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To reveal the influence of steel fiber content on the axial compressive properties of ultra-high performance concrete (UHPC), UHPC axial compression tests were conducted with steel fiber content as the control variable and constitutive simulations were conducted. The research show that the stress-strain curve of UHPC under compression consists of an ascending segment and a descending segment. After adding steel fibers, the descending section of the stress-strain curve of UHPC under compression becomes slower. With the increase of steel fiber content, the compressive elastic modulus, peak stress, and peak strain of UHPC all show a decreasing trend. Assuming that the UHPC compression damage area follows a Weibull random distribution, a damage variable is constructed, and a damage correction factor is introduced. A new UHPC compression damage model considering different steel fiber contents is established, and the development law of damage variables is analyzed. The reliability of the new model is verified using UHPC axial compression test data. The research results provide reference for the study of axial compressive properties and constitutive simulation of UHPC under different steel fiber contents. [ABSTRACT FROM AUTHOR]

Polyurethane concrete has excellent mechanical properties, rapid solidification and durability, but brittle damage is easy to occur at room temperature. To solve the problem of insufficient bending toughness of polyurethane concrete, steel fibers were added into the traditional polyurethane concrete to prepare steel fiber polyurethane concrete in this paper. A total of 8 test beams with dimensions of 150 mm × 150 mm × 550 mm were made. The influence of steel fibers with different length-diameter ratios and volume ratios on the flexural strength of polyurethane concrete was studied through four points bending tests. The results show that under the same volume ratio and diameter, as the length of steel fiber increases from 30 mm to 60 mm, the peak load decreased by 8.6%, and the displacement corresponding to the peak load decreased by 41.1%. Under the same length-diameter ratio, the steel fiber volume ratio from 0.5% to 2.0%, the peak load increased by 49.1%, and the displacement corresponding to the peak load increased by 100.8%. The toughening degree, relative initial flexural toughness ratio and relative residual flexural toughness ratio were proposed, and the inconsistencies of calculation criteria for flexural toughness in steel fiber reinforced concrete (JG/T 472–2015) were optimized.

Ultra-high-performance geopolymer concrete (UHPGC) emerges as a sustainable and cost-effective alternative to Portland cement-based UHPC, offering similar mechanical properties while significantly reducing carbon footprint and energy consumption. Research on UHPGC components is extremely scarce. This study focuses on the flexural and crack behavior of UHPGC beams with different steel fiber contents and longitudinal reinforcement ratios. Five UHPGC beams were tested under four-point bending. The test results were evaluated in terms of the failure mode, load–deflection relationship, flexural capacity, ductility, average crack spacing, and short-term flexural stiffness. The results show that all the UHPGC beams failed due to crack localization. Increases in the reinforcement ratio and steel fiber content had favorable effects on the flexural capacity and flexural stiffness. When the reinforcement ratio increased from 1.18% to 2.32%, the flexural capacity and flexural stiffness increased by 60.5% and 12.3%, respectively. As the steel fiber content increased from 1.5% to 2.5%, the flexural capacity and flexural stiffness increased by 4.7% and 4.4%, respectively. Furthermore, the flexural capacity, flexural stiffness, and crack spacing of the UHPGC beams were evaluated using existing methods. The results indicate that the existing methods can effectively predict flexural capacity and flexural stiffness in UHPGC beams but overestimate crack spacing. This study will provide a reference for the structural design of UHPGC. [ABSTRACT FROM AUTHOR]

A high strain rate occurs when the strain rate exceeds 100 s−1. The mechanical behavior of materials at a high strain rate is different from that at middle and low strain rates. In order to study the dynamic compressive mechanical properties of ultra-high-performance steel-fiber-reinforced concrete (UHPSFRC) at high strain rates, an electro-hydraulic servo universal testing machine and a separate Hopkinson pressure bar (SHPB) with a diameter of 120 mm were used, respectively. A quasi-static compression test (strain rate 0.001 s−1) and impact compression test with a strain rate range of 90~200 s−1 were carried out to study the failure process, failure mode, and stress–strain curve characteristics of UHPSFRC at different strain rates and quantify the strain rate strengthening effect and fiber toughening effect. Based on the statistical damage theory and energy conversion principle, a dynamic damage constitutive model considering the effects of strain rate and fiber content was constructed. The results showed that the rate correlation of UHPSFRC and the fiber toughening properties showed a certain coupling competition mechanism. When the fiber content was less than 1.5%, with an increase in the steel fiber content, the crack initiation and propagation time of the specimen was extended, and the strain rate sensitivity gradually decreased. When the fiber content was 2%, the impact compressive strength of the specimen was optimal. Compared with UHPC, the dynamic increase factor (DIF) of UHPSFRC was significantly lower. The dynamic damage constitutive model established in this paper, considering the influence of strain rate and fiber content, has a good applicability and can describe the mechanical behavior of UHPSFRC at a high strain rate. [ABSTRACT FROM AUTHOR]

To improve the transportation and lifting efficiency of precast staircases, a novel UHPC shaped thin-plate ribbed staircase was proposed and investigated under flexure by the accumulation load test. The flexural behavior of the proposed UHPC staircase was compared to the precast staircase made of Normal Strength Concrete (NSC), and the effects of fiber contents (0.75%, 1.0% and 1.5%) and the presence of steel bars in the UHPC staircase were experimentally investigated. The development of cracks and the comparison of load–deflection curves showed that the flexural behavior of the UHPC staircases was less susceptible to the disturbance of cracking than the NSC staircase. Besides, increasing the fiber content was beneficial to improve the crack resistance of the UHPC staircases, weaken the stress concentration effect of step roots on rib slabs, thereby improving the load-bearing capacity. The absence of rebar had no significant effect on the flexural behavior of UHPC staircases before cracking, but negatively affected the bending behavior after cracking. Furthermore, by means of the effective moment of inertia method and the introduction of a modified steel fiber conversion area parameter, a short-term stiffness model for UHPC stairs was proposed with a deviation within 6%. Finally, a parametric study was conducted based on a validated FE model, and suggestions are provided on the selection of section size to improve the flexural performance of the proposed UHPC staircases. [ABSTRACT FROM AUTHOR]

Copyright of Guangdong Architecture Civil Engineering is the property of Guangdong Architecture Civil Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Engineering Mechanics / Gongcheng Lixue is the property of Engineering Mechanics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Xinyang Normal University Natural Science Edition is the property of Journal of Xinyang Normal University Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Ultra-high-performance geopolymer concrete (UHPGC) emerges as a sustainable and cost-effective alternative to Portland cement-based UHPC, offering similar mechanical properties while significantly reducing carbon footprint and energy consumption. Research on UHPGC components is extremely scarce. This study focuses on the flexural and crack behavior of UHPGC beams with different steel fiber contents and longitudinal reinforcement ratios. Five UHPGC beams were tested under four-point bending. The test results were evaluated in terms of the failure mode, load–deflection relationship, flexural capacity, ductility, average crack spacing, and short-term flexural stiffness. The results show that all the UHPGC beams failed due to crack localization. Increases in the reinforcement ratio and steel fiber content had favorable effects on the flexural capacity and flexural stiffness. When the reinforcement ratio increased from 1.18% to 2.32%, the flexural capacity and flexural stiffness increased by 60.5% and 12.3%, respectively. As the steel fiber content increased from 1.5% to 2.5%, the flexural capacity and flexural stiffness increased by 4.7% and 4.4%, respectively. Furthermore, the flexural capacity, flexural stiffness, and crack spacing of the UHPGC beams were evaluated using existing methods. The results indicate that the existing methods can effectively predict flexural capacity and flexural stiffness in UHPGC beams but overestimate crack spacing. This study will provide a reference for the structural design of UHPGC.

Copyright of Engineering Mechanics / Gongcheng Lixue is the property of Engineering Mechanics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This research's primary objectives were first to verify a reliable structural health monitoring (SHM) experimental technique for reinforced concrete slab plates, and secondly, to introduce a special fiber Bragg grating (FBG) sensors cable system for continuous field monitoring of concrete. The particular focus was on the damage assessment, using an effective ambient vibration-based damage diagnostic technique of random decrement (RD). An investigation examined the extent of damage induced by progressive static loading through a numerical RD algorithm for four concrete plate specimens: three reinforced high-strength concrete (HSC) plates with different reinforcement ratios, and one ultra-high-performance fiber-reinforced concrete (UHP-FRC) plate. The extent of damage was measured through relative changes in the natural frequency and damping ratio as dynamic parameter damage indexes, which were obtained from RD signatures at cracking, yield, and ultimate loadings. Concurrently, the behavior of the concrete slabs was examined regarding the load-deflection relationship at service and ultimate load, crack pattern, and failure modes. [ABSTRACT FROM AUTHOR]

The single concrete has defects such as poor toughness and easy cracking. Tn order to enhance the application performance of concrete materials, the main solution is to mix steel fiber into concrete to make steel fiber reinforced concrete. Tn order to verified the effectiveness of this measure, the apparent density method was used to design the mix proportion, and the single concrete specimen and steel fiber reinforced concrete specimen were prepared, and the single concrete specimen was taken as the contrast test group.SEM,XRT) and universal testing machine were used to study the cross-section morphology, element composition and mechanical properties of the specimens. Tn the stage of mechanical property analysis, the mechanical properties of single concrete specimens and steel fiber reinforced concrete specimens under different loads and different steel fiber contents were studied. The results showed that the structure of steel fiber reinforced concrete was uniform and continuous, and had a large specific surface area, the friction of steel fiber surface could be increased after the specimen was stressed. The content of C in steel fiber reinforced concrete increased significantly, accounting for 44%，and the strength grade of steel fiber reinforced concrete increased. Through the study of compressive strength, flexural strength, splitting tensile strength, fracture toughness and elastic modulus, it could be seen that the overall mechanical properties of steel fiber reinforced concrete specimens were obviously better than that of single concrete specimens, which showed that steel fiber could effectively enhance the performance of concrete, improved the toughness of concrete and prevented cracks. [ABSTRACT FROM AUTHOR]

The utilization of ultra-high-strength concrete offers a weight reduction of concrete structures and improvements in disaster protection performance. Recently, porosity-free concrete (PFC) having the world's highest compressive strength of 400 MPa has been developed, and its basic mechanical properties were determined; however, its impact-resistant capacity is yet to be examined. In this study, investigation of the impact resistance behavior of PFC is performed using a weight dropping impact test on a fiber-reinforced PFC beam. Steel fiber-reinforced PFC is used for preventing brittle failure, and the full plastic moment of the PFC beam cross-section is determined based on material test results. Also, the estimation of maximum response deflection is attempted by a simple plastic analysis. It was demonstrated that the response deflection could be reduced by 30–50% by increasing the steel fiber mixing rate in the PFC beam from 1 to 2%. The proposed estimation method revealed that the response deflection of the PFC beam could be estimated with an accuracy of approximately 80% considering the calculated full plastic moment when the plastic hinge is clearly formed. In the future, to establish a design procedure for the impact-resistant capacity of protective structures from steel fiber-reinforced PFC, it is necessary to conduct experimental and numerical research focusing on ultimate strength, including statistical processing. [ABSTRACT FROM AUTHOR]

Wet-dry cycles and cracking are unavoidable problems of concrete structures and reduce durability by enhancing the penetration of harmful ions and water, which may have a synergistic adverse influence with severe surface damage caused by salt freeze-thaw cycles. This study aims to investigate the salt scaling resistance of ultra-high performance concrete (UHPC) under multiple harsh environments including wet-dry cycles and pre-cracking. The relationship between workability, absorption behavior, and scaling resistance with fiber content increases is assessed. Mass loss, chloride binding behavior, pore structure, and pore morphology are analyzed to describe the influences of pre-cracking and wet-dry cycles. The results reveal that the workability of fresh concrete and the distribution of steel fibers are the key factors in determining the salt scaling resistance of UHPC. Pre-cracking and wet-dry cycles inhibit the rapid scaling damage of UHPC by accelerating chloride accumulation, which reduces the icing pressure of pore liquid and refining the micropores (<200 nm) capable of remaining non-frozen at low temperatures through the chemical binding of chloride. However, the combined effect of pre-cracking and wet-dry cycles can lead to the corrosion of internal steel fibers and more scaling damage, and the crack width should not be greater than 0.1 mm. [ABSTRACT FROM AUTHOR]

In the study of steel fiber concrete beams, there are many design parameters that affecting stress-strain state, cracks formation and cracks development, etc. in beams. Changes of these design parameters will affect bearing capacity, displacement and cracks in beams. ANSYS can simulate the work of beams when design parameters be changed. Therefore, in this paper, the authors used ANSYS numerical simulation method to simulate design parameters of beams which be changed, to bearing capacity such as: steel fiber content in concrete, shear steel stirrups spacing at the ends of the beam, number of tensile steel bars, diameter of tensile steel bars, considering the nonlinear element of the materials, etc to consider the cracks formation and cracks development in beams from the beginning of loading to the damaged beams and then build the load and stress relationship, load and vertical displacement relationship in steel fiber concrete beams. Beam simulation results show that changes of these design parameters have affected the bearing capacity, stress-strain state, cracks formation and cracks development of beams, with the beams when increasing the content of steel fibers in concrete, increasing the number of tensile steel bars, increasing the diameter of tensile steel etc., making the beams reduce cracks, increase the bearing capacity, etc. for the beams. Simulation results were also compared with experimental methods. So, the study of these design parameters helps the design of steel fiber concrete beam structures to withstand impact loads and limit cracks in beams.

This paper presents an experimental investigation on the influence of splitting load on transport properties (air permeability and sorptivity) of UHPC incorporating different dosages of steel fibers (0%, 1%, 2% and 3%). ϕ 100 mm × 50 mm specimens were subjected to splitting loads with stress levels varying from 50% to 80% of the ultimate splitting tensile strength. The splitting load induced damage was characterized by the crack pattern, crack opening displacement (COD) and penetrable porosity. Gas permeability and water sorptivity tests were carried out to evaluate the transport property of UHPC specimens after exposure to different levels of splitting load. The correlation among splitting tensile stress level, COD and transport property degradation of UHPC was analyzed. The results indicate that gas permeability and sorptivity of UHPC before loading are much better than that of normal concrete. The splitting tensile strength of UHPC is almost doubled by the addition of 1 ∼ 3% steel fibers in volume and the peak lateral deformation is increased by more than 10 times. Both the maximum value of COD (COD max ) under loading and the residual COD (COD res ) after unloading of UHPC specimen increase with the more addition of steel fibers when exposed to the same stress level of splitting load. Both gas permeability and sorptivity of UHPC increase with the splitting load induced COD res . The higher dosage of steel fibers plays a positive effect on improving the transport properties of UHPC with the same COD res value. The sorptivity is more sensitive under a low deformation damage and the gas permeability is a better indicator to describe the durability degradation of UHPC under a high level of deformation. [ABSTRACT FROM AUTHOR]

An experimental investigation has been conducted to collect fundamental data and to develop more understanding of the dynamic response of ultra-high-performance fiber-reinforced concrete (UHP-FRC) plates. Six reinforced plates with identical dimensions are tested using multi-impact technique by dropping a 475.00 kg (1047.20 lb) steel weight from a clear height of 4.15 m (13.60 ft). Three parameters are investigated: concrete type, fiber volume content, and steel reinforcement ratio. The results of this investigation confirmed that UHP-FRC plates exhibited superior damage control characteristics compared to high-strength concrete (HSC) plates. Increasing the fiber content was shown to improve the dynamic performance of the UHP-FRC plates, resulting in reduced peak and residual displacements at the same impact loads and an increase in the specimen’s ability to sustain increased impact energy capacity before failure. The test results showed that steel reinforcement played an important role in specimens’ overall behavior and increasing impact capacity. [ABSTRACT FROM AUTHOR]

• HPB test on SRSCC with strain rate, steel fiber and rubber contents is conducted. • The effect of rubber content on DIF-σ at high strain rate is more obvious. • The effect of rubber content on DIF-σ is optimal when the rubber content is 20%. • Adding steel fiber at low rubber content could improve more strength and toughness. • The dynamic stress–strain relationship of SRSCC is proposed. Rubber has good elastic properties; however, its incorporation reduces the strength of concrete. Due to the high elasticity of rubber and the good crack resistance of steel fibers, the mixing of steel fibers and rubber can effectively improve the impact toughness index of concrete with sufficient strength. An impact test of steel fiber-reinforced rubber self-compacting concrete (SRSCC) was carried out using a split Hopkinson pressure bar (SHPB) in the present work, in which the strain rate ranges from 65.3 s−1 to 137.6 s−1 and steel fibers with four volume fractions of 0%, 0.5%, 1.0% and 2.0% and rubber contents with four volume fractions of 0%, 10%, 20% and 30% are considered. Experimental results revealed that, (i) the dynamic compressive strength, toughness index, stress impact factor (DIF- σ) as well as strain impact factor (DIF- ε) of SRSCC increase obviously with the increase of strain rate; (ii) with the increase of rubber content, the dynamic compressive strength decreases and the toughness index increases. When the rubber content reached 30%, the dynamic compressive strength decreased by 40–50% and the toughness index increased by 20–30%; (iii) the DIF- σ increases first and then decreases slightly with the increase of rubber content, which reaches the maximum value when the rubber content is 20%. What's more, the effect of rubber content on DIF- σ at high strain rate is more obvious; (iv) the steel fiber content shows strengthening effects on the dynamic compressive strength and toughness index and almost has no effects on the DIF- σ and DIF- ε of SRSCC. Finally, the dynamic stress–strain relationship of SRSCC was proposed. [ABSTRACT FROM AUTHOR]

Abstract: Using a shrinkage-restrained ring device with a clapboard, the effect of steel fiber content, sand-binder ratio and water-binder ratio on the cracking resistant behavior of reactive powder concrete (RPC) was investigated by an orthogonal experiment. The study results reveal that steel fiber content has the most significant effect on the cracking resistant behavior of RPC. Cracking ages and cracking coefficients can be used to evaluate the cracking resistant behavior of RPC. The earlier crack age means the poorer cracking resistant behavior of RPC, and the higher cracking coefficient denotes the poorer cracking resistant behavior of RPC. A linear sorting method can be used to approximately reflect the cracking resistant behavior of RPC. [Copyright &y& Elsevier]

• Typical three-segment axial stress-strain curves of FRP-confined UHPC are defined. • Stress reduction and the actual confinement ratio threshold reduce with the content of steel fibers. • Addition of steel fibers compromises effects of specimen size. • Performances of existing axial stress-strain models for FRP-confined concrete are verified. Ultra-high performance concrete (UHPC) usually exhibits a weak ductility under axial compression. However, the ductility can be enhanced by implementing confining devices such as fiber-reinforced polymer (FRP) wraps. In order to gain in-depth understandings on the compressive behavior of FRP-confined UHPC, axial compression tests on 52 FRP-confined and 12 unconfined UHPC cylinders were carried out in this study. The failure modes, stress-strain behaviors, confinement efficiency, and the influences of crucial variables (steel fiber contents, specimen sizes, FRP fiber types, and FRP thickness) on the compressive behavior of FRP-confined UHPC were investigated and discussed. Results show that the increase in steel fiber content could increase the first peak stress and its corresponding strain, hoop strain efficiency, avoid the abrupt stress reduction after the first peak stress, as well as alleviating the effect of specimen sizes. Addition of steel fibers also alters the actual confinement ratio threshold for sufficient confinement. Comparisons suggest that FRP confinement fiber types have limited influence on the normalized stress-strain behavior of specimens with similar level of actual confinement ratio. Additionally, performances of four existing axial stress-strain models for FRP-confined concrete are verified and the results reveal that Teng et al.'s model performs the best although this model is incapable in capturing the strain softening behavior after the first peak stress. [ABSTRACT FROM AUTHOR]

• The calculation method of effective restraint coefficient of composite stirrups is given. • The analytical model of restrained specimens of UHPC with different stirrup structure and fiber content is proposed. • A unified stress–strain constitutive equation of UHPC is established. • An experimental study on 11 groups UHPC specimens with and without stirrups was conducted. The influences of stirrups and steel fiber content on the compression performance of ultrahigh-performance concrete (UHPC) were investigated through the axial compression test of ten groups of UHPC short columns with stirrups and one group of columns without stirrups. The effects of volume stirrup ratio, stirrup form, stirrup spacing, and volume fraction of steel fiber on the peak stress and strain of confined UHPC were analyzed. Results showed that the failure modes of the specimens are the sharp increase and protrusion in circumferential deformation caused by core UHPC crushing, stirrup yielding, and "cracked but not broke into pieces. The protective layer of UHPC did not spall due to the pullout resistance of the end-configuration steel fiber. Constrained UHPC specimens with high stirrup ratio, small stirrup spacing, and large fiber content demonstrated enhanced constraining effects. The slope of the descending section of the constrained UHPC stress–strain curve was small, and the deformation capacity of the short column was improved. Compared with the constraint coefficient of the steel fiber content, the stirrup constraint coefficient exerted greater influence on the restraining effect of UHPC. A calculation formula for the constrained UHPC peak stress and the corresponding strain that considered the stirrup and fiber constraint coefficients was proposed on the basis of the experimental results and theoretical analysis. The proposed complete stress–strain curve equation of UHPC constrained by composite stirrups and steel fibers demonstrated consistency between the theoretical and experimental curves. [ABSTRACT FROM AUTHOR]

In this study, the shear behavior of reactive powder concrete (RPC) in terms of shear strength and shear slip was studied by direct shear tests on cubic specimens and the influences of water-binder ratio, steel fiber volume ratio and normal compressive stress ratio were investigated. The test results indicated that using a low water-binder ratio and a reasonable fiber content could enhance the shear strength of RPC specimens. The RPC specimen containing steel fiber will not be severed into two individual parts due to the connection of steel fiber. Moreover, the normal stress was the key contribution to the shear strength, and the residual shear capacity was mainly provided by the friction of the shear surface. The cracking of the specimens became more severe but the shear strength in the cyclic horizontal test did not decrease obviously compared with that in the monotonic horizontal test. Applying the twin-shear unified strength theory to the test data, it was indicated that the elliptic curve showed a good agreement. Therefore, the unified twin shear strength theory could predict the proper RPC strength envelope curve under combined compressive-shear stress states. [ABSTRACT FROM AUTHOR]