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This research examines the influence of high-volume fly ash (HVFA) on reinforced concrete (RC) beam deflections over 180 days of continuous loading. The study comprises eight fly ash-based concrete mixes with varying fly ash ratios (0–60%). Experimental assessments were conducted on two load levels, corresponding to 25% and 50% of the initial cracking load. Thirty-two full-scale RC beams, each measuring 100 × 150 × 1800 mm, were fabricated for both load levels. Long-term deflections were monitored for all concrete mixes through sustained four-point bending tests at ages ranging from 1 to 180 days. A comparative analysis of the overall mid-span deflection between conventional and fly ash concrete RC beams was carried out against established design codes. It was determined that high-volume fly ash RC beams exhibited less creep and shrinkage deflection compared with conventional RC beams. Moreover, artificial neural network (ANN) modelling was also carried out to propose a significant model helpful in predicting the total deflection of RC beams containing any fly ash content and at any age of concrete. The present study offers valuable insights for engineers and designers, facilitating the evaluation of age-dependent deflection patterns in RC beams constructed with reinforced high-volume fly ash concrete. [ABSTRACT FROM AUTHOR]

This work presents the application of a finite element model utilizing a three-dimensional (3D) probabilistic semi-explicit cracking model to analyze the rupture process of a large concrete wall beam. The numerical analysis predicts both the global behavior of the structure and its primary rupture mechanisms, utilizing three different finite element mesh refinements to ensure robustness. A Monte Carlo (MC) procedure is integrated into the modeling approach to account for probabilistic variations of the material properties. The statistical analysis derived from this probabilistic model may sometimes result in overly conservative safety coefficients, particularly when using a coarse mesh. Additionally, the detailed understanding of the structure's cracking process, regardless of its rupture mechanism, may experience some reduction in precision. Due to the necessity of numerous simulations to achieve statistically significant results, the MC procedure can become computationally expensive. To address this, a straightforward parallelization of the Monte Carlo procedure was implemented, allowing multiple finite element analyses to be conducted concurrently. This strategy significantly reduced computational time, thereby enhancing the efficiency of the numerical model in performing numerical simulations of structural engineering. [ABSTRACT FROM AUTHOR]

In reinforced concrete (RC) buildings, the seismic behaviour of RC beams with flush outside faces of beams and columns has not been verified by experiments. In this study, four large RC beam specimens were fabricated and an experimental verification was conducted. The results showed that all of the specimens (including three beam specimens with flush outside faces of beams and columns) could withstand ultimate drift angles up to 4% rad. In addition, the lateral strength and seismic behaviour of a specimen with a concrete cover of 85 mm were no less than those of the benchmark specimen, so a concrete cover thickness of 85–40 mm should be acceptable for RC beams. The seismic behaviour of two specimens with lateral U-shaped auxiliary transverse reinforcement and a concrete cover of 85 mm was better than that of the benchmark specimen, but the crack width of the latter was wider and the spalling degree of the concrete cover was more serious. Based on the results of this work, the practical recommendation is to adopt lateral U-shaped auxiliary transverse reinforcement in which the two legs extend beyond half the width of the hoop, with two auxiliary longitudinal reinforcements and the same spacing as the hoop. [ABSTRACT FROM AUTHOR]

The utilization of externally bonded carbon fiber-reinforced polymers (CFRPs) and glass fiber-reinforced polymers (GFRPs) for reinforcing and retrofitting components has garnered considerable interest recently, as such composites provide beneficial properties, including a high modulus of elasticity, high strength, and low weight. This work conducts a finite element analysis, verified through laboratory experiments on 14 reinforced concrete (RC) beams. The primary focus is the final load of these components, considering varying CFRP orientations relative to the loading direction. In this research, the performances of control beams and RC beams are compared to assess the effectiveness and efficiency of different strengthening methods. The results demonstrated that bonding CFRP sheets with V-shaped end anchorages on the tension side was highly effective in improving the flexural capacity of RC beams in the weaker concrete strength group. This strengthening method resulted in a substantial increase in strength (of around 29.8%) in the higher concrete strength group. In addition, utilizing V-shaped end anchorages to bond CFRP sheets on the tension side proved to be a highly efficient technique for improving flexural strength. Conversely, bonding inclined CFRP strips to the sides of RC beams was highly effective at enhancing the shear capacity of the beams. These outcomes convincingly demonstrate the effectiveness of FRP for the reinforcement of structural components. The specimens strengthened with inclined strips exhibited enhanced shear and deformation capacity compared to those strengthened with vertical strips. [ABSTRACT FROM AUTHOR]

Concrete half-joint beams (HJB) are characterised by local reductions in the overall beam depth at the support and are ideal for structural connections. However, the beam joint region is vulnerable to deterioration and design/detailing shortcomings. Non-linear numerical modelling of the behaviour of a series of impaired reinforced concrete HJBs was conducted in this study. The major defects considered were unavailability of diagonal bars/U bars, shear reinforcement inadequacy and reinforcement corrosion. The numerical simulations captured global and local behaviours of the beams. The load capacity prediction discrepancy was in an impressive range of −16.7% to +1.5%, in contrast to the predictions of the commonly used strut-and-tie model in the range of −39.2% to 16.9%. Subsequently, an experimental study was established using finite-element modelling to explore the retrofitting potential of defective HJBs using the deep embedment (DE) technique. The strength enhancement was almost 30% and the internal load paths and the failure mode of the defective beam were favourably altered with the post-installation of the retrofitting element. The DE technique was thus identified as an ideal option for the retrofitting of impaired HJBs. [ABSTRACT FROM AUTHOR]

The study was conducted to find the effect of using brick as a coarse aggregate in reinforced concrete (RC) beams and to obtain optimum replacement ratios without significantly reducing the durability (i.e. corrosion probability in reinforcement and chloride ion resistivity in reinforcement cover) and flexural strength of the specimen subjected to a marine environment. Specimens were exposed to alternate wetting and drying cycles in an artificially prepared corrosive environment (chloride ions with a concentration of 50 parts per 1000). A regression model for finding the overall mass loss in the reinforcement after the effect of corrosion is presented. A regression model to obtain the different fundamental properties of the concrete through replacing stone by brick aggregate is also presented. This regression model was validated using the k-fold validation approach. [ABSTRACT FROM AUTHOR]

This paper presents an overview of the deep embedment (DE) method – also referred to as the embedded through-section method – a promising technique for concrete shear strengthening. The aim of this work was to collate pull-out and beam test results with a view to identifying existing gaps in knowledge. A careful evaluation of pull-out test results showed that, except for the effect of embedded length, the bond performance of DE bars epoxy-bonded into concrete is not fully understood. Analysis of beam test results identified significant gaps in knowledge, particularly with regard to the effect of concrete strength, loading type, shear span-to-effective depth ratio, size effect and DE bar surface coating. Moreover, the analysis of beam test results revealed a novel interaction between steel tension and DE shear reinforcement. Finally, yet importantly, the paper summarises the research required for robust implementation of the DE technique. [ABSTRACT FROM AUTHOR]

A reinforced concrete beam with a recess is an example of a non-prismatic beam, which develops stress concentrations at the corner of the recess owing to the abrupt change in its depth. This entails appropriate detailing of internal reinforcement in order to avoid premature failure. This study presents the load transfer mechanism employing the strut-and-tie model (STM) for four non-prismatic beams with recesses in the shear span zone at both compression and tension sides, tested under a four-point loading scheme. The proposed STMs for the tested beams were developed based on both the cracking patterns near failure of experimentally tested beams and the developed stress contours based on linear static analysis. In addition, a simplified method is proposed to estimate the maximum mid-span deflection of simply supported beams with recesses. The results obtained reveal that the STM gave good predictions, with an average of about 86% of the ultimate experimental loads. Based on the results of the parametric study conducted, it was found that the most significant parameter was the recess depth from the viewpoint of stress concentration factor, cracking load and maximum crack width. Finally, recommendations and guidelines for the design of reinforced concrete beams with recesses are presented. [ABSTRACT FROM AUTHOR]

To study the acoustic emission (AE) characteristics of fibre-reinforced polymer (FRP)-reinforced concrete during the fracture process, three-point bending tests of FRP-reinforced concrete beams with cracks were carried out. The AE characteristics of FRP-reinforced concrete beams with different bonding lengths and different bonding layers were analysed based on the AE parameters, and the effect of the fracture parameters was studied. The test results reveal that the crack initiation load and peak load of single-layer FRP-reinforced concrete beams first increase and then decrease with the increase of bonding length. The failure mode of multi-layer FRP-reinforced concrete beams is a kind of dangerous brittle failure, which easily forms the 'super-reinforcement failure' mode. The ductility of single-layer FRP-reinforced concrete beams with a bonding length of 25 cm is optimal, which can effectively delay crack propagation. By combining the load–time curves, AE ringing count–time curves and AE energy–time curves, the time points of crack initiation load and instability load can be accurately determined. The analysis of RA–AF (ratio of ringing count to duration–ratio of rise time to maximum amplitude) and clearance factor index can be used to evaluate the damage state of FRP-reinforced concrete beams. [ABSTRACT FROM AUTHOR]

This article considers the prospects of the application of building structures made of polymer concrete composites on the basis of strength analysis. The issues of application and structure of polymer-concrete mixtures are considered. Features of the stress-strain state of normal sections of polymer concrete beams are revealed. The dependence between the stresses and relative deformations of rubber polymer concretes and beams containing reinforcement frame and fiber reinforcement has been determined. The main direction of the study was the choice of ways to increase the strength characteristics of concrete with the addition of a polymer base and to increase the reliability of structures in general. The paper presents the results of experimental and mathematical studies of the stress-strain state and strength, as well as deflections of reinforced rubber-polymer beams. The peculiarities of fracture of reinforced rubber-polymer beams along their sections have been revealed according to the results of the experiment. The peculiarities of fracture formation of reinforced rubber-polymer beams have also been revealed. The conducted work has shown that the share of longitudinal reinforcement and the height of the fibrous reinforcement zone are the main factors. These reasons determine the characteristics of the strength of the beams and their resistance to destructive influences. The importance and scientific novelty of the work are the identified features of the stress-strain state of normal sections of rubber-concrete beams, namely, it has been established that the ultimate strength in axial compression and tension, deformations corresponding to the ultimate strength for rubber concrete exceed similar parameters for cement concrete 2.5–6.5 times. In the case of the addition of fiber reinforcement, this increase becomes, respectively, 3.0–7.5 times. [ABSTRACT FROM AUTHOR]

It has recently been shown that the ever-increasing complexity and inability of methods used for the design of reinforced concrete (RC) structures to consistently safeguard against brittle types of failure is the outcome of the conflict between the assumptions of the underlying theory and the fundamental concrete material characteristics. This paper demonstrates that these drawbacks can be eliminated through a coherent alternative theory developed on the basis of simplified beam theory modified to account for true concrete behaviour. Through the use of experimental information obtained from the literature, the proposed theory shows that, in contrast with widely held views, a structural member's load-carrying capacity depends solely on the strength of the compressive zone, which was found to be significantly larger than what it is widely considered to be. Moreover, load transfer is accomplished by the bending action of the concrete cantilevers formed between consecutive inclined or flexural cracks in the tensile zone. The above findings essentially underline the development of an alternative design method – the compressive force path method – and this is an indication of the suitability of the proposed theory to open up new possibilities for improving RC design. [ABSTRACT FROM AUTHOR]

The progressive damage monitoring and fracture evaluation of plain concrete beam specimens subjected to three-point bending (TPB) are reported in this paper. The objective of the present research is to systematically correlate the fracture behavior of a concrete beam with acoustic emission (AE) data recorded during the present set of experiments. The damage growth and failure mechanisms of the beam specimens are investigated with AE parametric analysis, b-value analysis, and digital image correlation method. Eventually, a reasonable correlation between AE energy and the released fracture energy is established at various stages of loading, which is confirmed with the set of TPB beam experiments and further validated with nonlinear numerical finite-element analysis. The energy released during the cracking processes at different loading stages in the experiment is quantified and systematically analyzed. Acoustic and fracture energies are dependent on active concrete cracking, and their correlation is helpful in determining the extent of damage in the concrete structures. Such a relationship can be used as an operational tool for structural health monitoring of structures as an early warning system supplemented with numerical analysis, a well-calibrated laboratory, and in situ AE experiments. [ABSTRACT FROM AUTHOR]

The presented study investigates the efficiency of repairing damaged reinforced concrete beams by a novel technique, which is the injection of epoxy resin to the cracks. The two main test parameters were the amount of flexural reinforcement (low, medium, and high) and the level of seismic damage before repair (light, moderate, and heavy). Nine cantilever beams were tested under reversed cyclic transverse loading in the undamaged (original) and repaired (after damaging) states. The test results were examined and discussed in terms of the initial flexural rigidity and ultimate load capacity. The technique was shown to be the most effective in damaged beams with mid-sized cracks. The minor cracks particularly in lightly-reinforced beams were not suitable for proper injection of resin, while the major cracks resulted in the epoxy to govern the flexural behavior of the beam after repair. The experimental load capacities were shown to be in close agreement with the analytical flexural capacities of the respective beams. The sizes of the cracks before repair and the longitudinal reinforcement did not affect the repaired beam to reach the load capacity of the original counterpart but affected the extent of deformations before reaching this load level. [ABSTRACT FROM AUTHOR]

The availability of high-strength reinforcing bars has prompted engineers to use these in the design of reinforced concrete (RC) beams; their high tensile strength helps to reduce the steel consumption for a given set of design constraints. For every gain, however, there is a risk of some loss in one form or another; results from a parametric study presented herein indicate a substantial savings in the form of quantity of steel in RC beams with the use of high-grade reinforcing bars, albeit it happened with the increased midspan deflection, probable crack width, and bond stresses, as well as the need for the higher reinforcing bar anchorage. The steel grade Fe550 is found to be optimal among all other reinforcing bar grades considered in this study. [ABSTRACT FROM AUTHOR]

The River Dee Bridge is a 270 m long concrete box girder bridge constructed as part of the Aberdeen Western Peripheral Route. The detailed design commenced in 2014, with construction finishing in late 2018. The bridge has a mainspan of 120 m and was built using the balanced cantilever construction method. This paper focuses on the design challenges encountered during the detailed design of this structure, particularly associated with the tight geometrical constraints imposed by environmental and aesthetic considerations on the foundations and the superstructure. The post-tensioned tendon design, which was particularly challenging for this relatively narrow and shallow box section, is also discussed. [ABSTRACT FROM AUTHOR]

As the consideration of soil-structure interaction is increasingly being incorporated into design practice, there is a need for solutions that consider the most relevant aspects of the behaviour of both the concrete and the soil, some of which are time-dependent. The present work introduces a model that suits both the structure and the foundation - including the supporting soil - allowing the coupled analysis of hardening on cure, creep, shrinkage and cracking of concrete, and consolidation of soil. Both the structure and the foundation are modeled as one-dimensional finite elements. The timedependent behaviour of the concrete and soil is modeled using Kelvin chains. For the structural elements, a mixed finite element formulation is used. Validation tests were conducted in the proposed modeling, comparing its results with available experimental and analytical data. The study of a reinforced concrete continuous beam supported by foundations on consolidating clay considering the time-dependent behaviour of the materials showed considerable changes in the effects of the soil-structure interaction. [ABSTRACT FROM AUTHOR]

Externally applied carbon-fibre-reinforced polymer (CFRP) laminate is a viable, economic and durable option for strengthening deteriorated, damaged or under-designed concrete structures. Effective stress transfer at the CFRP–concrete interface is an important consideration and quantitative on-site inspection of CFRP application quality is still a challenging issue. In this study, a ground penetrating radar scanning approach was used to examine the bond quality in small-scale concrete beams with flexurally applied CFRP laminates. The parameters considered included the concrete surface roughness, concrete surface voids, epoxy thickness and CFRP type. A three-point bending test and numerical modelling were used to develop simple quantitative relationships between the scanning results and the parametric combinations. Non-destructive evaluation techniques are convenient and provide valuable information for the prediction of the interfacial bond quality and the actual capacity contribution of the CFRP laminate, which will allow a higher confidence level in CFRP application quality and better quality control of concrete structures. [ABSTRACT FROM AUTHOR]

A series of experimental tests on reinforced concrete specimens with normal uncoated and epoxy-coated reinforcing bars (ECRBs) was carried out. A comprehensive report of the specimens, from material level to overall performance, is presented in this paper. At the material level, evaluation of the epoxy coating thickness showed that the production quality was not good. Some mechanical properties of bars with a thinner coating were better than those of their uncoated counterparts, while an increase in coating thickness offset the better mechanical properties and decreased the bond strength. Regarding durability, a comparison of the corrosion behaviour of the reinforcing bars and chloride penetration of the concrete cover in unloaded, statically-loaded and fatigue-loaded test specimens showed that higher fatigue loads and longer fatigue loading cycles decreased the corrosion resistance of the bars and increased the chloride penetration. The ultimate loads of the specimens were reduced and comparatively lower values were obtained for beams with bars with thicker coatings. The results of this work highlight the interrelationships among materials performance, durability and ultimate performance to achieve sustainable design for concrete elements with ECRBs in chloride-containing environments. [ABSTRACT FROM AUTHOR]

This paper proposes a new technique for the construction of a concrete-beam health indicator based on the Kullback–Leibler divergence (KLD) and deep learning. Health indicator (HI) construction is a vital part of remaining useful lifetime (RUL) approaches for monitoring the health of concrete structures. Through the construction of a HI, the deterioration process can be processed and portrayed so that it can be forwarded to a prediction module for RUL prognosis. The degradation progression and failure can be identified by predicting the RUL based on the situation of the current specimen; as a result, maintenance can be planned to reduce safety risks, reduce financial costs, and prolong the specimen's useful lifetime. The portrayal of deterioration through HI construction from raw acoustic emission (AE) data is performed using a deep neural network (DNN), whose parameters are obtained by pretraining and fine tuning using a stack autoencoder (SAE). Kullback–Leibler divergence, which is calculated between a reference normal-conditioned signal and a current unknown signal, was used to represent the deterioration process of concrete structures, which has not been investigated for the concrete beams so far. The DNN-based constructor then learns to generate HI from raw data with KLD values as the training label. The HI construction result was evaluated with run-to-fail test data of concrete specimens with two measurements: fitness analysis of the construction result and RUL prognosis. The results confirm the reliability of KLD in portraying the deterioration process, showing a large improvement in comparison to other methods. In addition, this method requires no adept knowledge of the nature of the AE or the system fault, which is more favorable than model-based approaches where this level of expertise is compulsory. Furthermore, AE offers in-service monitoring, allowing the RUL prognosis task to be performed without disrupting the specimen's work. [ABSTRACT FROM AUTHOR]

Various mathematical expressions have been proposed to evaluate or check the lapped length in spliced bars subjected to tension in reinforced concrete members. In this work, 284 tests on spliced bars were assessed in an attempt to improve the previous formulas, with the aim of proposing a new model to predict the lapped length, the transverse reinforcement spacing and the bond stress distribution in concrete beams with different compressive strengths. A genetic algorithm was used to optimise the proposed formulation. For both normal- and high-strength concrete, different bond-stress profiles were developed to predict the resistance provided by bonded embedment. The results clearly show that the proposed bond stress profiles lead to a more accurate evaluation of the lapped length in spliced bars than the expression proposed by the American Concrete Institute. [ABSTRACT FROM AUTHOR]

The partial replacement of cement with nanomaterials such as nanosilica (NS) particles in concrete improves its strength and other properties. In this study, the effect of NS as a partial replacement of cement for concrete mixes and concrete beams was examined. The studied response characteristics of reinforced concrete beams included the compressive strength, failure mechanisms, load-carrying capacity and load–deflection behaviour. The results showed that compressive strength increased with an increase in NS content up to 2.0% replacement of cement weight. The rate of increase in compressive strength was no longer significant beyond 2.0% replacement, indeed there was a slight decrease in compressive strength for NS content of 3.0%. The effect of increased NS content on the flexural behaviour of beams was also studied. Increased NS content led to increases in the first-cracking and ultimate loads and reductions in the deflection at cracking and ultimate load levels. No major differences in the structural response parameters were observed for test beams with zoning of NS in the bottom tension or top compression zones. An increase in NS content led to a slight increase in the ultimate strain associated with the ultimate load. Good agreement was found between experimental and theoretical ultimate moments. [ABSTRACT FROM AUTHOR]

An experimental investigation of functionally graded reinforced concrete beams with layers of engineered cementitious composites was carried out. The main most objective was to evaluate the damage to the beams under free–free constraints using a non-destructive, vibration-based impact method. Damage levels were assessed at 50, 70 and 90% of ultimate load. Dynamic characteristics such as damping, fundamental natural frequencies, mode shapes and frequency response functions at each level were assessed by means of hammer excitation. The investigation showed that damage levels could be accurately evaluated through discrepancies in natural frequency compared to an undamaged beam. A finite-element analysis for the undamaged condition under free–free constraints was undertaken and compared with the experimental natural frequency values to validate the vibration-based test method. [ABSTRACT FROM AUTHOR]

This paper delivers a reliability-based method for the assessment of the elastic modulus (EM) of concrete in simply supported girders from dynamic identification. The correlation between the natural frequencies of the first bending modes and the concrete EM supports the use of the first natural frequency as a predictor of the EM value, which is a well-acknowledged indicator of the state of concrete. In the current application, the EMs of seven girders provide the prior state of knowledge about the considered bridge class, possibly to be obtained by more samples in working applications. The identified natural frequencies update the prior probability distribution of the EMs using Bayes inference. The resulting probability of exceeding a specific EM value expresses the degree of belief of the inspector in the obtained EM. The posterior probability, compared to a proper threshold, could be used in decision-making processes when prioritising the interventions in the maintenance plans. [ABSTRACT FROM AUTHOR]

Reinforced concrete shear walls linked with steel coupling beams (SCBs) are an established structural solution in seismically prone regions. However, while headed studs are widely used in composite structures to facilitate load transfer, the performance of such studs in SCB connections is not very well understood. The study reported in this paper considered the effect of headed studs and details of reinforcement around the connection zone as the main parameters using experimental and numerical approaches. The results showed that the studs strengthened moment transfer rather than shear in the connection. In addition, the headed studs were subject to shear and bending moments rather than axial forces. A model of the transfer load in the connection subjected to concrete pry-out failure was developed to predict the strength of the connection. This model showed a good accuracy in comparison with the results of the experimental testing and previous research. [ABSTRACT FROM AUTHOR]

Remaining useful life (RUL) prognosis is one of the most important techniques in concrete structure health management. This technique evaluates the concrete structure strength through determining the advent of failure, which is very helpful to reduce maintenance costs and extend structure life. Degradation information with the capability of reflecting structure health can be considered as a principal factor to achieve better prognosis performance. In traditional data-driven RUL prognosis, there are drawbacks in which features are manually extracted and threshold is defined to mark the specimen's breakdown. To overcome these limitations, this paper presents an innovative SAE-DNN structure capable of automatic health indicator (HI) construction from raw signals. HI curves constructed by SAE-DNN have much better fitness metrics than HI curves constructed from statistical parameters such as RMS, Kurtosis, Sknewness, etc. In the next stage, HI curves constructed from training degradation data are then used to train a long short-term memory recurrent neural network (LSTM-RNN). The LSTM-RNN is utilized as a RUL predictor since its special gates allow it to learn long-term dependencies even when the training data is limited. Model construction, verification, and comparison are performed on experimental reinforced concrete (RC) beam data. Experimental results indicates that LSTM-RNN generally estimates more accurate RULs of concrete beams than GRU-RNN and simple RNN with the average prediction error cycles was less than half compared to those of the simple RNN. [ABSTRACT FROM AUTHOR]

Reactive powder concrete (RPC) is a special type of concrete with a microstructure optimised by precise gradation of all particles in the mix to yield the maximum density. Therefore, RPC exhibits ultrahigh strength and durability. High-strength reinforcement has both high strength and good plastic deformation properties, so a combination of RPC and high-strength reinforcement can fully exploit their respective advantages. At present, there is little research on the shear capacity of beams made from RPC reinforced with high-strength steel, neither are there design guidelines for this type of structure. This paper reports on 32 full-scale shear tests of RPC beams containing high-strength steel reinforcement. The parameters affecting the shear capacity of this type of structure were studied and the major failure modes due to shear were identified. [ABSTRACT FROM AUTHOR]

Concrete structures in cold climates are susceptible to freeze-thaw (f-t) damage, which could lead to structural deterioration and stability issues. Accurate assessment of such damage is crucial for effective maintenance and repair strategies. However, current methods for evaluating concrete f-t damage rely on tedious testing procedures that lack automation and real-time capabilities, potentially delaying the repair process. This study proposes an automatic method to assess f-t damage in concrete by combining piezoelectric-based active sensing and deep learning (DL). Firstly, concrete beams with two different force states were prepared and subjected to different f-t cycles, during which measurements including surface characteristics, mass loss, dynamic elastic modulus and stress wave were performed. The relationship between concrete f-t damage evolution and stress wave signal variation was investigated. The collected signals were then converted into time-frequency maps using continuous wavelet transform (CWT), thereby establishing a CWT image-based dataset. More importantly, an innovative DL model (DSC-ACGRU) that integrates depth-wise separable convolution (DSC), convolutional gated recurrent unit (ConvGRU) and attention mechanism (AM) was developed to automatically extract damage-sensitive feature from CWT images and ultimately predict the degree of concrete f-t damage. Finally, the performances of the proposed DSC-ACGRU model were experimentally evaluated and compared with five machine/deep learning methods. The results show that the proposed model can rapidly and accurately assess the f-t damage degree in concrete and outperforms other learning algorithms, which is significant for identifying potential hazards and repairing damaged concrete. • An automatic method is proposed to assess concrete freeze-thaw damage using active sensing and deep learning techniques. • Stress wave signals were measured from concrete beams exposed to different f-t cycles using the active sensing approach. • A novel DL model was developed to automatically predict the degree of freeze-thaw damage from the time-frequency maps. • The feasibility of the proposed method in assessment of concrete freeze-thaw damage was experimentally verified. [ABSTRACT FROM AUTHOR]

When a partially exposed reinforced concrete beam deforms under tensile loading on reinforcements, the load-carrying capacity of the exposed reinforced concrete beam will significantly change, as the deformation of the exposed reinforcement bars and concrete do not follow a harmonising relationship. In this paper, the load-carrying capacity of a partially exposed reinforced concrete beam was investigated. By analysing a large quantity of test data, the changing patterns of the load-carrying capacity were obtained and two typical failure modes of the exposed reinforcement concrete were summarised. In the study, finite-element software was employed to simulate the test results. The simulated values were consistent with the test results. An extensive analysis of the influencing factors using a finite-element method was conducted. The length of the exposed reinforcement and the reinforcement ratio were considered as the controlling variables to obtain the changing failure modes of the exposed reinforced concrete beam. The analytical results confirmed the conclusions of a previous analysis. [ABSTRACT FROM AUTHOR]

This paper presents both experimental and analytical research results for predicting the enhancement of the flexural capacity of reinforced concrete (r.c.) beams strengthened in flexure with an innovative system based on the use of fabric reinforced cementitious matrix (FRCM). The patented system, called FRCM-U-Wrap Joist Tech provides a new methodology for beam strengthening capable of generating a higher internal couple of the cross section with no incisive change of the element weight. Experimental evidence gives back a 100% of increase in flexural strength than the non-reinforced beam. Analytical prediction shows a good accordance with the experimental data. The proposed strengthening system seems to be more effectiveness than the beam strengthened by means of traditional technology consisting in externally bonding the fibers directed to the beam intrados. [ABSTRACT FROM AUTHOR]

Lucinda Jetty was one of the first concrete structures in Australia to be identified with alkali–silica reaction (ASR). The prestressed concrete girders underwent cracking soon after construction and have been the subject of detailed investigations and monitoring since the late 1980s. The atmospherically exposed jetty roadway girders still show adequate serviceability, despite suffering from ASR. However, the girders at the jetty abutment are subject to constant seawater splash and have recently been found to have extensive corrosion of prestressing strands and stirrups, in addition to a higher degree of ASR damage. This paper examines the long-term performance of ASR-affected prestressed concrete in an aggressive marine environment and the interrelationships between ASR and corrosion. [ABSTRACT FROM AUTHOR]

A new reliability analysis approach for the flexural capacity of post-fire reinforced concrete (RC) beams retrofitted with carbon-fibre-reinforced polymers/plastics (CFRPs) is proposed. In this approach, the thermal parameters of RC beams are first determined to enable heat transfer analysis in Abaqus. Based on the thermal response obtained from the heat transfer analysis, a section method is used to calculate the post-fire residual flexural capacity of RC beams. Reliability analysis of the beams retrofitted with CFRPs is subsequently performed using the Monte Carlo method. The effects of fire exposure time, concrete cover thickness and CFRP usage on the reliability of the flexural capacity of RC beams after fire exposure were studied. This new approach was found to be accurate and effective. It provides an effective reliable model for the evaluation of the mechanical properties of post-fire RC beams strengthened with CFRPs. [ABSTRACT FROM AUTHOR]

Acoustic emission source localization is a promising monitoring technique for concrete structures. However, the accuracy of acoustic emission source localization is influenced by many factors, such as the presence of cracks, which are commonly observed in existing reinforced concrete structures. In this article, the acoustic emission source localization is evaluated using a numerical model with a total number of 11,827,200 independent simulated tests. In this work, the investigated influential factors include the presence of cracks, arrival time picking error, and senor layout. The accuracy of source localization is quantified by the characteristic error defined in this article. Using the proposed wave propagation properties, a relatively stable characteristic error of 150 mm is estimated in the detection zone with the maximum sensor spacing less than 1 m. The evaluation approach and simulated characteristic error are validated experimentally by comparing the 200 manually generated signals using hammer hits on a cracked concrete beam. [ABSTRACT FROM AUTHOR]

Precast segmental concrete beams (PSBs) prestressed with external tendons have become increasingly popular. This type of structure takes advantage of both the segmental construction method and the external prestressing technique. However, corrosion of steel tendons is still a great concern, which might increase the lifecycle costs of the structure. This study presents an experimental investigation into the use of carbon fiber–reinforced polymer (CFRP) tendons as an alternative to steel tendons for segmental concrete beams to mitigate the corrosion problems. To the best of the authors' knowledge, this is the first study using CFRP tendons to externally prestress segmental concrete beams. Four large-scale, T-shaped segmental concrete beams with different types of joints and tendon materials (steel/CFRP tendons) were built and cyclically tested under four-point loading. The test results show that CFRP tendons can replace steel tendons in segmental concrete beams as an external prestressing material. All the tested beams exhibited excellent performance regarding load-carrying capacity and ductility. The type of joint had an insignificant effect on the overall flexural behavior of the beams. After the joints opened, the beams with epoxy-coated joints behaved similarly to the beams with dry joints. The beams with CFRP tendons exhibited nonlinear behavior after the opening of joints; however, the level of nonlinearity was much less than that of the beams with steel tendons. Steel tendons achieved very high stresses at the ultimate stage, which were approximately 94% of their ultimate tensile strength. However, CFRP tendons ruptured at quite low stresses, which were approximately 78% of their nominal breaking strength on average. Finally, all the existing models examined in this study predict the tendon stress and the ultimate load of the beams with steel tendons well, but they encounter large scatter for the prediction of the tendons' stress and strength of the beams with CFRP tendons. [ABSTRACT FROM AUTHOR]

An experimentally based programme was conducted to assess the influence of heterogeneity on the long-term deflection of reinforced concrete (RC) elements with compression reinforcement and low-shrinkage concrete. These two structural measures are usually employed by designers to mitigate deflection of concrete beams, slabs and bridge decks due to creep and shrinkage effects. Control of creep and shrinkage deflections is important for successful design of concrete elements as the deflections influence their sizing and thus the associated costs. A 5 year experimental study was undertaken to address the most common alternative design approaches to alleviate long-term deflections of concrete. These included variable reinforcement ratios within the compressive zone, variable tensile reinforcement ratios, low-shrinkage concrete within the compressive zone and a combination of these measures. In total, 12 cantilever beam specimens were tested in the laboratory under controlled environmental conditions, supported by a time-dependent finite-element model. Both numerical and experimental results showed RC beam deflection reductions of up to 85% could be achieved when both compressive reinforcement and low-shrinkage concrete were employed. [ABSTRACT FROM AUTHOR]

Shear capacity is an important strength parameter required in the design of concrete flexural members; its reliable estimation is one of the important requirements of the design process. However, unlike other mechanical properties of concrete, the shear capacity of concrete beams is a complex phenomenon. The inclusion of steel fibers in concrete further adds complexity to the shear capacity determination, albeit with an enhancement of the shear capacity. In the past, efforts have been made to model the shear response of steel fiber-reinforced concrete (SFRC) members, mostly in the form of empirical relations derived from the results of experimental studies. A theoretical formulation is presented herein to predict the shear capacity of the SFRC rectangular beams without web reinforcement. Its efficacy is also checked using results computed from available design guidelines, empirical relations, and experimental test data. A good correlation is found between the predicted and the available test results. [ABSTRACT FROM AUTHOR]

An improved analytical model to predict the ultimate shear capacity of a self-consolidating concrete (SCC) flexural member is presented. SCC behaves differently to normal concrete because of its unique composition and mix proportions, which alter the shear resisting mechanisms in the member. SCC has found a wide range of applications due to its excellent deformability and high resistance to segregation and bleeding, but the lack of an adequate model that could help analysts predict the shear capacity of SCC beams is one of the main barriers to its acceptance in routine design practice. The model presented in this paper was developed considering all the factors that influence the shear capacity of SCC beams. The test results of an experimental study conducted to validate the accuracy of the proposed model are also provided in this paper; the model's efficacy was also checked using test results reported by other researchers. The results predicted by the model showed good agreement with the experimental test data. [ABSTRACT FROM AUTHOR]

This article describes an experimental program developed to study the influence of longitudinal prestress on the behaviour of high-strength concrete hollow beams under pure torsion. The pre-cracking, the post-cracking and the ultimate behaviour are analysed. Three tests were carried out on large hollow high-strength concrete beams with similar concrete strength. The variable studied was the level of longitudinal uniform prestress. Some important conclusions on different aspects of the beams' behaviour are presented. These conclusions, considered important for the design of box bridges, include the influence of the level of prestress in the cracking and ultimate behaviour. [ABSTRACT FROM AUTHOR]

This research presents the general design of a three-tower, self-anchored suspension bridge with a concrete stiffening girder based on practical engineering. The finite-element method is adopted to explore the structural behaviour of a bridge affected by shrinkage and creep of the concrete stiffening girder. The results show that shrinkage and creep of the concrete stiffening girder have a major effect on the mechanical behaviour of the side towers and stiffening girder. A new main cable system consisting of a prefabricated parallel wire strand (PPWS) cable with a polyethylene jacket and cold-cast anchorage is proposed to allow the main cables to be tensioned and the bridge cable force to be adjusted at any time. The experimental results of the PPWS cable show that the design and manufacture of the largest cable in China are safe and reliable. Moreover, the numerical simulation results for a new cable clamp connecting two main cables to a single hanger indicate that its design is reasonable. Furthermore, the anti-corrosive properties of the special cable system are investigated. The behaviour results as well as some key design technologies of this bridge style in the study provide valuable knowledge for its future application. [ABSTRACT FROM AUTHOR]

The composite T-beams investigated in this study consisted of precast concrete beams, precast concrete slabs and cast-in-place (CIP) slabs. Improvement measures were adopted in two types of the composite T-beams: additional tie bars located in semi-circular grooves were added for strengthening the connection of the precast concrete slabs and an inverted T-shape precast concrete beam was used for strengthening the flexural stiffness of precast beams. Nine full-scale tests were conducted under low reversed cyclic loading and positive and negative monotonic loading. The results showed that the composite T-beams failed in a flexural pattern that was similar to that of the control CIP T-beams. All the T-beams exhibited good energy dissipation capacity and small slip was measured in the composite T-beams. The flexural strength of the composite T-beams was about 7·5% lower than that of the CIP T-beams. The curvature ductility of the composite T-beams was more than 4·0 and about 13% lower than that of the CIP T-beams. Due to cumulative damage, the flexural strength and curvature ductility of all the T-beams under cyclic loading was about 30% and 40% lower than that under monotonic loading, respectively. The improvement measures used in this work were effective at ensuring good performance of composite T-beams. [ABSTRACT FROM AUTHOR]

The use of steel-fibre-reinforced concrete, mainly due to its improved mechanical characteristics beyond cracking, has been increasing recently. A particular purpose of using steel fibres is to enhance the shear characteristics of reinforced concrete beams against a brittle shear failure. While a considerable amount of research on the shear behaviour of steel-fibre-reinforced concrete beams without web reinforcement has been conducted, the studies on the shear behaviour of such beams with web reinforcement are still limited. In this study, an experimental programme aiming to examine the effects of steel fibres on the shear behaviour of reinforced concrete beams with web reinforcement was carried out. A total of nine beams having various amounts of steel fibre and web reinforcement were tested under three-point loading. In addition to the experimental study, a number of equations for predicting the shear strength of steel-fibre-reinforced concrete beams with web reinforcement were assessed by using a limited number of beams available in the literature. [ABSTRACT FROM AUTHOR]

There is a lack of sufficient information on the assessment of stress in unbonded tendons at ultimate in continuous post-tensioned members. Although many investigations have been conducted on simply supported members, few studies have focused on continuous members, particularly strengthened ones. An investigation into the stress in unbonded post-tensioned tendons at ultimate in continuous I-beams externally strengthened with carbon-fibre-reinforced polymer sheets is described, with special emphasis on the effects of non-prestressed steel and the implementation of ultrahigh-strength self-compacting concrete. Six two-span 9 m I-beams were constructed, monitored and tested until failure. Finite-element analysis (FEA) was carried out to analyse the ultimate stress in the tendons (fps) and generate the responses of non-strengthened and strengthened beams. The test results were compared with prediction equations proposed in design standards and other previous studies. The tendon stress approached the point of yielding at the onset of failure for the two groups of beams. This is an important finding, resulting in higher moment redistribution and ductility demands for such members. The FEA accurately predicted fps and was applicable to both non-strengthened and strengthened beams. The code equations were found to provide fps values for practical design on the safe side. [ABSTRACT FROM AUTHOR]

This study proposes a framework for predicting the remaining useful lifetime (RUL) of concrete structures using acoustic emission (AE) data. This framework presents two primary contributions: state indicator (SI) construction based on the Mann-Whitney U test (MWUT) and RUL prognosis using the damage accumulation indicator (DA) calculated from the SIs. The proposed indicators display an excellent description of the instantaneous and accumulated damage to the specimen, respectively. In the first stage, a deep neural network (DNN)-based constructor learns how to compute the SIs using raw AE data with MWUT-based SIs as training labels. The proposed SIs represent the instantaneous damage sustained in a time-step by highlighting the difference in the AE activity between the data of an unknown state from this time-step and a reference normal working condition. Through the aggregation of the SI values over time, a DA can be obtained, which represents the accumulation of damage in the time steps from the beginning to the time of inspection. Given a partial DA curve as the input, a prognosis model based on the gated recurrent unit (GRU) learns to predict the future DA values, from which RUL can be derived in the second stage. To evaluate the proposed method, multiple reinforced concrete beams (RCBs) were loaded under a four-point bending test scenario to collect AE data throughout their lifetimes. The results obtained from the validation show that the proposed SI can provide meaningful insight into the concrete structure's deterioration in comparison to the other indicators constructed from statistical features. Furthermore, the GRU-based prognosis model also outperforms reference methods based on recurrent neural networks (RNNs) and long short-term memory (LSTM) with a significantly smaller prediction error. [ABSTRACT FROM AUTHOR]

Wrapping is one of the effective ways of strengthening concrete elements. Several researchers have reported on the effectiveness of wrappings made from glass-fibre-reinforced polymers and carbon-fibre-reinforced polymers for improving the strength of concrete elements. Wrapping on three sides (‘U-wrapping’) is an effective method for enhancing the strength of beams supporting slabs, but scant literature is available on the strength enhancement of ‘U-wrapped’ concrete elements subjected to torsional loads. In the investigation reported in this paper, an attempt was made to quantify the improvement in the twist of U-wrapped rectangular concrete members subjected to torsional loads. Ferrocement was used as the wrapping material. Beams were cast with different amounts of reinforcement in the core and different wrapping portions, and the core concrete grade and wrapping mortar strength were also varied. The wrapped beams were analysed with the help of MARS software. An analytical model was subsequently developed to predict the secant stiffness at cracking torque (SSCT) using skew bending theory incorporating material properties. The model predictions for SSCT were found to be in good agreement with experimental test results. [ABSTRACT FROM AUTHOR]

This paper presents the results of eight seismic performance tests on end-perforated reinforced concrete beams strengthened with carbon-fibre-reinforced polymer sheets. The beams had different sizes of perforations and strengthening arrangements and were subjected to hybrid load–displacement control loading conditions. The ultimate load resistance, hysteretic performance, energy dissipation capability, ductility and stiffness degradation of the beams with and without strengthening were investigated. The test results show that the beams strengthened with polymer have better seismic performance, and that beam perforation size has a significant influence on seismic behaviour. An increase of hole diameter considerably decreases the hysteresis performance, energy dissipation capacity and ductility of the beams. [ABSTRACT FROM AUTHOR]

Non-linear finite-element analyses were performed to model the shear behaviour of deep beams with high-strength reinforcement and grade-60 conventional reinforcement, without stirrups. The FE model was compared with experimental results from recent tests of deep concrete beams reinforced with both types of reinforcement and loaded until failure. A detailed comparative study of the FE and experimental results is presented, which demonstrates the capability of the analytical model to describe the observed experimental behaviour. The shear behaviour of beams reinforced with high-strength steel (HSS) was compared with that of beams reinforced with grade-60 steel to demonstrate the benefits of using high-strength reinforcement. The shear design provisions of current codes and mechanics-based models were also compared with the results from the analytical model. The findings of the study showed that diagonal shear cracking strength is independent of the type of reinforcement, while beams reinforced with HSS exhibited higher post-cracking shear strength than beams with conventional reinforcement. Strut-and-tie modelling is recommended for the design of deep beams reinforced with HSS since this method accounts for high strains in reinforcement and accounts for large-size effects. The current code provisions are suitable for slender beams regardless of type of reinforcement. [ABSTRACT FROM AUTHOR]

The feasibility of using a carbon nanotube/cement composite as a crack sensor for concrete structures is evaluated. First, the relationship between the crack width and electrical conductivity of the composite material was investigated. Then, this analysis was repeated for the composite embedded in reinforced mortar beams, using three-point flexural loading. A conductivity model for the cracked composite was introduced and compared with experimental results. In addition, to evaluate whether monitoring was feasible under the conditions of crack closure by external loading, the cracked mortar beam was compressed along the vertical direction with respect to the crack and the conductivity of the composites embedded in the beam was measured. The conductivity of the composite decreased with increasing crack width and its reliability could be improved by increasing its original conductivity. [ABSTRACT FROM AUTHOR]

In many developing countries, existing reinforced-concrete buildings were originally designed to resist mainly gravity loads, and are vulnerable to earthquake loads. In particular, exterior beam-column connections might show brittle structural behaviour due to the discontinuity of the beams, weak confinement of concrete inside the connections, and unreliable load-transferring mechanism dependent on concrete tensile strength. The aim of this study is to investigate experimentally the seismic performance of six half-scale test specimens simulating exterior beam-column connections in existing reinforced-concrete buildings with non-seismic reinforcement details. The main test parameters of this study include the longitudinal reinforcement ratio of concrete beams and configurations of steel reinforcement inside the connections. The test results show that the structural performances of the beam-column connections (e.g. failure mode, load-drift ratio relationship, shear deformation and energy dissipation of the connections) are mainly affected by the amount of longitudinal reinforcing bars in beams. In addition, the existence of transverse hoops inside the connections slightly increases the lateral load-carrying capacity and reduces the shear deformation in the connections. [ABSTRACT FROM AUTHOR]

Concrete beams with notched ends are commonly used in construction. The strut and tie model is a familiar design method used for understanding such geometric discontinuities in concrete structures. The effects of applying carbon fibre-reinforced polymer laminates to strengthen the webs of notched-end concrete beams were studied in this work. To this end, 12 beams with two levels of shear reinforcement were cast and the effect of web strengthening the notched ends with polymers was studied. It was found that the beams with polymer strengthening showed up to 17% more load-carrying capacity than respective control beams without polymer strengthening. Furthermore, carbon fibre-reinforced polymer strengthening applied at an orientation of 45° was found to be more effective than that at 90°. Failure loads for both orientations were up to 9% higher than those of the respective control specimens. Retrofitting failed beams with polymer web strengthening resulted in the achievement of 90% of the failure load in comparison with the respective control beams. [ABSTRACT FROM AUTHOR]

A major highway underbridge has been subjected to a complex fatigue assessment to determine its present and future serviceability. Similar to approximately 100 other structures within Great Britain, reinforced-concrete deck hinge joints are positioned within longitudinal beams providing rotational flexibility. Concerns were raised as to the fatigue condition of the hinge joints considering repetitive rotations applied by traffic loading and pitting corrosion found on reinforcement bars. This paper describes the assessment work and associated research relating to this structure including finite-element analysis, laboratory models and space frame modelling of the structure. Comments are made on the applicability of current codes of practice for fatigue assessment of reinforced-concrete deck hinge joints. [ABSTRACT FROM AUTHOR]

This paper looks at the beneficial effects of geometric arching from haunches, web continuity and compressive membrane action in the design and assessment of box girder top slabs. The paper initially reviews tests relevant to arching action in box girders and then analyses recent tests on box girder slab strips. Finally, using the assessment of an existing box girder bridge as an example, a series of computer models is developed to illustrate a method for transverse analysis of a box girder top slab in which some of these arching effects can be utilised. For the analysis of tests and the assessment example, a three-dimensional frame model that considers the in-plane strength enhancement of the restrained slab is used. This simplified approach was verified by finite-element modelling and the results show good agreement. The analysis methods including arching action significantly reduce the required amount of reinforcement for the deck slab. The paper concludes that arching action from geometrical arching of haunches and frame action are significant and must be considered for any accurate analysis at both serviceability and ultimate limit states. It is also concluded that compressive membrane action may occur and can be used in the design and assessment of box girder structures within certain geometric parameters. [ABSTRACT FROM AUTHOR]