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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]

In this study, concrete canvas (CC) layers were used as a novel method to strengthen reinforced concrete (RC) beams because of their flexibility, rapid installation, fast curing, and rapid strengthening. Due to the importance of the CC mechanical properties, various combinations of cement including ordinary (OPC) and High Alumina (HAC), as well as silica fume, were investigated to determine the optimal mixture for strengthening RC beams. The results indicate that substituting 75% of HAC with OPC significantly boosted flexural strength by 33%, and increased tensile strength in the warp and weft directions by 25% and 21%, respectively. The study examined six RC beam specimens in a four‐point flexural test, assessing their flexural properties, ductility, cracking behavior, and energy dissipation. The number of CC layers and the bonding method, which involved either the conventional externally bonded reinforcement (EBR) technique or the externally bonded reinforcement on grooves (EBROG) technique were studied. The experimental results revealed the superiority of the EBR method over the EBROG technique due to the uniform bond between CC and the concrete surface. Using the EBR technique, improvements of 35% and 51% were observed in the load‐carrying capacity of the beams strengthened with one and two CC layers, respectively. It is while for the beam with an improved loading capacity of 51%, the crack width decreased from 5.3 to 2.1 mm, and the energy dissipation increased by three times compared to the control specimen. Theoretical analysis also was performed to calculate the load‐carrying capacity of the RC beams strengthened with CC layers. [ABSTRACT FROM AUTHOR]

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

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]

Many studies have suggested that engineered cementitious composite (ECC) could be a highly efficient and cost‐effective material for enhancing the flexural strength of reinforced concrete (RC) beams. Recently two effective retrofitting configurations using steel and polyvinyl‐alcohol hybrid fiber reinforced engineered cementitious composite (SPH‐ECC) were proposed (Qasim et al., Eng Struct, 2023, 284, p. 115992) and their high effectiveness for enhancing the flexural strength of RC beam was verified experimentally. However, to examine the performance of these strengthening configurations thoroughly by conducting experiments to cover practical ranges of design parameters is deemed to be too expensive and time consuming. In this study, a numerical parametric study of SPH‐ECC strengthened RC beams was conducted by employing a validated finite element (FE) modeling procedure developed by the authors. The effects of four key design parameters including the compressive strength of concrete and SPH‐ECC, the thickness of SPH‐ECC strengthening layer and the area of reinforcement bars embedded in SPH‐ECC layers on the flexural performance of the strengthened beams were studied. Parametric study results showed that the area of reinforcement bars in the SPH‐ECC layers could significantly affect the flexural strength of the strengthened beams. Furthermore, in order to allow engineers to predict the flexural strength of the strengthened beams quickly, two simple but accurate analytical models were also developed for the two strengthening configurations considered. Their reliability and accuracy were then verified and confirmed by comparing with the parametric study results. [ABSTRACT FROM AUTHOR]

The dual‐function retrofitting system that uses the carbon‐fabric reinforced cementitious matrix (C‐FRCM) as both the anode of impressed current cathodic protection (ICCP) system and the structural strengthening (SS) material, that is, an ICCP‐SS system, is investigated. The experimental program mainly focused on the shear behavior of C‐FRCM strengthened reinforced concrete (RC) continuous beam under the dual‐function retrofitting system. The influence of anode polarization on the shear strengthening of RC continuous beams is analyzed. Shear tests were conducted on a total of 14 corroded RC continuous beams to investigate the influence of key parameters, including anode polarization degree of prefabricated C‐FRCM plate, layer of carbon fiber mesh and side‐wrapping. The failure modes, shear capacities, and load‐deflection curves of the shear‐strengthened RC continuous beams are reported. Based on the test results, the applicability of relevant design codes was evaluated and found to provide rather conservative predictions for the shear capacity of the examined C‐FRCM strengthened RC continuous beams. [ABSTRACT FROM AUTHOR]

This article presents a review of state of the art on nonmetallic reinforcement in terms of bending moment redistribution in double‐span elements. The authors present a summary of existing research programs focused on moment redistribution in FRP (Fiber Reinforced Polymer) reinforced concrete (RC). On this basis authors created a database of concrete elements with all the important construction properties of the elements. Gathered data are presented with quantitative analysis of several variables effecting moment redistribution in published articles. In the following publication authors show a research review which includes an analysis of the influence of variable parameters from the point of view of the database, concerning: degrees of longitudinal reinforcement, ratio between degrees of reinforcement in span and over the support, type of reinforcement (FRP/steel/hybrid), concrete class and transverse reinforcement. [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]

The goal of this study is to propose a robust method for the analysis and design of recycled aggregate reinforced concrete (RAC) beams. For this purpose, a machine‐learning framework, named, GA‐XGBoost was designed. A comprehensive dataset of 276 tests of RAC beams was compiled from available literature for training, validating, and testing the models. The results confirmed that the proposed models can offer a precise tool for failure mode classification and capacity prediction of RAC beams. For the design framework, a Generative Adversarial Network for tabular data was utilized to produce synthetic data. These synthetic data can provide options for the selection of design variables. In this framework, the design variables are selected by specifying the design constraints, the objective function to be optimized, and validating the capacity requirements using the developed GA‐XGBoost models. Lastly, a web application was developed to make the proposed GA‐XGBoost models appropriate for practical design. [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]

Glass fiber reinforced polymer (GFRP) concrete beams reinforced by carbon fiber reinforced polymer (CFRP) grid reinforced engineering cementitious composite (ECC) have excellent flexural performance and corrosion resistance in marine environments. However, the lack of a reliable theoretical model for predicting the flexural behavior of the hybrid beams makes it challenging apply them in the practical engineering. To address this issue, a series of numerical models were established to investigate the effects of key parameters on the flexural behavior of the hybrid beams, including the peak load, the neutral axis height, and the sectional stress distribution. Subsequently, based on the influence of the failures of different materials on the flexural performance of the hybrid beam, the loads of four feature points were calculated in the theoretical model to predict the entire load–displacement curve. Finally, the application range of the theoretical model was given based on the neutral axis height. The results showed that the cover thickness of the ECC, the GFRP reinforcement ratio and the cross‐sectional area of the CFRP grid were the key factors affecting the flexural performance of the hybrid beams. The theoretical model established in this study can predict the load–displacement curve accurately and can provide a reference for the subsequent design of the hybrid beams. [ABSTRACT FROM AUTHOR]

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

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

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

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]

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]

As a sustainable concrete material, hemp and recycled aggregate concrete (HRAC) is produced by partial replacement of natural coarse aggregates (NCA) with recycled concrete coarse aggregates (RCA) and industrial hemp fibers. The objective of the reported research was to investigate the structural performance of reinforced concrete beams prepared with HRAC and designed to fail in flexure, shear, or bond splitting modes of failure, and to compare that performance with companion control beams cast with conventional concrete. The significance stems for the fact that no previous research is reported on mixtures using such a combination of hemp fibers and RCA. Test results indicated that HRAC beams with 0.75% volumetric percentage hemp fibers and 50% RCA replacement had comparable peak load capacities to the control beams with no RCA and no fibers, with ±4% difference for all tested modes of failure. Additionally, the fracture energy of the HRAC beam was higher than the control beam by 3.6%, 17.9%, and 14.4% for the flexure, shear, and bond modes of failure, respectively. Moreover, a life cycle analysis (LCA) was considered to compare HRAC mix with conventional concrete mix in terms of the environmental aspects. LCA results indicated that HRAC is a sustainable concrete, specifically with respect to structural performance and lower environmental impact. [ABSTRACT FROM AUTHOR]

The reinforced concrete (RC) beams could be upgraded in shear using steel and fiber‐reinforced polymer (FRP) having several shapes (bars, strips, or sheets). Using near‐surface mounted (NSM) Glass FRP (GFRP) bars is still limited compared to carbon FRP (CFRP) elements as shear reinforcement. Moreover, using reinforced high‐strength concrete layers (HSCL) as NSM shear strengthening for the RC beams is still limited. Herein, three RC beams internally reinforced in shear using different shear areas (without, 100 mm stirrups apart, and 200 mm stirrups apart) were experimentally tested as reference beams (CB). Other eight beams strengthened in shear using NSM HSCL, and bars were experimentally tested. Moreover, an extended finite element (FE) simulation was implemented through a verified FE model to study the effect of other NSM aspects on shear‐strengthened beam response. The results explained that, regardless of the internal stirrups area and external NSM characteristics, the shear‐strengthened beams showed higher load efficiency than the corresponding CB. The NSM upgraded shear beam had slightly higher load efficiency than the un‐strengthened beam having the same steel area as internally shear stirrups. Moreover, increasing the internal shear stirrups decreased the total efficiency of the NSM shear strengthening and the internal stirrups regardless of the NSM characteristics. Furthermore, the NSM HSCL was more efficient than the corresponding NSM bars in increasing the load capacity and stiffness of the shear‐strengthened beams. The reported analytical model predicted well the shear capacity of the tested beams. [ABSTRACT FROM AUTHOR]

Silica, a principal component of waste glass powder (GP) reacts with calcium hydroxide to form the hydration products, and the process is affected by the fineness of GP and the percentage of cement replaced. This study investigates the structural behavior of concrete incorporating GP in reinforced concrete members by 0%–25% (by weight) replacement of cement with GP along with 0%–0.45% addition of glass fibers (GFs). The compressive and tensile strengths, strength activity index (SAI), and failure mode of treated concrete mixtures have revealed the optimum values as 15% replacement of cement with GP with 0.3% of GF. In the second stage of experiment, reinforced concrete beams were cast at various percentages of GP and GF to investigate the load–deflection response. It was observed that the beam specimen treated with GP exhibited considerably less mid‐span deflection (14.8 mm) at failure as compared to the control beam (with no GP and GF) which failed at 29.4 mm. The beam specimen treated with GP only showed significant degradation in stiffness after the peak load due to the fact that a part of GP remains unreacted and acts as a filler. Moreover, the beam specimen cast at optimum percentages of GP (15%) and GF (0.3%) showed large mid‐span deflection and higher failure load as compared to the control beam. These results suggest that the partial replacement of cement with GP should be accompanied by the addition of fibers to avoid unwanted brittle responses of GP concrete, with the additional advantage of reducing the non‐biodegradable waste. [ABSTRACT FROM AUTHOR]

To study the influence of the defects on the flexural behavior of laminated T‐beams, full‐scale beam tests of three reinforced concrete laminated T‐beams with incomplete bonding and one non‐defective reinforced concrete laminated T‐beam were conducted under monotonic loading. The results showed that the failure modes and crack patterns of the defective beams were similar to those of beams without defects. However, horizontal cracks appeared in these defects. Although the peak loads of the four specimens were relatively close, the difference in the maximum deflection was distinct. The deflection span ratio of each specimen exceeded 1/17, and the displacement ductility ratio exceeded 15. The results indicate that internal defects have only a slight influence on the flexural capacity of laminated beams but significantly influence their ductility. [ABSTRACT FROM AUTHOR]

Ultra‐high performance concrete (UHPC) prefabricated beams are competitive in accelerated bridge construction. However, their broader application has been hindered by limited large‐scale tests and inaccurate design methods. To fill this gap, the authors conducted an experimental investigation on the shear and flexural performance of UHPC pi‐beams using two full‐scale specimens. One specimen was a precast UHPC beam, while the other was a composite beam with a normal concrete slab on the UHPC beam. The primary focus was on crack propagation, ultimate capacities, and failure modes. To complement the experimental findings, the extended finite element method (XFEM) was developed as a numerical approach. Nevertheless, relying solely on XFEM to understand real structural behavior is prone to misinterpretations. Moreover, the shear and flexural capacities were evaluated using existing codes and compared with the experimental results. The comparisons revealed that the predictions of shear capacities were at least 15% lower than the experimental values, whereas the flexural capacities showed acceptable agreement. To address this, the authors introduced the limit equilibrium method, leading to a more accurate prediction of shear capacity for UHPC beams with a deviation of <2%. [ABSTRACT FROM AUTHOR]

Iron tailings have been extensively studied as mineral admixtures and as coarse and fine aggregates. However, few studies have been conducted on the mechanical properties of iron tailings concrete structures. Using iron tailings powder as an mineral admixture, and iron tailings gravel and sand as coarse and fine aggregates, respectively, the flexural behavior of full iron tailings concrete (FITC) beams was investigated experimentally. Compared with conventional concrete (CC) beam, we showed that the crack‐resistant, yield, and ultimate moments of FITC beams are similar to those of the concrete strain of FITC beams, which is in good agreement with the plane section assumption before cracks appear. The low elastic modulus of FITC makes the deflection of three FITC beams larger than that of a CC beam. The current design code of China is appropriate for calculating the load‐carrying capacity of FITC beam; however, the deflection calculation formula should be modified. [ABSTRACT FROM AUTHOR]

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

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]

Reinforced concrete (RC) and prestressed concrete (PC) structural elements need to be designed in order to guarantee large plastic deformations, avoiding any loss in their load bearing capacity. In this framework, the rotation capacity of RC and PC beams has been demonstrated to be a function of concrete mechanical properties, reinforcement characteristics, and of the structural size. On the other hand, Theory of Plasticity as well as the International Standards completely disregard size‐scale effects and ductile‐to‐brittle transitions, leading to an overlook of the strain‐softening behavior of the concrete matrix and of the rotation capacity of RC beams. On the other hand, the Cohesive/Overlapping Crack Model is able to evaluate concrete cracking in tension and concrete crushing in compression, as well as snap‐back and snap‐through unstable phenomena, steel yielding and/or slippage. This Nonlinear Fracture Mechanics model predicts a reduction in the moment versus rotation plastic plateau by increasing the beam depth and/or the reinforcement percentage. The numerical investigations carried out on reinforced and prestressed high‐performance concrete beams having rectangular or T‐shaped cross‐sections highlight the size‐scale effects on plastic rotation capacity that allow to formulate new scale‐dependent upper and lower limits of reinforcement percentage to guarantee a stable and ductile postpeak behavior of reinforced concrete structures. [ABSTRACT FROM AUTHOR]

Polyethylene terephthalate (PET) is a new type of fiber‐reinforced polymer (FRP) composite material, which has the characteristics of high performance, high toughness, high tensile fracture load, low elongation, low creep, no rust, and safety in use. The good performance of PET can significantly improve the mechanical properties of its components. A total of six reinforced concrete (RC) beams were produced in the test, one of which was a comparison beam, and the other five were reinforced with PET. In the test, the PET reinforcement spacing, number of reinforcement layers, and laying method were used as control variables, and an experimental study on the normal section bending performance of the specimen was performed. The test analyses the failure characteristics, crack width, bearing capacity, and deflection of the specimens under different reinforcement conditions. The test results showed that PET reinforcement can effectively inhibit the occurrence and development of cracks in RC beams and improve the ultimate bearing capacity and ductility of the components. The smaller the PET reinforcement spacing, the higher the ultimate bearing capacity; the greater the number of PET layers, the better the ductility of the specimen. Additionally, the economy, environmental protection, and portability of PET are of great significance for its application in practical engineering reinforcement. [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]

Through this study, an attempt was made to produce concrete beams from self‐compacting concrete (SCC) contain expanded polystyrene (EPS) beads as coarse aggregate and waste plastic fibers (WPFs) produced from cutting disposed packing straps in site. The beams were designed according to ACI‐318‐14, where three different reinforcement ratios were chosen for the purpose of checking the conductance of thresholds made of this type of environmentally friendly concrete under bending loads. The use of EPS with WPFs had a significant positive effect in reducing the density of concrete, and the highest percentage of reduction was equal to (38.46%). Using WPFs had a positive effect in increasing the flexural toughness of concrete prisms, and the maximum increment was equal to (180%) compared with these made from the reference mix. The results proved the possibility of producing lightweight concrete from the use of EPS waste and WPFs, three of which are structurally can be classified as lightweight concrete combination of normal weight and lightweight aggregates according to specifications requirements of ASTM330/330M‐14. Reinforced lightweight SCC beams behaved under flexural loads similar to the reinforced concrete beams made from normal weight concrete counterparts under flexural loads. [ABSTRACT FROM AUTHOR]

A novel posttensioning technique using nickel‐titanium‐niobium (NiTiNb) shape memory alloy (SMA) wires for the repair of reinforced concrete beams was evaluated numerically. A finite element model of a reinforced concrete beam was developed within a damage mechanics framework to simulate concrete cracking and subsequent posttensioning. The predicted yield and ultimate moment capacities of the simulated posttensioned beams were up to 14% less than the corresponding experimental results. Cumulative discrepancies in the assumed material models led to the conservative model results. The effects of concrete tensile damage, SMA reinforcement ratio, SMA‐concrete interaction (bonded vs. unbonded), and the effective prestress on the service and ultimate behavior of the posttensioned beam were evaluated. Partial loss of prestress in the SMA due to elastic shortening of the concrete was insignificant (<3%) because of the relatively low elastic modulus of the SMA. Increasing the SMA reinforcement ratio by three times increased the yield moment of the posttensioned beam by 99%. Reducing the effective SMA prestress to 80% of the initial prestress to account for the possible losses resulted in a decrease in the yield moment by up to 7.8%. [ABSTRACT FROM AUTHOR]

Fiber reinforced polymer (FRP) bars have been widely used as a replacement for steel bars in civil engineering due to their high strength and superior durability. However, compared to steel reinforced concrete (RC) beams, FRP RC beams have insufficient ductility and are more expensive. Therefore, a hybrid beam reinforced with steel and FRP bars has been proposed recently. In this study, the flexural properties of steel bar RC beam, basalt FRP (BFRP) bar RC beam, and BFRP steel bars hybrid RC beams were studied based on numerical simulation. The effect of As/Af on the stress of longitudinal reinforcements, load–midspan curves, ductility, and overall performance of the hybrid RC beams is analyzed. Results indicated that the hybrid RC beams exhibited a second‐order stiffness after the steel bars yielded owing to the contribution of the BFRP bars. As As/Af increases, the ductility of the hybrid RC beam and the strength utilization of BFRP bars increase, and a preferable ductility and overall performance can be achieved when As/Af was close to 1.0. The theoretical calculation results of hybrid RC beams based on ACI, CSA, and GB codes are compared with the simulation results, and the accuracy of the ultimate flexural strength of the prediction results is verified. In addition, equations for predicting the deflection of hybrid RC beams are proposed, and they exhibit higher prediction accuracy compared to the prediction models based on the ACI code. [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]

Concrete, as the most widely used construction material, is associated with a high environmental impact. Within the present study, structural optimization is the method of choice to counter this issue. The entire process, from optimization, to design, experiments and numerical simulation is outlined. Embedded in the framework of a design competition (Concrete Girder Optimization Competition 2021), a bridge between structural engineering and mathematical optimization is demonstrated. Two design concepts for optimized concrete girders, one with internal and one with external reinforcement, yet both based on strut‐and‐tie modeling, were investigated. Within the boundaries of the competition, several conclusions can be drawn: The results indicate the importance of an adequate structural interpretation of topology optimization results to obtain satisfying structural performance. The environmental evaluation outlines that the reinforcement mass has a substantial share in the total Global Warming Potential. A successful numerical re‐simulation of selected girders can serve as a modeling base for other researchers. Compared to a conventionally designed girder an increase in resource efficiency, measured by load‐carrying capacity versus environmental impact, of more than 30% was achieved. [ABSTRACT FROM AUTHOR]

The study of damage processes in concrete and their effects on the residual properties represents a key point related to the service life of reinforced concrete (RC) structures. The use of steel fibers in RC beams mainly improves the cracking control and the shear bearing capacity. Considering the shear behavior, the presence of fibers not only leads to partial or total substitution of secondary reinforcement, but they can also result in a modification of the failure behavior from a shear failure (brittle) to a bending (ductile) one. The contribution of fibers on flexural and shear behavior of sound and damaged RC beams was investigated using alkali‐silica reaction as a damaging tool. First, the evolution of deformations and cracks were measured on creep tests of RC beams with and without fibers and reactive aggregates. Second, the flexural and shear behavior of damaged and undamaged beams incorporating steel fibers were compared. Results showed that alkali‐silica reaction damage can provoke a reduction of RC beam ductility, while the flexural strength is preserved. Regarding shear, it was observed that even in damaged concrete, fibers were able to control the crack propagation and increase the bearing capacity. [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]

To reduce the impact on global warming, many countries and regions are advocating the use of low‐carbon and green supplementary cementitious materials (SCMs) to improve the cement industry. This study investigates the shear behavior of reinforced concrete (RC) beams made with a novel green concrete, limestone, calcined clay, and cement clinker (LC3). Full‐scale shear tests were conducted on RC and LC3‐RC beams to evaluate their fundamental behavior for structural applications. The shear resistance of LC3 concrete beams was evaluated using Chinese, American, and Eurocode codes, while carbon emission and environmental impact were analyzed by life cycle assessment (LCA). Results showed that LC3‐RC and RC beams exhibited similar shear behavior in terms of crack initiation, propagation, and development. The increase in concrete strength improved the stiffness of LC3‐RC specimens, while RC specimens remained unchanged. The ductility of RC specimens was inversely proportional to concrete strength, while LC3‐RC beams exhibited optimal ductility. The increase in stirrup ratio significantly improved the shear resistance of both LC3‐RC and RC beams. With increased shear‐span ratio, the failure mode of LC3 specimens improved, changing from diagonal‐compression to shear compression or diagonal tension failure. The shear resistance of both LC3‐RC and RC beams was underestimated by GB 50010‐2010, ACI 318‐19, and Eurocode 2. LC3 concrete significantly reduced energy consumption and carbon emissions and achieved favorable environmental benefits in terms of GWP, PMFP, POFP, TAP, and TETP. Increasing usage of limestone in LC3 may further decrease environmental potential without sacrificing mechanical properties. The findings of this study contribute to the development of sustainable and environmentally friendly structures in engineering. [ABSTRACT FROM AUTHOR]

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

This study aims to develop a new hybrid strengthening approach for reinforced concrete beams by integrating near‐surface mounted shape memory alloys (SMAs) and externally bonded carbon fiber reinforced polymers (CFRPs). Due to the superelasticity and shape memory effect of SMAs, the proposed strengthening can enhance the flexural strength of concrete beams without compromising ductility. The recovery behavior of deformed SMA wires was studied to determine the optimal prestrain level that can achieve the highest recovery stress. Afterward, the flexural performance of concrete beams strengthened with SMA, CFRP and both was investigated by performing three‐point tests. The results show that integrating SMA and CFRP has more influence on increasing the ultimate moment than the cracking moment and leads to a more significant improvement in the ultimate moment than individually utilizing SMA and CFRP. Besides, the effect of the integrated approach on enhancing the ductility is more notable than increasing the ultimate moment. The ultimate moment was analytically calculated, and the calculations show reasonable agreement with experimental results. The effects of the SMA and CFRP amount on the ultimate moment were also clarified through a parametric study. [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]

The longitudinal shear forces are transferred through mechanical shear connectors at the steel beams and concrete slab intersection in composite beams. The shear connectors can be directly welded to the hot rolled steel beam, which is difficult in thin, cold‐formed steel beams. Thus, a cold‐formed double‐channel shear connector is proposed, and its suitability is investigated in this study. The double channel shear connector is a channel shaped shear connector formed from a flat plat and it is mounted on the flange of steel beam in pairs. The finite element model of the experimental Pushout test assembly was developed with the equivalent numerical constraints and interaction commands in a finite element software (ABAQUS). The developed models were fed with initial imperfection, load slip response, and material nonlinearity to achieve the proper experiment simulation. Initially, the developed models were validated against nine experimental test data reported by authors in the previous study. The parametric study was conducted to assess the behavior of cold‐formed channel shear connectors. The key parameters adopted in this study are the length of the shear connector, the grade of concrete and the grade and thickness of the steel connector. Three common failure patterns were witnessed among 107 numerical models. In this study, the factors influencing the control of failure patterns are presented, along with the factors influencing the shear connector's ultimate capacity. [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]

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 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]

Hybrid reinforced concrete (HRC) can be defined as a cementitious material in which the reinforcing secondary phase consists of a combination of continuous steel rebars and of short discontinuous fibers, randomly distributed within the concrete matrix. For these structural elements, experimental flexural tests highlight how the postcracking response of the composite is strongly affected by the amount of steel bars together with reinforcing fibers. In the present work, it is shown that the action of these two contributions can be clearly interpreted in the framework of Fracture Mechanics through the Updated Bridged Crack Model (UBCM). The model assumes nonlinear constitutive laws to describe the toughening action of the reinforcing secondary phases, which are related to the yielding of steel rebars and to the pull‐out of the short fibers. Under these assumptions, different postcracking regimes depending on three scale‐dependent dimensionless numbers can be predicted: the bar‐reinforcement brittleness number, NP, which is directly related to the steel bar area percentage, ρ; the fiber‐reinforcement brittleness number, NP,f, which is directly related to the fiber volume fraction, Vf; and the pull‐out brittleness number, Nw, which depends on the critical embedment length of the fiber‐reinforcement, wc. The couples of critical values of the two reinforcement brittleness numbers define the minimum reinforcement conditions of the HRC structural element—that is, the combination of ρmin and Vf,min required to guarantee a stable post‐cracking response—including its scale dependence. A parametrical analysis is presented together with the modeling of an experimental campaign reported in the literature in order to assess the effectiveness of the UBCM. [ABSTRACT FROM AUTHOR]

Thin‐walled textile‐reinforced concrete beams have recently emerged as a promising approach for material‐efficient design. However, the increased complexity of the formwork is a major challenge in implementing such elements for broader use in the construction industry. This study presents a novel type of stay‐in‐place flexible formworks with integrated textile reinforcement. The use of weft‐knitted textiles allows the integration of continuous high‐strength rovings as shear reinforcement and the introduction of spatial features within the fabric to guide bending‐active rods to shape the complex cross‐section geometry. The manufacturing procedure and the structural performance were investigated in an experimental campaign consisting of four concrete beams with I‐profile cross sections tested in three‐point bending, where aramid rovings were used for the shear and conventional deformed steel bars for the flexural reinforcement. The transverse reinforcement ratio proved to be essential in increasing the shear strength. Thereby, the use of digital image correlation measurements of the surface deformations allowed the direct assessment of the strains and, thus, the mechanical activation of the textile reinforcement. The full tensile capacity of all the aramid rovings crossing the governing crack could not be exploited due to the brittle material behavior, resulting in a progressive failure once the first roving reached its tensile strength. Compatibility‐based stress fields were used to predict the load‐deformation and failure behavior of the tested beams, which resulted in an excellent agreement of the ultimate loads and failure modes obtained from the model with the observations and results from the experiments. [ABSTRACT FROM AUTHOR]

Structural ductility in the case of plastic hinges forming close to a lap splice has been an open issue with the revision process of the next version of Eurocode EC2 concerning reinforced‐concrete structures. This research has provided experimental evidence by the large experimental campaign for the background for revision of the Eurocode EC2. Within this context, 38 specimens were tested in four‐point bending, with the longitudinal bars either lap‐spliced (partly or fully), or un‐spliced (for reference). The tests were carried out involving the variation of the bar diameter (12, 16, 20, and 25 mm), and the lap length (20–60 times the bar diameter). The main result is the sizeable enhancement of the structural ductility brought in by the extension of the lap length in excess of the length required by the yielding of the longitudinal bars. Based on these findings, a preliminary model is developed to describe the bond‐stress profiles in lap splices, after the yielding of the bars. [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]

In topology optimization with discrete model finite element analysis (FEA), feasible reinforcement domain determines to a large extent the result, and the trade‐off between accuracy and efficiency of optimization as well. Therefore, a cantilever reinforced concrete short beam was comparatively optimized based on five feasible reinforcement domains with complexity at different levels, respectively. The outcomes exhibit that, it is reasonable to evolve reinforcement layout by topology optimization with discrete model FEA. The orientation of diagonal reinforcement in optimal topologies from complex feasible reinforcement domains would correspond more to the orientation of the principal tensile stress than that using simple ones, since complex ones have rebar distribution with high density or diagonal reinforcement with various orientations. After optimization, the global stress level of the reinforcement decreases, and then utilization rate of the reinforcement strength increases. Additionally, the consumption of rebar and the workload of reinforcement engineering only slightly increased, although such optimal reinforcement topologies are relatively complex. Consequently, the mechanical properties of concrete members can be substantially improved by using a more complex feasible reinforcement domain for optimizing rebar distribution. A complex domain should be chosen on the premise of completing the optimization within a reasonable time in engineering applications. [ABSTRACT FROM AUTHOR]

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