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It is common knowledge that increased temperatures have a negative impact on the axial load‐capacity and stiffness of reinforced concrete (RC) rectangular columns. This is something that is commonly acknowledged. For the purpose of restoring the axial capacity and stiffness of heat‐damaged RC columns, it is absolutely essential to carefully pick a suitable method for strengthening and repairing the columns. This research paper investigates the performance of various strengthening methods, such as the use of carbon fiber‐reinforced polymer (CFRP) jackets with near‐surface mounted (NSM) steel bars and a combination of welded wire mesh (WWM) and CFRP strengthening techniques, for the rehabilitation of RC rectangular columns that have been damaged due to exposure to high temperatures. Specifically, the paper focuses on the performance of these methods in relation to the rehabilitation of RC rectangular columns. There were three groups of tested RC rectangular columns: pre‐heated and unstrengthened, post‐heated and unstrengthened, and post‐heated and strengthened. Over a period of 3 h, 600°C was applied to the heated columns. Both a scheme utilizing a combination of unidirectional CFRP strips and NSM steel bars and another utilizing a combination of unidirectional CFRP strips and WWM were evaluated. Axial compression tests were performed on each column until failure occurred. The experimental test outcomes revealed that exposure to high elevated temperatures led to a decrease in the axial load‐carrying capacity of 38.6% and a decrease of 75.9% in initial stiffness, compared to unheated RC columns. Both strengthening schemes proved effective in restoring and surpassing the initial load‐carrying capacity of undamaged RC rectangular columns by an average of 35%. Notably, the combination of CFRP strips and WWM exhibited superior performance in restoring the initial stiffness of post‐heated RC rectangular columns, representing a novel finding. The strengthening scheme employing WWM and CFRP recovered 61.3% of the lost axial strength caused by high temperature, while the NSM/CFRP scheme restored 34.5% of the lost axial strength. In addition, the utilization of NSM in combination with CFRP strips as well as utilization of the WWM and CFRP systems leads to stiffness enhancement of 52.1% and 123.7%, respectively, when compared to post‐heated and unstrengthened RC columns. However, the study's findings have clearly shown that combination of WWM and CFRP strips is efficient in enhancing the strength of heated and unheated damage RC beams. [ABSTRACT FROM AUTHOR]

This paper presents a study on the explosion protection of prestressed concrete box girder, which is a commonly used in concrete bridges. The explosion protection tests of four prestressed box beams were designed with 1:5 scale. In order to evaluate the explosion performance of different protective layers, steel plate, ultra‐high‐performance concrete (UHPC) layer, and composite protective layer were used to protect the box girder. The experimental results revealed that under the effect of deck explosion, local penetrating failure occurred in the top plate of the box girder, which exhibited characteristics of punching failure. The web and bottom plate of the box girder as a whole exhibited bending characteristic. Compared with the unprotected box girder, the damage of the top plate of the protected box girder was less severe, whereas the damage of the bottom plate was greater. In working conditions 2–4, the UHPC protective box girder suffered less damage to the top plate, whereas the other protective box girders suffered more. The explosion dynamic responses of the box girder were compared, and the influences of different protective layers on the explosion dynamic response of box girder were studied. Based on the box girder damage, the protective efficiency of each protective layer under near‐explosion was studied. Based on the explosion tests, three‐dimensional numerical analysis model of box girder explosion was established. The accuracy of the numerical simulations of the box girder explosion were verified by comparing with the experimental failure data. Through the numerical results, the explosive energy dissipation capacity of different protective materials was compared and analyzed. Finally, based on the dynamic response of the box girder under different working conditions, the sensitivity of the protective layer to the dynamic responses of the box girder were studied. The analysis showed that the UHPC layer was sensitive to the change of prestress and explosion damage area of the box girder but had little influence on the rebars stress and the overall response of the box girder. [ABSTRACT FROM AUTHOR]

Breakthrough technology of ultra‐high‐performance concrete (UHPC) introduced in the 1990s exhibits several exceptional mechanical properties that are advantageous in elements of bridge applications. Extensive research has aimed to industrialize UHPC and develop design models. This paper investigates several design models for shear, including a unified approach with that of conventional concrete based on the modified compression field theory (MCFT). An experimental database of UHPC prestressed concrete girders subjected to shear failure is compiled to evaluate model accuracy and a reliability study is conducted to establish appropriate safety factors. The analysis demonstrates that the proposed MCFT‐based model aligns well with experimental results, exhibiting a suitable level of conservatism for design. A reliability assessment of a typical prestressed girder designed according to Canadian Standards Association building and bridge loadings is performed, resulting in a structural reliability evaluation against a target reliability index. The study recommends specific strength reduction and safety factors for design approaches using UHPC. [ABSTRACT FROM AUTHOR]

Most of the Italian infrastructures have been built since the mid‐twentieth century. Prestressed concrete (PC) has been widely used, especially for bridges and viaducts. These structures have proved effective over time, but their performance could be affected by degradation phenomena (i.e., corrosion of the tendons and residual prestressing) or construction defects (i.e., grouting of the ducts), which need to be accurately modeled. This paper focuses on the flexural response of two reduced‐scale, posttensioned, PC bridge girders, prestressed with two different jacking forces and tested under four‐point bending configuration. Four multidimensional numerical models were developed to simulate the experimental behaviors of the selected specimens, using two alternative computational strategies, namely, the finite element method (FEM) and applied element method (AEM). Three FEM modeling were considered, ranging from one‐dimensional lumped‐plasticity models to two‐dimensional and three‐dimensional (3D) spread‐plasticity models. Besides, 3D AEM models were developed into another software package. The accuracy and the computational costs of the two numerical strategies are discussed in this paper. Also, the main features of each numerical modeling technique are addressed, including comparisons between numerical and experimental global response data as well as the statistical characterization of the model error. Based on these different features, the authors also suggest the most suitable numerical strategy for future studies on PC girders. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation into the flexural and cracking behavior of corroded reinforced concrete continuous beams with 11‐month wet–dry cycles strengthened by anodic polarized carbon‐fabric‐reinforced cementitious matrix (C‐FRCM) plates. The failure modes and flexural bearing capacities were discussed. The influences of the layer of carbon fabric mesh and complete carbon fiber‐reinforced polymer (CFRP) wrapping as end anchorage on the strengthening effectiveness were explored. The complete crack development patterns were captured by a digital image correlation system, and the results showed that the C‐FRCM system can provide satisfactory crack width control, as proved by the reduced crack spacing and the maximum crack width. The flexural capacities of the strengthened beams were effectively enhanced and the debonding failure can be eliminated through complete CFRP wrappings. Moreover, the design recommendations were proposed based on the estimation of the crack development as per related design guidelines. [ABSTRACT FROM AUTHOR]

This paper presents the experimental study and finite element modeling of the flexural behavior of concrete beams reinforced with reused steel bars as longitudinal reinforcements. The experimental program and results of eight reinforced concrete (RC) beams constructed with and without reused steel bars are described in detail. The replacement percentages of brand‐new bars with reused steel bars in the tested beams were 50% and 100%. The reused steel bars were coated with and without epoxy. Steel fibers with fractions of 0.5% and 1.0% of the concrete volume were added to the concrete mixes. The load‐deflection relationship, ductility index, toughness, and failure modes of the tested beams are presented and discussed. It is shown that utilizing reused steel bars decreases the ultimate load of RC beams but increases their deflection at the ultimate load compared with the control beam. Increasing the steel fiber ratio increases the ultimate load and the deflection at the ultimate load of RC beams incorporating reused steel bars. However, the zinc‐rich epoxy used to coat the reused steel bars does not affect the behavior of the beams. Three‐dimensional nonlinear finite element (FE) models of the tested beams were developed using ABAQUS and validated against the test results. The developed FE models are capable of accurately simulating the experimentally observed behavior of RC beams with reused steel bars. [ABSTRACT FROM AUTHOR]

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

Reinforced concrete deep beams in bridges and other critical infrastructure are subjected to millions of load cycles during their service life. At the same time, they typically work with high shear and develop critical diagonal cracks. The cyclic loading across the cracks results in fatigue damage of the shear‐resisting mechanisms, which needs to be taken into account in the assessment of existing structures, and in particular in members with small amount of shear reinforcement built according to early design codes. To aid the development of advanced assessment approaches for such structures, this paper presents five large‐scale fatigue tests of deep beams with a stirrup ratio of 0.134%. The beams are preloaded to develop complete diagonal cracks, and then are subjected to cycles with different minimum and maximum load. The focus is placed on detailed crack measurements, needed for the development of crack‐based assessment approaches. The crack data is analyzed with the help of the two‐parameter kinematic theory to quantify important deformations. It is shown that the fatigue across the shear cracks is associated mainly with degradation of aggregate interlock and progressive damage in the critical loading zones. It is also shown that as the maximum load is decreased, the fatigue life increases, and the failure mode can switch from shear to flexure. [ABSTRACT FROM AUTHOR]

The present paper proposes a mechanical model for the prediction of the response of slender reinforced concrete beams with corroded transverse and longitudinal reinforcements. The proposed model is based on the Modified Compression Field Theory and is able to predict the load–displacement curve of members subjected to monotonic displacement‐controlled tests up to their peak load. The corrosion‐damage effects are considered by means of an effective width of the beam and by means of reduced values of both cross‐sectional area and strain capacity of steel bars. The accuracy of the model is evaluated by comparison with results of tests reported in the literature. Moreover, a simple relation is suggested for the estimate of the shear strength of reinforced concrete beams with low values of the effective geometric percentage of (corroded) stirrups. [ABSTRACT FROM AUTHOR]

Since reinforced concrete members suffer from different types of loads during their service life, the steel bars embedded in reinforced concrete members can be easily corroded in chloride‐laden environment. To investigate the influence of combined effect of load and steel corrosion on the flexural stiffness of recycled aggregate concrete (RAC) beams, 12 RAC beams were prepared and tested. The effects of load level (i.e., the ratio of the load applied to beams to the ultimate load) and recycled coarse aggregate (RCA) replacement ratio (i.e., the ratio of RCAs to replace natural coarse aggregates) on the internal force arm coefficient of cracking cross‐section, the elastoplastic resistance moment coefficient of cross‐section, and the strain incongruity coefficient of corroded tensile steel bars were analyzed, and a calculation model for flexural stiffness of RAC beams under combined effect of load and steel corrosion was established. The results showed that when the ratio of bending moment to ultimate bending moment of the pure bending part of beams was within 0.55–0.80 and the average mass loss of tensile steel bars was less than 3.23%, 0.85 could be adopted as the internal force arm coefficient of cracking cross‐section. The elastoplastic resistance moment coefficient of cross‐section was approximately a constant when the corroded RAC beams were in the service stage, while it increased obviously with the load level. There was a strong linear relationship between strain incongruity coefficient and average mass loss of tensile steel bars during the service stage of corroded RAC beams, and the strain incongruity coefficient increased linearly with the load level. The calculated values of the model of flexural stiffness proposed in this paper were in reasonable agreement with the experimental values. [ABSTRACT FROM AUTHOR]

This paper presents an experimental program of the bond behavior of concrete beams reinforced with hybrid fiber‐reinforced polymer (FRP) and steel bars, and the bond behavior between flexural cracks is investigated. Under the static loading, both the slip of steel and glass FRP (GFRP) bars increased significantly after steel yielding, while the slip of steel bars presented a faster increase rate. A method of calculating the bond stress based on test data was proposed, and this method overcame the disadvantage of histogram distribution of the conventional method. An analytical model of calculating the bond stress was proposed, and was verified with the test results. Under the fatigue loading, the bond stress deteriorated more seriously with a higher upper limit of fatigue load. The slip increased rapidly at the initial stage, and remained approximately unchanged with the increase of fatigue cycles, and the slip increased dramatically when the beam was subjected to fatigue failure. After fatigue loading, the yielding strength and ultimate strength of steel bars showed an increase rate less than 5%, while the hardening phase decreased significantly. The ultimate tensile strength of GFRP bars after fatigue decreased in the range of 4.5%–32.3%, and the modulus for elasticity remained unchanged. [ABSTRACT FROM AUTHOR]

When shear cracking occurs in existing reinforced concrete deep members, engineers are faced with the challenge of determining the safety of the members. This paper presents a crack‐based assessment approach that utilizes the Two‐Parameter Kinematic Theory (2PKT) as a framework for the assessment of lightly reinforced concrete deep beams. The paper presents three assessment approaches with progressively increasing levels of approximation (LoAs). The first level of approximation (LoA I) involves using the 2PKT in a predictive manner for situations where the crack shapes are unknown, LoA II improves upon LoA I by incorporating more detailed modeling of the strain in the transverse reinforcement at the location of the critical cracks, and LoA III includes the details of LoA II but also uses the detailed crack geometry as an input in the assessment. Each of the LoAs is presented and compared with experimental data from a 4‐m deep beam test in the literature. The shear carrying mechanisms determined from the kinematic model are evaluated and compared across LoAs. Finally, the paper utilizes LoA III to study the size effect in shear for deep beams. The results quantify the influence of aggregate interlock on the size effect in shear critical deep beams. [ABSTRACT FROM AUTHOR]

This paper presents a modeling approach to analyze the flexural response of hybrid reinforced concrete beams with localized corrosion. A new mechanical model based on extensive uniaxial testing is proposed to describe the stress–strain relationship of corroded bars with a single pit. The proposed mechanical model is then incorporated into a sectional analysis to determine the moment curvature relationship of hybrid reinforced concrete sections with pitting corrosion. The actual crack pattern is used to divide a beam into discrete hinge elements which are then combined to compute the load–deflection response of statically determinate beams. The modeling approach is evaluated with available experimental data showing good predictive capabilities. A parametric study revealed the importance of the interaction between the tensile reinforcement ratio and the concrete postcracking residual stress. Furthermore, the deformation capacity of reinforcement bars with pitting corrosion levels beyond 0.25 was shown to have a dominant effect on the ultimate deflection of hybrid reinforced concrete beams. [ABSTRACT FROM AUTHOR]

High‐performance fibre reinforced concrete represents a promising alternative to conventional reinforced concrete for the construction of prestressed precast girders for road bridges. Specifically, all shear reinforcement is replaced by the use of steel fibres, which leads to important savings from the material and economical perspectives. Therefore, reliable shear formulations are required for these specific cases. In an effort to evaluate the accuracy of code expressions, this paper presents a database collecting 80 experimental shear tests on prestressed fibre reinforced concrete beams without stirrups. After illustrating its main characteristics, this database is used to verify the conservativeness and accuracy of shear formulation according to several codes and recommendations: i) Model Code 2010, ii) draft version of Model Code 2020, iii) draft version of the new Eurocode 2, and iv) Spanish National Code. The evaluation, carried out through the calculation of the model safety factor, indicated that the application of all shear formulations is largely conservative, leading to less unsafe tests than the desired 5% fractile. The relation between model safety factors and mechanical parameters is then investigated. Finally, the results obtained for the developed database are compared with those achieved from two larger databases of beams with similar features but without prestress. The comparison clearly proves the greater conservatism of code expressions when beams are prestressed. [ABSTRACT FROM AUTHOR]

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

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

The fanning compression stress pattern in RC deep beams under uniform load presents a challenge to formulating the configuration of strut‐and‐tie model (STM). To this end, this paper proposes an alternative method for creating a graphical discontinuous stress field model (DSFM) to fill up the whole beam continuum. It comprises a certain number of trapezoidal stress‐bands with varying bandwidths, and their stress values can be calculated based on force equilibrium conditions. Several stress subfields are defined through a certain stress combination from several directions. The DSFM is implementable for both service limit state (SLS) and ultimate limit state (ULS) in that its configuration is primarily oriented by elastic stress field and only a limited plastic redistribution is allowed for plastic failure. The graphical procedure of DSFM is demonstrated and examined by a test deep beam example, which shows that the predictions are fairly in good agreement with the test results. [ABSTRACT FROM AUTHOR]

Whether the performance of carbon fiber‐reinforced polymer (CFRP)‐strengthened concrete structure is affected by chloride penetration is the key to the application under chloride environments. In this paper, the effect of chloride penetration on tensile properties of CFRP sheet, bond behavior of CFRP‐concrete, and flexural performance of CFRP‐strengthened concrete beams were studied. Results show that chloride penetration has no effect on the elastic modulus of the CFRP sheet. The tensile strength and elongation of the CFRP sheet decrease with the exposure time increase, reducing by 10% and 12.7% after 240 days. The interface failure of CFRP‐concrete is likely to occur on the concrete surface. As the exposure time increases, the interface failure develops toward the epoxy resin layer; the sliding stiffness and end slip of the interface decrease. However, the ultimate bearing capacity of the interface first increases and then decreases. As the exposure time increase, the effective bonding length gradually increases, and the failure mode of CFRP‐strengthened beams changes from bending failure to shear failure. After 120 days, the ultimate bearing capacity of the beams is significantly reduced. From three parts of materials, interfaces, and components to provide an evaluation basis for the use, regular detection, and life prediction of CFRP‐strengthened reinforced concrete beams under chloride environments. [ABSTRACT FROM AUTHOR]

The structural performance and durability of reinforced concrete (RC) dapped‐end beams may be significantly threated by the effects of deterioration and environmental actions, compromising the structural robustness of important infrastructures such as bridges. The study of the critical role of dapped‐ends has grown in recent years, focusing in particular on the implementation of innovative retrofit solutions capable of extending the service life of these structural elements. In this paper, an experimental investigation on the contribution of Fabric‐Reinforced Cementitious Matrix (FRCM) retrofitting system to the load bearing capacity of RC dapped‐end beams is presented. A set of eight full‐scale dapped‐ends was subjected to monotonic loading tests. The presence of cracks prior to the application of the retrofitting composite, which may represent the actual state of conservation of existing RC half‐joints subjected to heavy traffic loads, is reproduced by testing the specimens up to the reaching of the ultimate design load. Different orientations of the alkali‐resistant glass fabric composing the FRCM system were tested, and the results allow to discuss the effectiveness of the retrofitting solution. [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]

This paper describes an experimental program, which investigates the validity of using Expression 7.21 in Eurocode 2 for calculating shrinkage curvatures of loaded reinforced concrete beams cracked in flexure, this Expression having previously been validated for use with uncracked sections but not for cracked sections. The experimental method used a heating technique, which exploited the differing coefficients of expansion of limestone concrete and stainless steel reinforcement to impose simulated shrinkage strains on a range of rectangular beams of various sizes and reinforcement percentages. The results indicate that Expression 7.21 is valid for use with sections cracked in flexure but may overestimate curvatures by significant amounts. It is shown that improved estimates of curvature are given by using Expression 7.18 in conjunction with Expression 7.21 with the best results being obtained by setting β = 0.3 or by using an adjusted value for the cracking moment (Mcr), as detailed in the paper. [ABSTRACT FROM AUTHOR]

The use of Recycled aggregate (RA) enhances concrete sustainability. If used on an industrial‐scale, structural verification, and testing will be required to confirm that RA concrete can meet relevant industrial standards and the requirements of manufacturers, especially in the precast‐concrete industry. In this paper, an experimental campaign with the participation of a precast‐concrete manufacturer is reported. The objective is to test a self‐compacting concrete (SCC) mix, designed for structural applications, that contains maximum amounts of 100% coarse RA, in order to establish its compliance with the habitual requirements of precast‐concrete manufacturers. Thus, scaled beams (12 × 24 × 180 and 24 × 24 × 130 cm) were subjected to bending, shear‐bending, shear, and long‐term‐deflection tests. In addition, the performance of that SCC mix in the bending and shear‐bending tests was compared with the performance of an SCC mix of similar compressive strength containing 0% coarse RA. In the failure tests, the experimental results were between 1.5 and 3 times higher than the required values. The elastic behavior of both SCC mixes was also very similar in those tests, regardless of the amount of coarse RA, due to the robust design of the water and superplasticizer content of the SCC, which balanced the decreased flowability and the lower compressive strength of SCC that resulted from the additions of coarse RA. The SCC mix with 100% RA showed a lower load‐bearing capacity after failure and narrow compliance margins with the deflection limits of the long‐term‐deflection test. Even though the SCC mix with 100% RA met all the standard technical specifications of the precast‐concrete manufacturer, reference should always be made to the serviceability limit states that are applicable at the time of the structural design phase. [ABSTRACT FROM AUTHOR]

Polyvinyl alcohol‐engineered cementitious composite (PVA‐ECC) exhibits strain hardening and multiple cracking characteristics under tension. Its superior tensile behavior may also influence the flexural behavior of reinforced PVA‐ECC beams. This paper investigates the load capacity and failure mode of reinforced PVA‐ECC beams in bending. Seven beams with different tensile reinforcement ratios, including six PVA‐ECC beams and one conventional concrete beam, were tested in the experimental program. The influence of reinforcement ratio on load capacity and failure characteristics was discussed in detail. Test results showed that with increasing reinforcement ratio, the ultimate load of beams was increased, but the failure mode was changed from fracture of PVA‐ECC in the tension zone to crushing in the compression zone, thereby limiting the full development of beam ductility. An analytical model is proposed to calculate the load and the vertical deflection of beams. In the model, the tension‐stiffening effect of reinforcement after cracking of PVA‐ECC is considered by defining the bond–slip relationship of reinforcement embedded in PVA‐ECC. Comparisons are made between experimental results in the literature and those calculated by using the analytical model to show the accuracy of the model in predicting the load–deflection relationship, the moment–rotation relationship, and the moment–curvature relationship. [ABSTRACT FROM AUTHOR]

This paper investigates the shear performance of corroded reinforced concrete (RC) beams with different stirrup corrosion rates and strengthening interventions. In this work, eight corroded beams strengthened with various interventions, including U‐shaped stirrup, bonded steel plate, and anchored steel plate strengthening techniques, were tested under static loading. The experimental shear capacity, load–deflection response, and failure modes of the unstrengthened and strengthened specimens were carefully studied. Three shear capacity models based on GB50010‐2010, ACI 318‐08, and Eurocode 2 codes were proposed and discussed. The results showed that all specimens have the same failure mode, that is, the shear–compression failure. The shear capacities are improved by 17.36%–23.61% and 23.76%–38.46% by these interventions for the specimens with 10% and 20% stirrup corrosion rates, respectively. The anchored steel plate technique provides the maximum improvement in the shear capacity. Additionally, the increased stiffness of corroded specimens with strengthening interventions is apparent when the corrosion rate is 10% but not obvious when the corrosion rate is 20%. The models based on GB50010‐2010 and ACI 318‐08 codes were proved to have higher accuracy but may overestimate the shear capacity. In contrast, the Eurocode 2‐based model comes with relatively low prediction accuracy but conservative results, and it is recommended for engineering design. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of material properties, boundary conditions, and related modeling and design uncertainties on the fire behavior of statically indeterminate reinforced concrete beams and slabs by means of a parametric study based on a comprehensive model. This model uses material properties specified by EN 1992‐1‐2, complemented by considerations concerning the biaxial compressive strength of concrete, strain hardening and limitations of the ultimate strain of reinforcement, as well as tension stiffening. The parametric study identifies and explains the most influential parameters governing the fire behavior of statically indeterminate reinforced concrete beams and slabs. The implementation and generalization of these parameters are evaluated and compared to current design rules in EN 1992‐1‐2 derived from the evaluation of experimental testing and real fire cases. Overall, the detailing rules given in EN 1992‐1‐2 are found to be reasonably safe, and they can be easily used for practical applications. Furthermore, the results of the study indicate that model predictions for the studied statically indeterminate systems are subject to considerable uncertainty because (i) information on the used material is possibly incomplete and (ii) the models given in design codes do not (or only insufficiently) cover all relevant aspects of the thermo‐mechanical behavior. Specifically, the concrete aggregate type with its corresponding thermal expansion, the strain hardening properties of the reinforcement and tension stiffening with its detrimental effect on the ductility of the tension chord may affect the rating across several standard fire resistance times of statically indeterminate reinforced concrete members subjected to bending. [ABSTRACT FROM AUTHOR]

This paper investigates the shear strengthening of reinforced concrete (RC) beams incorporating engineered cementitious composite (ECC) and stainless steel plates (SSPs). The use of ECC, characterized by strain‐hardening in conjunction with SSPs, was investigated in this study to improve the shear performance of RC beams. Total 10 RC beams were tested under static loading up to failure to investigate a few key parameters, namely: material of strengthening (ECC and SSPs), the thickness of ECC, and shape and configuration of SSPs. Experimental findings showed that the proposed strengthening methods can significantly improve the failure pattern and increase the ultimate shear capacity of the studied RC beams by 36%–97% compared to the unstrengthened beam. Experimental results were compared against the predicted ultimate shear strength of RC beams using design equations specified by various design codes. Nonlinear three‐dimensional finite element modeling was developed for beams strengthened with ECC layer and validated against the test results and found to be accurate. Based on the experimental and numerical results, new shear capacity formulae were proposed considering the ratio of ECC‐to‐concrete beam cross‐section (ρECC) and then verified against the numerical predictions. [ABSTRACT FROM AUTHOR]

Small amounts of shear reinforcement are often assumed to increase the shear capacity of RC beams, compared to an identical beam without shear reinforcement. However, in a recent experimental campaign, the shear capacity of beams with a shear reinforcement ratio below the minimum requirements according to the design standards turned out to be similar to identical beams without shear reinforcement. This paper presents a detailed analysis of why the shear capacity may be similar for beams without‐ and beams with small amounts of shear reinforcement. This includes the influence of small amounts of shear reinforcement on the shear behaviour and shear‐transferring mechanisms. The analysis shows that the crack development is more severe at the ultimate load for beams with a small amount of shear reinforcement compared to beams without shear reinforcement. This more severe crack development is shown to cause an overestimation of the shear contribution from aggregate interlock when applying a well‐known constitutive model often used for beams without shear reinforcement. Therefore, a new expression for the aggregate interlock stresses is proposed. A comparison of the proposed expression with Mixed‐Mode crack opening tests shows a good agreement with the test for both small and large crack openings. By applying the proposed expression on the measured crack kinematics it is shown that for a large shear contribution from aggregate interlock the shear contribution from the shear reinforcement is very limited and as the aggregate interlock stresses decrease the shear contribution from the shear reinforcement increases. This shift in the governing shear‐transferring mechanism can help to improve the requirements for the minimum shear reinforcement often found in the design standards. [ABSTRACT FROM AUTHOR]

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

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]

This paper numerically investigates three typologies of Gerber saddle in existing ordinary and post‐tensioned girder concrete bridges. The main goals of this work concern the evaluation of the effective load‐bearing capacity of Gerber saddles, and the identification of weak points (i.e., lack of enough diagonal reinforcement, loss of pretension in tendons) of existing dapped‐end connections, which lead to the re‐entrant corner diagonal crack, typical of these kinds of structural elements. At this aim, two analytical approaches, with different level of approximations, are used. First, different strut‐and‐tie models are arranged for each typology of Gerber saddle considered, and the global safety factor is estimated for several cases. Second, using nonlinear finite‐element method, the results obtained by strut‐and‐tie models are compared. In addition, several information about the condition of Gerber saddle at collapse are obtained (deformation and stress of concrete and steel rebar, crack patterns) also taking into account the corrosion‐damage effects. Moreover, the results of analyses allow identifying the potential modes of crisis of the dapped‐end connections and their critical aspects. [ABSTRACT FROM AUTHOR]

To investigate the combined effect of load and steel corrosion on the flexural performance of recycled aggregate concrete beams, considering three types of aggregate replacement ratios (i.e., 0%, 50%, and 100%) and four levels of load (i.e., 0, 0.2, 0.4, and 0.6), 12 beams were designed for accelerated corrosion test and four‐points bending test. The load was applied to beams by using a designed loading device before the accelerated corrosion test. After the accelerated corrosion test, four‐point bending test was conducted to measure the flexural performance of beams. The results showed that, with the increase of load level applied to beams before accelerated corrosion test, the number of bending cracks on the bottom of corroded beams after four‐points bending test decreased, while the average spacing of bending cracks increased. The effect of aggregate replacement ratio on the average spacing of bending cracks was more significant than that of steel corrosion. Yield moment capacity and ultimate moment capacity of corroded beams had a strong linear relationship with the maximum mass loss of tensile reinforcement, and both of which decreased with the increase of load level and aggregate replacement ratio. For every 1% maximum mass loss of the tensile reinforcement, the reduction of ultimate moment capacity of beams was approximately 4–6 times larger than that of ordinary concrete beams. The degradation model for ultimate moment capacity of corroded beams proposed in this paper had satisfactory prediction accuracy. [ABSTRACT FROM AUTHOR]

In this paper, the shear behavior of glass fiber reinforced polymer (GFRP) bars reinforced ultra‐high‐performance concrete (UHPC) beams was investigated through experimental tests. Eight GFRP bars reinforced UHPC I‐beams were tested until shear failure with various stirrup ratio, reinforcement ratio, and shear span to depth ratio. The shear capacity, load–deflection relationship, cracking pattern, and failure mode were investigated in detail. The results show that the shear span to depth ratio has the greatest influence on the shear capacity of the beam among the three parameters, followed by the stirrup ratio and reinforcement ratio. The stirrup configuration can significantly improve the shear capacity and deformation resistance of the beam and can effectively reduce the stress concentration caused by the uneven distribution of steel fibers, which affects the failure mode of the beam. Increasing the stirrup ratio and reinforcement rate can improve the stiffness of the beam after cracking, and the larger the shear span to depth ratio is, the more significant the improvement effect is. Moreover, the stirrup enables the full development of the tensile capacity of GFRP bars. The existing equations of shear strength from five design codes and seven literatures are compared to the experimental results of 54 UHPC beams. It showed that the formula from the codes AFGC‐2013 and JSCE‐2006 codes is more accurate. The equations by Kwak, Jin, and Thiemicke's provide the best predictions. [ABSTRACT FROM AUTHOR]

This paper presents two experimental campaigns carried out on 36 reinforced concrete (RC) beams (with and without shear reinforcement) subjected to a three‐point bending loading with a shear force on the one hand, an axial compressive load and a negative bending moment applied at each end of the beams on the other hand. Such a loading configuration makes it possible to investigate the influence of both axial compression and negative bending moment on the shear capacity of RC beams. For each campaign, three values of axial compressive force were studied, and the test beams were divided into two series with low and high negative bending moment. During the tests, Digital Image Correlation technique was used to capture the cracking evolution of the specimens. Besides, the experimental shear strengths of the beams are confronted to the predictions of Eurocode 2 in order to assess its practical validity. Finally, a semi‐analytical method proposed by Wahbi et al. 2021 (A failure criterion for RC beams subjected to axial and transverse loadings) for evaluating the resistance domain of RC elements subjected to transverse and axial loads, is extended in this paper to take into account the negative bending moment and compared to the experimental results. [ABSTRACT FROM AUTHOR]

Post‐installed connections are widely used in the rehabilitation, strengthening, and expansion of existing concrete structures. These connections accommodate the connecting of new elements to old concrete using post‐installed anchoring techniques. Attachment of new segments to concrete beams and columns requires the installation of anchors in slim concrete components. Under this condition, the behavior of connection is severely affected by the small width of concrete elements. Additionally, the behavior of anchors is influenced by the confining effects of stirrups in reinforced concrete elements. In this paper, the tensile behavior of chemical anchor connections in single and group formations of four and six anchors is investigated using the results of 36 individual experiments of adhesive anchors installed in plain and reinforced concrete beams. The key design parameters are embedment depth, section width, and effects of the reinforcement. The results indicate high levels of interaction between all studied parameters. The tensile capacities of the single and groups of anchors are compared against ACI 318 predictions. The main effects of parameters, as well as their interactions, are analyzed and discussed. Based on the test results, several recommendations are provided for the installation of adhesive bonded anchors in narrow concrete components. [ABSTRACT FROM AUTHOR]

The use of lightweight concrete can provide specific advantages that are favoring for mitigating seismic risk in building design. On the other hand, a significant reduction of carbon footprint could be possible through the use of geopolymer concrete. However, geopolymer concrete is mostly assessed through small specimens without reinforcement elements. This paper aims to couple the advantage of lightweight mixtures and ambient‐cured geopolymerization in reinforced beams. To do this, engineering performance of reinforced lightweight geopolymer concrete was extensively investigated with different aspects. In mixtures, pumice and volcanic tuff aggregates were used with an appropriate gradation. Flexural strength, deflection capacities, initial stiffness, ductility, and energy dissipation capacity of reinforced geopolymer beams were investigated with the proposed configuration. Compressive strength and unit weight of the developed mixtures were also evaluated to meet design requirements for lightweight concrete. Results indicated that certain engineering properties (energy dissipation capacity and initial stiffness) of developed lightweight geopolymer concrete were considerably comparable with lightweight Portland cement‐based concrete. Although compressive strength and unit weight of the developed geopolymer mixtures were satisfying, microstructural analysis indicated a weak bonding behavior between paste and lightweight aggregates. [ABSTRACT FROM AUTHOR]

This paper experimentally investigated the flexural and ductile behaviors of ultra‐high‐performance concrete (UHPC) beams. The failure modes, deflection, ductility, concrete strain, and reinforcement strain were tested using eight UHPC rectangular beams. The experimental parameters were the reinforcement ratio, the reinforcement diameter, and the UHPC cover thickness. The experimental results showed that all specimens exhibited flexural failure characterized by the yielding of steel rebars, multiple micro‐cracks, one localized macro‐crack, and slight crushing of UHPC. It was concluded that increasing the reinforcement ratio significantly enhanced the stiffness, flexural capacity, and ductility of the rebar‐reinforced UHPC beams, whereas showed little effect on their cracking load. Meanwhile, both the reinforcement diameter and UHPC cover thickness in the range investigated here had little influence on the flexural performance of UHPC beams in the elastic stage and crack development stage, whereas exhibited different influences in the yield stage. Besides, increasing the reinforcement ratio was in favor of presenting the deflection‐hardening behavior, while the reinforcement diameter and UHPC cover thickness had little influence on the deflection‐hardening behavior. The analytical models were established to predict the yielding load, peak load, and ultimate load of rebar‐reinforced UHPC beams, and the predictions showed good agreement with the experimental results in this study. Also, the steel reinforcement could show a dominant role in the bearing capacity by increasing the reinforcement ratio. A post‐yielding capacity factor λ was proposed, which could reasonably evaluate the deflection‐hardening and deflection‐softening behavior of UHPC flexural members in the present study. Based on other experimental results collected in literature, three different ranges for the post‐yielding capacity factor, namely, λ ≤ 0.7, 0.7 < λ < 0.9, and λ ≥ 0.9, were identified, corresponding to the deflection‐softening behavior, transition stage, and deflection‐hardening behavior, respectively. [ABSTRACT FROM AUTHOR]

Precast concrete structures have been widely applied in the construction industry worldwide. However, the current construction method for the reinforced concrete frame–shear wall structure (FSWS) is semi‐precast because the shear wall is commonly cast‐in‐place. This paper proposes a full precast FSWS and investigates three new vertical joints with different lap splices that can facilitate on‐site construction. Push‐off tests are conducted to investigate the shear performance on the aspect of cracking and failure patterns, the evolution of deformation, stiffness reduction, and energy dissipation. A finite element model with delicate consideration of the contact is developed and validated against experimental data. A further parametric study is conducted. This study shows that the lap splice with a more uniformly distributed reinforcement layout yields the crack distribution more uniformly and increases the ductility of the joints. The proposed three vertical joints exhibit an improvement in ductility compared to the monolithic one. Furthermore, the shear keys change the failure mechanism of the precast joints into the multi‐struts failure mechanism thus increasing the shear strength. The parametric study shows that the decreasing of the splice lap length could increase the shear capacity of the vertical joints but decreases the ductility. However, the ductility reduction depends on the variation of lap splices. [ABSTRACT FROM AUTHOR]

The demand on the longitudinal reinforcement due to shear has been traditionally based on statics but has rarely been measured. Empirical assumptions needed for the concrete stiffness and the variability of reinforcement strain due to cracking and disturbed regions complicate these measurements, and make the use of conventional strain gauges impractical. This paper investigates the use of distributed measurements from a large reinforced concrete beam test to study the effects of disturbed regions, forces at a crack, shrinkage, and the in situ modulus of elasticity of concrete. The increased demand due to shear on the longitudinal reinforcement was observed, and the Canadian code was shown to provide an accurate upper bound to the measured strain at service loads. The measured longitudinal strains were also used to estimate the average angle of principal compressive stress, and it was observed to decrease with applied load, reaching values as low as 14° near failure. [ABSTRACT FROM AUTHOR]

Realistic structural models incorporating the time‐dependent effects of concrete are essential in order to make accurate predictions of the time‐dependent deflections at any time of the service life. Experimental databases are used to calibrate and validate existing models for creep and shrinkage available in international standards. However, extensive research campaigns on large‐scale prestressed beams are scarce. In 1967–1985, a research program comprising a unique set of long‐term experimental data on concrete beams was conducted in joint collaboration with four Belgian research institutes to determine the influence of creep and shrinkage on the long‐term behavior of reinforced and prestressed concrete members. The main aim of the final part of the research campaign was the determination of the long‐term behavior of prestressed and partially prestressed beams subjected to permanent loads, considering the influence of the magnitude of the loads, the degree of prestressing, the shape of the cross‐section, the type of prestressing and the stress conditions. This paper reports on the obtained unique set of long‐term tests. Additionally, also information related to the creep and shrinkage data of prisms and the results of the static tests in a four‐point bending configuration until failure at the age of 28 days and 5 years are presented in this paper. The measurements of the prestressed members are compared with a simplified calculation method based on the direct stiffness method, which accounts for aging, creep, and shrinkage. The proposed simplified calculation model allows fast and accurate predictions of strains, stresses, and deflections as a function of time. The results show that the direct stiffness method in combination with the current models of EN1992‐1‐1 and fib Model Code 2010 can predict the long‐term behavior of concrete beams in good agreement with the available experimental data. The research allows to develop more accurate calculation guidelines with respect to the evolution of deflections, concrete deformations and stresses of prestressed beams as function of the prestress‐degree, shape of the cross‐section, and the type of prestressing. [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]

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

Structural reinforced concrete (RC) experiences cyclic loads during their service life, and in practice, the load amplitude can always change, which will lead to a mixed high and low‐cycle fatigue failure. This paper aims to investigate the fatigue behaviors of RC beams under different load levels and more importantly, their sequential effects. Based on the path‐dependent constitutive models, the structural degradation under different repeated loads are comprehensively investigated by numerical simulation of higher consistency with the reality. It is fairly indicated that a clear bi‐linear character may exist in the so‐called S‐N diagram, of which the high‐cycle fatigue failure is attributed to rupture of main reinforcement under tension, while the low‐cycle fatigue failure is controlled by the concrete failure in flexural compression zone. A simple design method to consider mixed low and high cycle fatigue is proposed to quantify this bi‐linear character. For the varying amplitude of cyclic loads, the high‐to‐low loading sequence may cause a shortened fatigue life. More interestingly, if a rather high heavy load (0.85 or 0.95 of the static capacity) is applied just once before ordinary fatigue loads (ex. 0.6), the deflection may significantly increase, while the stiffness and final fatigue life would be slightly reduced in view of nonlinear mechanics. [ABSTRACT FROM AUTHOR]

The paper describes the reliability‐based optimization of a TT‐shaped precast roof girder produced in Austria. An extensive experimental programme was performed using laboratory specimens to gain information on the mechanical fracture parameters of the utilized concrete. Subsequently, destructive shear tests were performed on scaled‐down and full‐scale girders under laboratory conditions. The experiments helped in the development of an accurate numerical model of the girder. The developed model was consequently used for the advanced stochastic analysis of structural response, followed by reliability‐based optimization, which was used to maximize the shear and bending capacities of the girder and minimize production cost under defined reliability constraints. The enormous computational requirements of the double‐loop optimization approach were significantly reduced by the utilization of an artificial neural network‐based surrogate model instead of the original nonlinear finite element model of the optimized structure. [ABSTRACT FROM AUTHOR]

Concrete‐encased concrete‐filled steel tubes (CFST) has extensive applications in the world. According to previous researches, if the CFST is placed in the compression zone, the confinement increases, and the compressive capacity of the concrete is completely used. The prestressed strands also increase the core concrete confinement and eliminate tension cracks. Therefore, in this paper, to achieve the benefits of CFST and prestressed strand, for the first time, a novel concept called prestressed concrete‐encased CFST (PCE‐CFST) beams were introduced. The main objective of the combination of steel tube and pre‐stressed strands is to increase the core concrete compressive strength and control the concrete crack in the tension zone. Six beams were constructed using self‐compacting concrete to investigate the influence of variations in the pre‐stressing force level of the pre‐stressed strands, the pre‐stressed strands eccentricity, and the steel tubes diameter‐to‐thickness ratio on the structural performance of these members. The specimens were tested under four‐point loading. The results showed that the pre‐stressed strands increased the confinement effect on the core concrete and improved the bearing capacity, ductility, and bending stiffness. The steel tubes improved the bearing capacity, ductility, and energy absorption, while they did not significantly affect the bending stiffness. Finally, it was shown that the pre‐stressed strands increased the bearing capacity, energy absorption, and bending stiffness in reinforced concrete beams. [ABSTRACT FROM AUTHOR]

This paper proposes an innovative precast through‐girder system that can be used in shallow bridge structures. It discusses various components of the through‐girder system, including the edge (through) girders, transverse beams, and longitudinal and transverse connections. The through girders are made of precast concrete box beam segments that are spliced longitudinally through posttensioning. The precast prestressed transverse beams span between the through‐girders involving the use of transverse posttensioning. An important feature of this system is to implement ultra‐high performance concrete (UHPC) at the all joints. The use of UHPC allows to minimizing the joint width and achieving superior durability. A numerical example is presented to demonstrate the analysis and design of the through‐girder bridge superstructure accounting for both high‐performance concrete (HPC) and UHPC options. The UHPC superstructure option can reduce the sizes of the structural members and allow to enhancing the structural performance. [ABSTRACT FROM AUTHOR]

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

In 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 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]

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

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