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Reinforced concrete flat slab projects usually require openings close to the columns for electrical and hydraulic installations. Since such openings reduce the punching shear of slabs, a comprehensive study is needed. In this paper, numerical models of slabs tested in literature were elaborated upon, using the commercial software in finite elements DIANA. The physical nonlinearity of the materials was considered. After the calibration and validation of the numerical parameters related to concrete and reinforcement, 62 numerical models were created for performing a parametric analysis. The numerical analysis aimed to study the effect of openings close to the columns and verify the punching resistance reduction. In this parametric study, the main variables were the compressive strength of the concrete, the bending reinforcement ratio, the number of openings, and the distance from the openings to the column's face. Finally, the numerical results obtained were compared with the punching strength values provided by the main structural design codes, viz., NBR 6118 (2014), Eurocode 2 (2004), ACI 318 (2019), fib Model Code (2010), and the next generation of Eurocode 2, which are constantly questioned in academic papers regarding their safety. [ABSTRACT FROM AUTHOR]

Alkali silica reaction (ASR) is an undesirable phenomenon that occurs between alkalis that usually originate from cement and certain types of siliceous aggregates in concrete. The result of this reaction is delayed expansion of hardened concrete in the presence of moisture, which may cause cracking and damage in an existing structure. The present paper investigates the general behavior and shear strength of pretensioned concrete bridge girders affected by ASR. Four identical pretensioned concrete AASHTO Type I girders were fabricated using reactive concrete and subjected to environmental conditioning at a relative humidity of 100% and a temperature of 45 degrees Celsius for up to 296 days to accelerate the development of ASR. During this period, ASR‐induced expansions, changes in surface strains of concrete, transfer lengths, and patterns of damage and cracking were monitored. Each specimen was subjected to shear‐critical loading until failure upon reaching the desired expansion level. The results showed that the existence of prestressing force played a significant role in limiting the ASR‐induced in‐plane expansion and cracking. Progress of ASR caused a reduction in the load corresponding to the first detected flexural crack but an increase by up to 14% in the load corresponding to the first diagonal cracking compared to the control specimen, likely due to the additional prestress caused by restrained ASR‐induced expansions. The ultimate shear strength of ASR‐affected girders was generally within 5% of the control specimens, and all specimens exceeded their nominal shear strengths according to AASHTO LRFD 2020 specifications. Until the unrestrained uniaxial expansion of 0.2%, no significant concerns were identified regarding the shear strength of the ASR‐affected pretensioned concrete specimens. [ABSTRACT FROM AUTHOR]

This paper describes the structural aspects of the Wieselburg Bridge collapse in Austria. The original design and reinforcing details for this integral concrete bridge are discussed. The collapse of the bridge is re‐constructed based on forensic documentation of the failure. The results of structural analysis carried out using material properties obtained after failure are compared to the shear capacity obtained from various models and from test results from literature. The results are used to explain the cause of failure of the integral bridge under dead load. [ABSTRACT FROM AUTHOR]

A growing body of research has shown that reversed cyclic shear loading of reinforced concrete (RC) causes effects that are not accounted for in monotonic behavioral models. Notable among these effects are a reduction in shear strength and significant plastic offsets. This paper presents the General Crack Component Model, a rational, mechanics‐based model that explicitly considers the constitutive behavior of cracks in RC. Cracked RC is treated as a series–parallel system of bonded and unbonded regions, where the crack interfaces have both crack closing hysteresis and a kinematic contact constraint. Validation was performed using data from monotonic and reversed cyclic experiments on panel elements, and has shown that this analytical model is able to accurately capture the salient features of reversed cyclic shear behavior. [ABSTRACT FROM AUTHOR]

The use of UHPC enables reducing the height of composite slabs, which may decrease the punching shear capacity. This paper investigates the punching shear behavior of steel‐normal concrete‐UHPC composite slabs with experiments and theoretical analyses. Results indicated that a 50 mm UHPC layer makes the nominal punching shear strength increase by 24.91%. Utilizing UHPC and increasing loading area can effectively enhance the punching shear capacity. Besides, theoretical punching shear model proposed based on rigid‐plastic theory can reliably predict the punching shear capacity of composite slabs. The punching shear angle derived from strength theory closely matches the experimental values. [ABSTRACT FROM AUTHOR]

In this paper, seven half‐scale specimens are used to investigate the effects of the beam–column width ratio, concrete strength, and axial load on the seismic performance of wide exterior beam–column joints. The test results show that all the specimens undergo bending damage at the beam end. The concrete damage in the core column is not significant, meeting the seismic requirements of strong column–weak beams and strong joint–weak members. For specimens with small beam widths, the increase in axial load can effectively reduce the damage to the concrete in the outer joint and increase the strength of the specimen. Increasing the beam width and concrete strength reduces the ductility of the specimen while increasing the strength of the specimen. The bonding performance of the longitudinal bars anchored outside the core column is poor, as bond–slip with the concrete is observed during the test. In addition, compared with ACI 318‐19, GB 50011‐2010 is more conservative for calculating the shear strength of exterior wide beam–column joints. Finally, a corresponding finite element model is established by MSC Marc and verified based on the experimental results. [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]

The paper presents the results of an original experimental program that was focused on punching shear behavior of flat slabs supported by rectangular columns with a column rectangularity index cmax/cmin = 1.0, 4.33, and 6.33 and slabs supported by elongated columns that were loaded by four different load patterns. Seven isolated flat slab specimens with a thickness of 200 mm were tested until their failure. An effect of the column geometry and the way of the flat slab loading on punching shear capacity of slab‐column connections were investigated. The obtained experimental results were confronted with predictions carried out with the design provisions from code of practice EC2 (2004), ACI 318‐19, and prEC2 (2021) and the original Critical Shear Crack Theory (CSCT) (2008) model developed by Muttoni. Experimental results confirmed an effect of column rectangularity on punching shear resistance when a value of shear strength ratio Vtest/Vmodel was below one in the specimens with cmax/cmin > 2. The highest punching resistance was achieved in slab specimen with loading pattern x/2y where x is an axis along the column dimension cmax. The lowest capacity was achieved with a loading pattern 9x/y where 90% of the load flew perpendicular to the axis "y" parallel with cmin. The most accurate and balanced predictions provided CSCT (2008) model. [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]

The calibration of most analytical models that assess the shear strength of wide reinforced concrete members without shear reinforcement is based on simply supported beam tests, which may not be representative of slabs and wide members failing in shear. This paper addresses the knowledge on the shear strength of wide members, identification of their most important parameters, and an evaluation of the accuracy and precision of the main models presented in codes of practice and literature. A database of 170 shear tests was built on wide members loaded over the entire width, with the ratio width to effective depth b/d > 1. This database includes members under concentrated loads (CLs) and distributed loads (DLs) in the span direction. A parameter analysis revealed such shear strength is mostly influenced by the shear slenderness and size effect rather than by the ratio b/d. Furthermore, the results show a clear decrease in the shear strength of continuous members under DLs to higher shear slenderness, similar to the behavior of members under CLs. This trend was well observed with the proposed model of shear slenderness, which assumes that continuous members with higher bending moment in the span than over the inner support behave closer to simply supported members. A comparison of the shear capacities predicted by the physical‐mechanical and semiempirical approaches showed the higher accuracy and precision of models based on the critical shear crack theory and critical shear displacement theory, regardless of the ratio b/d. Therefore, the same models derived based on beam tests are valid for wide members. Apart from that, the analyses of nonslender members with some strain‐based models combined with reducing factors of the acting shear load provide accurate results of shear strength for members without stirrups. [ABSTRACT FROM AUTHOR]

This paper investigated the shear transfer behavior between substrate recycled aggregate concrete and new natural aggregate concrete. A total of 72 push‐off tests with substrate‐to‐new concrete specimens were performed considering the effects of concrete strength grade, replacement ratios of recycled coarse aggregate, and lateral constraints ratios. Existing design codes and empirical models for calculating shear strength were reviewed and verified. Results show that concrete cracks occurred and developed along the shear transfer plane. Increasing the concrete grade and lateral constraints can both improve the crack stress and shear strength, while the incorporation of recycled coarse aggregate has a slight adverse effect on them. The model in fib Model Code 2010 based on shear‐friction theory gave the most accurate but still conservative values compared with experimental results and can be used to predict the shear transfer behavior between substrate recycled aggregate concrete and new natural aggregate concrete. [ABSTRACT FROM AUTHOR]

The paper presents a new model for predicting the resistance of anchorages with supplementary reinforcement loaded in shear toward and perpendicular to the edge in case of reinforcement failure. The model is based on the evaluation of the results of a comprehensive test program performed on anchorages with multiple anchor rows and supplementary reinforcement, reported in an earlier paper. It is shown that the existing models available in the codes and standards are conservative for low to medium amounts of supplementary reinforcement but tend to be unconservative for high amounts of reinforcement. The new model is able to predict the failure loads corresponding to reinforcement failure under shear loads very well. The approach to incorporate other failure modes into the design model for anchorages with supplementary reinforcement under shear loads toward the edge will be presented in another paper. [ABSTRACT FROM AUTHOR]

This paper presents a mechanical and numerical approach to model localized deformations occurring in concrete structures with less than minimum reinforcement. The presented models are based on, and validated against large‐scale experiments conducted in a previous study to investigate the behavior of a less than minimally reinforced slab in the framework of the structural safety assessment of an existing cut and cover tunnel. The model deploys rotational springs embedded in a nonlinear finite element analysis to capture deformations concentrating in an inclined crack. An iterative solution procedure ensures equilibrium and compatibility in the inclined crack section by adjusting the spring stiffnesses, which depend on the acting loads. A case study shows that the localized crack has a minor effect on the global structural behavior. In contrast, localization strongly influences deformations and stress resultants in the crack, and compressive membrane action significantly impacts the load–deformation behavior of the localized crack, which is relevant particularly for the shear strength. [ABSTRACT FROM AUTHOR]

Transfer of shear strength across the concrete‐to‐concrete interface is important to the strength of reinforcement concrete structures and is extensively existing in repairing and strengthening existing reinforced concrete members, the connections between prefabricated members and the connection joints between concrete sections cast in situ. Steel fibers improve the mechanical properties of concrete and steel fiber‐reinforced concrete (SFRC) has been universally applied as the repaired materials and the connection materials in reinforced concrete structures. The aim of this paper is to evaluate the interface shear transfer (IST) strength of SFRC. One hundred twenty‐seven‐group experimental results are collected from previous studies to establish a reliable database, which the investigated parameters include the compressive strength of concrete, the diameter, length and volume friction of steel fibers, and the volumetric ratio and yield strength of shear reinforcement. Based on the established database, an artificial neural network (ANN) model is developed and the parameters sensitive is analyzed based on the proposed ANN model. Based on the parametric sensitive analysis, the linear regression model is established to evaluate the IST strength of SFRC, which is applied to evaluate the design of the concrete‐to‐concrete connections. [ABSTRACT FROM AUTHOR]

The present paper summarizes the findings of an experimental programme to investigate a strengthening/repair technique through the introduction of a new RC layer to an existing slab. Six RC slabs, composed of twelve cantilever and six interior spans, were tested under monotonic transverse loading. The behaviour of statically determinate cantilever spans and indeterminate interior spans was examined by comparing the test results of these specimens to the results of reference slabs, in which the existing and additional layers were cast monolithically. The influences of recovering the permanent slab deformation before repair and the spacing of the shear connectors between the existing and additional layers were investigated. The tests indicated that recovering the permanent deformations of a slab before repair substantially reduces its rigidity while having little influence on the ultimate load. Furthermore, debonding of the reinforcement was observed to considerably decrease the load capacities and rigidities of the slabs. [ABSTRACT FROM AUTHOR]

Today, the development of innovative shear connectors for steel-concrete composites is accompanied by a large number of experimental investigations, which are obligatory when proposing suitable design formula and carving out their limitations of use. Using the example of the so-called pin connector, the present paper illustrates to what extent validated finite element models of novel shear connectors can be used to replace expensive and time-consuming shear tests and how these finite element models can support the deduction of design concepts. The pin connector considered was developed for connecting steel sections to very slender high-strength concrete slabs in which conventional shear connectors such as headed studs cannot be used due to the limited embedment depth. In order to clarify the shear behaviour and load-carrying mechanisms of these novel connectors, non-linear finite element models were set up using the commercial FE software Abaqus. Subsequently, the FE models were used to perform systematic parametric studies. This paper describes the numerical results and also explains the stepwise development of an entire engineering model for determining the longitudinal shear capacity of small-scale pin connectors, including all the necessary limitations of use. The proposed modelling strategy and the methodology for the deduction of design rules can be transferred and assigned to other types of shear connectors. [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 the results of an experimental campaign carried out to investigate the effects of in‐plane transverse tensile forces on the shear strength of linearly supported one‐way reinforced concrete (RC) slabs without shear reinforcement subjected to concentrated loads. A total of 5 half scale slabs (1650 × 1650 × 120 mm), subjected simultaneously to different levels of in‐plane tensile forces and a concentrated load were tested up to failure. The clear shear span to effective depth ratio av/d was equal to 3 in all tests, to minimize the effects of the direct transmission of the load to the closest support, the so called arching action. As observed, the shear strength barely decreases with increasing values of the tensile force applied, even for values of the external force that cracked the concrete cross‐section of the slabs in the direction perpendicular to the span. These observations may indicate that the shear–flexural behavior in the spanning direction is not significantly affected by the membrane forces in the transverse direction. [ABSTRACT FROM AUTHOR]

The level of maximum punching strength is of major importance to design highly stressed slab‐column connections and to choose the type of punching shear reinforcement. Since a couple of years, there is consensus that the maximum punching strength of shear‐reinforced concrete slabs can be defined as a multiple of the reference punching strength without shear reinforcement. The upper bound of this load‐increasing effect depends mainly on the anchorage and arrangement of shear reinforcement elements. Despite numerous research studies and database evaluations, there are ongoing discussions regarding the final effectiveness of stirrups and double headed studs installed in flat slabs and column bases. In this paper, a strictly filtered punching database is used to highlight the significant impact of underlying reference strength comparing the maximum load increase according to current Eurocode 2 and the draft for the next generation of Eurocode 2 (prEC2). Based on this unifying database, the origin of current discrepancies is discussed and a combination of constant lower bound coefficients with a refined formula as specified in prEC2 is proposed. Additionally, the effect of adapting current European Technical Approvals for double‐headed studs and punching shear optimized lattice girders to prEC2 is shortly analyzed. A further database evaluation also allows for setting the basis for optimized detailing provisions regarding the maximum permissible diameter of shear reinforcement. [ABSTRACT FROM AUTHOR]

Many post‐tensioned girders of existing bridges contain a low amount of transverse reinforcement. The shear strength of these girders, calculated according to current semi‐probabilistic design codes, like Eurocode 2, is often less than that required in the codes. In this paper, the experimental results of four shear tests on post‐tensioned bridge girders of existing bridges are presented. The specimens were extracted from two different road bridges, both built in 1959. In this paper, the results of this test series are used to analyze the shear behavior and failure modes of existing post‐tensioned bridge structures with a low amount of shear reinforcement. Furthermore, the experimental results are compared with the shear strengths calculated according to various design codes. Finally, the shear behavior is analyzed according to the zone‐based, shear assessment concept with its refined shear models. The calculation results agree well with the data from the experiments. [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]

In this paper, a three‐dimensional finite element method (FEM) model of push‐off tests for specimens made with recycled aggregate concrete (RAC) was presented. The FEM model used ABAQUS/Standard module software. The model considered the plasticity of concrete and the concrete‐to‐concrete contact properties, and was found to agree with experimental data from shear transfer tests. The verified model was then used for a parametric study that investigated lateral reinforcement, concrete strength, and recycled coarse aggregate (RCA) replacement ratio. The parametric study shows that the ultimate shear strength increases by 23.1% when the lateral reinforcement ratio increases from 0.56% to 1.12%; the ultimate shear stress increases almost linearly when the concrete strength increases from 30 MPa to 60 MPa; the ultimate shear stress is reduced by 13.8% when the RCA replacement ratio increases from 0% to 100%. [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]

The rectangular concrete‐filled steel tube (RCFST) has been widely applied into many engineering fields like buildings and bridges. However, the shear mechanisms and the universal design methods under lateral shear forces still remain to be fully understood. In this paper, the composite action of RCFST columns under lateral shear forces was systematically investigated with improved 3‐dimensional finite element simulations. The models adopted the improved material constitutive models and detailed contact interactions between the encased steel tube and core concrete. On the basis of available test data and numerical results of parametric studies, the critical shear span ratio and its variation range were determined. The composite effect and interactions between the encased steel tube and core concrete under different configurational dimensions and loading conditions were investigated. Calculation formulas of the shear stiffness and capacity were proposed based on identified features. The cooperative working mechanism and the constraining effect of steel tube were considered. The proposed calculations were then compared to available design regulations in different countries, and yielded more accurate predictions than the others. [ABSTRACT FROM AUTHOR]

In the last decades, increasing traffic loads have led to higher requirements on the bearing capacity of existing and also new bridges. In particular, many bridge structures built in the 1960s and 1970s often contain less web reinforcement than the nowadays required minimum web reinforcement. In this context, the shear resistance under cyclic loading is of special interest. For this reason, experimental tests were conducted on prestressed concrete beams with and without shear reinforcement at the Institute of Structural Concrete of RWTH Aachen University within the last years to investigate the shear fatigue strength. The specimens were able to resist more load cycles than predicted by the approaches implemented in the Eurocodes for bridges. Based on the test results, design models for shear under cyclic loading should be reviewed and improved, especially with regard to the assessment of existing structures. This paper describes the recent tests on 20 I‐shaped prestressed beams with web reinforcement. [ABSTRACT FROM AUTHOR]

A new finite element model is developed for nonlinear finite element analyses of structural behavior of fiber-reinforced polymer (FRP)-strengthened steel-reinforced concrete (RC) beams under cyclic loading in this paper. All the components of the beam, including concrete, steel rebar, FRP sheet, adhesive, and shear strengthening stirrups, are included in the model. Material nonlinear properties of concrete and steel rebars are accounted for, while the FRP and adhesive are considered to be linearly elastic until rupture. The degradation of each material under cyclic loading is considered and defined using the user-programmable features in ANSYS. The developed finite element model is validated against experimental results, and demonstrated to be effective for structural analyses of FRP-strengthened RC beams under cyclic loading. Furthermore, parametric studies are carried out to learn the effects of types, thickness, and length of FRP on the structural behavior of FRP-strengthened RC beams based on the new model. Research findings are summarized finally. [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]

While tests of deep fiber‐reinforced concrete (FRC) beams have shown that steel fibers enhance the crack control and shear strength, the modeling of these effects in a simple and rational manner remains a challenging problem. Because FRC features enhanced tension behavior, it is not well suited for the traditional strut‐and‐tie approach which neglects the tensile strength of the concrete. Therefore, this paper proposes an alternative approach which focuses on the displacements in the critical shear cracks. The displacements are described with a kinematic model with two degrees of freedom, and are used with appropriate constitutive relationships to estimate the shear contribution of the fibers. This kinematics‐based approach is validated with experimental data, and it is shown to capture adequately the complete pre‐ and postpeak behavior of deep FRC beams. It is also shown that the model predicts well the effect of beam aspect ratio, fiber volume ratio, longitudinal reinforcement ratio, and concrete strength on the shear strength of deep FRC beams. [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]

Many research efforts have so far been devoted to the topic of shear design of members without transverse reinforcement since the first development in structural concrete. This has allowed a number of significant advances in the understanding of the phenomenon, which is currently acknowledged to depend upon a number of shear‐transfer actions in cracked concrete such as aggregate interlocking related to crack opening and sliding, the residual tensile strength of concrete after cracking, dowelling of the reinforcement and the inclination of the compression chord. In the last years, independent teams of researchers have confirmed this by means of detailed measurements on tests performed with Digital Image Correlation and by integrating constitutive laws governing the transfer of shear. In agreement to the observed physical reality, clear and scientifically based theories have been developed allowing researchers to reproduce the shear response in a realistic manner and to perform more accurate predictions on the strength of members. One of these theories, grounded on experimental facts and supported by mechanical modeling, is the Critical Shear Crack Theory (CSCT). In this paper, the fundamentals of the theory are reviewed, linking them to the experimental response of beams in shear. Based upon these fundamentals, a general physical‐mechanical model is presented to implement the CSCT basic ideas. On the basis of these results, the aptness of defining a criterion to assess failures in shear is justified, which can be formulated in a simplified manner and is suitable for design. The aim of this criterion is to lead to consistent design expressions, sufficiently simple to be used in practice. It is particularly interesting that the mechanical basis of the model allows natural reproduction of physical phenomena, such as size and reinforcement strain effects, that can be assessed in an accurate manner considering the nonlinear response of a potentially cracked reinforced concrete member. This approach is consistent with the underlying physics and is significantly more general than approaches followed in the past, where empirical formulas were corrected with a size effect term to account for this phenomenon (imposing an effect on a formula which is not necessarily consistent or valid outside its ranges of calibration). Based on the evidence reviewed, this article replies in a scientific, detailed, and transparent manner to a number of criticisms by A. A. Dönmez and Z. P. Bažant on the assumptions of the CSCT. [ABSTRACT FROM AUTHOR]

Failures of shear keys in precast concrete segmental bridges (PCSBs) have been attributed to fracture of concrete along the joints with shearing off the keys. The principal goal of this study is to investigate the effect of specimen thickness and coarse aggregate size on shear strength of single‐keyed dry joints in PCSBs, which are noticed by bridges designers in deciding box geometry and requiring the concrete constituents. In this paper, shear performance of match‐casting single‐keyed dry joints is assessed in terms of cracking shear strength, ultimate shear strength, residual shear strength, and failure modes. It was found that there tended to be slightly positive correlation between specimen thickness and ultimate shear strength, while the influence of coarse aggregate size was obscure. The measured shear capacity was compared with several provisions of design formulae. [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 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]

A review of current studies in concrete shear walls shows considerable uncertainty in the effective stiffness of these elements. Based on statistical analyses of 154 existing experiments on slender and squat walls, this paper proposes relations to determine the effective stiffness. Linear regression analyses are applied to determine the relationship between effective stiffness parameters such as axial load, reinforcement ratio, and aspect ratio. The results show the axial load plays a major role in the effective stiffness of the slender wall with correlation coefficient of 0.81. While, in case of squat shear walls, the axial load and the aspect ratio of the wall are the most significant parameters with correlation coefficient of 0.75 and 0.65, respectively. Finally, 2 relations are suggested for the effective stiffness of the slender and squat shear walls by linear regression analyses and are compared with the existing relations. [ABSTRACT FROM AUTHOR]

In this research, the precast segmental construction of composite hollow reinforced concrete (RC) columns was studied. The precast segmental construction of composite hollow RC column requires guidelines for the connections between the bent cap and column segment, connections between column segmental joints, and connections between column segment and footing. The connection methods for different precast composite hollow RC piers were experimentally studied for rational resistance against shear force and bending moments. Two types of precast composite hollow RC columns and cast‐in‐place column were studied in this paper. The performance of these columns was evaluated through experiments. The precast column erected with a base‐plate connection exhibited a performance similar to the cast‐in‐place column. [ABSTRACT FROM AUTHOR]

This paper presents findings from a study on punching shear capacity of high‐performance concrete slabs reinforced with macrobasalt fibers. The punching shear failure is simulated through a simple method introduced by Hassan et al. The test specimens comprised 14 small‐scale slabs with circular notches. To investigate the effect of fiber content, 5 different fiber volume fractions of 43 mm macrobasalt fibers have been studied. The results show that the punching shear capacity and the ductility of the slabs were slightly improved with increasing the fiber content. Furthermore, the results also indicate that the outcome of the experimental method is valid when the rotation of the slabs is negligible. [ABSTRACT FROM AUTHOR]

Despite the intensive efforts dedicated in the last decades to better understanding punching shear failures, there is still no consensus on the mechanics governing this phenomenon and on how to implement it within a physical approach. In this paper, an analysis of recent detailed measurements on the kinematics and crack development associated with punching failures is presented. This allows classifying the observed cracks by their nature and to address their interaction and development on the eventual punching failure surface. On this basis, a complete mechanical model is formulated consistently with the principles of the critical shear crack theory (CSCT). This model generalizes previous approaches based on the CSCT by accounting for the various crack types and failure modes as well as for their associated kinematics. The generality of the model is verified by extensive comparisons to test data, showing accurate and consistent agreement. Its results are eventually used to investigate the role of the various potential shear‐transfer actions as well as the pertinence of the assumptions adopted to simplify the CSCT by describing its failure criterion with analytical expressions. [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]

A traditional difficulty in the understanding of the role of the various shear‐transfer actions in members without transverse reinforcement has been a lack of detailed measurements on the development of shear cracking and their associated kinematics during the process of failure. In this paper, this issue is addressed on the basis of an experimental program on 20 beams investigated by means of digital image correlation. The measurements are shown to allow a clear understanding of the mechanisms leading to shear failure and their evolution (transfer of forces between the various potential shear‐carrying actions) during the loading process. The amount of shear carried by the various potential shear‐transfer actions is estimated for varying levels of load accounting for the cracking pattern and actual kinematics on the basis of fundamental constitutive laws for concrete and steel. The results are shown to be consistent and provide a rational basis for the understanding of the phenomenon of shear transfer in reinforced concrete members without transverse reinforcement. [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]

This paper deals with the experimental and theoretical evaluation of punching shear capacity of steel fiber reinforced concrete (SFRC) slab–column connections. Five experimental specimens with a thickness of 160 mm, different fiber volume contents (0, 1.0, and 1.5%) and different flexural reinforcement ratios (0.75 and 1.5%) have been tested. The experimental results were evaluated using a physical–mechanical model based on the critical shear crack theory (CSCT). The model has given a good approximation of experimental punching shear strengths. In general, tests have highlighted a significant increase in load and deformation capacity of fiber reinforced concrete slab–column connections in comparison with reinforced concrete connections. [ABSTRACT FROM AUTHOR]

The mechanical model of the critical shear crack theory (CSCT) has been used in the past to investigate a number of shear‐related problems, such as punching of slab–column connections with and without transverse reinforcement. In this paper, a discussion on the differences and analogies between slender slabs and squat members (footings) without transverse reinforcement is presented on the basis of the CSCT. This discussion highlights how bending and shear deformations influence the opening of the critical shear crack and eventually its ability to transfer shear forces. On that basis, it is investigated and justified a power‐law expression to characterize the failure criterion of the CSCT. This criterion, in combination with a suitable load–deformation relationship, can be used to derive closed‐form expressions for punching shear design. The accuracy of these expressions is verified against databases of slender slabs (121 specimens) and footings (34 specimens) with consistent agreement. [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]

Large efforts have been devoted in the past to understanding size effect in shear failures of members without transverse reinforcement. Experimental works have demonstrated that increasing the size reduces the nominal shear strength provided that the failure mode is brittle. For large specimen sizes where a linear behavior can be assumed between the opening of the shear cracks and the acting shear force, the size effect agrees with linear‐elastic fracture mechanics (LEFM). In this case, the reduction of nominal shear strength is characterized with respect to the specimen size by an asymptotic slope (in double‐log scale) of −1/2. However, such a linear relationship between crack widths and applied shear force is not present in most reinforced concrete structures, where the response is characterized by a nonlinear behavior at a cracked stage. In these cases, the influence of size effect shall be milder, and the slope (in double‐log scale) characterizing it shall be lower than −1/2. In this paper, the influence of size effect on structures characterized by internal redundancy (continuous one‐way members and slabs in case of punching shear with a nonlinear response) is investigated in the frame of the critical shear crack theory. The theory predicts the same influence as LEFM with respect to size effect when a linear behavior can be assumed, but it yields consistently milder influence of size effect for structurally redundant elements with a nonlinear response. [ABSTRACT FROM AUTHOR]

Ceiling and floor slabs made of horizontal layers of regular and lightweight concrete could lead to an efficient use of materials. In this context, the bond between the different types of concrete is of particular importance. This paper shows the shear strength and failure mode of unreinforced concrete interfaces with high‐quality, lightweight concretes in dependence of different interface roughness. To achieve this, a regular and a structural lightweight concrete were bonded to an infra‐lightweight and a foam concrete. Small‐scale shear specimens consisting of five layers were manufactured and loaded to investigate their shear behavior as a whole. Both concrete and interface failures were detected in dependence of interface roughness and the type of core layer concrete. Additionally, it is shown that the observed behavior can be satisfactorily reproduced by a finite‐element model using the material parameters of concrete standard tests. The experimental and numerical investigations provide clearly defined interface parameters to design efficient load‐bearing slabs made of different concrete layers. [ABSTRACT FROM AUTHOR]

T-beams are acknowledged as economic and efficient structural members widely used for floor slab construction systems. In many cases, according to practice in some countries, the beams do not present transverse reinforcement, and their shear strength is governing for dimensioning the width of the web. Although experimental investigations have shown that the presence of the compression flange enhances the shear capacity with respect to equivalent rectangular cross sections, most current design codes neglect this phenomenon, which leads to the overdesign of these members. In this paper, the role of the compression flange of slender T-beams with concentrated loads is investigated with reference to its influence on the shape of the critical shear crack and to the associated shear transfer actions (STA) of the beam. The flanges are considered elements that allow the smearing of applied loads over a certain length of the web. This consideration, in combination with the mechanical model of the Critical Shear Crack Theory ( CSCT), allows a consistent treatment of the phenomenon and leads to simple design expressions accounting for the role of flanges. The results of the proposed model are compared together with design codes (Model Code 2010, Eurocode 2, and ACI 318-11) and other shear design approaches to a database of 239 beams on T-shaped members. The comparison shows that the role of flanges is finely accounted with the proposal based on the CSCT, leading to consistent agreement and to strength predictions that are more suitable for design purposes than the other investigated design models. [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]

Many existing reinforced concrete bridges in The Netherlands are suspected of having insufficient shear strength, hence a methodical approach is necessary to assess them. The aim of this paper is to provide a structured approach for assessment of the reinforced concrete slab bridges, which make up a considerable proportion of the Dutch bridge stock. The proposed method uses the levels of approximation introduced in the fib Model Code for Concrete Structures 2010. The recommendations at all levels are linked to experimental research. The different levels include spreadsheet-based calculations (the 'Quick Scan'), linear finite element models, nonlinear finite element models, the analysis of a structure with cracked concrete, and, for exceptional cases, proof loading of the structure. The result of this approach is a structured method of levels of assessment that can be used when many bridges need to be assessed. For most bridges, assessment at the lowest level will prove sufficient. For a limited number of cases, higher levels of assessment will offer options and guidelines for a more in-depth study of the structure being assessed. [ABSTRACT FROM AUTHOR]