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The near surface mounted (NSM) carbon fiber-reinforced polymer (CFRP) strengthening technique, combined with gradually anchored prestressed technique, is utilized to delay the occurrence of concrete cover separation (CCS) and enhance the ductility of reinforced concrete beams. The load-carrying capacity of fully prestressed beams and gradually prestressed beams are investigated under both static and fatigue loading conditions. The study focused on the effect of gradient prestress on flexural behavior of strengthened beams, analyzed the failure mode, characteristic load, ductility, and stress distribution at CFRP-concrete interface under both prestress and load conditions. Results indicate that gradually prestressed beams outperform fully prestressed ones in restraining crack development, delaying yield of tensile reinforcement, improving bearing capacity and avoiding CCS failure. Bearing capacity was significantly increased by up to 35.48%, while ductility was greatly improved by 100.33% with ultimate deflection for gradually prestressed beams compared to fully prestressed ones. The fatigue life of gradually prestressed beams, which experienced a transition from CCS failure mode to fatigue fracture of tensile reinforcement, was significantly extended. Additionally, their ductility at failure was also greatly enhanced, thus confirming the effectiveness of gradually prestressed NSM CFRP strengthening technique. [ABSTRACT FROM AUTHOR]

According to ACI 318-19(SI), in the plastic hinge zone of RC beams, the longitudinal reinforcement at each corner and every other longitudinal reinforcement must be enclosed by the corner of the closed hoop or the hooks of crossties. However, in RC construction practice, the longitudinal reinforcement of RC beams is densely arranged, making construction difficult. In this study, four large RC beam specimens were designed and fabricated to conduct experiments to verify the effect of hoop spacing and crosstie configuration on the cyclic performance of reinforced concrete beams. It is found that: (1) The crosstie configuration with seismic hook engaging the longitudinal reinforcement at the bottom is recommended and that during construction, within the range of twice the beam depth from the RC column outer face, the bottom and side formwork should be completed after the crossties are assembled, which should solve the problem of difficult construction. (2) The transverse reinforcement spacing between 4 and 6 times the smallest longitudinal reinforcement diameter of RC beams may have no significant effect on the cyclic performance of RC beams. (3) The requirement that in the plastic hinge zone of RC beams, every corner and alternate longitudinal bar on the perimeter must have lateral support provided by the corner of a tie or crosstie in ACI 318-19(SI) may not have a major impact on the cyclic performance of the RC beam. (4) The ultimate drift angle of each specimen in the negative direction was between 4.3% rad and 4.5% rad; thus, all the specimens satisfied the ACI requirement. However, the cyclic performance (plasticity rotation angle) of all specimens basically did not meet the requirement of 3.0% rad for earthquake-resistant structures. [ABSTRACT FROM AUTHOR]

This study solves the following tasks: a comparative analysis of theoretical, computer, and experimental data on the bending of experimental beams is given, the influence of various forms of reinforcement on the strength and stability of beams with a corrugated web is determined; the deformability of a beam with a corrugated web with perforations and without perforations in the elastic and elastic-plastic stage is studied. Experimental studies of models have allowed establishing the main characteristics of the load-bearing capacity, the features of the loss of stability of shelves and corrugated webs with various methods of reinforcing perforations. The given test results showed the necessity and economic feasibility of the work carried out to identify the optimal ways of reinforcing perforations, to meet the requirements of technologists for passing equipment within the construction height of the beams, reducing the consumption of steel for their reinforcement and reducing the complexity of production. The conducted mathematical modeling, laboratory tests, and the performed dispersion analysis allow the study to draw conclusions about the effectiveness of the improved BGS-3 and BGS-5 models and about the need to develop recommendations for introducing two proposed options for reinforcing the perforations of the BGS-3 and BGS-5 models. [ABSTRACT FROM AUTHOR]

Creating the openings in the existing reinforced concrete (RC) beams causes sudden deterioration, especially in the shear zone. This study investigates the effectiveness of a novel strengthening technology using externally reinforced fibre-reinforced polymer (FRP) strips in groves (EBRIG) on the shear behaviour of RC beams, compares it to that of externally reinforced (EBR) strips, and uses hybridisation between them to address the weakness brought on by the presence of an opening in the shear zone. Also, an innovative anchorage mechanism is suggested and studied to postpone the beginning of the strengthening system's debonding. The strengthening material used in this research is glass fibre-reinforced polymers (GFRPs). For this study, 11 RC beams with an opening and a control beam without an opening, each measuring 120 × 300 × 2600 mm in size, were cast and subjected to the four-point loading test. All test beams had the same geometry and reinforcement details. The effect of the following parameters was investigated in this study: the dimension of the opening (square '150 × 150' or rectangle '100 × 300' mm), the strengthening technique used (externally bonded reinforcement [EBR], EBRIG and hybrid technique 'EBRIG + EBR') and the wrapping configuration of the strengthening (fully warped strips or U-shaped sheets with anchors). All techniques used raised the efficiency of shear resistance to approximate the fading effect of the opening, especially the technique of hybridising EBRIG and EBR. All strengthened beams showed an increase in the ultimate shear capacity ranging from 74% to 142% compared with the reference beams with the opening. The EBRIG technique shows numerous advantages over the EB system and can employ the strength of FRP materials. It also deals with the problems of weather factors that were facing EBR, and this is because of the covering that protects in the EBRIG technique. The technique to hybridize EBRIG and EBR was more effective at withstanding shear. [ABSTRACT FROM AUTHOR]

The probabilistic evaluation of the capacity and response of structural systems is often done by probabilistic simulation. This approach relies on a considerable number of deterministic analyses to obtain an accurate estimation of the desired statistical characteristics. However, the need of performing a large number of analyses hinders the application of probabilistic simulation in practice, especially when the deterministic calculation of the structural response is computationally expensive in itself (e.g. nonlinear finite element analysis). To increase the appeal of probabilistic simulation, the number of analyses should be very small (i.e. ten or less). This study shows how different sampling techniques can be adopted to select a very small sample subset of analyses to be run, and how they can yield accurate results in estimating the shear capacity of prestressed reinforced concrete beams. Based on the results of the study, the Fractile Based Sampling (FBS) method emerges as a more promising sampling strategy than other sampling techniques, like Latin Hypercube Sampling (LHS). For the same small number of samples, the results show that FBS is preferable over LHS and other sampling techniques for capturing both the general distribution of the response and the tails of the distribution, which shows its usefulness in assessing probability of failure and reliability. [ABSTRACT FROM AUTHOR]

The Bouc--Wen model and subsequent improvements are widely used to simulate the hysteretic behaviour of mechanical elements subjected to load reversals. Within such class of analytical models, an enhanced version is proposed. Elaboration is simple, nevertheless it features: (i) convenient parameters to govern deteriorating stiffness and strength, (ii) asymmetry, and (iii) versatile pinching. The latter capability is necessary for variously pinched loops observed in the experimental tests on reinforcedconcrete elements. Relevant parameters have physical meaning, consistent with phenomenological application of the model at the member scale. Depending on such parameters, the reloading branch can be made initially concave, convex, or almost linear. The proposed model is validated by simulation of cyclic and pseudo-dynamic experimental test results available in the literature. An asymmetric Tbeam, and code-conforming and substandard columns failing under either flexure or shear, are considered. The error on force is normally distributed with mean value less than 4% and standard deviation less than 9% of the experimental strength. The greatest errors on final energy and residual displacement are on the order of 20% with severe damage. The proposed model proves to be effective to simulate the hysteretic response for engineering performance assessment of building and bridge elements. [ABSTRACT FROM AUTHOR]

Recycling rubber and/or steel fiber components of waste tires in construction applications is a venue for maximizing the recycling rate of these items. Additionally, it supports the move towards producing sustainable construction materials and conserving natural resources. Previous research explored the viability of employing recycled waste rubber particles as an alternative for natural aggregate. Despite the adverse effect of rubber on the mechanical properties of concrete (e.g., lower compressive strength), it produces several advantages, including excellent dynamic and ductility properties, which can be utilized in structural members critical to dynamic loads, e.g., blasts, earthquakes, and impacts. In an effort to expand the adoption of waste rubber in concrete beams and to eliminate key concerns associated with the degradation of their flexural behavior, the functionally graded (FG) beams concept was utilized. The present investigation comprised the testing of five beams using a four-point bending configuration. Plain concrete, rubberized concrete (RuC), and steel-fiber reinforced rubberized concrete (SFRRuC) beams were cast along with FG beams arranged in two layers. The top layer of the FG beams comprised plain concrete, while the bottom layer consisted of RuC or SFRRuC. Experimental findings indicated that the flexural behavior of the FG beam with layers of SFRRuC and plain concrete exceeded the flexural strength, displacement ductility ratio, and toughness performances of the plain concrete beam by 9.9%, 12.9%, and 24.4%, respectively. The moment–curvature relationship was also predicted for the tested beam and showed an excellent match with the experimentally measured relationship. [ABSTRACT FROM AUTHOR]

This study presents a comprehensive investigation into the mechanical properties of Basic Magnesium Sulfate Cement Concrete (BMSC) in comparison to Ordinary Portland Cement Concrete (OPC) within reinforced concrete components. The main objective is to evaluate BMSC's applicability for practical engineering purposes, with a focus on its with early high strength, improved toughness, and superior crack resistance compared to conventional concrete. Experimental procedures involved fabricating beam specimens using OPC concrete with a C40 strength grade, alongside BMSC beams with varying strength grades (C30, C40, and C50). These specimens underwent bending resistance tests to analyze crack patterns and mechanical characteristics. The findings reveal that BMSC beams demonstrate enhanced bending and tensile properties at equivalent strength grades compared to OPC beams. Particularly, cracking mainly occurred at the mid-span region of BMSC beams, characterized by narrower cracks, indicating superior crack resistance. However, it was noted that the toughness of BMSC beams decreases as the strength grade increases. The maximum mid-span deflection of the BMSC test beam was smaller than that of the OPC test beam, which was 3.8 mm and 2.6 mm, respectively. The maximum crack width of the OPC beam was 4.7 times that of the BMSC beam. To facilitate practical implementation, the study developed calculation models for estimating the crack bending distance and ultimate bending distance in BMSC beams, offering valuable tools for engineering design and optimization. Overall, this research provides significant insights into the mechanical behavior of BMSC, presenting potential advantages for structural engineering applications. [ABSTRACT FROM AUTHOR]

In order to evaluate the structural performance of repaired RC beams with partially debonded longitudinal rebars, structural experiments were conducted. In the experiments, real-scale and half-scale RC beam specimens underwent cyclic loading of 1.0% or less in terms of deformation angle, repaired with epoxy resin injection method, and multiple cyclic loading again. As a result of the experiments, damage was suppressed in specimens with partially debonded longitudinal rebars even after repairs. Further, the specimens with partially debonded longitudinal rebars exhibited high recovery of initial stiffness after repair compared to the specimen with bonded longitudinal rebars. In addition, from study of the costs required to repair cracks, it was confirmed that RC beams with partially debonded longitudinal rebars used smaller quantities of materials used for repairs and could potentially reduce repair cost by approximately 50% compared to RC beams having standard bonding properties. [ABSTRACT FROM AUTHOR]

In recent years, assembled bridges have become widely utilized in bridge construction, raising concerns about durability-related bridge diseases over time. These issues significantly impact the fatigue life of assembled bridges, necessitating an in-depth exploration of their fatigue performance. While existing research primarily concentrates on the transverse connection of multiple longitudinal beams, there is a notable dearth of studies on longitudinal precast segmental assembled bridges. This paper addresses this gap by establishing a fatigue benchmark finite element model for segmental assembled concrete beams, building upon existing experiments. The study employs numerical simulation to analyze the entire fatigue process, examining stress distribution, damage development, and considering the influence of reinforcement corrosion. Furthermore, a fatigue life prediction method, based on fatigue residual strength (R), is proposed for predicting the fatigue life (N) of concrete in precast segmental assembled beams. Results reveal that prestressed and ordinary reinforcements experience increasing stress with loading cycles, peaking around 100,000 cycles. Throughout fatigue loading, compressive stress in concrete remains low, preventing fatigue compression failure. However, tensile stress near joints gradually rises, initiating cracks at the mid-span beam's bottom. With continued cyclic loading, these cracks propagate towards the loading point. The upper and lower limits of fatigue life predicted by the fatigue life prediction method closely align with the compressive fatigue test values of concrete, proposed fatigue life prediction method is efficient and accurate. [ABSTRACT FROM AUTHOR]

Prestressed concrete (PC) box girder is an innovative structure that is widely used in large-span bridges. Under eccentric loads such as vehicles, PC girders are inevitably under combined bending and torsion. To study its bending-torsional behavior, a refined full-range analysis model based on the combined action softening truss model (CA-STM) was proposed, where a simple and effective solution procedure and failure criteria were provided. The equilibrium equation, initial estimation equation for torque, and material constitutive model were modified by considering the prestressing effect to improve the CA-STM. An optimized algorithm was also employed to simplify the solution procedure instead of the traditional trial-and-error method, thus increasing the solution rate and stability. The theoretical curves predicted from the improved CA-STM exhibited great agreement with the available experimental results, and the predicted cracking and ultimate loads were also close to the experimental values. Hence, the improved CA-STM can reasonably predict the full-range mechanical response and failure modes of PC box girders subjected to combined bending and torsion, which provides great support to the design evaluation of such bridges. [ABSTRACT FROM AUTHOR]

In this study, a high-strength bolted prefabricated concrete beam-column junction is presented, and the prefabricated concrete beam-column joint parts are put through eight quasi-static tests. The axial compression ratio and the steel plate hoop thickness were used in extended parameter research using finite element software to completely examine the seismic performance of the construction. According to the findings, this node's ductility coefficient ranges from 2.57 to 3.69, which is bigger than 3. The specimen loses part of its bearing capacity and constantly loses ductility as the axial compression ratio rises. The failure displacement of the specimen decreases with an increasing axial compression ratio, but the yield displacement of the specimen is very slightly affected by the axial compression ratio. This node has an excellent energy dissipation capacity despite having a low viscous damping coefficient between 0.2 and 0.4, and when the axial pressure ratio rises, the capacity grows in response to the elevated pressure. Despite this, the energy consumption of the beam-column member is not significantly affected by the steel plate hoop thickness. Additionally, according to the variable-angle truss-arch model and taking into account the representation of the truss-arch model under different conditions, this paper presents the equation for the shear load capacity of diagonal sections of prestressed high-strength spiral hoop-restrained concrete beams under various conditions. [ABSTRACT FROM AUTHOR]

Deviation of the flexural reinforcement spacing from code specifications appears to underly the cause of the loss of bond (LoB) between concrete and steel that preceded the unexpected collapse of the top-floor balcony of a building under service load conditions on 15 October 2021 in Athens. Although rare, LoB has also been identified as the cause of collapse of buildings under similar conditions in the UK and Canada. However, the codes of practice for reinforced concrete (RC) design neither make reference to the effect of LoB on structural behaviour, nor include LoB in the parameters that the formulae currently used for assessing load-carrying capacity are dependent on. In view of this, a description of the effect of LoB on the function of RC beams is provided in this paper and this description is used as the basis for the derivation of a formula linking LoB with load-carrying capacity. The validity of the proposed formula is verified using published experimental information on the subject. The proposed formula is used for the structural assessment of the collapsed balcony, taking into account the design details, physical state and loading conditions of structural members similar to the one that collapsed. [ABSTRACT FROM AUTHOR]

In order to study the effect of high temperatures on the thermomechanical properties of reinforced concrete (RC) beams, fire and mechanical tests were carried out on four fully dimensioned simply supported beams. A numerical analysis model based on the measured information was developed, and validated through experimental tests and theoretical calculations. The effects of fire exposure time, different physical parameters and concrete spalling parameters on the thermodynamic properties were further analysed. The results show that the measured vibration frequencies exhibit a fluctuating trend of decay with increasing fire exposure time. The simulated frequency decays as a power function of fire exposure time. The frequency decreases with increasing span-to-height ratio and increases with section width, elasticity modulus of the concrete and reinforcement ratio. Cross-sectional temperature field is most significantly affected by spalling depth, and increases rapidly with an increase in this parameter. With the increase in spalling area ratio, the increase in the temperature field gradually becomes smaller. The effect of spalling area ratio was relatively stable after more than 15%. Flexural bearing capacity shows a linear trend of decrease with increase in spalling depth. With the increase in spalling area ratio, it shows a power function of the decreasing trend. [ABSTRACT FROM AUTHOR]

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

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]

Experimental study of reinforced concrete beams without stirrups under impact: performance evaluation and structural response Experiments on reinforced concrete beams without stirrups are often utilized as a simplified basis to calibrate numerical models of reinforced concrete slabs. This paper details an experimental study on the behavior of reinforced concrete beams without stirrups subjected to impact loading. For this study, the 11‐meter‐high drop tower at the Otto Mohr Laboratory of TU Dresden was used to accelerate a cylindrical impactor with a diameter of 100 mm. Compressed air accelerated the impactor to velocities between 2.7 m/s and 25.8 m/s. The impactor masses were 14.22 kg and 21.66 kg, respectively. Data on impactor and support forces, displacements, and accelerations were collected. Digital image correlation supplemented the measurements. The study revealed that the behavior of the beams exhibited different failure modes depending on the impactor velocity and mass. The shear cracks started to form at impactor velocities of approximately 11 m/s, corresponding to the lighter impactor's kinetic energy of 860 J. Furthermore, the formation of a punching cone near the loading point at impactor velocities of around 22 m/s was observed. These findings provide valuable insights for designing and thoroughly assessing the performance of shear‐deficient reinforced concrete beams under impact loading. The results serve as a foundation for enhancing the precision and reliability of numerical models, facilitating further investigations into complex structural systems. [ABSTRACT FROM AUTHOR]

Sustainable construction becomes a highly key topic in the construction sector owing to its benefits and advantages over economy, environment, and society. This study considers one such application of sustainable construction, rehabilitation of RC beams. Through such rehabilitation, it is possible to extend the life of existing concrete structures. A numerical analysis approach has been framed to study to this phenomenon. Total 10 criteria have been selected to evaluate the rehabilitation material alternatives on RC beams with ultra-high-performance concrete. 9 Alternative materials have been considered for rehabilitation of RC beams. DEMATEL-ANP and PROMETHEE has been used as a methodology in two phases, the first phase used DEMATEL-ANP to analyze the considered criteria and the second phase used PROMETHEE to evaluate the considered alternative materials based on the analyzed criteria. Finally, this study concludes with the effective rehabilitation material for RC beams with ultra-high-performance-concrete. The considered numerical framework can be adopted in various forms of similar or different applications. [ABSTRACT FROM AUTHOR]

This study investigated the flexural behavior of hollow concrete beams reinforced with GFRP bars with longitudinal openings of different sizes and shapes. A total of seven beams were tested, including two solid GFRP-RC beams, four hollow GFRP-RC beams with longitudinal holes accounting for between 6 and 15% of the total cross-sectional area, and one hollow conventional steel-RC beam with a longitudinal hole of 9% of the total area. The beams were tested in flexure, and the results in terms of cracking and the ultimate loads, strains in steel and concrete, and failure modes were reported. The circular cavity performed slightly better than the square cavity, with a 3.8% higher cracking load and 4.5% higher ultimate load for the same area and location. In addition, an analytical study of the flexural capacity of the hollow beams was developed. It was found that the proposed analytical model predicted the cracking and ultimate load of the tested hollow GFRP-RC beams with good agreement. Finally, a detailed parametric study was conducted to investigate the effects of several key factors, including the size and location of the holes, as well as the concrete grade and the reinforcement ratio. The results indicated that the position of the holes had a significant effect on the behavior of the hollow GFRP-RC beams. The parametric study showed that the compressive strength of the concrete was the most influential factor on the flexural capacity of the beams, while the GFRP reinforcement ratio had a minor effect on the cracking load. [ABSTRACT FROM AUTHOR]

High-strength concrete is extensively used in the construction industry due to its higher stiffness and modulus, but it is inherently brittle. In order to reduce its brittle behavior, steel fibers are being used to increase their application in the construction industry. In this experimental study, a fixed volume fraction (Vf = 1.5%) of steel fiber was used in the concrete, whereas the type of confinement (steel tube and carbon fiber-reinforced polymer CFRP strip) was varied. Five high-strength concrete beams with and without steel fibers strengthened with different confinements (steel sheet and CFRP) were cast and evaluated for flexural performance. (Four-point loading tests were done here.) Conventional steel was used for reinforcing concrete as it has the same lateral and longitudinal strengths. The high initial cost of steel tubes is compensated by eliminating the cost of formwork required for casting regular concrete members. For conventional reinforcement, a balanced steel ratio was used. All specimens were tested under monotonic loading. The tested structural elements showed good plasticity and increased flexural capacity. The improved ductility and energy absorption capacity of the members indicate their promising use in building structures. [ABSTRACT FROM AUTHOR]

This study investigates the effect of strengthening self-compacted concrete (SCC) beams using CFRP sheets on flexural behaviour subjected to repeated loads. During the experiment, six rectangular reinforced SCC beams were evaluated; two were reference beams without strengthening, while the remaining four were strengthened with CFRP sheets. The beam's length, depth, and width are 2100 mm, 300 mm, and 200 mm, respectively. A monotonic load was applied to one of the reference beams, while repeated loads were applied to the remaining (compression cyclic loads). The main parameters studied in this experimental work were the type of loading (monotonic and repeated), the positions of strengthening and the dimensions of CFRP sheets. The flexural behaviour of these beams was investigated through experimental examination by recording the ultimate load and maximum deflection. Meanwhile, the cracks' pattern and failure modes were observed. The findings of the present study demonstrated that the limited cycles of repeated loads have marginal effect on the flexural behaviour of the beams. This results in an ultimate load reduction of no more than 11%. It was also noted that SCC beams strengthened using CFRP sheets subjected to repeated loads significantly affected the flexural behaviour of these beams. Consequently, the ultimate load of the strengthened beams was improved by up to 18%. Besides, the maximum deflection of the strengthened SCC beams was reduced by 45% compared to those without strengthening. Using strengthening throughout the beams' entire width and length that are subjected to repeated loads improved their ultimate load to surpass that of non-strengthened beams under monotonic loads by as much as 7%. [ABSTRACT FROM AUTHOR]

The utilization of fiber-reinforced polymer (FRP) reinforcements in structural design is increasing due to their non-corrosive nature. However, the anisotropic features and linear elastic behavior of FRP rebars have led researchers to explore the use of hybrid combinations of FRP and steel reinforcements. Current codes and guidelines predominantly focus on the design of glass FRP (GFRP) reinforced structural elements, leaving a gap in incorporating the hybrid use of FRP-steel combinations and different types of FRP materials, such as carbon FRP (CFRP). This study conducted experimental investigations on concrete beams reinforced with GFRP, CFRP, and hybrid (GFRP-steel and CFRP-steel in combination) rebars, comparing the results with theoretical models. Ten full-scale beams were tested under monotonic loading. Test results revealed that existing codes overestimate GFRP reinforced beam displacements while underestimating CFRP reinforced beam displacements. A reduction factor is proposed for the effective moment of inertia expression given by ACI 440.11-22 to predict the deflections of CFRP reinforced and hybrid reinforced beams. The experimental data for CFRP and hybrid reinforced concrete beams align well with the predictions calculated using the proposed equations. [ABSTRACT FROM AUTHOR]

Concrete-filled steel tube (CFST) arch bridges have a high center of gravity and a substantial mass, resulting in a discernible seismic response. Consequently, long-span CFST arch bridges must retain exceptional seismic performance and appropriate seismic control design. In this study, the dynamic response and seismic performance of a unique swallow-type CFST arch bridge when subjected to longitudinal earthquake forces were analyzed using numerical simulation methods. The displacement and axial force response results and their laws of the key bridge components were obtained. Taking into account seismic checking calculations, two damping measures were proposed for the CFST arch bridge, as the relative displacement of the girder end exceeded the allowable value specified. The appropriate design parameters for viscous dampers and lead shear dampers were examined. Additionally, the seismic performance of these dampers was verified through a shaking table test using a 1:16 scale model. The findings indicated that when subjected to Wenchuan Wolong wave action, the relative displacement between the steel box girder and the concrete girder of the bridge was significantly larger, leading to girder end pounding. The limit values were surpassed by 32.5% and 50%, when subjected to the uniform and traveling wave excitations, respectively, thus indicating that the expansion joint was the most vulnerable component. Following the selection of optimal parameters for the dampers, the dampers exhibited the capability to mitigate seismic and pounding impacts. Long-span CFST arch bridges with dampers were found to effectively reduce the seismic response of the skewback strain and vault, as well as the relative displacement of the girder ends. Furthermore, the average maximum damping rates achieved by the viscous damper and the lead shear damper reached 44.9% and 44.6%, respectively. [ABSTRACT FROM AUTHOR]

This paper conducts modeling and vibration analysis of a spinning cylindrical shell attached with a beam, namely, an assembled cylindrical shell-beam structure, which is reinforced by graphene nanoplatelets (GPLs). The available performance attributes of the beam and cylindrical shell, determined by the Halpin-Tsai model together with the rule of mixture, are deemed to change continuously along their thickness directions. In accordance to the Euler-Bernoulli beam theory and the Donnell's shell theory, the Lagrange's equation is applied to obtain the coupled governing equations of the assembly. Besides, the substructure modal synthesis method is used to acquire vibration behaviors of the nanocomposite assembled shell-beam structure. The influences of the graphene nanoplatelet (GPL) distribution pattern, GPL weight fraction, length-to-width ratio and length-to-thickness ratio of GPLs, and spinning speed on the vibration performance of the assembled shell-beam structure. The findings could provide an important light on the design of coupled nanocomposite cylindrical shell-beam assembly for outstanding mechanical performance. [ABSTRACT FROM AUTHOR]

The lifespan of a reinforced concrete (RC) structure can be greatly influenced by the spatial variability of its material characteristics which, in particular, explains the observed or measured reduction of the tensile strength at first crack when the volume under tension increases. This paper discusses the ability of accounting for the spatial variability of the tensile strength of concrete in RC structures using a stochastic finite element (SFE) method based on random field simulations. In this work, the generation of random fields on the concrete tensile strength aims at computing the force corresponding to the first crack occurrence, and the reduced tensile strength of the structure. The method can be applied in particular to large‐sized structures, which show a pronounced size effect, for different types of loading. The method consists of, first, estimating the mean of the random field, using the analytical approach of the weakest link and localization method (WL 2A${2}_A$). Then, the discretized random field is defined on a particular 2D or 3D grid, and it is finally projected on the finite element mesh of the studied structure. The study of the parameters that influence the prediction of the cumulative density functions (CDFs) of the rupture force or the tensile strength is highlighted using experimental series of concrete beams having different volumes and subjected to 4‐point bending loading. Moreover, the SFE method is applied to a RC tie‐beam under tensile loading, characterized by a weak stress gradient, which complicates the prediction of crack positions. [ABSTRACT FROM AUTHOR]

The shear behaviour of fibre-reinforced polymer reinforced concrete (FRP-RC) beams without web reinforcement suffers from low strength, low stiffness, more brittleness and wide and quick propagated cracks. Fortunately, the addition of various types of fibres could improve most of these weaknesses. On the other hand, the shear strength prediction of FRP-RC beams with various types of fibres is one of the most complex cases in structural engineering applications. Developing generalised, precise and consistent prediction models are necessary and very limited. This paper investigates the impacts of various types of fibres on shear strength and presents proposing four new prediction models, utilising artificial neural networks and empirical nonlinear regression analysis, and modifying the combination of available models based on a collected database of 49 shear test results of FRP-RC members with various types of fibres. The comparison of the developed models with the available equations from the literature indicates that the developed models yielded excellent performance, great efficiency and a high level of accuracy over all other existing models. Additionally, the parametric study confirmed that all the developed models have great abilities to accurately predict the actual response of each parameter, in spite of its complexity, on the shear strength of FRP-reinforced fibrous concrete beams without stirrups. [ABSTRACT FROM AUTHOR]

Distortion deformation usually imposes a potential threat to bridge safety. In order to comprehensively understand the distortion effect on thin-walled ultra-high performance concrete (UHPC) box girders, an innovative approach encompassing the governing distortion differential equation is introduced in this study based on the general definition of distortion angle within the cross-section plane. The analytical results obtained from the proposed method are in accordance with those obtained from the energy method, and exhibit favorable agreement with experimental findings documented in the existing literature. Furthermore, a finite element model is developed on the ANSYS 2021 R1 software platform with the employment of a Shell 63 element. Numerical outcomes are also in good agreement with the experimental data, affirming the validity and reliability of the findings. In addition, parameter analysis results indicate that the distortion angle remains approximately constant at a location approximately 1/10 of the span from the mid-span cross-section of the box girder, regardless of changes in the span-to-depth ratio. Increasing the web thickness yields a notable reduction in the distortion effects, and decreasing the wall thickness can effectively mitigate the distortion-induced transverse bending moment. Compared with normal-strength concrete box girders, UHPC box girders can reduce the distortion angle within the span range, which is beneficial for maintaining the overall stability of the box girders. The outcomes obtained from this study yield engineers an enhanced understanding of distortion effect on the UHPC girder performance. [ABSTRACT FROM AUTHOR]

RC double-column medium height bents (DCMBs) are widely applied in the mountain areas as the substructure of highway bridges, and the two columns are normally connected by RC link beams to enhance the lateral stability. However, serious damage and/or large residual displacement were repeatedly observed in the DCMBs after many major earthquakes, which may make the bridges lose functionality and have to be demolished and rebuilt. In order to improve the seismic performance of the bridges, a novel self-centering variable friction dissipation brace (SCVFB) using SMA plates is developed to replace the traditional RC link beams in the DCMBs in this study. The mechanical properties of the shape memory alloy (SMA) plate were investigated experimentally. Then, the analytical model of the DCMBs with inverted-V SCVFBs (DCMB-SVFB) is built, and the corresponding design philosophies of the SCVFB in the DCMB are proposed based on the concept of structural fuse. Subsequently, the hysteretic behaviors of the DCMB-SCVFB in the transverse direction are analyzed, and the dynamic responses of the whole bridge under near-field ground motions are also investigated. For comparison, the seismic behaviors of the bridges with original bents (the bridges with and without link beams) and the bridges retrofitted with buckling restrained braces (BRBs) are also presented. The results show that the SCVFB has stable energy dissipation capability and excellent self-centering ability, even without the need of prestressing. Compared with the original bridge, the bridges with SCVFBs and BRBs are featured by higher strength, larger stiffness, better energy dissipation capacity, and less damage. In particular, the SCVFB can effectively reduce the residual displacement of the bridge and quickly restore the traffic capacity. [ABSTRACT FROM AUTHOR]

The reliability of corroded reinforced concrete (RC) structures relies on the accurate minimum cross-sectional area of corroded rebar. In this study, the accurate morphologies and self-magnetic flux leakage (SMFL) field strengths of twenty-eight non-uniformly corroded rebars were obtained using 3D structural light scanning and micromagnetic detection technologies, based on which three indices of the SMFL field variation ratio dH, the corrosion non-uniformity degree d S n , and the cross-sectional area ratio K0.25 are proposed. The statistical results show that the probability densities of d S n and K0.25 obey the Weibull distribution and Gamma distribution at the 95% confidence level, respectively, and their distribution parameters are linearly or inversely proportional to dH. The probability density distribution of the minimum cross-sectional area of corroded rebar can be determined using indices d S n and K0.25, based on which a feasible SMFL-based reliability assessment method of corroded RC structures is proposed. The case study of a real specific corroded RC beam shows that the reliability assessment error of the SMFL-based method is only 1.2%, which is much lower than the 20.7% error of the existing method. This SMFL-based method provides a novel idea that can automatically and accurately assess the effect of rebars' corrosion non-uniformity on the reliability of specific in-serviceRC structures. [ABSTRACT FROM AUTHOR]

This study analyzes the Unibridge system, a modular steel box girder employing two pins for longitudinal connections, thereby expediting construction compared to traditional girders. A finite element model was developed to analyze the stress on these pins in a single-box girder with five segments and a reinforced concrete floor slab. Various loads were applied following the Indonesian bridge loading standard, SNI 1725:2016. The model considers operational load analysis and assumes full composite behaviour between the top flanges of the girder and the concrete floor slab. The results indicate that the Von-Mises stress on the pins reaches a maximum of 490.95 MPa under combined service loads, consistently remaining below the specified material yield stress limit of 1200 MPa. Consequently, the Demand Capacity Ratio (DCR) is 0.41. As a result, the Unibridge girder connection pins do not experience plastic deformation under the applied loads. [ABSTRACT FROM AUTHOR]

The use of explosives to target civilian buildings and other structures around the world is becoming a growing problem in modern societies. This paper focuses on RC beams exposed to free air blast loads. The paper first presents a parametric study on the behavior of RC beams subjected to blast loads using finite element simulation and then proposes an Artificial Neural Network (ANN) model to predict that behavior in a simple and easy manner. The ABAQUS program is used to simulate RC beams under blast loads. Experimental data was collected from the literature and used to validate the ABAQUS models. Deflection, reaction forces, ultimate stress, ultimate strain, and failure mode of RC beams are investigated. The considered design parameters in the parametric study are the characteristic compressive strength of concrete (fcu), the transverse reinforcement ratio (ρT%), the longitudinal reinforcement ratio (ρL%), and the scaled distance (Z). In this paper, the proposed ANN model was trained and tested using datasets produced using ABAQUS. The input parameters of the ANN model are TNT weight, standoff distance (D), characteristic compressive strength of concrete, transverse reinforcement ratio, longitudinal reinforcement ratio, width-to-thickness ratio (b/t), and length-to-thickness ratio (L/t). The predicted behavior using the ANN model showed the credibility of the model. The results indicated that L/t, b/t, and Z have significant effects on the behavior of RC beams under blast loads compared with fcu, ρT%, and ρL%, the cracks area increases with the decrease in Z, fcu, and b/t and decreases with L/t decrease. [ABSTRACT FROM AUTHOR]

In this study, the flexural bearing behavior of corroded reinforced concrete (RC) beams reinforced with U-type Textile Reinforced Concrete (TRC) was investigated using a four-point bending loading method. Nine test beams were produced: one original beam, three RC beams with corrosion alone, and five corroded beams strengthened with U-type TRC. The analysis focuses on assessing the impacts of the steel corrosion degree and the number of textile layers on various aspects of the bending behavior, such as failure modes, bearing capacity, and load displacement curves, in U-type TRC-strengthened corroded beams. The experimental results revealed three distinct failure modes in the U-type TRC-strengthened corroded beams. TRC effectively enhanced the bearing capacity. With sufficient textile layers, it can be restored to the level of the original RC beams. Moreover, in the cases of severe corrosion in RC beams, the bearing capacity increased more significantly. The TRC also enhanced the ductility. Finally, a calculation equation for the ultimate bearing capacity of U-type TRC-strengthened corroded beams was presented and validated, demonstrating consistent alignment with the experimental data. [ABSTRACT FROM AUTHOR]