Addition Of Steel Fibers Research Articles

Laminated Steel Fiber-Reinforced Concrete Hingeless Arch: Research on Damage Evolution Laws

In the context of reinforced concrete (RC) arch bridges, while the incorporation of full sections of steel fibers can enhance the bridge’s toughness, cracking resilience, and bearing capacity, achieving an optimal balance between structural performance and economic viability in this manner remains challenging. This article introduces a novel computational approach—the distributed steel fiber concrete (LSFRC) arch—which considers the spatial distribution of damage in RC arches. The static performance of SFRC elements and LSFRC beams was compared and analyzed using the concrete plastic damage model (CDP) in ABAQUS software. This study validated the rationality of the model and investigated the impact of varying steel fiber volume ratios and steel fiber layer heights on the damage evolution of LSFRC arches. The results of this study demonstrate that the cracking load and bearing capacity of an RC arch can be effectively enhanced through the addition of steel fibers to a local area under static loading. Furthermore, the deflection and damage to the arch waist and arch roof can be significantly reduced. Furthermore, the incorporation of steel fibers at an increased volume rate and at a greater height within the doped section can effectively slow the rate of damage evolution within the section. This results in the inhibition of crack extensions and in an improvement in the ductility and reliability of the damage stage. The LSFRC arches offer superior economic and practical advantages over their full cross-section doped steel fiber (FRC) counterparts. This study offers novel insights and methodological guidance for the design and implementation of concrete arch bridges.

Parametric study on the flexural behavior of steel fiber reinforced concrete beams utilizing nonlinear finite element analysis

Reinforced concrete beams undergo significant internal forces and deformations under extensive loading and have flexural or shear failure based on the reinforcement detailing and geometric properties. The addition of steel fibers increases the deformation and load carrying capacities that leads to ductile behavior. The main contribution of fibers is the improvement of the composite tensile capacity, which results in improved flexural and shear responses. This study numerically investigates the effect of fiber properties on the flexural behavior of steel fiber reinforced concrete (SFRC) beams for both compression and tension failure. First, three specimens from prior experimental studies are modeled using the nonlinear finite element program ABAQUS and the analytical results are verified by comparison with the test results. Contrary to prior nonlinear models, the developed model accurately predicts the damage pattern, descending portion of the load-displacement relationship, and ultimate displacement, which lead to a reliable estimation of energy dissipation capacity and ductility. A comprehensive parametric study is then conducted to examine the effect of tension reinforcement ratio, fiber volume fraction, and fiber aspect ratio on the flexural behavior of both reinforced concrete and SFRC beams. The influence of these key parameters is investigated by comparing the peak load, displacement ductility, peak stiffness, service stiffness, energy dissipation capacity, and damage pattern for both reinforced concrete and SFRC beams. The analytical results indicate that the addition of steel fibers up to 2.0 % leads to a slight increase in the load carrying capacity, while the displacement ductility and energy dissipation capacity are significantly improved. Furthermore, the utilization of 1.0 % steel fibers is observed to be sufficient to modify the failure mode of over reinforced concrete beams from brittle compression failure to tension failure.

A response-based internal pressure risk assessment method for PCCV with steel fiber reinforcement

The probabilistic risk assessment (PRA) is a hot topic for highlighting the reliability and safety of infrastructures, especially for nuclear power plants (NPPs). The current internal pressure risk assessment method for prestressed concrete containment vessel (PCCV) generally adopts the internal pressure to characterize its fragility (namely internal-pressure-based fragility), even though the failure of PCCV is factually more tightly associated with PCCV’s realistic responses. This study proposes a novel response-based probabilistic risk assessment method for PCCV under internal pressure. The method adopts the response of the containment to characterize the fragility of components. Additionally, the steel fiber is introduced to form steel fiber reinforced concrete (SFRC) PCCV and the fragility and risk of the SFRC PCCV are quantitatively studied. The results indicate that a real and larger dispersion for the internal pressure risk of the PCCV would be induced by adopting the proposed internal pressure risk assessment method. The strategy of the addition of steel fiber to the conventional PCCV can decrease the internal pressure risk by about 72.1 % on average.

Effects of amount and geometrical properties of steel fiber on shear behavior of high-strength concrete beams without shear reinforcement

This study aims to investigate the effects of the geometrical properties and volume content of steel fibers on the shear resistance of reinforced high-strength concrete (HSC) beams without stirrups. Hooked-end and twisted steel fibers with different aspect ratios ranging from 60 to 100 were used at volume fractions of 0.5%–1.0%. The shear strength of HSC beams without stirrups significantly increased due to the addition of steel fibers and by increasing their volume fraction by up to 1.0%, resulting in approximately 1.7 times higher shear resistance. A higher fiber aspect ratio was effective in improving the resistance to shear failure of HSC beams without stirrups and in enhancing beam deformability relative to the increase in shear strength. Using twisted steel fibers led to better shear resistance than hooked-end steel fibers, resulting in 1.11- and 3.34-times higher shear strength and ductility at the same fiber volume fraction on average. The shear strength of steel fiber-reinforced concrete (SFRC) beams was also predicted using eight different models. Narayanan's model most precisely predicted the shear strengths of reinforced SFRC beams without shear reinforcement, with an average vu,exp/vu,pred ratio of 1.16. The shear strength increased with the decrease in shear span-to-depth (a/d) ratio and the increase in the fiber factor. The contribution of steel fibers to shear strength was greater for deep beams than slender beams. The predicted shear strengths of deep beams and high-strength SFRC showed a significant deviation from the actual value and required careful consideration.

High-strength steel fibre-reinforced geopolymer concrete utilising recycled granite waste and rice husk ash

A limited number of research studies have managed to attain high-strength geopolymer concrete, especially by utilising waste materials. In this study, granite waste (GW) from the mining industry, which contaminates the surrounding environment and causes air pollution, and rice husk ash (RHA) from agricultural waste were used to produce high-strength steel fibre-reinforced geopolymer concrete (HSFRGC). To reduce natural sand consumption, GW was utilised as a fine aggregate. RHA was added at 0%, 1%, 3%, and 5% by weight of coal fly ash to enhance the properties of HSFRGC. In addition, hooked-end steel fibres were employed as reinforcement at 0%, 0.5%, and 1% by volume of the concrete. The objective of this study is to investigate the effect of incorporating GW and RHA into HSFRGC, examining properties such as workability, strength, durability, and microstructure. Additionally, an assessment was conducted on the environmental impact and cost-effectiveness of the HSFRGC system with additives to determine its feasibility for practical scenarios. The results showed that the addition of 1% RHA as an additive in the geopolymer system, which led to microstructural homogeneity in the geopolymer matrix, could effectively enhance the mechanical properties and durability. Moreover, the addition of hooked-end steel fibres along with 1% RHA further improved the mechanical performance compared to samples without steel fibres, increasing both compressive strength by 25% and flexural response by 70%. Meanwhile, incorporating 1% RHA in mixtures could assist in mitigating chloride migration by approximately 10% due to the filler effect occurring in the geopolymer matrix. Regarding to environmental impact and cost-effectiveness, the incorporation of 1% RHA and 0.5% steel fibre demonstrated a suitable balance, exhibiting eco-strength efficiency with an increase of 15% compared to plain geopolymer concrete, making it a reasonable choice for both environmental concerns and cost efficiency.

Influence of Extra-Short Extra-Fine Steel Fibers on Mechanical Properties of Self-Compacting Concrete with Single-Doped Fly Ash

This study assesses the influence of extra-short extra-fine steel fibers on the performance of self-compacting concrete (SCC) modified with fly ash. Replacing standard steel fibers with volume fractions ranging from 0%, 1.5%, 3%, 5% and 6%, the study optimizes the mix design for enhanced workability and mechanical properties. The findings reveal that, although the addition of steel fibers had a negative effect on the flowability, the cohesion is significantly improved, providing a basis for a significant improvement in the mechanical properties. The optimal fiber content is identified at 5%, achieving the highest compressive strength of 71.7 MPa, split tensile strength of 8.2 MPa, and flexural strength of 12.8 MPa at 28 d. However, further increases in fiber content beyond 5% lead to a deceleration in compressive and splitting tensile strength improvement and a 27.5% drop in flexural strength at 28 d. The study also emphasizes the good dispersion within the concrete, which helps to enhance its ductility and crack resistance, to some extent.

Achieving thermoelectric properties of ultra-high-performance concrete using carbon nanotubes and fibers

The study investigated the impact of carbon nanotubes (CNTs), carbon fibers (CFs), steel fibers, and varying water-to-binder (W/B) ratios on the thermoelectric and mechanical properties of ultra-high-performance concrete (UHPC). Flowability tests revealed reduced flow with decreased water content and the addition of CNTs or CFs, particularly pronounced at a lower W/B ratio. Thermal gravimetric analysis and Fourier-transform infrared spectroscopy demonstrated differences in peak intensities and shifts in peaks related to the hydration products of the UHPC by the incorporation of the CNTs and CFs. The compressive strength and tensile performance increased with reduced W/B ratios and the inclusion of steel fibers, whereas the CNTs and CFs affected the strength differently based on their dispersion and interaction with other components that influenced porosity. The presence of steel fibers reduces the percolation threshold for CNTs and CFs, indicating a synergistic effect that enhances electron transport connectivity. The thermal conductivity increased with the addition of CNTs, CFs, and steel fibers, enhancing heat transfer within the UHPC. The thermoelectric figure of merit (ZT) values highlighted the combined impact of CNTs, CFs, steel fibers, and W/B ratios on the thermoelectric efficiency of the UHPC, showing significant improvements with the inclusion of steel fibers and the interplay between the CNTs and W/B ratios. Ultimately, upon introducing 1.5 % steel fibers and 0.3 % CNTs, a substantial enhancement in the thermoelectric ZT was observed, surpassing the standard UHPC values by 12 orders of magnitude.

Investigating the role of steel and polypropylene fibers for enhancing mechanical properties and microstructural performance in mitigating conversion effects in calcium aluminate cement

Fiber reinforcement is widely employed in numerous industries due to its exceptional mechanical properties; however, its specific role in enhancing the strength of calcium aluminate cement (CAC) composites remains inadequately understood. This study investigates the influence of fiber addition on the mechanical characteristics of CAC composites during curing. Two types of fibers, steel and polypropylene, were incorporated into CAC composites, and their mechanical properties, chemical composition, and microstructural performance were evaluated using various methods. Assessments including flowability, bulk density, volume of permeable voids, water absorption, and mechanical strength tests were conducted, alongside X-ray diffraction (XRD) analysis, thermogravimetric analysis (TGA), and Field Emission Scanning Electron Microscopy (FESEM) analysis. Results reveal a significant enhancement in mechanical strengths with the inclusion of fibers in CAC composites. The addition of 1% fibers to the composites resulted in significant improvements. Steel fibers (SF) led to notable enhancements of approximately 19.7%, 68%, and 26.4% in compressive, direct tensile, and flexural strengths, respectively, while polypropylene fibers (PF) resulted in enhancements of 1.9%, 20%, and 16.7%, respectively. Microstructural analysis revealed that SF and PF contribute to pore refinement, enhancing strength and durability. Findings suggest that SF addition effectively mitigates strength loss induced by the conversion effects of stable phase C3AH6 in CAC, thereby fostering the development of an environmentally friendly, quick-setting, high-performance concrete system. This research offers valuable insights for the design and potential enhancement of CAC-based composites to improve performance and durability under severe conditions.

Comparative impact behaviours of ultra high performance concrete columns reinforced with polypropylene vs steel fibres

Polypropylene (PP) fibres have primarily used to control shrinkage cracks or mitigate explosive spalling in concrete structures exposed to fire or subjected to impact/blast loads, with limited investigations on capacity improvement. This study unveils the possibility of using PP micro-fibres to improve the impact behaviour of fibre-reinforced ultra-high-performance concrete (FRUHPC) columns. Results show that the addition of fibres significantly improves the impact behaviour of FRUHPC columns by shifting the failure mechanism from brittle shear to favourable flexural failure. The addition of steel or PP fibres affected the impact responses differently. Steel fibres considerably increased the peak impact force (up to 18%) while PP micro-fibres slightly increased the peak (3%–4%). FRUHPC significantly reduced the maximum mid-height displacement by up to 30% (under 20° impact) and substantially improved the displacement recovery by up to 100% (under 20° impact). FRUHPC with steel fibres significantly improved the energy absorption while those with PP micro-fibres reduced the energy absorption, which is different from the effect of PP-macro fibre reported in the literature. The optimal fibre content for micro-PP fibres is 1% due to its minimal fibre usage and low peak and residual displacement. This study highlights the potential of FRUHPC as a promising material for impact-resistant structures by creating a more favourable flexural failure mechanism, enhancing ductility and toughness under impact loading, and advancing the understanding of the role of fibres in structural performance.

Evaluating the fresh and mechanical properties of steel slag aggregate concrete reinforced with steel fiber

In this study, steel slag (SS) and steel fiber (SF) were used to make environment-friendly high-strength concrete. Natural coarse aggregate (NCA) was initially substituted partially with SS at various substitution levels, i.e., 25 %, 50 %, 75 %, and 100 %, respectively, for getting the optimum substitution levels of SS in concrete. Afterward, SF, having an aspect ratio of 60, was considered with volume fractions of 0.15 %, 0.3 %,0.45 %, 0.6 %, 0.75 %, 0.90 %, 1.05 %, and 1.2 % in concrete. The water-to-binder ratio was taken as 0.35 for all the concrete mixes. For the fresh property, slump and compaction factor of concrete were determined. Similarly, for the mechanical property compressive strength (CS), split-tensile strength (STS), and flexural strength (FS) have been tested after the curing age of 28 and 56 days. Additionally ultrasonic pulse velocity (UPV) test was conducted to measure the quality of concrete. X-ray diffraction (XRD) was also performed to analyze crystalline phases and identify mineralogical composition within the concrete matrix. All the tests were compared with the standard concrete made with NCA. It has been found that the addition of steel slag aggregate (SSA) and SF enhances the mechanical properties of concrete, whereas it reduces workability. Substituting 50 % of SSA for NCA alongside 1.05 % of SF results in the highest CS, while employing 1.2 % SF achieves maximum STS, FS, and UPV.

Performance of Steel Fiber Reinforced Concrete under Different Cooling Methods at High Temperature

Performance of Steel Fiber Reinforced Concrete under Different Cooling Methods at High Temperature

Behaviour of Steel Fiber Reinforced Concrete in Deep Beam for Flexure

Use of deep beam in construction field saves money as well as increase the strength of structure. Reinforced concrete deep beams have very useful structural application such as piles-caps, water tanks and tall buildings. Addition of steel fibers gives good results to both load carrying capacity and increase the flexural strength of the deep beam. Steel fiber is kind of newly developed reinforced material for concrete widely adopted globally now a day, which features good performance in anti-crack, pressure resistance, anti-abrasion bending toughness, affinity with concrete, reinforcement for construction element compjonent and lengthy service life. Thus by using the steel fiber reinforced deep beam with varying percentage of steel fibers increases the first crack load and the ultimate load which gives the high flexural strength to the structure and achieves economy. This paper includes study of behaviour of steel fiber reinforced concrete in deep beam with advantages, disadvantages, properties of steel fiber etc. Keywords: Steel Fiber, Beam, Anti-Abrasion Bending Toughness, Affinity, Reinforcement

Research on the Mechanical, Thermal and Induction Healing Properties of Asphalt Wearing Course with Steel Fibers.

Induction healing technology can effectively repair microcracks in asphalt mixtures and is a promising maintenance technology for asphalt pavements. However, it requires the addition of steel wool fibers to asphalt mixtures and cannot be directly used to repair existing pavements. In order to improve the practicality of the induction healing technology, this article designs a wearing course asphalt mixture with induction healing function that is going to be paved above the existing road surface. The AC-10 asphalt wearing course for induction heating was prepared by adding steel fiber (SF). Analysis of the overall temperature of the surface revealed the unevenness of the temperature distribution, and the healing properties were investigated through protective heating that controlled the maximum temperature of the upper surface. The results show that the addition of SF can improve the high-temperature stability, low-temperature and intermediate-temperature crack resistance, and moisture stability of asphalt wearing courses; however, it has adverse effects on volumetric performance and skid resistance. The heating temperature increases with the increase in SF content, but higher maximum temperature heating rate causes worse heating uniformity and lower healing effect. The maximum heating rate of the sample with 10% SF reaches 3.92 °C/s, while its heating rate at minimum temperature is similar to that of the sample with 6% SF, which is only 0.7 °C/s, indicating the worst heating uniformity. The best healing effect occurs when the maximum temperature of the upper surface reaches 160 °C. The recommended optimal SF content is 6% of the asphalt volume. The asphalt mixture with 6% SF has an appropriate volume performance, moisture stability, and skid resistance; additionally, it has the best high-temperature stability, as well as low-temperature and intermediate-temperature crack resistance. Meanwhile, it also has uniform temperature distribution and efficient healing efficiency.

Structural behavior of steel tube reinforced resilient RAC shear walls under static cyclic loading

This paper proposed a method to enhance the energy dissipation capacity of recycled aggregate concrete (RAC) shear walls reinforced with ultra-high strength bars (UHSB). The proposed method encases circular steel tubes within the boundary elements of walls. With the presence of steel tubes, steel fibers and axial load level as primary research variables, five RAC shear walls were fabricated and tested under reversed cyclic lateral force and constant axial compression to verify the effectiveness of the proposed method. The test results showed that the presence of steel tubes upgraded lateral resistance and enhanced energy dissipation capacity, while causing some subtle splitting cracks. Due to the yielding of the steel tubes, the encasement of the steel tube increased residual drift ratio at large drift, but the measured residual drift ratios of test walls still were kept less than 0.5 % until 2.5 % drift ratio. The addition of steel fibers delayed cracking, constrained the cover concrete and reduced damage to the specimens. Test results also indicated that increasing concrete strength and axial compression level could enhance the lateral resistance of the proposed wall. In addition, a numerical analytical method is presented to analyze the cyclic behavior of the proposed shear walls. Good agreement was observed between the measured and calculated hysteretic loops.

Study on fracture characteristics of steel fiber reinforced manufactured sand concrete using DIC technique

Incorporation of steel fibers to improve the defects of manufactured sand concrete (MSC) has received a great deal of attention, while the fracture mechanism of the MSC by volume fraction of steel fibers (Vf) has been less studied. To investigate the effects of steel fibers on the fracture characteristics of the MSC, three-point bending tests were conducted on the MSC beams with different Vf (0, 0.5 %, 1.0 % and 1.5 %) using digital image correlation technique. The effects of Vf on the fracture parameters and crack propagation paths of steel fiber reinforced manufactured sand concrete (SFRMSC) were analyzed. In addition, fracture process zone (FPZ) of the SFRMSC was analyzed via the length of the FPZ (lFPZ) and area of the FPZ (AFPZ). The results indicated that the residual strength, initiation fracture toughness, unstable fracture toughness, fracture energy and characteristic length of the SFRMSC increased with the increase of Vf, whereas the crack propagation paths were not sensitive to the changes of Vf. The addition of steel fibers increased the interaction between the aggregate and the matrix, which led to an increase in the number of microcracks. Before approaching the Pc, both the lFPZ and AFPZ showed essentially stable changes. As Vf increased, the lFPZ and AFPZ developed faster to their corresponding maximum values. The AFPZ reached a maximum and increased with the Vf. At the Pc, the lFPZ and AFPZ changed in a similar trend when Vf ≤ 1.0 %. When Vf > 1.0 %, the lFPZ changed slightly while the AFPZ increases sharply.

Experimental and Analytical Study on Recycled Aggregate RC Columns: Short and Slender Loaded Axially and Eccentrically

To protect the environment and preserve natural resources, it is crucial to use recycled aggregate (RA) in construction. The recycled coarse aggregate reinforced concrete columns with the addition of steel fiber evaluated under concentric and eccentric loadings for short and slender columns were examined experimentally and analytically in this research. Twenty-four column specimens were built for this study to examine the impact of steel fiber, recycled aggregate, slenderness, and eccentricity on the behavior of reinforced concrete columns. This research examined the failure mode, maximum load-carrying capacity, strain in the concrete, strain in the reinforcement, and ductility. Based on the results, it can be concluded that employing recycled concrete aggregate is a potential approach to meet design codes. The addition of 1% steel fiber effectively prevents concrete from crushing and spalling. Steel fiber, however, improved the columns’ ductility and strength. The results showed the maximum load-carrying capacity of the specimens and the results of using ACI-318 code equations agreed very well. Furthermore, a model is proposed for columns with both natural and recycled aggregate and which accounts for the eccentricity and slenderness to forecast the load-carrying capacity. The outcomes demonstrated that the design principles were met well. Plots of load–moment interaction diagrams for short and slender columns made with the ACI-318 method are compared to the findings of the experiments.

Investigation of electromagnetic interference shielding performance of ultra-high-performance mortar incorporating single-walled carbon nanotubes and steel fiber

For security amenities and key infrastructure, construction materials with extraordinary mechanical, durability, and electromagnetic interference (EMI) shielding performance are essential. This study investigates the EMI shielding performance of ultra-high performance mortar (UHPM) incorporating single-walled carbon nanotubes (SWCNT) and steel fibers. Currently, no such work is present in the existing literature. Eight mixtures were prepared with varying SWCNT dosages (0%–0.03 % by weight of cement) and steel fiber additions (1.2 % of the volume of the UHPM mixture). The performance of UHPM incorporating SWCNT and steel fibers was evaluated through flow diameter, compressive strength, flexural strength, Schmidt hardness, ultrasonic pulse velocity, EMI shielding performance, and scanning electron microscopy analysis tests. It is observed that increasing the SWCNT content enhances the compressive strength, flexural strength, ultrasonic pulse velocity, and Schmidt hardness of UHPM. The addition of steel fibers further enhances compressive (up to 22 %) and flexural (up to 92 %) strengths. In terms of the transmittance behavior, the improved EMI shielding performance of UHPM with the increasing SWCNT content is observed prominently at high electromagnetic frequencies (i.e., 2500 MHz–5100 MHz). However, the improved shielding performance is observed to be quite low, limited to 10 dB. Moreover, combining steel fibers and SWCNT enhances the EMI shielding performance of UHPM in terms of the transmittance behavior. As a result, UHPM incorporating SWCNT and steel fibers behaves as an absorbent material, shielding a significant amount of energy, approximately 45 dB, at a frequency of 5000 MHz. Based on the results, UHPM incorporating SWCNT and steel fibers can be used effectively as EMI shielding material. The findings of this study will enhance the practical applications of UHPM incorporating SWCNT and steel fibers.

Structural Behavior of Circular Concrete Columns Reinforced with Longitudinal GFRP Rebars under Axial Load

This paper presents experimental and theoretical assessments of the structural behavior of circular steel fiber-reinforced concrete (SFRC) columns reinforced with glass fiber-reinforced polymer (GFRP) bars subjected to a concentric axial compressive load. Laboratory experiments were planned to evaluate and compare the effect of different design parameters on the structural behavior of column specimens based on experiments and finite element (FE) analysis. The experimental variables were (i) concrete types, i.e., conventional concrete (CC) and fiber-reinforced concrete (FC), (ii) longitudinal reinforcement types, i.e., steel and GFRP bars, and (iii) transverse rebar configurations, i.e., tied and spiral with different pitches. Sixteen column specimens were fabricated and categorized into four groups with respect to rebar configurations and concrete types. The results showed that the failure modes and cracking patterns of those four column groups were comparable, particularly in the pre-peak branches of load-deflection curves. Even though the average ultimate load of the columns with longitudinal GFRP bars was 17.9% less than that with longitudinal steel bars, the ductility index (DI) was 10.2% greater than their counterpart on average. The addition of steel fibers (SF) to concrete increased the axial peak load by up to 3.1% and the DI by up to 6.6% compared to their counterpart CC columns without SFs. The DI of specimens was increased by higher volumetric ratios (up to 12%) and spiral types (up to 5.5%). The concrete damage plastic (CDP) model for FC columns was updated in the finite element software ABAQUS 6.14. Finally, a new simple equation was theoretically proposed to predict the axial capacity of specimens by considering the inclusion of longitudinal GFRP rebars, volumetric ratio, and steel spiral/hoop ties. Good agreement between the proposed model predictions and the experimental/numerical results was observed.

Experimental study and modelling of flexural behaviour of continuous fibre-reinforced lightweight aggregate concrete one-way slab at ambient and elevated temperatures

An experimental study on the flexural behaviour of six fibre-reinforced lightweight aggregate concrete (FRLWAC) one-way slab strips under ambient and elevated temperatures is presented in this paper. Two slabs, one simply-supported and one continuous, were loaded to failure at ambient temperature as references for the fire tests, while another simply-supported and three continuous slabs with varying degrees of design moment redistribution were loaded and exposed to elevated temperatures until failure. The ambient tests showed that the steel fibre addition prevents premature flexural-compression failure commonly observed in lightweight aggregate concrete structures. The rotations of FRLWAC plastic hinges were concentrated in a single crack under ambient temperature and a few cracks under fire exposure. The fire tests revealed significant moment redistribution towards the hogging moment area in the continuous slabs due to restrained thermal-induced deflection. Furthermore, the reinforcement configuration that catered for moment redistribution towards the hogging area was found to enhance the fire resistance of continuous FRLWAC slabs. A fibre-reinforced concrete (FRC) plastic hinge model, based on the rigid-body rotation concept, was proposed and validated. This model predicts the moment-rotation behaviour of FRC hinges at ambient temperature and the fire resistance of FRLWAC one-way slabs with good accuracy.

Study on stress–strain relationship and constitutive model of recycled aggregate concrete under axial cyclic compression

AbstractThe effects of dry or saturated state, water–cement ratio, coarse aggregate type and steel fiber on the stress–strain relationship of RAC under cyclic loading were studied. What is more, the characteristics of stress–strain curve, plastic strain, stress degradation and stiffness degradation of RAC under cyclic loading were analyzed. The microstructure of RAC was analyzed. Based on the principle of surface energy, the reason for the decrease in compressive strength of wet concrete was analyzed. In addition, the envelope equation of stress–strain curve under cyclic loading, unloading and reloading curve was established. The test results showed that the peak stress of the envelope line of RAC under cyclic loading was affected by dry or saturated state, water–cement ratio and coarse aggregate type, but the addition of steel fiber could reduce the degradation rate of stress and stiffness of RAC after peak strain. The plastic strain accumulation of RAC before and after the peak stress was quite different, but dry or saturated state, water–cement ratio, coarse aggregate type and steel fiber have no obvious influence on the plastic strain accumulation of RAC. The pores and cracks of RAC provide space and channels for the moisture absorption and water absorption. The Weibull–Lognormal statistical distribution envelope model, unloading curve model and reloading curve model established were in good agreement with the experimental curves. The research results provided a reference for the study of the full curve constitutive model of RAC under cyclic loading.