthened in shear with different CFRP properties and steel fibre reinforced concrete (SFRC).

Evaluation of Mechanical Performance of High Performance Hybrid Fiber Reinforced Concrete Containing Micro Silica

In the extended use of concrete in military applications, runway pavements and infrastructures, concrete is subjected to heavy impact loads that vary both in velocity and intensity. The addition of fibers in high performance concrete (HPC) can overcome its shortcomings such as brittleness, high shrinkage and less resistance to impact and also improve the ductile behavior and energy absorption capacity. In this study, development on strengthening of HPC using steel and Polypropylene fibers was focused. Moreover, an inclusion of volume fractions of both steel and polypropylene fibers, leads to an increase in the mechanical properties of concrete matrix. The present study represents the adding steel and Polypropylene fibres at 0.5, 1.0, 1.5, and 0.25, 0.5, 1% by volume of concrete, respectively. A concrete mix has been designed to achieve the M60 grade concrete, mixes proportioned for FRC to determine the compressive strength, split tensile strength and flexural strength of high performance hybrid fiber reinforced concrete at 28 days. The experimental results showed that the use of hybrid fibers with 1.5% steel and 1% Polypropylene fiber in HPC concrete has improved the strength of the concrete by 36% and 25.1% HPC with single fibers. The statistical tool was formulated to predict the strength properties of fiber reinforced concrete (i.e., compressive, flexural and split tensile strengths). The response surface method (RSM) was used to analyze the data and develop a regression equation. RSM was able to predict the experimentally tested values within an acceptable range.

A comparative flexural performance of an over-reinforced high strength concrete beam with normal strength beam

This research work compared the flexural behavior of an over-reinforced High strength concrete beam with normal strength concrete beam. Totally 26 beams are casted in which 13beams for high strength concrete and remaining 13 are designed for normal strength concrete. Out of 13 one beam was kept as reference and remaining 12 beams are casted with varying volume fractions of steel and polypropylene fibers. All the beams are provided with more than the required percentage of steel which is slightly more than the balanced percentage. Providing a reinforcement in the tensile region itself behaves as an over-reinforced one. In general concrete fails by brittle manner hence forth in this study an attempt has been made to prove that even an over-reinforced beam offers resistance against the load applied and to ensure that the beam was casted by adding hybrid fibers along with proper confinement (stirrups with closed spacing) at the maximum moment section which enhances the flexural performance of the beam. As per ASTM C 78 all the beams were tested under third point loading and the deflections were measured using dial gauges at the respective places. Based on the experimental results it was proved that ductile behavior of the beams was improved just because of adding fibers in hybrid form along with stirrup confinement at the possible hinging region. Also, it was ensured that load carrying capacity of the beams was in turn improved not just in high strength concrete beam but also performs well with normal strength concrete beam.

Effect of Steel Fiber Volume Fraction on the Mechanical Behavior of Ultra-high Performance Concrete Composites

In order to investigate the effect of fiber volume fraction on the mechanical behavior of ultra-high performance concrete composites (UHPCC), five different volume fractions of macro steel fibers (Vf = 0.5, 1, 1.5, 2 and 2.5%) are used within identical mortar matrix. Ultra-high performance fiber reinforced concrete (UHPFRC) mix was designed to achieve a compressive strength of 155 MPa based on the particle packing method. For 12 series of UHPCC mixes, compressive strength, splitting tensile strength, flexural strength, and modulus of elasticity at 28 days are determined. Test results showed a significant improvement in splitting tensile and flexural strengths of UHPFRC with the addition of steel fibers. The maximum values of compressive, splitting tensile and flexural strengths were 155.39, 17.76, and 32.50 MPa, respectively. Stress-strain behavior of fiber-reinforced concrete composites is studied and elastic modulus values evaluated are in the range of 39.52-47.99 GPa. Empirical expressions are developed based on the test results in terms of fiber volume fraction to predict the 28-day strengths of UHPFRC. Comparing the experimental values of earlier researchers to the ones predicted by empirical equations, the average absolute error (AAE) value obtained is within 5%. The proposed model's predictions are in good agreement with the experimental values. Relationship between compressive and flexure strengths of UHPFRC isdeveloped with R2=0.99 and validated.

High Strength Concrete Beams Reinforced with Hooked Steel Fibers under Pure Torsion

A study of the behavior of fibers in high-strength reinforced concrete beams is presented in this paper. Twelve reinforced concrete beams were tested under a pure torsion load. Different compressive strengths (45.2, 64.7, and 84.8 MPa) and fiber volume fractions (0, 0.25, 0.5, and 0.75) with variable spacing between transverse reinforcements have been used. It was discovered that the maximum torque of a high-strength concrete beam is increased by about 20.3, 25.6, and 27.1% when the fractional volume of fiber is increased from 0 to 0.25, 0.5 and 0.75 respectively (when the compressive strength is 45.2 MPa and the transverse reinforcement spacing is 100 mm). The test results show that the ultimate torsional strength becomes higher when the concrete compressive strength increases, and this percentage increase becomes higher with increasing steel fiber volume fraction. When the spacing between transverse reinforcements decreases from 150 to 100 mm, the ultimate torque increases by 19.9%. When the spacing between transverse reinforcements decreases from 100 to 60 mm, the ultimate torque increases by 17.0%. In these beams, the fibers’ compressive strength and volume fraction were kept constant at 45.2 MPa and 0.75, respectively. Doi: 10.28991/CEJ-2022-08-01-07 Full Text: PDF

Mechanical Property Test and Damage Evaluation Analysis of Steel Fiber Stainless-Steel Reinforced Concrete Beams (SFSRCBs) under Impact Load

In this paper, the ultra-high drop hammer impact test system is adopted for the vertical impact experiment on six SFSRCBs with steel fiber volume fraction of 2.0% and build the relevant numerical model. The research variables mainly include impact energy, impact mass and cumulative impact mode. The results show that, under a single equal energy impact, with the increase of the impact speed, the crack distribution of the specimen gradually tends to the mid-span local position. Compared with the impact mass, the impact speed has a greater effect on the failure mode, deformation resistance and deformation recovery ability of SFSRCBs. When the total cumulative impact energy is the same as the single impact energy, then the overall damage of the specimen caused by high-mass low-velocity cumulative impact is less significant than that caused by low-mass high-velocity cumulative impact. Combined with the finite element analysis, the calculation formula of the maximum deflection of SFSRCB under impact load is obtained. Finally, the calculation method of the impact damage evaluation factor of SFSRCBs is proposed.

Research on the Fracture Behavior of Steel-Fiber-Reinforced High-Strength Concrete.

The behavior of steel fiber concrete, which is the most widely used building material, has been widely examined. However, methods for calculating Fracture parameters differ by fracture behavior of SFHSC with different strengths. In this study, the fracture behavior of steel-fiber-reinforced high-strength concrete (SFHSC) was -investigated using three-point bending tests. A total of 144 notched concrete beams with a size of 100 mm × 100 mm × 515 mm were tested for three-point bending in 26 groups. The effects of the steel fiber volume ratio, steel fiber type, and relative notch depth on the fracture toughness (KIC) and fracture energy (GF) of SFHSC specimens were studied. The results show that an increase in the volume fraction of steel fiber (ρf) added to high-strength concrete (HSC) significantly improves the fracture behavior of HSC. As compared to milled and sheared corrugated steel fibers, cut bow steel fibers significantly improve the fracture behavior of SFHSC. The effect of incision depth changes on the KIC and GF of SFHSC and HSC for the comparison group has no common characteristics. With an increase in incision depth, the values of KIC of the SFHSC specimens decrease slightly. The GF0.5/GF0.4 of the SFHSC specimens show a decreasing trend with an increase in ρf. According to the test results, we propose calculation models for the fracture behavior of SFHSC with different strengths. Thus, we present a convenient and accurate method to calculate fracture parameters, which lays a foundation for subsequent research.