Increase Of Steel Fiber Content Research Articles

Effects of fly ash, activator ratio and steel fiber on freeze–thaw cycle, sulfuric acid, thermal conductivity and impact resistance of silica fume based AAHSMs

This study is focused on the effects of Class C fly ash (FA), NaOH/Na2SiO3 (SH/SS) ratio and steel fiber (STF) on the freeze–thaw (F-T) cycle, sulfuric acid, thermal conductivity and impact resistance of silica fume (SF) based alkali activated high strength mortars (AAHSMs). In the AAHSM mixtures, FA in different proportions (10%, 15%, 20% and 25%) is used instead of SF by weight. All the mixtures are prepared with water-to-binder rate of 0.32. F-T cycle results exhibit that the flexural strength (ffs) and compressive strength (fc) values of SF based AAHSMs without and with STF are less affected than those of ordinary Portland cement (OPC) based high strength mortars (OPCHSMs) without and with STF. After 300 F-T cycles, the ffs and fc values of SF based AAHSMs without and with STF are still over 14MPa and 95MPa, respectively. After exposure to 20% sulfuric acid solution for 90 and 180 days, the SF based AAHSMs without and with STF exhibit super performance (i.e., fc values between 78.95MPa and 96.81MPa), while the surfaces of OPCHSMs without and with STF are disintegrated. Additionally, the effects of F-T cycle and sulfuric acid solution on SF based AAHSM and OPCHSM are examined with the microstructure analyses. Thermal conductivity results show that the SF based AAHSMs without and with STF perform better than the OPCHSMs without and with STF. The thermal conductivity results of OPCHSMs without and with STF vary between 0.630W/m.K and 0.697W/m.K, while the thermal conductivity results of SF based AAHSMs without and with STF range from 0.507W/m.K and 0.623W/m.K. Thermal conductivity results are adversely influenced by increasing STF content in the SF based AAHSMs and OPCHSMs. Impact resistance results show that the SF based AAHSMs without and with STF perform better than the OPCHSMs without and with STF. Moreover, the impact resistance values increase, as the amount of STF used in the SF based AAHSMs and OPCHSMs increases.

Optimized mix design method of ultra-high performance concrete (UHPC) and effect of high steel fiber content: Mechanical performance and shrinkage properties

In this study, UHPC was successfully prepared based on the Modified Andreason and Andersen (MAA) model (distribution modulus m= 0.23 was confirmed) and Excel solver tool. Subsequently, the effect of steel fiber content (0%–6% by volume) on the mechanical properties and shrinkage properties was investigated. It was found that the compressive and flexural strengths increased significantly with the increase of steel fiber content from 0 % to 5 %, but decreased when it exceeded 5 %. The split tensile strength was always increased. In addition, the plastic shrinkage, autogenous shrinkage, and drying shrinkage of UHPC were reduced by 18.3%–67.4 %. It indicated that incorporating higher content of steel fiber into UHPC could enhance mechanical strength, but the mixing approach should be optimized when content of steel fiber exceeds 5%. In addition, the prevalence of steel fiber agglomeration was shown under X-CT, but the agglomeration of steel fiber still led to an increase in UHPC properties within a certain range. The air content of UHPC with 6 % fiber content is 3.5 %, which shows the reasonableness and good performance of the mix proportion calculated by the Excel solver demonstrated in the article. The article can lay a light on the industrial design and preparation of UHPC.

Mechanical properties and damage modeling of hybrid fiber reinforced concrete under freeze-thaw cycles

This study aimed to investigate the mechanical properties of steel-polyacrylonitrile hybrid fiber reinforced concrete and its durability under freeze-thaw damage. Firstly, the mechanical properties of hybrid fiber reinforced concrete were studied by compressive strength and flexural strength tests. Secondly, with the help of rapid freeze-thaw test, the variation rules of mass loss rate and relative dynamic elastic modulus were characterized. Based on the test results and freeze-thaw damage theory, the evolution equation of freeze-thaw damage of hybrid fiber reinforced concrete based on Weibull distribution was established. The results show that the enhancement effect of hybrid fiber on the mechanical strength of concrete is better than that of single mixed fiber, especially in the improvement of flexural strength; Accordingly, compared with the single mixing of steel fibers or single mixing of polyacrylonitrile fibers, hybrid fibers are more effective in improving the durability of concrete against freezing and this improvement effect increases with the increase of steel fiber content; The freeze-thaw damage model of Weibull distribution can better reflect the freeze-thaw damage process of hybrid fiber reinforced concrete .Through the freeze-thaw damage evolution curve, it can be found that after 500 freeze-thaw cycles, the freeze-thaw damage degree of the hybrid fiber reinforced concrete with different steel fiber content has been very close, which means that the influence of steel fiber content on the freeze-resistant performance of hybrid fiber reinforced concrete will be limited. This study provides a theoretical basis and technical basis for the design of concrete structures in alpine regions.

Non-linear finite element analysis of SFRC beam-column joints under cyclic loading: enhancing ductility and structural integrity

Brittle shear failure of beam-column joints, especially during seismic events poses a significant threat to structural integrity. This study investigates the potential of steel fiber reinforced concrete (SFRC) in the joint core to enhance ductility and overcome construction challenges associated with traditional reinforcement. A non-linear finite element analysis (NLFEA) using ABAQUS software was conducted to simulate the behavior of SFRC beam-column joints subjected to cyclic loading. Ten simulated specimens were analyzed to discern the impact of varying steel fiber volume fraction and aspect ratio on joint performance. Key findings reveal that a 2% volume fraction of steel fibers in the joint core significantly improves post-cracking behavior by promoting ductile shear failure, thereby increasing joint toughness. While aspect ratio variations showed minimal impact on load capacity, long and thin steel fibers effectively bridge cracks, delaying their propagation. Furthermore, increasing steel fiber content resulted in higher peak-to-peak stiffness. This research suggests that strategically incorporating SFRC in the joint core can promote ductile shear failure, enhance joint toughness, and reduce construction complexities by eliminating the need for congested hoops. Overall, the developed NLFEA model proves to be a valuable tool for investigating design parameters in SFRC beam-column joints under cyclic loading.

Bond strength model between steel rebar and ultrahigh performance concrete containing coarse aggregates

To clarify the bond performance between steel rebar and ultrahigh performance concrete containing coarse aggregates (UHPC-CA), a total of 33 pull out specimens was cast. The effects of coarse aggregate particle size, coarse aggregate content, and steel fiber content on the failure modes and bond stress-slip curves of the specimens were studied. Based on the virtual crack model, considering the tensile contribution of steel fibers and the bridging effect of coarse aggregates, a model for the bond strength between UHPC-CA and steel rebar was established. The research findings indicated that there was a corresponding matching relationship between coarse aggregate particle size and the spacing of steel rebar ribs. In the 5–8 mm particle size group, the specimens showed 7.95% and 9.01% increases in bond strength compared to the 3–5 mm and 8–10 mm particle size groups, respectively. When the coarse aggregate content of UHPC-CA was 20%, the bond strength was the highest, increasing by 11.39% compared to specimens without coarse aggregates. The bond strength first increased and then decreased with increasing steel fiber content. Excessive steel fiber content could lead to the clustering of steel fibers, reducing the effective number of steel fibers contributing to toughening. The calculated results from the established bond strength model were compared with experimental and literature results, yielding an average ratio of 0.993 and a standard deviation of 0.166. This model effectively predicts the bond strength between UHPC-CA and steel rebar.

The rainstorm waterlogging resistance of a novel fiber-reinforced self-compacting recycled pervious concrete after freeze-thaw cycles

The poor permeability of pervious concrete after freeze-thaw (F-T) cycles is a difficult issue in the face of frequent extreme rainstorms, causing urban rainstorm waterlogging problems (stagnant water depth exceeds 150 mm). A novel fiber-reinforced self-compacting recycled pervious concrete (NSPC) with low tortuosity artificial pore channel (APC) is a pervious material with high permeability and strength, and has potential application in pervious pavement at the coupling action of F-T cycles and rainstorm. In this study, the frost resistance, mechanical properties and permeability of C60 NSPC (pore diameter of 3 mm, porosity of 1.13%) with various steel fiber contents (0 vol%, 0.5 vol%, 1 vol%, 1.5 vol% and 2 vol%) were investigated, and then the rainstorm waterlogging resistance of NSPC after 300 F-T cycles was examined under 20-, 50- and 100-year rainstorm. Results showed that the macroscopic destruction of NSPC surface after F-T cycles always started near the APCs, and the existence of APCs aggravated the mass loss and the decrease of the relative dynamic modulus of elasticity. As the increase of steel fiber content, the compressive strength loss of NSPC decreased first and then increased after F-T cycles. The use of steel fiber enhanced the integrality inside the APCs of NSPC and reduced the APC clogging rate, which improved hydraulic-conductivity properties after F-T cycles. After 300 F-T cycles, NSPC with 2% steel fiber achieved an excellent rainstorm waterlogging resistance (stagnant water depth of 0 mm), regardless of the rainstorm return period. Through F-T damage analysis, in order to cope with waterlogging, the maximum FT failure thresholds of NSPC to prevent stagnant water of 50, 70 and 100 mm are 0.097, 0.125 and 0.161 respectively, equivalent to 196, 243 and 264 F-T cycles. This study designed a NSPC that can dissipate stagnant water after F-T cycles, which provided a promising route towards solving urban rainstorm waterlogging.

Mechanical properties and compressive constitutive model of steel fiber-reinforced geopolymer concrete

Geopolymer concrete is an environmentally friendly material, and the addition of steel fibers can overcome its brittleness and improve its performance, which has broad application prospects. However, there are currently few studies on the comparative analysis of mechanical properties between steel fiber-reinforced geopolymer concrete (SFGPC) and steel fiber-reinforced ordinary Portland concrete (SFOPC), as well as uniaxial compressive constitutive models for SFGPC. Therefore, 144 cubes and 36 prisms were tested for SFGPC and SFOPC. The main variables were the volume content of steel fibers (0 %, 0.5 %, 1 %, 1.5 %, and 2 %), curing age (7 and 28 days), and water-to-binder ratio (0.45, 0.5, and 0.55). The slump, failure pattern, compressive strength, splitting tensile strength, elastic modulus, peak strain, toughness index, and compressive stress−strain curves were obtained. The results indicate that with the increase of steel fiber content, the compressive strength, splitting tensile strength, peak strain, and toughness index of SFGPC increase, while the elastic modulus remains almost unchanged. Compared with the plain geopolymer concrete, the above corresponding indexes of SFGPC with 1 % steel fiber content can be increased by 9.9 %, 20.5 %, 23.3 %, and 52.2 %, respectively. The 7-day compressive and tensile strengths of SFGPC can reach about 80 % of the 28-day strengths. Under the same conditions, SFGPC exhibits higher strength, peak strain, and lower elastic modulus than SFOPC. The scanning electron microscope (SEM) test results show that the geopolymer matrix has a denser structure and a tighter bond with steel fibers than the cement matrix. Based on the plain geopolymer concrete, formulas for mechanical indexes and a uniaxial compressive stress−strain model of SFGPC were proposed.

Study on the impact resistance of steel fiber-reinforced self-compacting concrete after high temperature

The present study explored the dynamic mechanical properties of steel fiber-reinforced self-compacting concrete (SFRSCC) after a high temperature. The impact test was conducted using a φ80 mm split Hopkinson pressure bar (SHPB) device, with a focus on the factors of influence and the regularity of steel fiber content (0.5 %, 1.0 %, and 1.5 %), impact strain rate (55 s−1, 90 s−1, and 140 s−1), and temperature (20 °C, 300 °C, 600 °C, and 900 °C) on the failure form, dynamic strength, impact toughness, and dynamic increase factor (DIF-σ) of SFRSCC after high-temperature exposure, and the mechanism analysis based on the results of the SEM examination. The impact test results revealed the following: (1) With the increase in the steel fiber (SF) content, the dynamic strength (fp) of the SFRSCC exhibited a further evident growth trend after high temperature compared to that at normal temperature reaching 105 % and the toughness index also increased by more than 20 %. (2) While the effect of SF content on DIF-σ of SFRSCC was not significant under normal temperature conditions after high-temperature exposure, the DIF of SFRSCC can increase by over 40 % with the increase of SF content. In addition, the strain rate effect was also further significant, and the DIF-σ can increased by about 30 % after high-temperature treatment compared to normal temperature. (3) A prediction formula was proposed for DIF-σ of SFRSCC after high temperature, and the results were in good agreement with the results of the impact test. This prediction formula can better provide theoretical data support for disaster prevention and reduction in subsequent projects. The findings of the present study would serve as a valuable reference for subsequent research on the impact resistance of SFRSCC after high-temperature exposure.

Dynamic stress-strain relationship of steel fiber-reinforced rubber self-compacting concrete after exposure to high temperature

The purpose of this study was to investigate the dynamic compression characteristics of steel fiber-reinforced rubber self-compacting concrete (SFRSCC) after exposure to high temperatures by using the split Hopkinson pressure bar (SHPB) impact test. The study considered four parameters: strain rates of 55 s−1, 90 s−1, and 155 s−1; volume fractions of steel fibers of 0%, 0.5%, 1.0%, and 1.5%; volume fractions of rubber contents of 0%, 10%, 20%, and 30%; and temperatures of 25 ℃, 300 ℃, 600 ℃, and 900 ℃. Experimental results revealed that: (I) The toughening effect of rubber decreases after exposure to high temperature, which decreases the specimens' dynamic compressive strength and toughness index after high temperature with the increase of rubber content. (II) The dynamic compressive strength, toughness index, and dynamic increase factor (DIF) of the specimens increased with the increasing steel fiber content after exposure to the same temperature. (III) The dynamic compressive strength of the specimens decreased linearly as the temperature increased, and the toughness index initially increased and then decreased. However, the incorporation of steel fiber mitigated this reduction. (IV) The impact of strain rate on compressive strength, toughness index, and DIF-σ was more significant for specimens exposed to high temperatures than for those at room temperature Finally, a stress–strain curve prediction formula considering temperature, rubber content, steel fiber content, and strain rate of SFRSCC was proposed.

Punching Shear Behavior of FRP Grid-Reinforced Ultra-High Performance Concrete Slabs

Fiber-reinforced polymer (FRP) grid-reinforced ultra-high performance concrete (UHPC) slabs are new structural solutions that take advantage of the mechanical properties of FRP and UHPC. However, the punching shear behavior of this new slab type has not been characterized. Therefore, punching shear tests were conducted to eight carbon fiber-reinforced polymer (CFRP) bars or grid-reinforced UHPC square slabs (600 mm side width × 40 mm thick). Several influential factors [e.g., use of CFRP bars or grids as flexural reinforcements, type of strengthening short fiber, steel fiber (SF) content, and presence of shear reinforcements] were investigated. The test results showed that FRP grids and short fibers helped to distribute the applied loads and dissipate the input energy; therefore, more cracks were observed, and higher punching shear capacities were achieved. Furthermore, increasing the reinforcement ratio in the FRP grids led to a more significant postcrack ductility response, which increased the punching shear capacity by 17%. In addition, SF addition could enhance the initial cracking load of the slab (Vcr), and polyethylene (PE) fiber addition could intensify the postcrack ductility response, both enhanced the punching shear capacity. The installation of shear reinforcements (eight pieces of 80 mm long CFRP grid strips) appeared to be more cost-effective than increasing SF content. Finally, compared with the current design provisions for conventional reinforced concrete slabs, a more accurate (average error of 8%) punching shear model was proposed for FRP grid-reinforced UHPC slabs with or without SF additions. However, the robustness of the proposed model will be assessed with more test data in the future.

Flexural toughness and its evaluation method of ultra-high performance concrete cured at room temperature

This study investigates the effects of water-binder ratio and steel fiber content on the flexural response characteristics of UHPC cured at room temperature by four-point bending tests. These flexural properties include load-deflection curve, flexural strength, initial cracking strength and flexural toughness. Based on the review of existing evaluation methods about flexural toughness, a deflection offset method that can quantitatively determine the initial crack point of UHPC in bending tests is proposed, and the optimized evaluation indicators of UHPC flexural toughness are further established from the perspective of equivalent strength. The proposed method with clear physical meaning and strong applicability can be used to evaluate the flexural toughness of UHPC cured at room temperature during the whole loading process. The results indicate that: (1) The flexural strength and deflection decrease as the water-binder ratio increases from 0.14 to 0.20, in which the decrease of peak deflection is the most significant (56.95%). (2) Although the flexural strength increases linearly with the increase of steel fiber content, the peak deflection increases slowly when the fiber content exceeds 1.0%. (3) The strength and deflection corresponding to the initial cracking point are about 2/3 of the flexural strength and 1/3 of the peak deflection respectively. (4) The flexural toughness decreases with the increasing water-binder ratio, especially when the water-binder ratio exceeds 0.18. (5) The flexural toughness of UHPC increases and the toughening effect of fiber first increases and then decreases with the increase of steel fiber content, and UHPC mixed with 1.5% steel fiber achieves the most remarkable toughening effect. Therefore, the superior flexural toughness and load-bearing capacity of UHPC cured at room temperature are highlighted when the water-binder ratio is less than 0.18 and the steel fiber content exceeds 1.0%.

Experimental and numerical investigations on direct shear performance of UHPC dry joints

Ultra-high performance concrete (UHPC) has great prospects in the field of precast segmental bridges. The excellent mechanical properties of dry joints between the UHPC segmental have become the focus of scholars all over the world. Currently, there are few studies on UHPC dry joints with a compressive strength between 120 MPa and 140 MPa. In this study, the direct shear performance of UHPC dry joints was tested and simulated with parameters of steel fiber content, confining stress, key number, shear key interlocking depth-height ratio (the depth-height ratio was used later), and key height. The results showed that the cracking resistances and ultimate strength of UHPC joints could be significantly improved with the increase of steel fiber content. All the UHPC specimens showed a little brittleness behavior with the average cracking load being 78.4% of the average ultimate load. Different cracking patterns occurred in single-keyed UHPC dry joints, while sequential failure arose for multi-keyed UHPC dry joints. Compared with monolithic specimens, the direct shear strength of keyed UHPC dry joints was reduced with a range of 51.4%–66.0%, and the decreasing trend was alleviated with the increase of the key number. The direct shear capacity of UHPC dry joints increased with the increase of key height and depth-height ratio, and the optimized depth-height ratio was 0.40–0.50. Compared the calculated results of existing formulae with the test results incorporated with the previous studies, it was found that Jiang's formula predicted the shear capacities of UHPC dry joints more accurately than the other formulae. In addition, the influence of the depth-height ratio on the direct shear capacities of UHPC dry joints cannot be reflected by the existing formulae, which need further improvement.

Torsional capacity of ultra-high-performance concrete beams using rectangle stirrup

This study studies the torsional capacity of rectangular ultra-high-performance-concrete (UHPC) beams. Nine UHPC beams were tested under pure torsion load. The failure modes were presented and the influences of parameters, including reinforcement ratio, stirrup ratio and steel fiber content were discussed. The experimental results showed that longitudinal reinforcement ratio had little effect on crack width and plastic stiffness in serviceability stage. Increasing the stirrup ratio and steel fiber content effectively inhibited the development of crack width and improved plastic stiffness. The torsional ductility of UHPC beams decreased with the increase of longitudinal reinforcement ratio but increased with the increase of stirrup ratio and steel fiber content. The cracking torque and elastic stiffness of UHPC beams were less affected by the reinforcement ratio and increased with the increase of steel fiber content. The twist, energy consumption, and ultimate torque of UHPC beams increased with the increase of longitudinal reinforcement ratio, stirrup ratio, and steel fiber content. The damage index of UHPC beams was 0.85–0.90, and the plastic stiffness accounts for 1/25–1/10 of the elastic stiffness.

Fatigue behavior and calculation methods of high strength steel fiber reinforced concrete beam

Adding steel fibers into concrete was considered as one of the most effective ways to restrain the crack development and improve the stiffness for reinforced concrete (RC) structures. To explore the reinforcement mechanism of steel fibers on the fatigue behavior of high-strength RC beam, eight high-strength steel fiber reinforced concrete (HSSFRC) beams subjected to fatigue loading were tested in this study. The main design parameters considered in this work were stress level and steel fiber content. The failure mode, crack patterns, fatigue life, crack width, and stiffness degradation of HSSFRC beams under fatigue loading were discussed. The results showed that steel fibers could significantly increase the fatigue life, restrain crack development, and improve crack patterns of HSSFRC beams under fatigue loading compared to ordinary RC beams. Both the crack width and stiffness degradation rate of beams decrease with increasing steel fiber content. Besides, the empirical formulas for calculating the maximum crack width and midspan deflection of HSSFRC beam under fatigue loading were proposed and validated using experimental results.

Analysis and prediction of the compressive and splitting tensile performances for the novel multiple hooked‐end steel fiber reinforced concrete

AbstractIn recent years, the application of the novel multiple hooked‐end steel fiber has gradually become a hot spot in the engineering due to its several excellent properties. In this study, the splitting tensile and compressive properties of the SFRC with 3D single hooked‐end and 4D/5D multiple hooked‐end steel fibers were studied. The variables of the experimental investigation included the concrete matrix strength, steel fiber content, and aspect ratio. The results showed that the compressive strength of steel fiber reinforced concrete (SFRC) increased first and then decreased with the increasing steel fiber content. The concrete matrix, aspect ratio, and end hook number of steel fiber had the significant effect on the optimal steel fiber content. In addition, increasing the content of steel fiber was the most effective way to improve the splitting tensile strength of SFRC, and the splitting tensile strength increased with the increase of the aspect ratio and end hook number of steel fiber. Finally, the splitting tensile strength prediction model of SFRC with novel multiple hooked‐end steel fiber was proposed by introducing the steel fiber number in the SFRC section, and the accuracy of the model was verified by comparison with experimental data.

Experimental and Numerical Study on Steel Fiber Concrete under Blast Loading

In this paper, 30 SFRC (Steel Fiber Reinforced Concrete) spindle specimens with different steel fiber contents were subjected to static loading tests and blast wave loading tests on spindle specimens with different steel fiber contents using a self-developed planar blast wave loading device (a new type of patent recognized by the State Intellectual Property Rights). The dynamic response, impact performance and damage mode of Steel Fiber Reinforced Concrete under blast loading were investigated. The experimental results show that with the increase of steel fiber content (within 2%), the strength of the Steel Fiber Reinforced Concrete increases slightly. The flatter the falling section of the stress-strain curve, the better the energy absorption effect. With the increase of explosive equivalent(24 g RDX and 36 g RDX), the more obvious the strain rate effect, the greater the increase of peak stress, and the SFRC with 2% steel fiber content has the best energy absorption effect. Furthermore, the dynamic response of SFRC spindle specimens was numerically simulated using the improved K&C material model with LS-DYNA explicit finite element dynamic analysis software. The results verify the validity and reliability of the improved K&C material model.

Experimental Study on Frost Heave Behavior of Steel Fiber Improved Soil

The incorporation of steel fibers into the natural soil is generally considered to be a novel and effective way to reduce the amount of frost heave induced by an artificial freezing process in underground engineering. In order to analyze the frost heave behavior of the steel fiber improved soil, a one-dimensional frost heave test under the open recharge system was conducted in this paper, focusing on the influence of steel fiber content, size, and soil properties. The results show that small amounts of steel fibers in the soil will not significantly affect the freezing process and temperature distribution, while the water-conducting properties of the steel fibers and the effect of limiting the ice lens growth can reduce the frost heave rate of the samples incorporated with 0.5% steel fibers by 26.93%. At the same time, the reduction effect of the frost heave rate increases linearly with the increase of steel fiber content and length but weakens with the increase of steel fiber diameter. In terms of soil property influence, the frost heave rate of the clay samples was reduced by 14.31% compared to the silt samples, while the water migration was reduced by 11.99%. In addition, the cementation of the steel fibers with the soil will also inhibit the growth of the ice lens and reduce the external water migration, thus significantly lowering the frost heave rate. The results can provide a reference for the research of the frost deformation of similar modified soils.

Shear Resistance of Fibrous Reinforced Concrete Deep Beams with Opening – A Critical Review

Reinforced concrete deep beams are more prone to shear failure. Thus, it is important to study the shear behavior for structural reinforcements. The presence of web openings in reinforced concrete deep beams is frequently required to provide accessibility such as doors and windows or to accommodate essential services such as ventilating and air conditioning ducts that affect the shear resistance. This research highlights the limited research on the shear resistance of fibrous reinforced concrete deep beams containing openings worldwide and illustrates their influence on shear behavior. This review has shown that the ultimate and the first cracking loads increase, increasing steel fiber content to a certain limit. End hooked steel fiber with 1.5% gave the highest shear resistance and ultimate load capacity compared with other types of steel fiber. Moreover, the stiffness of reinforced concrete deep beams increased with increasing fiber content from 0 to 1.5%. In addition, the effect of web openings on the shear strength of deep beams at the ultimate and cracking loads depends on the degree of interruption of the natural load path joining the loading.

Condition Detection and Maintenance of Steel-Fiber-Reinforced Concrete Based on Markov Random Matrix

The condition detection and maintenance of steel-fiber-reinforced concrete (SFRC) involves a combination of qualitative and quantitative assessment methods, while the ineffectiveness of the Markov chain can analyze the fluctuation law of gray fitting accuracy indexes and use this to correct the detection results of the residual gray model, having outstanding advantages. On the basis of summarizing and analyzing previous works of literature, this study expounded the research status and significance of the condition detection and maintenance of SFRC, elaborated the development background, current status, and future challenges of the Markov random matrix, introduced the methods and principles of feature extraction network and loss function, proposed the detection process analysis of SFRC based on Markov random matrix, constructed a detection model of SFRC, analyzed the maintenance monitoring method of SFRC based on Markov random matrix, discussed the maintenance effect evaluation of SFRC, and finally carried out a simulation experiment and its result analysis. The results show that the most important feature of Markov random matrices is the absence of aftereffects, which means that the condition evolution of SFRC can be regarded as a multiple Markov chain. When carrying out the dynamic condition maintenance of SFRC, the maintenance object should be first determined, then the condition detection of the object should be carried out to obtain information characteristics and to assess its condition, and then the condition should be compared with the condition set to determine its position in the set to make fault prediction based on the Markov chain constructed from the set of conditions. Under other excepted standards and maintenance conditions with the increase of steel fiber content, the flexural strength of concrete decreased first and then increased, but the difference of maintenance conditions had obvious influence on the flexural strength of concrete. The results of this paper provide a reference for further research on the condition detection and maintenance of SFRC based on the Markov random matrix.

Axial Behavior of Concrete Filled-steel Tube Columns Reinforced with Steel Fibers

Concrete filled steel tube (CFST) columns are being popular in civil engineering due to their superior structural characteristics. This paper investigates enhancement in axial behavior of CFST columns by adding steel fibers to plain concrete that infill steel tubes. Four specimens were prepared: two square columns (100*100 mm) and two circular columns (100 mm in diameter). All columns were 60 cm in length. Plain concrete mix and concrete reinforced with steel fibers were used to infill steel tube columns. Ultimate axial load capacity, ductility and failure mode are discussed in this study. The results showed that the ultimate axial load capacity of CFST columns reinforced with steel fibers increased by 28% and 20 % for circular and square columns, respectively. Also, the circular CFST columns exhibited better ductility than the square CFST columns due to better concrete confinement. Circular and square CFST columns with steel fibers showed improved ductility by 16.3% and 12%, respectively. The failure mode of the square CFST columns were local buckling which occurred near the end of columns, while, for the circular CFST columns, local buckling occurred near the mid-height. Also, the study involved sectional analysis that captured the behavior of CFST columns very well. The sectional analysis showed that increasing steel fiber content to 2% increased the axial load capacity by 51 and 38% for circular and square CFST columns, respectively. Furthermore, sectional analysis showed that doubling section size increased axial load capacity by approximately 4 and 5 times for circular and square columns, respectively.