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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]

Dowel action of the longitudinal reinforcement in RC beams without and with small amounts of shear reinforcement is typically considered a constant shear contribution determined from the splitting strength of the concrete cover. However, in a recent experimental investigation by the authors, it was shown that the shear force transferred by dowel action for beams without shear reinforcement should be determined from the dowel displacement and a linear elastic model and a rigid plastic dowel model. This article is aimed at extending this model to also cover members with small amounts of shear reinforcement. To that aim, a novel approach to calculate the shear force carried by dowel action of the longitudinal reinforcement in both beams with and without shear reinforcement is presented. The model is derived by establishing an equilibrium of work between the internal stored elastic or dissipated plastic energy and the external work performed by the shear force in the dowel. Additionally, a method to determine the displacement of the dowel from DIC measurements is presented. For the remaining shear‐transfer actions, reasonable constitutive models from the literature are adapted. On the basis of DIC measurements, the shear force carried by each of the shear‐transfer actions is calculated for 16 shear tests of beams without and with small amounts of shear reinforcement. The sum of shear force carried by each of the shear‐transfer actions is shown to predict the applied shear force fairly well, from the development of the critical shear crack until failure. Additionally, it is shown that for beams with shear reinforcement below the minimum requirements according to the current design standards, the shear capacity is governed by aggregate interlock, residual tensile stresses, and the inclination of the compression chord. While for beams with shear reinforcement above the minimum requirements, the shear capacity is governed by the shear reinforcement and dowel action. [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]

The shear strength of prestressed concrete girders with a low amount of web reinforcement is an ongoing subject of research, in particular with regard to the assessment of existing concrete bridges. In this paper, a series of experiments is presented that addresses this question and at the same time significantly lowers the degree of longitudinal reinforcement in line with efficiently designed bridge cross‐sections and contrary to the vast majority of representative scaled test series. The limit case observations allow for a shear failure of the system even in the case of yielding longitudinal reinforcement due to the incremental strain in the tendons that could be activated. The focus of the presented analysis lies within the load‐dependent crack kinematics of the beam elements on the basis of the digital image correlation. It is shown that, depending on the longitudinal strain of the cross‐section, load‐bearing components associated with aggregate interlock do not seem to be mechanically reasonable and an extent of plasticity‐theoretical ideas through a compression chord component appears to be more consistent. [ABSTRACT FROM AUTHOR]

Corrosion of stirrups (generally with small diameters and concrete covers) significantly affects the shear strength of reinforced concrete elements. As shear failures may lead to brittle collapses, hence the need to avoid them during structures' entire service life. The Compression Chord Capacity Model (CCCM), a shear mechanical model, was recently extended to predict the strength of corrosion‐damaged beams by identifying the model parameters that could be most affected by steel corrosion. In this paper, the CCCM is combined with two material deterioration models included in the new Spanish Structural Code, and considers carbonation of concrete or chloride ions, to predict long‐term shear strength evolution. Finally, a parametric analysis is carried out to explore the effect of the most influential parameters on shear strength degradation according to the used models and depending on different exposure classes. [ABSTRACT FROM AUTHOR]

Application of fiber‐reinforced polymer (FRP) reinforcement in concrete beams may cause large deflection and crack width, as well as low shear capacity and ductility due to relatively small stiffness of FRP materials. To avoid these unfavorable factors and evaluate the shear behavior of FRP‐reinforced structural members, a high‐performance strain‐hardening cementitious composite (SHCC) is introduced to substitute conventional concrete in reinforced beams, and four‐point bending test is conducted in this study. Six FRP‐reinforced SHCC beams with different transverse reinforcement ratios and shear spans, as well as one concrete reference beam, were tested. According to the test results, the FRP‐reinforced SHCC beam showed enhanced shear carrying capacity and superior ductility compared with the concrete beams. The shear span to effective depth ratio as well as the stirrup ratio has a great influence on the shear behavior of FRP‐reinforced SHCC beams, including the failure mode, load‐carrying capacity, crack propagation, and ductility. Finally, a simplified truss‐strut model for predicting shear carrying capacity of steel or FRP‐reinforced SHCC beams is proposed, and a good agreement is achieved with the experimental results. [ABSTRACT FROM AUTHOR]

In this research, the influence of using steel fibers on the shear action of reinforced concrete beams, made of recycled concrete aggregate (RCA), was investigated through experiment and finite element analysis (FEA). First, 12 reinforced concrete beams were tested with varying amounts of steel fibers. These beams contained normal concrete aggregate (NCA) as reference beams besides RCA beams. All beam models had the same 150 mm x 250 mm cross‐section and 2000 mm length. The beams had three bars of 16 mm reinforcement and two bars of 12 mm reinforcement at its bottom and top, respectively. Three replacement ratios of recycled aggregate (RA) were considered; 0%, 30%, and 70%. Moreover, steel fibers were introduced in the beams at 0%, 0.5%, 1%, and 1.5% content by volume. The beams were evaluated under a four‐point bending test while the load‐deflection diagram and failure load for all beams were considered as the criteria for comparing the shear response of different beams. A thorough FEA was carried out using ANSYS to model these beams. The FEA results were compared with the outcomes of the experimental tests, and a clear agreement was obtained. The results showed that using steel fibers improved the shear strength of the beams by 2.94%, 15.88%, and 34.71% for NAC beams, 1.39%, 11.11%, and 16.67% for 30% RCA beams, and 24.53%, 40.57%, and 59.44% for 70% RCA beams, respectively by using steel fibers with ratios of 0.5%, 1%, and 1.5%, respectively. [ABSTRACT FROM AUTHOR]

In this study, steel reinforced grout (SRG) is proposed for shear strengthening of reinforced concrete (RC) beams using the near‐surface embedded (NSE) technique. It is believed based on several research contributions in the literature that the NSE technique precludes or delays the onset of premature debonding and achieves higher strength increase in strengthened beams compared to the externally bonded (EB) counterpart. The tests conducted in this study used 13 RC beams to determine the shear behavior of RC beams strengthened in shear using SRG. The effect of the strengthening technique (NSE versus EB), SRG fabric density, strengthening scheme (side‐bonded vs. U‐wrapped), and the strengthening configuration (continuous vs. discontinuous) on RC shear enhancement was studied. The strengthening effectiveness of the SRG system was assessed in terms of the shear capacity, failure mechanism, load‐deflection response, and strain results. The NSE‐SRG increased the beam shear strength by an average of 100%, alleviated SRG debonding, and enhanced the deformation characteristics. The average increase in the shear strength of the EB‐SRG strengthened beam was 54% and 105% for the continuous and discontinuous SRG strips, respectively. An analytical model is proposed to predict the shear capacity of both the NSE‐SRG and EB‐SRG strengthened beams and give accurate and safe predictions. [ABSTRACT FROM AUTHOR]

This contribution is addressing the investigation on the effect of axial tension on the shear strength of transversally reinforced concrete beams. It presents the results of a test program of 27 beams with different amounts of shear reinforcement subjected to varying levels of axial tension. After a general discussion about the truss model, the experimental shear strength results from the present study along with the results from some previous studies are analyzed, mainly with respect to the ultimate angle of the concrete struts. Then, several design codes are discussed in order to assess their practical validity, and finally a new method is proposed for the design of the longitudinal and transverse reinforcements, valid irrespective of the levels of the axial tensile force. [ABSTRACT FROM AUTHOR]

This contribution is addressing the investigation on the effect of axial tension on the shear strength of reinforced concrete beam elements without stirrups. The paper presents the results of a test program of 15 beams without stirrups that differed from each other mainly by the intensity of the axial tensile force N. During the tests, cracking was measured by Digital Image Correlation technique to identify the crack evolution mechanisms. After some consideration on the resisting mechanisms, the experimental results are compared with several code formulas to predict the shear strength VRc. Then an empirical formula is proposed for the variation of VRc between its two limits: the values for N = 0 and for VRc = 0 at the ultimate limit state of axial tension. This formula makes it possible to easily design for shear and tension. [ABSTRACT FROM AUTHOR]

In the present investigation, the structural behavior of reinforced geopolymer concrete (RGPC) beams containing steel fiber has been studied. Four‐point flexural loading condition was applied in this experimental study; for testing the RGPC beams. The deflections of the RGPC were gauged at the mid‐span of the specimens. The crack patterns and failure mode of RGPC beam specimens were measured during the testing process. From these measurements, it has been observed that the steel fibers control cracking due to plastic and drying shrinkages. The length and width of cracks generally improved with the increment of steel fiber content. The findings also indicate that the flexural strength and elastic modulus of RGPC are remarkably enhanced due to the incorporation of steel fibers. Furthermore, the failure mode of RGPC is almost similar to the failure mode of conventional concrete. However, the RGPC performed better than the conventional concrete in terms of flexural strength and other mechanical properties. It has also been noticed that the increase of a/d ratio results in shifting the flexural failure mode in the mid‐span regions towards the support points. The experimental results have been compared with the relevant published literature as well as with the different standard codes. [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]

In this study, shear tests were conducted to investigate the effect of corrosion damage induced in longitudinal reinforcement on the shear resistance mechanisms of reinforced concrete (RC) members without transverse reinforcement. A total of eight RC beam specimens were carefully designed and fabricated, and accelerated corrosion and typical shear tests were conducted considering various anchorage conditions and corrosion rates that were introduced in the longitudinal tension reinforcement as the key test variables. Test results showed that when the tensile reinforcement was not sufficiently anchored at the end regions of the RC members, the shear strengths of the test specimens decreased as the corrosion rate increased. In contrast, when the longitudinal reinforcement was properly anchored using the hook detail, the shear strengths showed a clear trend of increase, even when the longitudinal reinforcement was severely corroded. [ABSTRACT FROM AUTHOR]

Deep concrete beams often feature web openings that disrupt the flow of forces from the loads to the supports and reduce the shear strength of the member. While such openings can significantly impact the safety level of the structure, the research on deep beams has been focused mostly on the shear behavior of solid members. To address this issue, this paper proposes a new model for deep beams with rectangular openings that stems from a two‐parameter kinematic theory (2PKT) for solid beams. The model is established based on an analysis of the shear behavior and failure modes of test specimens using nonlinear finite element and strut‐and‐tie models. In the new model, a deep shear span with an opening is represented by two solid shear spans, one above and one below the opening. By linking the two sub‐models, the proposed kinematics‐based approach describes the complete deformed shape of the shear span with four degrees of freedom (DOFs). These DOFs are predicted by combining the kinematic conditions with equilibrium conditions and constitutive relationships for the mechanisms of shear resistance across the critical shear cracks. The model is validated with 27 tests from the literature showing adequate shear strength predictions. [ABSTRACT FROM AUTHOR]

The models to predict the shear behavior in reinforced concrete (RC) members are still far from be consensual. Thus, a detailed understanding of the physical phenomenon and a detailed monitoring of shear tests on RC members is fundamental. Identify and quantify separately the contribution of each component of the shear transfer mechanism it is a challenge. The traditional instrumentation usually results in the evaluation of a limited number of sections. Additionally, technologies based on image analysis have been applied to structural monitoring with excellent results. In this paper, the method Photo‐Shear, developed to monitoring shear tests based on photogrammetry, is presented. The method allows a better understanding of the shear strength mechanism by acquiring data from the surface of RC members. Then, postprocessing procedures leads to outputs with the redundancy and complementarity necessary to characterize: (a) displacement and strain fields; (b) overall shear deformation (distortion and rotation); (c) load path and direction of the compression strut; (d) shear cracks' characterization; and (e) the aggregate interlock effect. The method was validated by monitoring two RC beams tests. Based on the results obtained, several advantages of the proposed Photo‐Shear method were demonstrated over the traditional instrumentation, namely, the quantity and quality of the information obtained, and the redundancy and complementarity of the results analyzed. [ABSTRACT FROM AUTHOR]

Prior studies point to high model uncertainty in shear prediction. Model factors for various shear prediction models are characterized here, based on a recent and well‐vetted database of shear failures. Characterization includes estimation of main statistical parameters; and importantly also correlation and regression analysis to assess consistency of model factors over ranges of design parameters. The aim of the study is to identify models suitable for use as general probabilistic model (GPM) in future reliability assessments. The Variable Strut Inclination Method (VSIM), shear level of approximation III of the fib Model Code 2010, and ACI 318 displayed high bias, variability and various correlations with shear input parameters which make them unsuitable choices for GPM. The compression chord capacity model and the modified compression field theory displayed low bias and variability with consistent model factors over the ranges of shear design parameters and are thus suitable as GPM. Concerns stem from observed inconsistency in capacity prediction by VSIM and size effect in ACI. Reliability assessment is advised. [ABSTRACT FROM AUTHOR]

The size effect of Muttoni et al.'s critical shear crack theory (CSCT) is shown to be quite close (with differences up to 15%) and asymptotically identical to the energetic size effect law (SEL), which has been extensively verified experimentally and theoretically (and is adopted for the 2019 ACI Code, Standard 318, for both beam shear and punching). However, the CSCT derivation and calculation procedure obfuscates the mechanics of failure. It is shown to rest on six scientifically untenable hypotheses, which would have to be taught to students as an article of faith. They make CSCT untrustworthy outside the testing range; ditto for beams with T, I and box cross section, or for continuous beams. The present conclusions are supported by experimentally calibrated finite element simulations of crack path and width, of stress distributions and localizations during failure, and of strain energy release. The simulations also show the CSCT to be incompatible with the "strut‐and‐tie" model, which is (for 2019 ACI Code) modernized to include the size effect in the compression strut. Finally, further deficiencies are pointed out for the Modified Compression Field Theory (MCFT), currently embedded in the Model Code. [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 the newly established ACI‐DAfStb database of shear tests on slender prestressed concrete beams without stirrups subjected to point loads. From the 574 collected tests 214 tests remain for the comparison with shear design approaches after the control and selection procedures were applied. The main features of these tests are described. Subsequently, these tests are used to perform evaluations of the shear design procedures of EC2, fib Model Code 2010, and ACI 318‐14. [ABSTRACT FROM AUTHOR]

This paper presents findings from an experimental study on shear properties of high‐performance concrete beams reinforced with basalt fiber reinforced polymer bars and macrobasalt fibers. The test specimens comprised seven beams for shear testing and five beams for measuring the residual tensile strength of fiber concrete. No stirrups were used in the test beams. As part of the experiments, the compressive strength and bulk electrical resistivity were measured. To assess the influence of fiber dosage on shear capacity of concrete beams, five‐volume fractions of 43 mm macrobasalt fibers were investigated. The experimental results verified the hypothesis that shear capacity of concrete beams is associated with the fiber dosage. Furthermore, the results show a good correspondence with the predictions of Swedish standard (SS 812310:2014) and the fib Model Code 2010 predictions of shear strength of fiber reinforced concrete beams without shear stirrups. [ABSTRACT FROM AUTHOR]

The dual potential capacity model (DPCM) was proposed in this study to evaluate the shear strengths of short and deep reinforced concrete (RC) members with the shear span‐to‐depth ratios less than 2.5. In the proposed model, the nonlinear flexural analysis considering the bond mechanism between steel reinforcements and surrounding concrete was conducted to estimate the local stress increase in the steel reinforcements between flexural cracks, and the shear demand force of the cracked tension zone in an RC section can also be determined on this basis. The crack concentration factor was introduced to consider the size effect in estimation of the potential shear capacity corresponding to the shear demand force to be resisted by the cracked tension zone. For the compression zone, different plasticity models were adopted depending on the shear span‐to‐depth ratio to estimate the potential shear capacity of the intact compression zone. For the verification of the proposed model, a total of 466 test results of RC short and deep beams with various shear span‐to‐depth ratios less than 2.5 were collected from existing literature, and accuracy of the proposed model was verified in detail by comparing the shear strengths of the RC short and deep test specimens estimated from the proposed DPCM with those of the test results. [ABSTRACT FROM AUTHOR]

The behavior of steel fiber reinforced concrete (SFRC) has been extensively investigated in the last four decades. For the most part, however, existing design models for shear are based on empirical equations where fiber–concrete is considered as a unique material and fibers and concrete components to shear are considered collectively, or where the concrete and fiber components to shear are considered separately and each are derived independently. As demonstrated in this paper, the problem with this latter approach is that the influence of the concrete and the fiber components are each affected by the other—that is, they are coupled. In this paper, a rational model is outlined for determining one‐way shear strength of SFRC beams and slabs. The model is developed from the modified compression field approach with due consideration given to the inter‐relationship between the concrete–steel–fiber components to the shear resistance. Introduced into the model is an inverse analysis method for determining the post‐cracking residual tensile strength of SFRC from prism bending tests, a core materials property needed for design. In determining this strength, due attention is provided to the influences of notches, specimen boundaries and bias in fiber orientation that occurs as part of the casting process. The results of the design model predictions are compared with a dataset of test specimens collected from the literature, with very good correlation observed. [ABSTRACT FROM AUTHOR]

A design approach based on the simplified modified compression field theory, but with the advantage of not requiring an iterative procedure, is proposed for evaluating the shear capacity of beams without including shear reinforcement. This model is capable of simulating beams flexurally reinforced with steel and fiber reinforced polymer (FRP) systems. To appraise the predictive performance of the proposed model, a database (DB) composed of 215 reinforced concrete beams without shear reinforcement is set. By applying the model to this DB, an average value for Vexp./Vana. of 1.05 with a COV of 24% is obtained, where Vexp. and Vana. are the shear capacity registered experimentally and obtained with the model, respectively. By applying the approach proposed by ACI Building Code to the DB, average and COV values of 0.91 and 42% are determined, revealing the higher predictive performance of the proposed model. This was even higher in the beams flexurally reinforced with FRP systems, since the proposed model conducted to average and the COV values of 1.0 and 22%, while 0.76 and 32% were obtained with the ACI approach. When proposed model was applied to the beams tested in the experimental program carried out, an average and COV values of 1.02 and 5.23% were determined. [ABSTRACT FROM AUTHOR]

Load bearing capacity can be predicted by appropriate modeling of material properties, geometry variables, and uncertainties associated with an applied model for the failure mechanism under consideration. The submitted study investigates shear resistance model uncertainties for reinforced concrete beams with and without shear reinforcement, considering large test databases and various levels of approximation offered by fib Model Code 2010. Model uncertainty is treated as a random variable and its characteristics are obtained by comparing test and model outcomes. The sensitivity of model uncertainty with respect to basic variables is analyzed. For beams with stirrups, Level III is recommended for practical applications. Its predictions are shown to be independent of the amount of shear reinforcement and have reasonable bias and dispersion around test results. For beams without shear reinforcement, the use of Level II is advisable and a distinction between lightly reinforced and moderately to heavily reinforced beams should be made. [ABSTRACT FROM AUTHOR]

The development of a nonlinear numerical computational model for the detailed description of destructive tests generally requires a multiple‐stage, strategic model updating procedure. In this contribution, a model updating procedure is applied to the simulation of prestressed reinforced concrete (RC) beams. The combined ultimate shear and flexure capacity of the beams is affected by many complex phenomena, such as the multi‐axial state of stress, the anisotropy induced by diagonal concrete cracking, the interaction between concrete and reinforcement (bond), and the brittleness of the failure mode. In this research, a series of material, small‐scale component fracture tests were carried out by two collaborating laboratories. These tests provided advanced statistical identification of the fracture‐mechanical parameters of the optimized concrete mixtures for the prestressed laboratory‐tested beams mentioned above (with a span of 5.00 m) and associated field‐tested, long‐span concrete TT roof elements (with a span of 30.00 m). Ten scaled laboratory‐tested beams with heights of 0.30, 0.45, and 0.60 m were used in a procedure for the comprehensive updating of the nonlinear numerical model with respect to shear resistance performance. The objectives of this research are, in addition to the analysis, the effective development of an updating process for nonlinear numerical modeling which is based on the information from different monitoring systems. Hence, this contribution focuses on the presentation of a comprehensive updating procedure for the shear capacity of nonlinear numerical models of prestressed beam elements using information about fracture‐mechanical material parameters gained from (a) different monitoring systems and (b) code‐based methods. [ABSTRACT FROM AUTHOR]

In an effort to calibrate design methods and code provisions, an ACI‐DAfStb database was assembled for deep beams and non‐slender beams with vertical stirrups and horizontal web/skin reinforcement subjected to point loads. This collection database includes 218 tests, and with the exception of a few, all tests have a shear span to effective beam depth ratios less than 2.4, that is, κ = a/d < 2.4. For the purposes of evaluating the accuracy and conservativeness of design provisions, several control and filtering criteria were applied, and after this process, 89 beams remained in the evaluation database. In light of this database, the performance of shear design provisions of ACI 318‐14 and Eurocode 2, as well as strut‐and‐tie models (STMs) of the FIP Recommendations were examined. The analyses conducted using this database indicated that the application of STMs of ACI 318‐14 is conservative, that is, the database analyses yielded less unsafe tests than the desired 5% fractile. Furthermore, statistical evaluations showed that shear design expressions of Eurocode 2 and FIP Recommendations for non‐slender beams and deep beams are conservative too. [ABSTRACT FROM AUTHOR]

There are different approaches to predict the shear strength of reinforced concrete (RC) beams, but their predictive performance is still relatively low due to several and complex resisting mechanisms involved in shear. In addition, most of design approaches ignore the influence of the flange of T cross section beams on the ultimate shear capacity. This paper aims to present a design‐oriented approach to predict the load carrying capacity of RC beams failing in shear. This approach is based on the simplified modified compression field theory (SMCFT). A sensitivity analysis is carried out to assess the importance of the input parameters that mostly affect the shear strength of RC members. Taking into account the results of the sensitivity analysis, two simple equations are proposed for obtaining the: (a) tensile stress factor in the cracked concrete (β) and (b) inclination of the diagonal compressive stress in the web of the section (θ). The obtained equations eliminate the iterative process required by the SMCFT and provide a straightforward design methodology to find β and θ with suitable accuracy for design purposes. In addition, a coefficient is presented to take into account the effect of the flange on the shear capacity of T shaped cross section beams. To appraise the predictive performance of the new approach, a database is set. By evaluating the ratio between the experimental results and the analytical predictions, an average value of 1.24 with a coefficient of variation of 20.9% is obtained. [ABSTRACT FROM AUTHOR]

In this paper, a finite element model (FEM) based on a concrete damage‐plasticity approach was developed to investigate the size effect of ultra‐high performance fiber reinforced concrete (UHPFRC) and normal‐strength concrete or high‐strength concrete (NSC/HSC) composite beams. The material behavior of UHPFRC was modeled by introducing a suitable tension stiffening model to simulate the behavior of UHPFRC beams in tension. Specimens containing UHPFRC with different fiber volume content that have an overall height between 300 and 1,200 mm, a constant shear span‐effective depth ratio of 3 and no stirrups were investigated. The validity of the proposed model was established through comparisons between the experimental test results and those obtained in other studies. The results revealed that the size effect of UHPFRC members was diminished for fiber volume content higher than 1.5% due to the high ductility of UHPFRC material. [ABSTRACT FROM AUTHOR]

This computational investigation focused on numerical modeling of the shear behavior of ultra‐high‐performance concrete (UHPC) beams reinforced longitudinally with high‐strength rebars and ordinary‐strength steel (stirrups). Nonlinear three‐dimensional finite element model, using the concrete damaged plasticity model and material properties obtained from uniaxial compressive and tensile laboratory tests, was conducted to simulate UHPC concrete beams within a commercial finite element software package ABAQUS 6.13. This investigation included the effects of various parameters; shear span‐to‐effective depth ratio (a/d), volume fraction of steel fibers, Vf, longitudinal reinforcement ratio, ρ, and stirrups spacing, s, on shear behavior of UHPC beams. Numerical results compared with previously obtained experimental results in terms of shear force–midspan deflection and cracking‐propagation behaviors. The results showed that finite element analysis predicted the shear behavior of UHPC beams in good agreement with the experimental data and predicted the response of the beam with variation in various parameters with a good accuracy. [ABSTRACT FROM AUTHOR]

In this work, the second part of an experimental campaign investigating the efficiency of an alternative retrofitting method for increasing the flexural and/or shear capacity in reinforced concrete beams, based on the use of prestressed stainless steel ribbons and steel angles, is presented and analytically reproduced. This group of tests focuses on the ability of the adopted retrofitting method to improve the shear strength and ultimate deformation of reinforced concrete structural elements. As described in a companion paper, the adopted retrofitting method is alternative to traditional techniques of reinforced concrete retrofitting, being easy to install and usually reversible, and characterized by high fire resistance and avoiding corrosion. The experimental results obtained from shear tests carried out on nine reinforced concrete beams are presented. The efficiency of stainless steel ribbons as shear reinforcement that wrap a portion of cross-sectional depth are analyzed, and the interaction between existing stirrups and stainless steel ribbons examined. The tests results are critically analyzed, highlighting the ability of the retrofitting method in increasing the shear strength and ductility of reinforced concrete beams. The experimental shear strength was also analytically evaluated by extending the theoretical approach of the fib Model Code 2010 formulation, originally suggested for reinforced concrete beams with or without stirrups. [ABSTRACT FROM AUTHOR]

A simplified mechanical model is presented for the shear strength prediction of reinforced and prestressed concrete members with and without transverse reinforcement, with I, T or rectangular cross-section. The model, derived with further simplifications from a previous one developed by the authors, incorporates the contributions of the concrete compression chord, the cracked web, the dowel action and the shear reinforcement in a compact formulation. The mechanical character of the model provides valuable information about the physics of the problem and incorporates the most relevant parameters governing the shear strength of structural concrete members. The predictions of the model fit very well the experimental results collected in the ACI-DAfStb databases of shear tests on slender reinforced and prestressed concrete beams with and without stirrups. Due to this fact and the simplicity of the derived equations it may become a very useful tool for structural design and assessment in engineering practice. [ABSTRACT FROM AUTHOR]

FRP rebars with low compressive strength concrete is desirable in order to avoid the accelerated corrosion processes that could occur with steel rebars. For this purpose, an experimental programme was designed to identify the failure modes and bending behaviour. The experimental results are compared with equations from ACI 440.1R-06, CSA S806-12 and other design codes as well as with other results from a review of the literature. The comparisons indicate that the resistance moment is well predicted by codes for flexural failure. At ultimate loads, the deflection of the beams is further underestimated compared with the deflection of Reinforced Concrete beams with a higher compressive strength. An analytical simulation of 690 beams indicates that deflection is the major limiting criterion at the serviceability limit state. Finally, the formulation problem of the optimal FRP design for reinforced concrete beams can be turned into a programming problem. The space of the feasible design solutions and the optimal solutions can be obtained using only a reduced number of design variables and an existing design method. [ABSTRACT FROM AUTHOR]

This paper presents a critical comparison of the existing code provisions for the shear strength of concrete beams. The comparison is based on the computerized filtering-out of the inevitable statistical bias from the available multivariate database on shear strength, on an examination of the predicted size effects on shear strength and their underlying hypotheses and on the results of recent high-fidelity numerical simulations of shear failure. In addition to examining the existing models, the present comparison also provides several key considerations for testing the scientific soundness of any model of shear failure in concrete beams, which is necessary for future revisions to the design code provisions. [ABSTRACT FROM AUTHOR]

The shear resistance mechanisms of a reinforced concrete (RC) member with shear reinforcement can be divided into the contributions of the concrete and the shear reinforcement. The shear resistance mechanisms of concrete can be further divided into the shear resistance of the intact concrete in the compression zone, the aggregate interlock in the cracked tension zone and the dowel action of the longitudinal tension reinforcement. The shear demand curves and potential shear capacity curves for both tension and compression zones have been derived in this study, with the assumption that the shear failures of RC members are dominated by the flexural-shear strength. The shear capacity model was also proposed on this basis. In the proposed model, the crack width and the local stress increase in reinforcement were calculated based on the bond behaviour between the reinforcement and its surrounding concrete. Further, the crack concentration factor was introduced to consider the formation and propagation of the critical shear crack that developed from the flexural cracks. The results of a total of 1,018 shear tests were collected and compared with the analysis results provided by the proposed model. It was demonstrated that the proposed model provides a good estimate of the shear strengths of RC beams. [ABSTRACT FROM AUTHOR]

This paper presents a proposal for estimating the shear capacity of reinforced concrete deep beams. The proposed model is based on the fixed-angle softened truss model and utilizes a newly proposed formula for the effective transverse compressive stress acting on the beam web. The proposed formula is developed using a stepwise multiple linear regression analysis of the reported shear capacity values of 445 experimental deep beams. The validity of the mathematical model is examined by comparing its response with the experimental results as well as the predictions of other formulas available in the literature, and it results in the one best fitting the measured shear strengths. The mathematical model leads to an explicit single closed-form expression for computing the shear strength of deep beams. The proposed expression is dimensionless and contains four variables that express the horizontal and vertical reinforcement ratios, the concrete strength and the shear span-to-depth ratio. On the basis of the results of this paper, a design formula is proposed with predictions that are more consistent and also more reliable than those of the ACI Code and the Eurocode. [ABSTRACT FROM AUTHOR]

High-performance concretes such as high-strength concrete (HSC) or lightweight aggregate concrete (LWAC) are generally used to reduce member sizes and self-weight, and to optimize the construction of reinforced concrete structures. The bond between the aggregate particles and the cement paste can be strong enough in HSC and LWAC to cause the aggregate to fracture at cracks, which in turn reduces the shear stress that can be transferred across cracks by means of aggregate interlock. Relatively smooth cracks can also develop in self-compacting concrete due to the low coarse aggregate content. The contribution of aggregate interlock to the shear strength of RC beams is uncertain and depends on parameters such as the amount of shear reinforcement or the contribution of arching action for loads applied close to the support. Existing tests on slender RC beams without shear reinforcement have shown that shear strength is reduced by aggregate fracture. However, there is a lack of similar test data for members with stirrups and for members with varying shear span/effective depth ratios. This paper reviews the findings and contributions in this area from the experimental and analytical research of the author's PhD thesis, which was awarded the fib Achievement Award for Young Engineers in 2011. [ABSTRACT FROM AUTHOR]