Steel Fiber Reinforced Concrete Beams Research Articles

Development of Torsional Strength Model for Steel Fiber Reinforced Concrete Beams with Transverse Reinforcement

Development of Torsional Strength Model for Steel Fiber Reinforced Concrete Beams with Transverse Reinforcement

Standardized RC beam tests for modeling the fiber bridging effect in SFRC

Fiber reinforcement is a promising solution to cracking problems and improving the concrete’s structural performance. The residual strength of the cracked concrete can characterize the reinforcement efficiency. However, quantifying the residual performance of steel fiber-reinforced concrete (SFRC) is challenging. The existing methodologies provide empirical formulas for estimating the residual strength using test results of SFRC elements in which a predominant crack governs the mechanical resistance. For instance, the 0.5 mm crack width determines the minimum value considered in the RILEM standard formulas. Thus, the SFRC strength evolution at earlier cracking stages remains unknown. At the same time, such a crack approximation is irrelevant to structural cases when reinforcement bars stimulate the formation of multiple cracks, and the 0.1–0.2 mm crack typically corresponds to the yielding of the steel bars. This study describes an alternative approach for quantifying the average residual stresses in SFRC elements with multiple cracks. It hypothesizes the possibility of separating the mechanical resistance components, corresponding to tension stiffening and fiber bridging effects characteristic of SFRC elements with bar reinforcement, using standardized small-scale specimens to estimate the fiber contribution. The laboratory tests of the plain concrete and SFRC beams with bar reinforcement illustrate the proposed technique. The Rilem standard three-point bending tests and the numerical simulation of full-scale beams verify the analysis’s adequacy. The developed model is suitable for finite element simulations (employing the smeared crack model); the capability of separating the tension stiffening and fiber bridging effects ensures its versatility.

Investigação da contribuição do engrenamento dos agregados em vigas de concreto armado e concreto reforçado com fibras de aço

Abstract Shear strength in reinforced concrete (RC) beams, especially in steel fiber reinforced concrete (SFRC) beams is a subject of great interest in structural engineering. In the case of beams without transverse reinforcement, the failure is explained based on a predefined crack pattern and kinematics, and the transfer of shear force accomplished through different mechanisms. Among these mechanisms, the aggregate interlock is present in most of the existing shear strength mechanical models in the literature, with divergences regarding its performance and preponderance. Thus, this paper focuses on evaluating the contribution of aggregate interlock throughout the critical crack formation process up to the ultimate load by performing bending tests on small-scale rectangular RC and SFRC beams without considering the effect of transverse reinforcement. The Digital Image Correlation (DIC) technique is used to track the patterns of shear cracks and their associated kinematics by measuring the relative displacements of opening (w) and sliding (δ). A detailed description of the shear behavior of these beams is provided by quantifying the aggregate interlock using the simplified Walraven model. The results help to understand the level of contribution of the aggregate interlock, and the main differences between structural elements of concrete with and without steel fibers in the scope of the shear strength.

Multiscale soft computing-based model of shear strength of steel fibre-reinforced concrete beams

Concrete is weak in tension, so steel fibres are added to the concrete members to increase shear capability. The shear capacity of steel fibre-reinforced concrete (SFRC) beams is crucial when building reinforced concrete structures. Creating a precise equation to determine the shear resistance of SFRC beams is challenging since many factors can influence the shear capacity of these beams. In addition, the precision available equations to predict the shear capacity are examined. The current research aims to examine the available equations and propose novel and more accurate model to predict the shear capacity of SFRC beams. An innovative evolutionary polynomial regression analysis (EPR- MOGA) is utilized to propose the new equation. The proposed equation offered improved prediction and increased accuracy compared to available equations, where it scored a lower mean absolute error (mathrm{MAE}) and root mean square error (mathrm{RMSE}), a mean (mu) close to the optimum value of 1.0 and a higher coefficient of determination ({R}^{2}) when a comparison with literature was conducted. Therefore, the new equation can be employed to assure more resilient and optimized design calculations due to their improved performance.

Modelagem computacional de vigas de concreto simples e reforçados com fibras de aço sem armadura transversal

Abstract Finite element analysis with nonlinear material behavior modeling can be used to design concrete structures. This study aimed to develop a computational model to represent the shear behavior of concrete beams without transverse reinforcement described in the literature, with or without steel fibers. Two different approaches of finite element analysis were investigated, namely smeared and discrete crack models. The results of the smeared crack model were compared with the results of double-notched push-through tests, and an empirical equation for the shear retention factor of plain concrete was suggested. The computational model using a discrete crack approach with representation of the aggregate interlocking mechanism was compared with the results of push-of test, and an accurate correlation was observed up to the maximum shear stress. It was concluded that the discrete crack approach provided the most accurate representation of the shear behavior of a non-reinforced beam with a shear span-to-depth ratio of 2.17. However, for a non-reinforced beam with a shear span-to-depth ratio of 2.66, the smeared crack approach accurately represents the shear strength and stiffness of the beam. The shear retention factor had little influence on the overall behavior of a steel fiber-reinforced concrete beam. Finally, it was concluded that a variable shear retention factor should be used in the smeared crack approach with fixed crack, as a constant shear retention factor tends to overestimate the shear strength of beams.

APPLICATION OF DIGITAL IMAGE CORRELATION TO CAPTURE THE CRACK MOUTH OPENING DISPLACEMENT OF THE NOTCHED STEEL FIBER REINFORCED CONCRETE (SFRC) BEAM

The application of digital image correlation (DIC) to capture any point in the experimental test is found to be promising. Using the DIC and appropriate tool can overcome the limitation of the traditional sensors to capture the movement or displacement in the tested specimen. In this study, an open-source DIC called Digital Image Correlation Engine (DICE) is used to capture the crack mouth opening displacement (CMOD) of the notched steel fiber reinforced concrete (SFRC) beam with points tracking method. There are three beam specimens with different sizes and similar aspect ratios reported in this paper. All beams have 0.5% steel fiber volumetric content. The SFRC beams are marked with points and tested under a three-point bending flexural test. Custom firmware for Canon DSLR 650D digital camera called Magic Lantern is used to capture the pictures per one second. DICE software is used to analyze the point movements and dumped the output file. ParaView 5.9.0 is then used to visualize the data. A method to calibrate the point coordinate with actual measurement is proposed. A small script is written in Visual Basic Application (VBA) in Microsoft Excel to correlate the displacement for each point of interest with the recorded applied load. With the developed script, any point of interest tracked with DICE can be related to the recorded data from the data logger. From this study, the obtained CMOD with the corresponding applied load is presented, which can be used to investigate the flexural fracture energy of the SFRC beam.

Evaluation of Deformation for Steel Fiber Concrete Beams with BFRP Tendons Eroded by Seawater under Cyclic Loading

Steel fiber-reinforced concrete (SFRC) beams with fiber-reinforced polymer (FRP) bars are promising new composite structures. To investigate the durability of BFRP-SFRC beams, eleven beams were fabricated and conducted via four-point bending tests under cyclic loading. The experimental variables included BFRP reinforcement ratios, pre-cracked widths and environments (Natural or Seawater erosion). Experiment results revealed that the load-deflection curves of BFRP-SFRC beams showed bilinear growth. With the increase in loading and unloading cycles, the peak load and energy consumption of the tested beams decreased, and the impact of loading and unloading cycles on the flexural performances of the BFRP-SFRC beams enhanced with the increase in displacement. Under the same load, as the pre-crack width increases, the deflection of the BFRP-SFRC beam decreases. The deflection of the beam with a pre-crack width of 0.4 mm was 1.34 times than that of the beam without a pre-crack at the load of 100 kN. What is more, the pre-crack width had a bad effect on the energy consumed by the BFRP-SFRC beams. Compared with no pre-crack beam, the energy consumed by the beams with 0.02, 0.2 and 0.4 mm pre-crack width were decreased by 1.5%, 7.8% and 11.0% at the 18 mm displacement, respectively. Significantly, the effect of sea water erosion on the energy consumption of tested beams with high BFRP reinforcement ratios were smaller than that of tested beams with low BFRP reinforcement ratios. Finally, a calculation model of deformation of BFRP-SFRC beams under seawater erosion environments was proposed based on the effective moment of inertia methods. Compared with the existing calculation methods, this model was better correlated with the experimental results.

SFRC used RC Beam and its Increasing Torsional Strength

Steel Fiber Reinforced Concrete (SFRC) is the most often employed method for improving the flexural, shear, and torsional properties of concrete in the modern era. It is capable of withstanding cracks and crack propagation. As a consequence of this capacity to arrest fractures, fiber composites may improve extensibility and tensile strength, both at the initial crack and at the final load, and fibers can help keep the matrix together after significant cracking. Steel fibers are short in length and are employed in concrete in proportion to their aspect ratio (i.e., the ratio of length to diameter); this ratio ranges from 20 to 100. Torsion is often associated with bending moment and shear force, and so the interplay of these forces is critical. Torsion occurs when a slab or beam is supported on just one side or when stresses acting transverse to the beam's longitudinal axis are applied. Numerous researchers have worked with SFRC to boost the flexural and shear capacities of the material, but the amount of work done on torsional strengthening is insignificant. This article introduces steel fiber, reviews prior experimental investigations on torsional strengthening, and compares the torsional strength and angle of twist of normal concrete and SFRC beams when varying percentages of steel fiber used.

Diagonal tension performance of concrete panels reinforced with hooked end steel fibers

The increase in strength of Steel Fiber Reinforced Concrete (SFRC) depends mainly on factors such as the dosage, aspect ratio and number of hooked ends of the fibers. Previous studies proposed models to estimate the flexural and shear strength of SFRC beams, but the shear behavior of SFRC panels has not been extensively studied. The study includes diagonal tension tests on concrete panels to assess the shear performance of SFRC. The experimental program comprises 19 square concrete panels having 600 mm side and 75 mm thickness, including three nominal dosages of steel fibers (20, 40 and 60 kg/m3) and three different number of hooked ends (1, 1.5 and 2). The study proposes models to predict the shear strength and deformation capacity, stiffness degradation and toughness of SFRC panels with different number of hooked ends when subjected to diagonal tension. The models include four characteristic limit states of diagonal cracking, maximum residual strength, code-based acceptable degradation, and maximum deformation.

A practical approach for monitoring reinforcement corrosion in steel fiber reinforced concrete elements exposed to chloride rich environments

AbstractThe use of fibers in Reinforced Concrete (RC) elements changes their cracking pattern, leading to narrower and more closely spaced cracks. In addition, the presence of fibers can improve the steel‐to‐concrete bond behavior reducing the steel‐to‐concrete interface damage after cracking. Cracks and steel‐to‐concrete interface damage work like paths, for aggressive agents, to reach the rebar in cracking elements, reducing the initiation period of the corrosion process, and favoring the corrosion at the intersection between cracks and reinforcement. In this context, this article discusses an experimental program on tension ties mechanically cracked and exposed to a chloride‐rich environment with the purpose to check and eventually adequate the typical electrochemical measurements, used in the case of RC elements, for Steel Fiber Reinforced Concrete (SFRC). Adjustments related to degradation morphology and interference of steel fibers are proposed and used on Fiber Reinforced Concrete (FRC) elements for monitoring the influence of cracks and fibers on corrosion propagation. Finally, these proposed modifications were checked and validated against the results obtained by monitoring SFRC beams in the cracked stage.

Calculation of Cracks in Partially Steel Fiber Reinforced Concrete Beams with BFRP Bars

The effects of steel fiber volume rate and steel fiber concrete thickness on the crack development and crack resistance of basalt fiber reinforced polymer (BFRP) beams were investigated by flexural tests on six partially reinforced BFRP steel fiber reinforced concrete beams. The results showed that the addition of steel fibers effectively limited the extension height of the initial crack and the crack expansion after cracking, and the difference in the extension height of the crack between the partial steel fiber test beam and the full-section steel fiber test beam was small. For BFRP reinforced concrete beams partially reinforced with steel fibers, the development of the maximum crack width can be effectively suppressed under ultimate load. Its crack arresting effect is more similar to that of full-section steel fiber reinforced concrete beams with BFRP bars; it shows that adding steel fibers only in the compression zone of the beam can not only improve the load capacity of the beam but also obtain good economic benefits. According to the test results, on the basis of the bond-slip theory and the no-slip theory, a comprehensive calculation method of the crack spacing considering the bond effect between the steel bar and the concrete and the influence of the concrete protective layer is proposed. According to the calculation formula of crack width, and according to the influence of the actual plastic deformation of concrete in the tensile area of the section, the calculation formula of the normal section crack resistance of BFRP reinforced steel fiber concrete beams is carried out, and the calculation results are compared with the test results, which are in good agreement.

Research on Deflection of Partial Steel Fiber Reinforced Concrete Beams with BFRP Bars

In this study, the flexural behavior tests of steel fiber reinforced concrete beams with BFRP bars under static load are carried out by means of statics experiment and theoretical analysis. A total of seven beams were designed for this experiment, and the effects of two factors on the mid-span deflection of the beams were investigated with the steel fiber incorporation rate (0%, 0.5%, 1%, 1%/0.5%, 1.5%) and the height of steel fibers in the concrete layer in the compression zone (180 mm, 210 mm, 300 mm) as the main variables. In this study, based on the existing research results and combined with the actual test results, the formulae for calculating the cracking section moment of inertia applicable to BFRP reinforced steel fiber (full section/pressure zone reinforced) concrete beams are derived. At the same time, the results obtained from the formula and the results of the ACI code in the United States are compared with the data of the results obtained from this test, and the calculated results of this formula are in good agreement with the actual values.

Tensile strength and fracture toughness of steel fiber reinforced concrete measured from small notched beams

Steel fiber reinforced concrete (SFRC) is a kind of multiphase composite material and its tensile strength (ft) and fracture toughness (KIC) cannot be easily measured using small samples due to its highly heterogeneous microstructure. In this study, a novel evaluation is proposed for calculating ft and KIC of brittle heterogeneous solids. The results obtained by this method have been confirmed by three-point bending (TPB) test results of 75 notched SFRC beams in which the length of the corrugated steel fibers is 36 mm. Considering the heterogeneity and discontinuous fracture failure characteristic of SFRC samples, a virtual crack propagation calculation model is established, and the accurate prediction of ft and KIC can be obtained by incorporating the model into the Hu-Duan boundary effect model (BEM). The reasonable range of tensile strength of SFRC used in this paper is about 3.77–5.66 MPa. Compared with the median value of this range, the calculation error of BEM is only 7.69 %. By discussing the influence of α-ratio (defined as the ratio between the height W and the initial notch depth a0) on the predicted results, a value that is less affected by the front and rear boundary is obtained, and the value range is 0.16–0.24. Meanwhile, the exact ft and KIC can be obtained by using only 1–2 groups of samples with reasonable α-ratio. Based on the failure curve of SFRC established by using ft and KIC, the theoretical minimum size of samples with different α-ratio is determined under the condition of linear elastic fracture mechanics (LEFM). This method provides a valuable reference for the estimation of concrete mechanical parameters.

The Use of GA and PSO in Evaluating the Shear Strength of Steel Fiber Reinforced Concrete Beams

Shear failure in concrete specimens and beams is one of the most sensitive cases in construction projects. Since the shear strength of specimens is affected by various parameters, it is important to study them to arrive at a predictive relationship or model. This research has used the computational methods of machine learning to achieve a new evaluation of the shear strength of reinforced concrete (RC) beams. In the first step, 85 laboratory samples were examined. These samples had different geometric and non-geometric properties. The effect of each parameter was examined for smart models, then the optimal state of the parameters was determined. By optimizing the number of parameters, basic models were developed. The different structures of these models were investigated for the accurate evaluation of the shear strength of the samples. Finally, in the second step, the particle swarm optimization (PSO) and genetic algorithm (GA) were used to perpetuate and optimize the weights of the base models. The hybrid models were developed and applied with different structures for evaluation of shear strength and the best models were selected from them. The results showed that both models offer better performance than the base model. However, the GA-based model achieved higher accuracy and less error than the PSO-based model. Finally, the performance of these models was used for new data to evaluate their performance. As the main achievement of this research, these methods can be recommended and implemented for other conditions as well.

Robust Prediction of Shear Strength of SFRC Using Artificial Neural Networks

The assessment of shear behavior in SFRC beams is a complex problem that depends on several parameters. This research aims to develop an artificial neural network (ANN) model that has six inputs nodes that represent the fiber volume (Vf), fiber factor (F), shear span to depth ratio (a/d), reinforcement ratio (ρ), effective depth (d), and concrete compressive strength (fc′) to predict shear capacity of steel fiber-reinforced concrete beams, using 241 data test gathered from previous researchers. The proposed ANN model provides a good implementation and superior accuracy for predicting shear strength compared to previous literature, with a Root Mean Square Error (RMSE) of 0.87, the average ratio (vtest/vpredicted) of 1.00, and the coefficient of variation of 22%. It was shown from parametric analysis the reinforcement ratio and shear span to depth ratio contributed the most impact on the shear strength. It can also be noticed that all parameters have a nearly linear impact on the shear strength except the shear span to depth ratio has an exponential effect.

Mesoscale analysis of Fiber-Reinforced concrete beams

Unlike traditionalconcrete,steel fiber reinforcementimproves durability and crack control. The current work developed an extensive numerical study, using a three-dimensional mesoscale model, to investigate the effect of steel fibers on the mechanical properties of steel fiber-reinforced concrete (SFRC) beams. The proposed model was developed using the numerical computing environment MATLAB. Concrete was simulated using solid elements with a damaged plasticity model. The steel fibers were randomly located and modeled by truss elements with an elastic–plastic material model, while the interface was represented by springs connecting the nodes of the concrete and steel fiber elements. Traction separation model behavior was assumed for the springs at the direction tangent to the fibers’ major axis and elastic with high stiffness in the normal directions. The proposed model was validated using experimental results with different fiber ratios. Moreover, a parametric study was conducted to investigate the effect of steel fiber ratios and orientations as well as the effect of the beam size. Good agreement with differences of 3%−5% at the peak loads and 3%−18% at the post-peak loads were obtained. The orientation of the steel fibers had a big effect on the behavior of the SFRC beams. A 73% increase in the peak load of the SFRC beams with aligned fibers in the flexural direction was obtained relative to the random alignments. Whereas the beams with steel fibers aligned in different directions showed unchanged behavior and strength. The beams with smaller sizes experienced higher variation between realizations and higher peak stresses than those with larger sizes for all fiber ratios. A clear size effect of type II in peak stresses was obtained for beams with different fiber ratios.

Assessing the shear behavior of corroded steel fiber reinforced concrete beams without shear reinforcement using nonlinear finite element analysis

The shear behavior of steel fiber reinforced concrete (SFRC) beams has been assessed in a large number of previous studies. However, the shear strength of corroded SFRC beams without shear reinforcement is still an unresolved topic. In this paper, the finite element models of non-corroded and corroded SFRC beams have been constructed and verified regarding load-displacement curves, crack patterns, and failure modes. Finally, a parametric study also was performed to assess the effect of essential design parameters on the shear strength of SFRC beams under corrosion attacks. The results show that the reinforcement corrosion degree and concrete compressive strength are the most influencing parameters on the shear strength of SFRC beams, followed by the shear span-to-depth ratio and the steel-reinforced ratio.

Comparison of flexural behaviors between plain and steel-fiber-reinforced concrete beams with hybrid GFRP and steel bars

This study investigates the flexural behavior of steel-fiber-reinforced concrete (SC) beams with hybrid glass fiber reinforced polymer (GFRP) and steel bars. The experimental results of current SC beams are compared with those of the plain concrete (PC) beams conducted in our previous research. Taking account of the differences in nominal reinforcement ratio and reinforcement layout of seven tested SC beams, the test results including cracking load, ultimate load, failure mode, crack spacing and width, and mid-span deflection were firstly discussed. Then, a comprehensive comparison of flexural behaviors between SC beams and PC beams with same reinforcements was conducted in this paper. Especially, the crucial effects of type and strength of concrete on flexural capacity and failure mode of test beams were analyzed in detail. Finally, for concrete beams reinforced with hybrid (GFRP and steel) bars, the optimization of two balanced nominal reinforcement ratios was proposed to ensure the beam’s flexural failure in an appropriate-reinforced mode without rupture of GFRP bars.

Acoustic emission monitoring of steel fiber reinforced beams under simultaneous corrosion and sustained loading

This paper presents an experimental study on monitoring the deterioration in Reinforced Concrete (RC) and Steel Fiber Reinforced Concrete (SFRC) beams under simultaneous corrosion exposure and sustained loading using Acoustic Emission (AE) Technique. AE method can be effectively used to detect damage initiation and progression of micro and macro-cracking during the entire period of corrosion in RC as well as SFRC beams. Addition of steel fibers in concrete leads to delay in AE parameters of AE hits and AE energy, revealing that SFRC beams can sustain the corrosion exposure for longer duration due to their crack-arresting properties. This study also reveals that beams subjected to simultaneous corrosion exposure and sustained loading are susceptible to brittle failure with reduced load carrying capacity and this is well depicted by increased AE activity.

Assessing the shear behavior of steel fiber reinforced concrete beams corroded under chloride attacks

Steel corrosion affects the failure mechanism of deteriorated reinforced concrete (RC) beams. Meanwhile, there is a lack of research on the shear behavior of corroded RC beams, particularly corroded steel fiber reinforced concrete (SFRC) beams. This paper investigates the shear behavior of corroded SFRC beams with a 1.5 shear span-to-depth ratio. All beam specimens included steel fibers with 50 kg/m3. In particular, tensile longitudinal reinforcements were subjected to a corrosion degree of 16.4%, while stirrups were subjected to an approximately 24.1% corrosion degree. These results are compared to those obtained on a non-corroded beam. The obtained results from the four-point loading tests show that the corroded SFRC beams preserve a softening behavior as opposed to the sudden shear failure of RC beams without steel fibers.