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In this study, we designed six polypropylene fiber‐reinforced concrete (PP‐FRC) beams and three reinforced concrete (RC) beams for experimental studies. Then, we analyzed the effects of incorporating PP fibers on the cracking performance of PP‐FRC beams from the perspectives of load‐displacement response, crack distribution, crack depth, crack width, crack spacing, and deformation coordination. The research results showed that the cracking load and number of cracks were positively correlated with the volume ratio of PP fibers, while the maximum crack width, average crack spacing, and average crack depth were negatively correlated with the volume ratio of PP fibers. Due to the bridging effect of fibers, the PP‐FRC beam body and reinforcement could deform in a coordinated manner within a specific loading range after cracking, which increased the deformation coordination ability between the body and reinforcement. In this study, the cracking mechanism of PP‐FRC beams was investigated. Firstly, the formula for calculating the cracking moment of PP‐FRC beams was derived from the perspective of equivalent bending tensile strength. Then, based on the fiber bridging law and the bond strength between PP‐FRC and reinforcement, theoretical formulas were proposed to predict the average crack spacing and maximum crack width of PP‐FRC beams. Finally, through comparison, it was found that the proposed formulas could be used for characteristic crack prediction. [ABSTRACT FROM AUTHOR]

The positive effect of fiber‐reinforced concrete (FRC) on shear capacity of reinforced concrete beams is well presented in many experimental studies since 1970s. However, as the main effect of fibers is in the cracking stage, it increases the complexity to analyze such structures numerically. With the increased availability of nonlinear finite element analysis software, structural designers are encouraged to use them to solve complex structural problems. In such cases, understanding and correct definition of material laws in cracked stage of FRC structures are crucial. A blind competition was organized by fib WG 2.4.2 to address this issue. It revealed that the numerical predictions of almost all of the participants overestimated the shear capacity of a T‐beam subjected to bending. The aim of the current study is to demonstrate critical aspects in the definition of input parameters of FRC analysis. A comprehensive parametric analysis is performed considering tensile softening law, shear stiffness, and shear strength definition in cracked stage as well as shrinkage effects. The results suggest that most important aspect is the correct definition of tensile softening law, which should correspond to the lower bound of residual strength obtained by standard notched prisms tests according to EN 14651 or even smaller. [ABSTRACT FROM AUTHOR]

Fibers are mixed within reinforced high‐strength recycled aggregate concrete (RHRAC) beams to improve their flexural performance. This study experimentally and analytically investigates the effect of using RAC combined with polyvinyl alcohol fiber (PVAF) and steel fiber (SF) on the flexural performance of RHRAC beams. A total of 11 RHRAC beams (150 × 300 × 2600 mm3) are manufactured and subject to four‐point flexural testing. The parameters of the concrete are investigated, including the volume content of the PVAF and SF. The experimental results show that SF increases the flexural strength of RHRAC beams more than PVAF does. Conversely, the effect of PVAF on deformability is more significant than that of SF. In addition, the positive influences of hybrid fiber (PVAF and SF) on the crack load, flexural capacity, and deformation capacity are superior to those of single‐mixed PVAF or SF. Three different specifications are used to calculate the flexural capacity of the test beams, among which, JGJ/T465‐2019 is the most reliable. [ABSTRACT FROM AUTHOR]

Ductility is one of the most important requirements of RC design besides other requirements such as strength and stiffness. In recent years, concrete beams with a large amount of tensile reinforcement ratio (ρ) have been required in large projects, such as high‐rise buildings and bridges. Using high (ρ) increases the strength and stiffness of the beams and leads to a decrease the ductility. This paper aimed to investigate the effect of using steel fibers reinforced concrete (SFRC) layer in compression zone on the flexural behavior of over‐reinforced concrete beams. Partial replacement of concrete with SFRC layer in compression zone was used to avoid the brittle compression failure of concrete. For this purpose, 12 over‐reinforced concrete beams with a span of 1300 mm and a cross‐section of 120 mm × 180 mm were cast and tested under a three‐point loading. The first beam was used as a reference beam and others as strengthened beams using SFRC layer. The effects of thickness and length of strengthening layer, (ρ), volume fractions of steel fibers, and strengthening methods on flexural performance of tested beams were investigated. The flexural capacity, failure modes, crack patterns, load–deflection relationships, load–strain relationships, ductility index, and toughness were evaluated. The results showed that the suggested technique (SFRC layer in the compression zone) is an effective technique to increase ultimate load, ductility, and toughness by up to 35.72%, 121.01%, and 349.16%, respectively, compared to the reference beam. Furthermore, the failure mode changed from brittle to ductile failure. Also, one of the main advantages of this technique is allows to increase of (ρ) up to 8.55% (4.15ρb) without needing the compressive reinforcement. The results of this study indicate that the using SFRC layer in the compression zone is an appropriate and economical method to provide high flexural capacity and ductility over‐reinforced concrete beams. [ABSTRACT FROM AUTHOR]

This paper aims to contribute to a more rational understanding of the shear strength behavior of steel fiber‐reinforced concrete beams without stirrups. For this purpose, an experimental program comprising eight slender beams varying the fiber content and type, tested in three‐point bending configuration with a complete monitoring of the displacement fields of the failure span, was carried out. A detailed analysis of the shape and kinematics of the critical crack, associated with the investigation of the shear transfer mechanisms during the test given by mechanical models available in the literature, was performed. The theoretical–experimental analyzes proved to be a promising approach for quantifying the contribution of each relevant parameter to the shear capacity, such as the fiber concrete residual tensile response. The study, therefore, presents a contribution toward a rational and comprehensive methodology for the shear design of concrete members. The influence of shape and kinematics of the critical crack on the shear response is also reported and a theoretical explanation is provided to justify the fact that beams with the same characteristics have different cracking patterns but similar shear strength. [ABSTRACT FROM AUTHOR]

High‐performance fiber‐reinforced concrete (HPFRC) can be considered a promising material for the construction of precast concrete girders for road bridges. This paper presents conceptual considerations and numerical analysis to support this statement. The HPFRC is a compromised alternative between FRC and UHPFRC mixes. Specifically, a tailor‐made mix design of HPFRC jointly developed by ACCIONA and the authors is presented, and then compared with the other types of fiber‐reinforced concretes collected from the technical literature. In addition, some trends observed in the database are described. This material characterization is followed by a conceptual analysis of the advantages of the application of HPFRC to road bridges. Specifically, a proposed bridge for the case of a 60 m‐span box girder is analyzed. A comparison between alternatives based on the use of HPFRC and conventional reinforced concrete is discussed. The results shed light on the viability of this material for bridge application. Specifically, the main finding show potential significant material savings in structural elements of the superstructure. Finally, ongoing and future research for a wide application to the construction sector are briefly discussed. [ABSTRACT FROM AUTHOR]

This article describes the second blind simulation competition (BSC) organized by the fib WG 2.4.1, which aims to assess the predictive performance of models based on the finite element method (FEM) for the analysis and design of fiber reinforced concrete (FRC) structures. Slabs supported on columns or piles have becoming competitive applications for FRC due to the technical and economic benefits may be obtained by combining properly the fiber reinforcement mechanisms to those provided by conventional reinforcement placed, as a strip, in the alignment of columns/piles. Therefore, a representative zone of this structural system, namely a hybrid fiber reinforced concrete (R/FRC) shallow beam, is chosen in this BSC to show the potentialities of FRC in these types of applications, as well as to assess the predictive performance of FEM‐based computational models on the design verification at serviceability and at ultimate limit state conditions (SLS and ULS, respectively). Two statically indeterminate shallow beams of two equal spans were tested up to their failure, by recording the applied loads, the strains in the conventional reinforcements and in the FRC of the critical zones of the structure. By using digital image correlation, the average crack width at the level of the flexural reinforcements was recorded. The participants had to predict these results by receiving information about the mechanical properties of the materials, the geometry of the prototypes and their loading and support conditions. In this article, the rules and the results of this 2nd BSC competition are presented, and the data obtained experimentally is thoroughly analyzed. [ABSTRACT FROM AUTHOR]

In this work, the theoretical model for predicting the flexural behavior of steel‐reinforced basalt fiber‐reinforced concrete (RBFRC) beams was developed and the results were experimentally validated. The experimental results presented two failure modes of the RBFRC beams including flexural failure and flexural‐shear failure. The load‐carrying capacity, deformation ability, and crack resistance of RBFRC beams failing in flexure can be significantly enhanced with the addition of chopped basalt fiber. To verify the theoretical model, the predicted results were compared with the experimental results of RBFRC beams, and the relative error between the two methods is very small. Based on the theoretical method, a parametric study was conducted to identify the influence of several crucial materials and structural parameters on the flexural behavior of RBFRC beams. [ABSTRACT FROM AUTHOR]

A study on the shear model uncertainty and structural reliability of ultra‐high‐performance fiber reinforced concrete (UHPFRC) beams with stirrups is presented. Model uncertainty for the shear models given in the JSCE, AFGC and ACI 544 standards are characterized by comparison to nonlinear finite element analyses (NLFEA). In comparison to other shear basic parameters, a notable negative correlation between model uncertainty the transverse shear reinforcement ratio (ρwfywm) is observed. When combined with stochastic descriptions of the remaining parameters that describe these analytical models, reliability values for beams designed to the JSCE and AFGC specifications are found to fall 6%, and 12%, respectively, below the target values of these standards, while reliability values for the ACI 544 exceed the target value specified for this standard by 8%. [ABSTRACT FROM AUTHOR]

There are only a few studies related to the effect of the hybrid fiber reinforcement on the flexural behavior of full‐scale beam specimens having lap‐spliced length. Thus, this study will ensure important experimental data about the effect of macro steel fibers blended with micro steel fibers on lap‐spliced length. The aim of this study was to investigate the influence of hybrid steel fiber reinforcement on the flexural behavior of full‐scale reinforced concrete beams having different lap‐spliced bars. A sum of three traditional concrete mixtures including a total of 1% fiber by volume fraction was adopted: control mixture without steel fiber, only macro steel fiber and hybrid steel fiber reinforced mixtures. For this purpose, 18 full‐scale beams (200 × 300 × 2000 mm) having three different lap‐spliced length (15, 25, and 35Ø) as tension steel bars were produced and tested under four‐point bending to examine flexural behavior, mode of failure, ductility, and energy absorption capacity properties. In conclusion, the hybrid fiber reinforcement caused the highest increase in the load carrying capacity of the beam specimens. Besides, the hybrid fiber reinforced beam specimens exhibited excellent ductility and energy absorption capacity compared to single fiber reinforced beam specimens. On the other hand, it can be addressed that the hybrid fiber reinforced structural elements had a vital important to compensate the application errors and carelessness in steel bar workmanship, inadequate the lap‐spliced length as per the codes. It can be emphasized that the lap‐spliced length as per the building codes can be reduced in 40% by containing hybrid steel fiber (0.8% macro‐0.2% micro) reinforced concrete without a reduction in load carrying capacity, ductility, and energy absorption capacity compared to control beam specimens without fiber. [ABSTRACT FROM AUTHOR]

Investigations on steel fiber reinforced concrete (RC) beams in torsion show, that the steel fibers positively influence the torsional load‐bearing behavior. Since a systematic evaluation of the previously known test results and the derivation of a generally valid design model were lacking until recently, current codes such as Model Code 2010 do not contain any design models for the consideration of the steel fiber load‐bearing effect in the torsion design. Due to this, the existing torsion tests on steel fiber RC were summarized in a database. Furthermore, on the basis of the test results and observations, the space truss model developed by Rausch and later refined by Lampert and Thürlimann, among others, was further developed and supplemented by additional longitudinal and transverse steel fiber tension struts. This modified space truss model was validated with the database and shows good to very good predictions to the torsion test data. [ABSTRACT FROM AUTHOR]

The shear crack width, crack behavior, and crack development of 24 reinforced concrete beams have been experimentally investigated. All the beams reinforced with longitudinal reinforcement and hooked‐end steel fibers in place of transverse reinforcement. Hooked‐end steel fibers 35 and 60 mm long are used at volume fractions ranging from 0.75% to 1.5% in the first case, and from 0.5% to 1% in the latter case. For extending the scope of the investigation, two types of concrete matrices (normal‐strength of 25 MPa and medium‐strength of 45 MPa) have been investigated. A simple mechanics‐based mathematical model is developed by determining the strains in the transverse direction of shear cracks and the average horizontal spacing between the shear cracks. The accuracy of the model has been confirmed with the experimental results and conservative predictions have been observed with mean, SD, and coefficient of variation as 0.99, 0.19, and 18.96, respectively. Based on detailed mathematical and experimental investigation, the minimum approximately observed shear crack width has value of 0.4 mm for all SFRC beams therefore the allowable shear crack width of 0.4 mm, for steel fiber reinforced concrete has been recommended. [ABSTRACT FROM AUTHOR]

In the present study, monitoring of damage initiation and progression in steel fiber reinforced beams (SFRBs) subjected to half cyclic loading under flexure is attempted using acoustic emission (AE) technique. Variation in AE parameters of cumulative AE hits and acoustic energy with damage progression in these beams along with their flexural performance is studied and compared. Further SFRB beams failed to 90% damage level are repaired using GFRP wraps and are subjected to flexural loading and simultaneous AE monitoring. Variation in AE parameters along with load deflection behavior for control SFRB and retrofitted SFRB beams have been discussed and compared. Based on AE and load–deflection data, Damage Index values were calculated and Damage States have been proposed which can help in providing an early warning of failure proximity. Subsequently empirical relationships have been developed between Damage Index and AE parameters using genetic programming (GP) technique and are in excellent coherence with experimental results. It can be concluded from the study that AE analysis is an effective tool for damage monitoring in SFRB and GFRP repaired SFRB beams. [ABSTRACT FROM AUTHOR]

Fiber‐reinforced concrete (FRC) has been proved to be a competitive solution for structural purposes. Extensive research has highlighted the benefits of adding fibers on the post‐cracking strength, reduced crack spacing and crack width, and improved durability, among others. However, these aspects are related to serviceability limit states, and significant work remains to be done in terms of ultimate limit state behavior of FRC members. As recent publications have emphasized, reinforced concrete beams with low reinforcement ratios may result in a reduction of deformation capacity and, hence, to a loss of ductility. To further investigate this topic, this paper presents the results of a numerical parametric study of simply and continuous supported hybrid‐reinforced concrete (HRC) beams made with different amounts of fibers and reinforcement ratios. The deformation, rotational, and moment redistribution capacity of those were assessed by means of a finite‐element model previously calibrated using experimental results available in the literature. The results showed that there is a significant reduction of rotation capacity and moment redistribution for lightly reinforced (hybrid) members. Finally, the paper contains practical recommendations in terms of minimum reinforcement ratios that guarantee adequate rotation and redistribution capacity of HRC members. As such, the results of this study can provide a contribution toward more reliable structural designs of HRC members. [ABSTRACT FROM AUTHOR]

For ultra‐high performance fiber‐reinforced concrete (UHPFRC) beams subjected to shear the bearing mechanisms differ significantly depending on the type of cross‐section. For I‐shaped cross‐section, existing models superimposing the contribution of concrete, prestressing, stirrups, and fibers were found to predict the shear bearing capacity appropriately. These models may, however, not be generally applicable. The aim of the present study is to investigate the shear bearing mechanisms for UHPFRC beams with compact cross‐section and, in particular, the influences of fiber volume fraction and prestressing on the development of the critical shear crack and the shear bearing capacity. This paper presents the experimental results of 22 three‐point test on 11 beams with varying fiber volume fraction and prestressing. It was found that increasing the fiber volume fraction increases the shear bearing capacity, but however, the benefit was less than proportional to the residual flexural tensile strength of UHPFRC. As expected, prestressing also affects the bearing capacity favorably. [ABSTRACT FROM AUTHOR]

A 3‐stage model is used to evaluate the results of an experimental campaign, previously carried out with the aim of studying the deflection of reinforced concrete structures made with reinforced concrete (RC) and fiber‐reinforced concrete (R/FRC). In particular, 12 four‐point bending tests were performed on beams, whose cross‐sections were obtained by combining four effective ratios of the tensile reinforcement (i.e., 0.73%, 1.7%, 3%, and 6.3%), two concrete covers (i.e., 32 mm and 82 mm), and three amounts of steel fibers (0, 0.5%, and 1.0% in volume) recycled from end‐of‐life tyres. In reinforced beams with low reinforcement ratios, there is a reduction in deflections and the load at yielding of steel increases with the content of fibers. On the contrary, the mechanical behavior of R/FRC and RC beams does not substantially differ in presence of a high effective reinforcement ratio. These experimental observations are in accordance with the results of the three‐stage model, introduced herein to predict the possible variation of the load‐deflection curves. For a given deflection, the model provides a possible range of applied loads, whose upper bound is related to the situation of incipient cracking (i.e., the maximum tension stiffening effects), whereas the lower bound concerns a fully cracked beam (i.e., the minimum tension stiffening effects). Regardless of the content of fibers, the difference between the upper and lower bounds vanishes in highly reinforced concrete beams. [ABSTRACT FROM AUTHOR]

Depending on the ratio of fiber contribution to conventional reinforcement contribution (quantified for example, by I f i SB 0.5 sb [or I f i SB I R i 1 sb ] and SB I s i sb , respectively), the overall behavior of the member (i.e., the sum of the two contributions) may display a hardening or a softening response. Abbreviations f 0.5 residual axial tensile stress offered by fibers at a Crack Opening Displacement COD = 0.5 mm f 1.5 residual axial tensile stress offered by fibers at a COD = 1.5 mm f R 1 residual flexural tensile stress offered by fibers at a Crack Mouth Opening Displacement CMOD 1 f R 3 residual flexural tensile stress offered by fibers at CMOD 3 f u ultimate strength of reinforcing bar f y yield strength of reinforcing bar s r 0 crack spacing Ø s diameter of reinforcing bar su ultimate strain of reinforcing bar sy yield strain of reinforcing bar s longitudinal conventional steel reinforcement ratio s, min minimum reinforcement ratio of conventional steel The paper1 presents useful and valuable information on the flexural behavior of fiber reinforced concrete (FRC) beams with varying fiber types, fiber dosages and longitudinal reinforcing ratios. [Extracted from the article]

The behavior of fiber reinforced concrete (FRC) depends on the characteristics of both the concrete matrix and fibers. Previous studies have concluded that the number of hooked ends increases the contribution of steel fibers to the tensile performance of concrete. ACI 318 code, MC10 fib code and RILEM TC 162‐TDF standard permit the use of steel fiber reinforced concrete (SFRC) for example, the minimum shear reinforcement made of deformed steel bars in flexure‐controlled elements. Other investigations have demonstrated the suitable performance of SFRC in shear‐controlled members and for seismic rehabilitation applications. It has become apparent that the adequate use of SFRC depends on the knowledge and prediction capabilities of its tensile performance. The results of three‐point bending tests on SFRC beams using the test procedure established by the European standard EN‐14651 are presented and discussed herein. Tests were executed with 20 standardized beams made of concrete with a nominal compressive strength of 24 MPa and hooked end steel fibers with an aspect ratio of 65 were applied. Variables were the fiber dosage (0, 20, 40, 60 kg/m3) and the number of fiber hooked ends (1, 1.5, and 2). A numerical model aimed at estimating the residual flexural tensile strength of the SFRC is developed. The proposed model was calibrated using a database of 256 tests, 20 from this study and the remaining 236 from 15 other studies. [ABSTRACT FROM AUTHOR]

Experimental research has shown the extraordinary potential of the addition of short fibers to cement‐based materials by improving significantly the behavior of concrete structures for serviceability and ultimate limit states. Software based on the finite element method has been used for the simulation of the material nonlinear behavior of fiber‐reinforced concrete (FRC) structures. The applicability of the existing approaches has often been assessed by simulating experimental tests with structural elements, in general of a small scale, where the parameter values of the material constitutive laws are adjusted for the aimed predicting level, which constitutes an inverse technique of arguable utility for structural design practice. For assessing the predictive performance of these approaches, a blind simulation competition was organized. Two twin T‐cross section steel FRC beams, flexurally reinforced with steel bars and without conventional shear reinforcement in the critical shear span, were experimentally tested up to failure. Despite the experimental data provided for the definition of the relevant model parameters, inaccuracies on the load capacity, deflection, and strain at peak load attained 40, 113, and 600%, respectively. Inadequate failure modes and highly different results were estimated with the same commercial software, indicating the need for deeper analysis and understanding of the models and influence of their parameters on their predictive performance. [ABSTRACT FROM AUTHOR]

The use of fibers in reinforced concrete (RC) beams mainly improves both the bearing capacity and the cracking control. In this way, positive effects on the service life of RC structures can be expected. In this paper, the fiber influence on the flexural behavior of RC beams with different longitudinal reinforcement ratios (0.5% ≤ ρs ≤ 1.2%) is analyzed by testing small‐scale RC beams. Concretes incorporating 0, 25 and 50 kg/m3 of steel, 6 and 12 kg/m3 of glass macrofibers, and 5 and 10 kg/m3 of polymer macrofibers were studied. Crack and deflection control, as well as bearing capacity and crack localization were evaluated for a broad range of fiber‐reinforced concrete (FRC) toughness. It is verified that fibers, in the longitudinal reinforcement ratio considered, improve the bending behavior at serviceability limit state (SLS) and ultimate limit state (ULS) of RC beams, without limiting the structure ductility. It was also confirmed the philosophy of the fib Model Code 2010, such that FRC can be considered as a composite material where performance parameters govern its mechanical behavior. Finally, the several data available allowed to deeply analyze fib Model Code 2010 formulations (mean crack spacing and flexural bearing capacity) and to propose modifications where needed. [ABSTRACT FROM AUTHOR]

Deep beams with shear span‐to‐depth ratios a/d ≤ 2.5 are used to resist large shear forces due to their ability to develop direct strut action. To further enhance the shear strength and crack control of such members, researchers have studied the use of fiber‐reinforced concrete (FRC). However, while this solution is promising, there is a need for rational mechanical models capable of predicting the shear strength of FRC deep beams in a sufficiently simple manner. This paper proposes such a model based on first principles: kinematics, equilibrium, and constitutive relationships. The proposed model simplifies an earlier two‐parameter kinematic theory (2PKT) for the complete shear behavior of FRC deep beams, to predict the shear strength and components of shear resistance in a straightforward manner. The new simplified method is validated by comparing the predicted results to 22 tests from the literature, as well as to FEM and 2PKT predictions. It is shown that the proposed simplified kinematic approach predicts well the shear strength with an average experimental‐to‐predicted shear strength ratio of 1.12 and a coefficient of variation of 12.9%. Furthermore, the model is used to discuss the effect of shear span‐to‐depth ratio and fiber volumetric ratio on the shear strength of FRC deep beams. [ABSTRACT FROM AUTHOR]

Fiber‐reinforced concrete exhibits a heterogeneous microstructure formed by aggregates, fibers and a matrix, where the stress from external forces can lead to cracking and fracture. This paper discusses the development of a computational measure for predicting the fiber's efficacy by means of the energy absorbed within the initiated area of the cracks. The analytical development was verified with experimental data from the literature and the results were justified with numerical simulations in the elastic regime. This development couples the localization of the stress in the crack tip with the random distribution of the cracks, which leads to the spatial strain field. Such percolation‐based quantification of the cracks in the early‐stage particularly is useful for effective utilization of fibers during the cracking progress. [ABSTRACT FROM AUTHOR]

The redistribution of moment within a statically indeterminate reinforced concrete beam at the ultimate limit state occurs through variations in the flexural rigidities and through the formation of hinges. The phenomena of moment redistribution (MR) is used to increase the efficiency of reinforced concrete design by allowing moments to be transferred away from critical cross sections thereby resulting in lower design moments. To allow for this effect in design, two main approaches are adopted. The first is to perform an elastic analysis and then to adjust the resulting distribution of moment using a codified MR factor. The second is to apply a plastic analysis allowing for the formation of hinges, and to calculate the rotational requirements at the hinges from first principles. This paper uses fundamental plastic analyses to derive closed‐form expressions for the hinge rotational requirements for full MR (that required to achieve the theoretical maximum applied load within the beam based on the moment capacity of sections within the beam). These closed‐form solutions are then used to quantify the maximum load on a beam when the rotational capacities at a hinge are less than the rotational requirements for full MR (partial MR). Closed‐form solutions are then used to derive MR factors which do not require semimechanical calibration. [ABSTRACT FROM AUTHOR]

Steel fibers may be added to self‐compacting concrete (SCC) to improve its mechanical performance; however, such improvement is subject to a number of conditions, an important one of which is the distribution and orientation of the fibers. The objective of this study is to propose a new method capable of predicting the variation of the distribution and orientation of steel fibers immersed in the SCC during flow. The flow of the steel fiber reinforced SCC is simulated by a computational fluid dynamics software, in which the volume of fluid method is used to track the free surface of concrete. On the basis of the velocity field of concrete obtained by the software, the motion of steel fibers is calculated by solving the rigid body dynamics equation. To validate the proposed method, a casting process of a concrete beam with steel fibers is simulated. The effectiveness of the numerical simulation is confirmed by a comparison with the experimental results. Meanwhile, the variation of fiber orientation during the flow of SCC is discussed by analyzing the fiber orientation factor. [ABSTRACT FROM AUTHOR]

This paper presents the efficiency of using prefabricated ultra‐high performance fiber reinforced concrete (UHPFRC) plates in shear strengthening of reinforced concrete (RC) beams experimentally and numerically using finite element method. In order to ensure high quality and facilitate the strengthening process on site applications, it has been considered to apply UHPFRC as a plate pasted on concrete surface using epoxy. Tested specimens included four strengthened beams besides three control beams. Strengthening the RC beams was based on the use of two different techniques; (a) one longitudinal side strengthening (b) two longitudinal sides strengthening. Moreover, strengthening RC beams with reinforced or non‐reinforced prefabricated UHPFRC plates was also investigated. Results show that UHPFRC plates significantly increased the maximum load capacity, ductility and mid span reinforcement strain of the strengthened RC beams comparing with reference beam failed in shear. Also, steel connectors used in reinforcement of UHPFRC plates prevented debonding failure mode. A three‐dimensional (3D) finite element model (FEM) of the tested beams was also developed to predict the behavior of these specimens strengthened in shear. The adhesive layer was simulated using cohesive surface model to consider the slippage between concrete surface and UHPFRC plates. Results of the FEM showed good agreement with experimental results, as they were able to predict the behavior of the beams with high accuracy. [ABSTRACT FROM AUTHOR]

Numerous models have been developed to determine the strength contributions of steel fibers in reinforced concrete beams in flexure; however, little work has been undertaken on determining their reliability, particularly when combined with use of inverse analysis procedures for determining the postcracking residual tensile strength provided by the fibers. Recently, leading codes have accepted design guidelines for designing flexurally reinforced concrete structural elements that also contain steel fibers using rational principles that are compatible with conventional reinforced concrete design. To provide confidence to the designer, it is imperative to verify the design models against experimental results and test their reliability. Despite extensive studies, design models have not been validated against large amount of test data. In this paper, 50 flexurally reinforced steel fiber reinforced concrete beams from the literature are analyzed for flexural strength. Ultimate moment capacities are predicted using the design procedures of NZS 3101–2–2006, fib Model Code 2010, DAfStb Guideline‐2015 and AS3600–2018. The results of the analyses show that the models perform well, with the AS3600 being the most conservative of the models assessed, and the NZS 3101–2–2006 the least conservative. The model errors for each are determined, and model reliability is discussed. [ABSTRACT FROM AUTHOR]

The awareness of damage caused by impacts in civil structures has increased during the last decades. Existing research has shown that impact strength of concrete structures can be improved with the addition of steel fibers, but little attention has been paid at the assessment of the structural condition after the impact. In fact, the residual capacity of reinforced steel fiber‐reinforced concrete (SFRC) can be considered as one of the main advantages of the employ of SFRC in structures expected to suffer impact damage. The understanding of the residual capacity of impact‐damaged structures, in terms of strength and energy absorption, might be decisive to safely perform evacuation and recovery operations, as well as evaluate rehabilitation tasks. This paper presents a research on the residual capacity of preimpacted reinforced SFRC beams. Seven mixtures of SFRC are evaluated, including three types of steel fibers and two values of fiber amount (as well as companion unreinforced plain concrete mixture). The research includes an experimental campaign as well as a model to understand the contribution of the SFRC to the strength and ductility of undamaged and damaged specimens. Among the conclusions, it has been found out that the failure mode (i.e., shear‐ or flexure‐governed) of damaged specimens depends on the crack pattern caused by the impact, and it can be different from the failure mode of undamaged specimens. [ABSTRACT FROM AUTHOR]

This paper presents a simple yet accurate technique for determining the strength of steel fiber reinforced concrete beams loaded in pure torsion. The results of the model are compared with 21 beams found in the literature as well as two new beams tested by the authors and reported herein. The model considers the beneficial effect of the fibers in resisting tension after the concrete matrix has cracked, and it is implemented into the widely accepted space truss analogy for reinforced concrete members subjected to pure torsion. The proposed model provides good correlations to the collected test data with a test to predicted ratio of 1.10 and COV of 0.19. A simplified method of the aforementioned model, suitable for design, is also presented and is shown to provide good predictions to the test data. [ABSTRACT FROM AUTHOR]

This paper presents the results of experimental and theoretical studies undertaken to assess the flexural performance of high‐strength steel‐ultra‐high‐performance fiber reinforced concrete (HSS‐UHPFRC) beams. A total of nine HSS‐UHPFRC beams were tested, and the influence of fiber volume fraction, fiber type, longitudinal reinforcement ratio, and concrete strength on the flexural response was evaluated. The results indicate that sufficient longitudinal reinforcement should be provided in a UHPFRC beam to avoid abrupt failure and possible catastrophic collapse. After the loss of the fiber bridging effect, corresponding to the fibers being pulled out from the matrix, which occurs one by one with audible sound which is sizzling, redistribution, and homogenization of the concrete stress beside cracks, induced by the dispersed fibers, takes place and more flexural cracks with small spacing appear besides the existing cracks. The beam stiffness was about 85% of the initial beam stiffness at flexural cracking state and was only approximately 25% of the initial beam stiffness at the ultimate state. A constitutive model is proposed, including a bilinear model for compression and a drop‐down model for tension, taking into account uniform distribution, embedment length, and orientation of fibers for the multi‐scale mechanics analysis. A flexural strength model was subsequently derived on the basis of the proposed mesoscale constitutive model; strain compatibility and force equilibrium were taken into account. The prediction of the ultimate flexural capacity and the overall post‐cracking response with the proposed model show a good agreement with the test results. [ABSTRACT FROM AUTHOR]

Authors' closure on the discussion of the article: "Assessing the influence of fibers on the flexural behavior of reinforced concrete beams with different longitudinal reinforcement ratios" (discussion by Marki'c et al.) The authors would like to thank the discussers for their interest and for opening a discussion on the ductility of RC elements with fibers, which is a very important topic. This possible negative influence is related to both longitudinal reinforcement (type and ratio) and the weighted ratio between the post-cracking performances of fiber reinforced concrete (FRC) and reinforcement strength properties. [Extracted from the article]