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In this paper, seven specimens were designed to study the influence of the height (h), width (b), and reinforcement ratio (ρ) of ring beam on the failure mode, bearing capacity, deformation, and equivalent stress–strain relation of joint core reinforced with ring beam for connection of polyvinyl chloride fiber‐reinforced polymer confined concrete column and reinforced concrete beam. The experimental results indicated that the crushing of concrete in the joint core dominated the failure of specimens. The ultimate, yield bearing capacity and axial strain decreased with the increase of height, while raised with the improvement of width or reinforcement ratio. The growth of the strains of reinforcement and concrete accelerated with the increment of height, while decelerated with the rise of width or reinforcement ratio. Subsequently, based on the local compression theory, confined concrete theory, and the principle of superposition of multiple confinement, considering the influence coefficient of joint height βh and the enhancement coefficient of stirrups αs, a new formula was proposed to estimate the ultimate bearing capacity of specimens under axial local compression. Then, on the basis of Mander's model, taking the correction parameter η into consideration, a new model of equivalent stress–strain relationship was established. Verification results showed that the models proposed in this research agreed well with the experimental results. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study on the development of material properties over time (up to around 2 years) and the structural behavior of reinforced beams, for two types of alkali‐activated concrete (AAC). Compressive strength, flexural strength, tensile splitting strength, elastic modulus, and flexural behavior of reinforced beams are investigated. Tested material properties of AAC are compared with the properties of conventional concrete, as predicted by Eurocode. For the mixes of AAC and the conventional concretes with the same 28 days compressive strength, flexural and tensile splitting strength at 28 days are found to be similar, whereas the elastic moduli of AAC mixtures is up to 30% lower than those of conventional concrete. Related to the long term behavior, after 28 days moist‐curing and subsequently exposing AAC specimens to laboratory conditions (50% RH/20°C), a reduction of flexural strength, tensile splitting strength and elastic modulus, is observed. Structural behavior of the reinforced AAC beams in four‐point bending test seems not to be affected significantly by the observed decrease in material properties, and is found to be similar to that of conventional concrete beams. The acquired results indicate that the observed decrease of material properties over time might be related to drying (moisture loss). However, more research is needed to understand the phenomenon, especially related to the aimed structural application and safe upscaling of AAC. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of cyclic preloading on the fatigue behavior of reinforced concrete (RC) beams rehabilitated with near surface mounted (NSM) carbon fiber reinforced polymer (CFRP) reinforcement. The study includes eight RC beams with dimensions of 152.4 × 152.4 × 1,521 mm. Strengthened and nonstrengthened specimens were tested under monotonic loading to obtain the flexural static capacity. Two strengthened specimens were tested as a reference under constant amplitude cyclic stress without prefatiguing. Four nonrehabilitated RC beams were prefatigued to simulate service loading conditions. Later, these RC beams were rehabilitated with NSM CFRP reinforcement and tested under the same cyclic stress range of the reference specimens. Mid‐span deflection, strain of tension steel rebars and CFRP rods, stiffness degradation, and energy dissipation were analyzed and evaluated. Experimental results show that the rehabilitated prefatigued RC beams had similar stiffness degradation and failure modes to the reference strengthened RC beams. The rehabilitated RC beams had an improvement in the fatigue responses when compared to the reference strengthened RC beams. Moreover, the postfatigue monotonic behavior of the rehabilitated RC beams showed an increase in the elastic modulus and a decrease in ductility. [ABSTRACT FROM AUTHOR]

An experimental study is carried out to test 25 reinforced concrete (RC) beams in order to investigate the torsional behavior of the beams using welded and unwelded transverse reinforcement. Four different transverse reinforcement configurations were considered: ordinary, continuous circular spiral, continuous rectangular spiral, and continuous advanced rectangular spiral configuration. Welded configuration includes welding the hoops to the longitudinal reinforcement at their intersections. Three different spacing of 200, 150, and 100 mm were used. The experimental torsional capacity results are compared with the theoretical values determined by the ACI 318–14 code, Eurocode‐2, fib model code2010 and other available equations in the literature. The results showed that the welding effect varies based on the transverse reinforcement configuration and spacing and the maximum improvement in the ultimate torsional capacity of RC beams is obtained in the specimens made with continuous circular spiral stirrups. Furthermore, the ACI‐318, Eurocode‐2, fib model code2010 and other equations available in the literature are generally conservative in predicting the ultimate torsional strength of welded and unwelded RC beams with continuous transverse reinforcement but the predicted torsion moments obtained using Eurocode‐2 and fib model code2010 are closer to the test results. [ABSTRACT FROM AUTHOR]

This paper presents the fresh and hardened concrete properties with fly ash (FA) and copper slag (CS). M30 grade of concrete has been designed with a constant water–cement ratio as 0.4. Twenty four concrete mixtures are arrived by cement is partially replaced by FA from 0 to 30% with 10% increment and natural sand is replaced by CS from 0 to 100% at 20% increment. The compressive strength of the concrete was verified at 3, 7, 14, 28, 56, and 90 days curing periods. Five reinforced concrete (RC) beams of size 150 mm × 250 mm × 3200 mm were cast based on the optimum mix proportion and flexural behavior of RC beams was monitored by a four‐point bending test. From the experimental results, compressive strength, and flexural strength were increased for concrete with 30% FA and 80% of CS because the smaller surface area of CS per unit volume is exposed with a large quantity of concrete matrix and workability of concrete also increased. [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 efficiency of shear capacity models of reinforced concrete beams with stirrups depends on the assumed mechanism and in few cases depends also on critical shear crack angle prediction. In the present study, three mechanics‐based shear capacity models (the limit analysis‐based models presented by Nielsen and Hoang, and the Mari et al. model) are considered covering the range space of shear span to effective depth ratios greater than 2.5. The statistics of modeling error associated with these models are determined using the database created in this study. The database contains limited results of experimental investigations, available in literature, on shear capacity of reinforced concrete beams with stirrups. The randomness in shear capacity is quantified by performing probabilistic analysis of one set of nominally similar beams taken from the database. Based on the shear capacity distribution obtained, characteristic design equations of reinforced concrete beams are proposed. The results of reliability analyses show that the reliability of a beam, for a given mean live to dead load ratio, varies when different shear capacity models are used in the analysis. Thus, calibration studies need to be performed for selecting a model for design. [ABSTRACT FROM AUTHOR]

Recycled aggregate concrete (RAC) has emerged as a viable solution for solving some of the environmental problems of concrete production. However, design guidelines for deflection control of reinforced RAC members have not yet been proposed. This study presents a comprehensive analysis of the applicability of the fib Model Code 2010 (MC2010) deflection control model to reinforced RAC beams. Three databases of long‐term studies on natural aggregate concrete (NAC) and RAC beams were compiled and meta‐analyses of deflection predictions by MC2010 were performed. First, the MC2010 deflection control model was tested against a large database of long‐term tests on NAC beams. Second, a database of RAC and companion NAC beams was compiled and initial and long‐term deflections were calculated using the MC2010 model. It was shown that deflections of RAC beams are significantly underestimated relative to NAC beams. Previously proposed modifications for MC2010 equations for shrinkage strain and creep coefficient were used, and new modifications for the modulus of elasticity and empirical coefficient β were proposed. The improved MC2010 deflection control model on RAC beams was shown to have equal performance to that on companion NAC beams. The proposals presented in this paper can help engineers to more reliably perform deflection control of reinforced RAC members. [ABSTRACT FROM AUTHOR]

This study was based on findings from the Norwegian Public Roads Administration's Bridge Management System and field investigations on corrosion damage in pretensioned Norwegian standard I‐beam (NIB) girders in 227 coastal climate bridges. The main durability design parameters are summarized and related to regulations over the last 80 years. Environmental exposure is discussed in the light of the global, local, and micro climate. We found that 51% of the bridges have girder corrosion damage. The percentage is highest for bridges built when the cover thickness required was lowest. Cover thickness below that required (resulting from production faults) caused 74% of corrosion damage. Most of the severe chloride‐induced corrosion damage in bridges was found in the inner NIB girders, particularly in the support‐zones and their vicinity. This can be due to interaction between geometry and exposure. Corrosion of reinforcement in support‐zones can impact structural behavior, particularly NIB girder shear performance. [ABSTRACT FROM AUTHOR]

For this purpose, a database of experimental crack widths for load-induced flexural cracking was compiled from reputable sources to obtain the measured maximum crack widths, I w i SB exp sb . Design crack width predictions were obtained for each of the three crack models as a best estimate of the predicted maximum crack widths, using the geometric and material properties from the experimental data. The predicted maximum crack width corresponds to a 5% probability of exceedance[3] by design code formulations, which may not probabilistically match the measured maximum crack width, thus contributing to model uncertainty. [Extracted from the article]

In this study, the effects of fiber orientation within the carbon fiber reinforced (CFRP) sheets, on the fracture mode and crack growth of specimens were investigated by constructing five groups of initially notched self‐consolidating concrete beams, and strengthening them with CFRP sheets in the tensile area. Furthermore, the bearing capacity, strain variation along the sheet, crack mouth opening, and the midspan displacement were recorded by varying the height of the beams and the initial notch lengths. The results indicate that the load‐crack mouth opening curves have two peak load points. First, the applied load increases up to one peak value and then there is a drop in the load‐caring capacity. Afterwards, the applied load is improved to another peak value due to the relatively high cohesive effect of the CFRP sheet. The results show that as the height of the beam section increases, or the initial notch length decreases, the first and the second peak loads increase. By comparing the specimens with different fiber angles in each group, it was observed that the specimen with fiber angle 0° has a higher capacity relative to other angles, yet its failure occurs in a lower displacement. Furthermore, with the help of finite element software and nonlinear static analysis, the behavior of the aforementioned beams including the stress and strain distributions in the CFRP sheet, and the sheet‐to‐concrete bond zone have been examined and compared with the existing experimental results for validation. [ABSTRACT FROM AUTHOR]

This paper studies the fire resistance time of hybrid reinforced concrete beams. A method of calculating the strength reduction coefficient of the longitudinal reinforcement of the hybrid reinforced concrete beams is proposed. Then, an allowable flexural reduction coefficient is suggested for the fire endurance of hybrid reinforced concrete beams. Based on the section properties of the hybrid reinforced concrete beams and the allowable flexural reduction coefficient, a method of calculating the fire resistance time that considers the ratio of the longitudinal reinforcement and the thickness of the concrete cover is described. This method uses mechanical properties of the materials at high temperatures proposed by scholars from various countries and analytic calculations of the temperature profiles in the rectangular beams. Fire resistance tests of six hybrid reinforced concrete beams were carried out. The temperatures measured from the test and the calculated temperatures are well fitted. The calculated fire resistance times and those obtained from a test are similar. Finally, the fire resistance time of the hybrid reinforced concrete beams is calculated under different conditions to provide two samples. The influence of the thickness of the concrete cover and the ratio of the longitudinal reinforcement on hybrid reinforced concrete beams is studied. [ABSTRACT FROM AUTHOR]

This paper deals with the fatigue life of corroded reinforced concrete (RC) T‐beam. A fracture mechanics‐based formula incorporating reduction in cross section and nominal strength of reinforcement is developed for determining the fatigue life of a RC beam. A simplified model considering rebar fatigue damage was employed for numerical modeling. In the numerical investigation, the mathematical model was implemented in ANSYS workbench. In the experimental investigation, different degrees of corrosion were induced to the beam reinforcement by using the impressed current technique (ICT). After that, the beams were tested for fatigue by structural actuator subjecting them to three‐point loading arrangement. The fatigue lives of corroded bars were also examined experimentally after removing the bars from the tested beams. It was found that the difference between the fatigue lives obtained from the numerical and experimental models compared well. As the corrosion level increased, fatigue life also decreased. All the beams failed due to fatigue fracture of steel bars under cyclic loading. This paper aims to present an easy to implement numerical method to estimate coupled fatigue‐corrosion life of a RC T‐beam so that the requirements of tedious, time‐consuming, and costly physical testing for determination of coupled fatigue‐corrosion life can be eliminated. [ABSTRACT FROM AUTHOR]

The deformation characteristics of cracked reinforced concrete beams are largely dependent on the tension stiffening effect. As one of the serviceability analysis approaches, the employment of a concrete tensile stress block that reflects the flexural tension stiffening behavior is useful for evaluation of beam deflections. In many practical applications, however, beams have to withstand a small degree of axial compression. There has been little research on axial load effects on tension stiffening, and tensile stress block for beams subject to compressive axial load has not been developed. In this study, finite element method is employed to analyze beams under different levels of compressive axial load. The numerical results reveal that the tensile stress block is considerably influenced by the presence of axial load. Using the tension stress fields obtained, values of stress block parameters under different levels of axial load are determined. Adequacy of the proposed model was verified using the test data reported in the literature. [ABSTRACT FROM AUTHOR]

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

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]

Test setups and loading histories aim to replicate the real conditions of the building structures. However, most of the tests on beams found in literature do not include gravity loads in the cyclic loading history. An experimental campaign was carried out. Two beam specimens, named CB0 and CB1, designed to exhibit different failure modes were subjected to a loading protocol that involved the imposition of reversed cyclic loading and simultaneous gravity load. The aim was to validate the test procedure for different beam failure modes. Consequently, specimen CB1 failed by rupture of the tensile reinforcing bars while specimen CB0 failed due to concrete crushing and buckling of the compressed reinforcing bars. Results show that the presented loading protocol does not control the failure mode of the specimens. The specimens were also simulated numerically, and the results were comparable with the experimental observations in terms of load capacities, crack patterns, and failure modes. [ABSTRACT FROM AUTHOR]

Hence, this new invention effectively copes with increasing CFRP waste, by reusing it in new CFRP composites, the cost of which is much lower than that of newly produced composites, whereas the mechanical properties are the same. This could be realized if the strengthening material, which is normally carbon FRP (CFRP), bonded to the concrete with epoxy, could simultaneously be used as an anode in the cathodic protection system. Synthesized intervention method to prolong service life of reinforced concrete structures: ICCP-SS. [Extracted from the article]

Most of the Dutch bridges were built around middle of the last century and it is vital for designers to find out if these bridges can still be considered safe for the traffic of modern times. The capacity in shear is especially critical as it was not considered in design recommendations before 1976. Therefore, experiments on a 1:2 scale model of a transversely prestressed concrete bridge deck cast between concrete girders were carried out to investigate the bearing (punching shear) capacity. The scale was selected based on the space available in the laboratory and the expected failure loads that would have to be applied. Also, a three‐dimensional, solid, nonlinear finite element model was developed in the Finite Element Analysis software package TNO DIANA to study the structural behavior of deck slabs and is the focus of this paper. The results of the experimental and numerical analyses leads to the conclusion that existing bridges still have significant residual strength due to the presence of transverse prestressing and the membrane forces, and nonlinear finite element models can predict the load carrying capacity quite accurately. [ABSTRACT FROM AUTHOR]

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

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

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

In statically indeterminate systems, imposed deformation generally cannot set freely. In order to achieve the deformation compatibility, constraint forces are required. From this, it can be deduced that the constraint forces for a given deformation are dependent on the stiffness of the system. The greater the stiffness, the greater the internal constraint forces. For this reason, constraint forces in reinforced concrete structures are generally worth mentioning and must be taken into account in the design. The accurate development of a constraint force depends on numerous factors. These are mainly the stiffness distribution over the length, stiffness of the cross section, ductility of the reinforcement and creep ability of concrete. To gain more information about the real behavior, experiments were carried out on reinforced concrete beams and prestressed beams. [ABSTRACT FROM AUTHOR]

In order to develop a calculation method for the ultimate flexural capacity of high strain‐hardening ultra‐high performance concrete (UHPC) T‐beams, four‐point loading tests on five specimens were carried out. The design parameters were the ratio and the strength of reinforcement. Based on the assumption of plane section, a linear regression analysis was carried out and the ultimate tensile strain of high strain‐hardening UHPC was obtained. The analysis results proved that the bond between reinforcement and UHPC is reliable and these two materials can maintain strain consistency before the reinforcement reaches its yield strain. A finite element model of the specimens was established using ANSYS and distributed reinforcement was added to simulate the behavior of UHPC after cracking. Considering the tensile contribution of the high strain‐hardening UHPC after cracking, the calculation method for flexural capacity of high strain‐hardening UHPC T‐beams was derived. The finite element simulation method and the theoretical formula calculation method proposed in this paper are in good agreement with the experimental values, and they can be applied for the theoretical analysis and the design of high strain‐hardening UHPC beams. The theoretical calculation method proposed in this paper is compared with calculation methods proposed by standards. The study shows that the proposed calculation method is accurate and generally applicable. [ABSTRACT FROM AUTHOR]

The use of fibers can improve the behavior at serviceability limit states (crack and deflection control) and ultimate limit states (bearing capacity) of reinforced concrete (RC) elements under flexure. Fibers reinforcement provides a postcracking resistance, leading RC element to have a more diffused crack patterns characterized by narrower and more closely spaced cracks. Some doubts are instead related to RC element ductility, which can be affected by crack localization after rebar yielding. However, most of experiments present in literature relate only to elements in steel fiber reinforced concrete with significant residual strengths (fR,1 and fR,3 greater than 3.5–4.0 MPa). This paper aims to evaluate the influence of different fiber type (steel, glass, or polymer macrofibers) on the cracking and strength capacity of RC beams under flexure by using a broad range of Fiber Reinforced Concrete (FRC) toughness (1.6 ≤ fR,1 ≤ 5.1 MPa and 0.8 ≤ fR,3 ≤ 4.5 MPa). Twenty‐one small scale RC beams with a typical value of longitudinal reinforcement ratio (0.87%) were tested under flexure. Crack and deflection control, as well as bearing capacity and crack localization were evaluated as a function of FRC toughness. Finally, results were compared against mean crack spacing and strength capacity predictions of fib Model Code 2010. [ABSTRACT FROM AUTHOR]

Experimental study is reported on the seismic behavior of a type of exterior beam–column connections, which feature service holes in the connecting ends of the beams. Specimens with three typical lengths of the holes (450, 500, and 400 mm) are tested under quasi‐static reversed cyclic loading with constant axial compression on columns. Failure modes, hysteretic and skeleton curves, energy dissipation capacity and ductility are investigated and effect of the length of the hole on the seismic behavior of the connection is studied. The results reveal satisfactory seismic performance of the connections with plastic hinges developed at the connecting ends of the beams and no damage to the joint regions. Comparisons between the specimens demonstrate that the connection with 500‐mm long hole performs the greatest energy dissipation capacity and the greatest ductility with comparable load‐carrying capacity to the connection with 400‐mm long hole. Finally, it is feasible and reliable to follow the Chinese code to predict the load‐carrying capacity of the connection, when the longitudinal reinforcement is symmetrically arranged. [ABSTRACT FROM AUTHOR]

The definition of performance limit states for progressive collapse design and assessment of civil structures is an open issue and deserves special attention in view of future building codes and standards. In this study, the main findings of a multilevel sensitivity analysis are presented to characterize the progressive collapse capacity of a selected class of modern European buildings having a reinforced concrete framed structure. After that a group of capacity model properties are assumed as random variables on the basis of earlier studies, the sensitivity of both ultimate load capacity and corresponding maximum and residual drifts to the ultimate steel strain and location of column‐removal scenario is assessed. Then, the influence of the capacity model properties on maximum drift demand corresponding to a code‐compliant design gravity load is evaluated. Finally, five performance limit states associated with increasing levels of damage are introduced and the corresponding load capacity is quantified under varying capacity model properties. Analysis results indicate a high sensitivity to the ultimate steel strain, column location in plan, beam span and yield steel strength. [ABSTRACT FROM AUTHOR]

Ultra‐high performance fiber reinforced concrete (UHPFRC) is a unique class of fiber‐reinforced concrete featuring ultra‐high compressive strength and ductile tensile strain hardening behavior, accompanied by multiple narrow cracking. Although many studies have confirmed its superior mechanical and damage tolerance properties under monotonic or blast loading, limited research has been carried out on the cyclic performance of UHPFRC structural members. This paper proposes the use of UHPFRC to improve the cyclic performance of structural elements. An experimental program was carried out on a large number of UHPFRC beam‐column joint specimens under a cyclic lateral load. After the cyclic loading test, the following results were obtained: (a) hysterical performance, (b) maximum load, (c) maximum displacement, (d) the maximum energy dissipation (measured by hysteresis cycles), (e) stiffness degradation, (f) the cracking pattern, and (g) the cracking area. The analysis showed that UHPFRC specimens have at least 157% higher energy dissipation than nonfiber conventional reinforced concrete (RC). The initial stiffness of UHPFRC specimens without fibers (NF) was at least 23% higher than the RC specimen. For UHPFRC with fiber, initial stiffness was at least 45% higher than RC specimen. [ABSTRACT FROM AUTHOR]

Engineered cementitious composites (ECCs) are materials featuring strain‐hardening behavior with the formation of multiple cracks. When ECC is incorporated in structural applications such as beam, it is expected to significantly improve their mechanical performance. In this study, finite element analysis is performed to investigate the characteristics of the plastic hinge in reinforced ECC (RECC) beams. The plastic hinge lengths of RECC beams, involving rebar yielding zone, concrete crushing zone and curvature localization zone, are found to be much larger than those for reinforced concrete (RC) beams. Based on the above results, parametric studies on the plastic hinge lengths in RECC beams are conducted to study the influences of the tensile\compressive properties of ECC, yielding strength\hardening modulus\ultimate strain of tensile reinforcement, tensile\compressive reinforcement ratio and beam size. This theoretical study has shown that the existing empirical models for RC beams' plastic hinge length are not applicable to RECC beams which exhibit much longer plastic hinge length. A new empirical equation for predicting the plastic hinge lengths of RECC beams is thus proposed. [ABSTRACT FROM AUTHOR]

The bond between concrete and steel reinforcing bars is a very important functional requirement of reinforced concrete as a composite building material. This paper focuses on the comparison between the outcomes of the investigation dealing with bond strength at different levels of depth of concrete. The levels of concrete can be found in reinforced concrete columns, walls, and slabs. This paper presents an experimental and analytical analysis of the pull‐out test on 32 concrete specimens. In the experimental part, eight concrete specimens grouped into normal self‐compaction concrete (SCC) and lightweight SCC, as well as mixtures between them, were tested. In each sample, four steel bars were embedded in concrete at different locations: at the top, two samples in the middle, and at the bottom of the sample. Moreover, the slip and bond strength of each steel bar was measured using the pull‐out test. It was found that, in all the studied mixes, the average bond strength is greater in normal SCC than in lightweight SCC. This study recorded about 27.86% difference for mix CM compared with mix MCF100. An analytical analysis of nonlinear finite element (FE) was conducted for 12 reinforced concrete specimens; three different mixes are considered. A nonlinear FE analysis has been carried out to analyze the specimens that were tested experimentally. The results obtained from the experimental analyses and FE are compared with each other. The results revealed that the FE failure behavior indicates a good agreement with the test behavior. [ABSTRACT FROM AUTHOR]

To prevent airport pavements from suffering fatigue failure before the end of designed life and to construct high‐grade airport concrete pavements quickly, this study has developed a method which applies the prestressed concrete to airport pavements. A three‐point bending loading scheme has been designed to conduct the bending, flexural strength, and fatigue tests on 96 concrete beams. The results showed that, compared with ordinary concrete beams, the resistance of prestressed concrete beam to bending deformation was greatly enhanced. For the beams subjected to the vertical load with increasing prestressing force, however, the deflection of the beams was decreased by a minor degree while both of their tensile stress and tensile stress area showed a sharp decrease. Moreover, the flexural strength of the concrete showed an evident increased with verified degrees while both the numbers and the width of cracks generated at the bottom of specimens decreased significantly. The average fatigue life of the prestressed concrete beams was extended 3 to 6 times longer than that of the ordinary concrete beams depending on the increasing levels of prestressing force. In general, the bending fatigue life of the prestressed concrete beams follows the two‐parameter Weibull distribution with a correlation coefficient greater than 0.96. Based on this Weibull distribution, a double‐logarithmic fatigue equation among three parameters, that is, the survival rate P, the stress level S, and the fatigue life N has been developed. [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]

The construction of integral abutment bridges is becoming more common. Since these bridge structures have no expansion joints or bearings, it is possible to build low‐maintenance and long‐lasting structures. The length of most existing integral abutment bridges does not exceed 20 m, but larger lengths are also increasingly being implemented. Structures up to approximately 70 m are considered to be unproblematic. In longer integral abutment bridges, problems often occur in regard to surface cracks and settlements behind the abutments. To address these challenges, intensive research work has been conducted. A new jointless roadway transition structure for long integral abutment bridges has been developed at the Institute of Structural Engineering of TU Wien. The design principle of the new transition structure is based on the distribution of the deformations, which occur in the bridge due to temperature changes, shrinkage, creep, and external loading, over a longer area behind the abutment. Because the deformations are distributed, it is possible to build a seamless pavement structure across the expansion joint, from the bridge to the embankment. The Research Center for Road Engineering, TU Wien, has developed a special multilayer bituminous pavement structure just for this purpose. Based on the design considerations for the transition structure, a full‐scale prototype was built. The prototype was tested at various construction stages to obtain relevant data for practical use. [ABSTRACT FROM AUTHOR]

Although the use of near‐surface mounted (NSM) fiber reinforced polymer (FRP) reinforcement satisfactorily enhances the flexural capacity of deficient reinforced concrete beams, the concrete beams strengthened with NSM FRPs typically exhibit brittle behavior. Aluminum alloy (AA) bars possess non‐corrosive characteristics like FRPs but also exhibit a nonlinear tensile response with a clear yield point. This paper investigates the failure modes of reinforced concrete beams strengthened with either NSM glass FRP (GFRP) bars or AA bars. A total of six concrete beams including one control beam were tested under four‐point bending. The effects of NSM reinforcement type, internal steel reinforcement ratio, and NSM reinforcement ratio on the failure behavior of the strengthened beams were examined. The ultimate flexural load capacity, ductility index, energy absorption capacity, strains in steel reinforcement and in concrete, and cracking behavior for each tested beam were determined and analyzed. The results indicated that for the same NSM reinforcement ratio, the NSM GFRP bars provided considerably higher increases in the flexural strength of reinforced concrete beams compared to the AA bars. However, the beams strengthened with AA bars showed more ductile response compared to the beams strengthened with NSM GFRP bars. [ABSTRACT FROM AUTHOR]

Europe and United States exert a worldwide influence in the field of concrete control, proof of this is that many countries adopt their regulations, due to lack of own regulations. When there are problems with concrete strength, cores are used, and this situation usually involves two or more parties with different views on the proper interpretation of the core results. An experimental study was carried out, with five lots of prototypes concrete slabs of 20, 30, and 35 MPa specified strength, 210 cylinders of 10 × 20 cm, 296 cores of 10 cm diameter, and slenderness 2, as well as temperature and maturity control. Estimated strength of cores and cylinders was compared according to the criteria of European standards UNE‐EN 13791 and the American code ACI 318. Tests were performed at 3, 5, 7, and 28 days. It is concluded that the European and American regulations present similar results for concretes with specified strength between 30 and 35 MPa, whereas in the range of 16–30 MPa, the European standard is more rigorous than the American Code, being the latter more favorable to the concrete producer. [ABSTRACT FROM AUTHOR]

Thirty‐two reinforced concrete beams were tested under static and fluid impact loads. Hoop (rectangular) and spiral transverse reinforcement of various configurations were used to confine the specimens. The objectives were to observe the effect of shape of beams and configuration of confinement reinforcement on the impact resistance, and to estimate the limiting fluid velocity that causes total failure. [ABSTRACT FROM AUTHOR]

Fluid impact tests on reinforced concrete beams with rectangular or circular transverse reinforcement were modeled and simulated using explicit finite element analysis software, LS‐DYNA. The mid‐span displacements were measured and compared with the results of simulations. The objective was to test the accuracy and fidelity of the numerical modeling and simulation approach and to confirm that damage caused by fluid impact on the beams can be estimated with a reasonable accuracy over a wide range of impact velocity. [ABSTRACT FROM AUTHOR]

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

Discrete steel fibers are known to control crack widening in concrete members thereby enabling them to carry loads up to large deflections. This study examined the flexural behavior of steel fiber reinforced concrete (SFRC) beams reinforced with steel fibers by conducting four‐point bending tests on eight beam specimens. The effect of reinforcing index (defined as the product of the volume fraction and the aspect ratio of steel fibers), fiber type, and beam depth was investigated. The load‐carrying capacity corresponding to different beam deflections was predicted using available constitutive stress–strain/crack width laws in tension. Although existing constitutive relations in tension predict the peak load capacity well, they fail to accurately predict the load‐carrying capacity at large deflections. Subsequently, a constitutive law is proposed using a back‐calculation technique which was validated with the results from four‐point bending tests conducted on 24 SFRC beams including 16 results found in the literature. The deviation of the predictions of the proposed model with regard to the average load‐carrying capacity at large deflections is within 12% from the observed values. [ABSTRACT FROM AUTHOR]

This paper presents the outcome of an experimental study on the performance of mechanical rebar coupler (MRC) in broken reinforcement connection over the conventional technique. An in‐house‐made hybrid MRC is introduced to connect broken rebars ranging from 10 to 16 mm in diameter. A detailed experimental program is conducted to explore the influence of MRC with filler as a broken rebar connector. Four types of reinforced concrete (RC) beams with different reinforcement configurations are used with and without MRC at tension zone. RC beams with and without MRC are used and tested under monotonic loading. Rebar connector in different locations is used to examine the load distribution behavior of the connector. The effectiveness of rebar connector is investigated using the uni‐axial tensile test of rebar with MRC, load–deflection behavior, energy dissipation, stiffness behavior, and failure pattern of RC beams and is compared with conventional specimens. The significant enhancement in post‐yield behavior and energy dissipation of RC beam specimen with rebar connector authenticates the effectiveness of employed technique in structural engineering work. [ABSTRACT FROM AUTHOR]

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

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]

This paper aims to investigate the shear failure mechanisms in beams exclusively reinforced with longitudinal glass fiber reinforced polymer bars and to propose a design‐based approach to predict the shear capacity of this type of beams. An experimental program composed of seven T cross section shaped concrete beams was executed to analyze the influence of the flexural reinforcement configuration on the shear capacity and deformability of the beams. Three values of the flexural reinforcement ratio ( ρl), 1%, 1.4%, and 1.80% were adopted. Digital image correlation technique was used to better capture and analyze the cracking process up to the formation of the shear failure crack. Test results indicated that the shear capacity was not dependent of ρl up to a limit of around 1.4%, but a tendency of the shear capacity to increase with ρl was registered above this limit due to a more pronounced favorable contribution of aggregate interlock and dowel effect. [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]