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Geopolymer concrete (GC) is an innovative and sustainable type of composite resulting from the chemical reaction between waste materials containing and alkaline activators. The researchers have been focused to reduction of the greenhouse‐gas release, especially during the production of cement. Although numerous studies have been conducted on alkali‐activated cement or GC at the material level, there is limited research in the literature on the structural performance of reinforced GC members. The aim of this study is to investigate the effect of fiber combination on the shear and flexural performance of RC beams with maximum and minimum reinforcement ratio. To investigate the shear and flexural behavior of GC beam, four‐point and three‐point tests were performed on 12 GC with hybrid fibers, 4 GC with trio fibers, and 2 GC fiber‐free as references beams. The test parameters were the combination of fibers (steel, glass, carbon, and basalt), the longitudinal reinforcement ratio, and loading type. The key test results include the load‐deflection behavior, characteristics of the cracks, the effect of fiber type on the shear and flexural performance, ductility and stiffness properties, microstructure, the strain in the concrete, and the bars and code predictions. The test results showed that as expected, reducing the longitudinal reinforcement ratio decreased the strength, but the decrease in strength was tolerated by using different types of fibers. The use of trio fibers in beams under bending increased the strength capacity, considerably. Finally, the capacity prediction performance of current codes, that is, GB50010, EuroCode‐2, TS500, and ACI318, were also examined, and the calculations resulted that the current code equations had a percentage error of approximately 25% and 82% on average for flexural and shear, respectively, although EuroCode‐2 equations performed slightly better. [ABSTRACT FROM AUTHOR]

It is well‐known that shear failure is a collapse mechanism that is the riskiest, fastest, and catastrophic and occurs with no visible signs of damage or prior warning for RC beams. Therefore, to prevent brittle shear failure, the RC beams should include sufficient shear reinforcement, such as stirrups, and be designed to have sufficient shear capacity. However, the RC beams' shear capacity becomes inadequate for various reasons. One of these reasons may be the acting of the impulsive impact load, which is uncommon and disregarded in the design phase on the RC beams. An experimental program was conducted to examine the impact behavior and failure mode of shear‐deficient RC beams in the scope of the present study. Besides, it aims to investigate the effectiveness of the strengthening method using CFRP strips in improving the general behavior, failure mode, and performance of shear‐deficient RC beams exposed to impact load. The time histories of the accelerations, displacements, impact loads, and strains in the CFRP strips were measured. They were interpreted how they are affected by experimental variables examined in the experimental study. Furthermore, the finite element model of the specimens was generated in the LS‐DYNA software, and the experimental and numerical results were compared by performing finite element analysis in terms of failure modes and general behavior. [ABSTRACT FROM AUTHOR]

Many design regulations around the globe rely on member deflection as a governing criterion for resistance assessment in fire. The deflection evaluation in fire is generally achieved by conducting expensive experiments or computationally expensive finite-element analyses. This often restricts practicing engineers from using robust performance-based design philosophy for typical structures. Instead, they rely on objective design guidelines, often resulting in inefficient sizes of reinforced concrete (RC) members. Therefore, semiempirical relations are derived in the current study to determine the maximum deflection of the RC beam and RC column in a fire. Three separate end conditions are considered within the beam category: fixed-fixed beam, propped cantilever beam, and simply supported beam. Plausible variables are first identified that could affect the overall deflection of the member, and their proportionality is subsequently determined by performing one-on-one regression analysis. Furthermore, these relations are developed in terms of the most suitable fire intensity measures derived from the literature, which makes them applicable irrespective of the type of fire framework. The credibility of the deflection equations is validated through visual analysis followed by the three popular error indicator parameters, namely, Pearson's correlation coefficient, relative root-mean squared error (RRMSE), and performance index. Results indicated that all deflection equations accurately predict the RC member behavior under fire. [ABSTRACT FROM AUTHOR]

In this paper, the suitability of digital image correlation (DIC) technology in evaluating the flexural behaviour of as-built and carbon-fiber-reinforced polymer (CFRP) strengthened reinforced concrete beams was verified by conducting a four-point bending test on four large-size beams. The DIC data obtained during the tests were compared to the results measured using traditional techniques such as displacement sensors and electrical strain gauges, as well as the findings derived from finite element (FE) numerical simulations. A good agreement was achieved between the local displacement and strain measurements and the data from DIC as a function of the applied load. Moreover, the crack patterns generated by the FE modelling were validated by the corresponding patterns derived from DIC. This suitability study is expected to contribute to the future field implementation of DIC technology to monitor the CFRP-strengthened members of critical structures such as bridges. [ABSTRACT FROM AUTHOR]

Flexural strengthening of reinforced concrete (RC) beams is an important research topic due to its huge practical demand. In the present study, a new flexural strengthening method for RC beams, called the Shear-key Mounted Unbonded Rebar (SMUR) technique, is proposed and its effectiveness is examined through an experimental investigation. A total of 12 RC beams were cast and tested under four-point loading. Ten were strengthened and the remaining two the original or control beams. Before casting the RC beams, their constituent materials, such as cement, aggregate and rebar, were tested to ensure the quality of casting. The beams were strengthened with unbonded rebars attached to their tension faces through shear keys. One of the main advantages of the proposed technique was its speed and ease of application. As well as its effectiveness, the effects of other important aspects, such as the size and location of the rebar, were also examined. It was found that the proposed method noticeably enhanced the flexural capacity of a control beam. The ultimate load capacity of a strengthened beam was 60% higher than that of a control one. The flexural performances of the beams could be further improved by increasing the bar size and its location. The welding and conventional flexure were the dominant modes of failure in the strengthened beams.

The use of fiber-reinforced polymer (FRP) strips as an external strengthening method has gained widespread acceptance for enhancing the capacity of aging reinforced concrete (RC) beams. Despite extensive research and practical applications, there exist unresolved issues necessitating further investigation, including interface bonding, failure mechanisms, and the development of accurate predictive models for shear strength, considering diverse parameters. This paper systematically reviews shear strength formulas applied in the strengthening of RC beams using FRP strips. An extensive experimental dataset is compiled from diverse sources to support the analysis. Utilizing this dataset, a novel ensemble learning model is developed for predicting the shear strength contributed by FRP strips. Following the training of this model, the important score of each input parameter is also assessed. The findings presented herein contribute to a deeper understanding of the strengthening effectiveness of FRP strips on RC beams.

Strengthening reinforced concrete (RC) beams with fiber-reinforced polymer (FRP) grids and engineered cement composites (ECCs) can significantly enhance their shear capacity. However, the specific contributions of the components in reinforced RC beams remain unclear, necessitating further investigation into the flexural shear performance of RC beams. The numerical model was used to analyze the flexural shear performance of RC beams strengthened with an FRP grid and ECCs. Subsequently, the parameters affecting the flexural shear performance of beams were discussed. This included the compressive strength of concrete prism, the shear span ratio, the tensile strength of ECCs, the thickness of the ECC cover, the cross-sectional area of the FRP grid, and the number of FRP grid layers. Finally, a calculation formula was established to predict the shear capacity and verified by the outcomes from numerical models and experimental data. The findings indicated that the ECC-strengthened layer significantly contributed to increasing the shear capacity. Additionally, the FRP grids helped to reduce stress concentration in the flexural shear zone, thereby preventing premature concrete cracking. The max load increased by 8.06% when the ECC's tensile strength increased from 4 MPa to 10 MPa. In addition, increasing the cover thickness from 8 mm to 20 mm caused the peak load to increase by 14.42%. The calculation formula introduced in this research accurately predicts the shear capacity of the oblique section of RC beams. [ABSTRACT FROM AUTHOR]

The alkali‐silica reaction (ASR) is one of the durability issues that affect the safety of concrete structures. Numerical simulation is useful for monitoring the internal condition of a reinforced concrete (RC) structure with ASR damage and predicting its long‐term behavior. Since discrete methods of simulation suit situations where concrete undergoes durability issues associated with expansion and cracking, a mesoscale discrete analysis method known as the three‐dimensional Rigid Body Spring Model (3D RBSM), as already used to simulate concrete ASR damage at the material scale, has been further developed to simulate ASR damage at the structural scale. In this development, the aggregate is not separately modeled and expansive elements are included to simulate ASR expansion, allowing a larger element size (1–2 cm). The number of elements and computation time are reduced to less than 1%. This proposed model is used to simulate ASR damage in a RC beam and the beam's residual flexural capacity. The simulation allows the internal stress and cracking condition to be visualized, leading to an explanation as to why the loading capacity of a RC beam is not affected by ASR damage: first, almost no cracks form at the core of the beam section due to the stirrup confinement, so the effective depth of the cross section is maintained after ASR damage; second, the tensile reinforcements have already yielded although ASR damage exists. Besides, the inhibited development of shear cracks may be one of the reasons for the slight improvement of flexural capacity of the damaged‐RC beam in experiment and simulation. [ABSTRACT FROM AUTHOR]

Corrosion of steel reinforcement from chloride exposure can compromise the strength of reinforced concrete structures. Rust formation expands, applying pressure on concrete, resulting in cracks and spalling. Prompt repair is crucial for severe cases of spalling. This research assessed the efficacy of repair strategies for reinforced concrete beams post-spalling, including grouting and different techniques involving Glass Fiber Reinforced Polymer (GFRP) reinforcement. The research examined four variations of reinforced concrete beams, each sized at 150 mm × 200 mm × 3300 mm. Results showed that the standard beam (BK) had an average maximum load capacity of 29.74 kN. In contrast, the grouted beam (BGR) demonstrated a reduced maximum load of 14.39 kN, along with decreased steel and concrete strain compared to BK. This suggests that the grouting repair did not fully restore the beam's flexural capacity after spalling. Incorporating GFRP strips (BGRS) led to a marginal increase in the beam's maximum load, albeit remaining below BK, with lower steel and concrete strain than BK. However, the steel and concrete approached their yield points, indicating enhanced flexural performance. The full-wrap GFRP beam (BGRSF) experienced an 8.08% increase in maximum load compared to BK, with concrete strain surpassing BK, suggesting an enhancement in flexural stiffness. [ABSTRACT FROM AUTHOR]

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Ultra-high-performance concrete (UHPC) is considered to be a promising material for the strengthening of damaged reinforced concrete (RC) members due to its high mechanical strength and low permeability. However, its high material cost, limited code provisions, and scattered material properties limit its wide application. There is a great need to review existing articles and create a database to assist different technical committees for future code provisions on UHPC. This study presents a comprehensive overview focusing on the effect of the UHPC layer on the flexural and shear strengthening of RC beams. From this review, it was evident that (1) different retrofitting configurations have a remarkable effect on the cracking moment compared to the maximum moment in the case of flexural strengthening; (2) the ratios of the shear span and UHPC layer thickness have a notable effect on shear strengthening and the failure mode; and (3) different bonding techniques have insignificant effects on shear strengthening but a positive impact on flexural strengthening. Overall, it can be concluded that three-side strengthening has a higher increment range for flexural (maximum, 81%–120%; cracking, 300%–500%) and shear (maximum, 51%–80%; cracking, 121%–180%) strengthening. From this literature review, an experimental database was established, and different failure modes were identified. Finally, this research highlights current issues with UHPC and recommends some future works. [ABSTRACT FROM AUTHOR]

Ultra-high-performance concrete (UHPC) is considered to be a promising material for the strengthening of damaged reinforced concrete (RC) members due to its high mechanical strength and low permeability. However, its high material cost, limited code provisions, and scattered material properties limit its wide application. There is a great need to review existing articles and create a database to assist different technical committees for future code provisions on UHPC. This study presents a comprehensive overview focusing on the effect of the UHPC layer on the flexural and shear strengthening of RC beams. From this review, it was evident that (1) different retrofitting configurations have a remarkable effect on the cracking moment compared to the maximum moment in the case of flexural strengthening; (2) the ratios of the shear span and UHPC layer thickness have a notable effect on shear strengthening and the failure mode; and (3) different bonding techniques have insignificant effects on shear strengthening but a positive impact on flexural strengthening. Overall, it can be concluded that three-side strengthening has a higher increment range for flexural (maximum, 81%–120%; cracking, 300%–500%) and shear (maximum, 51%–80%; cracking, 121%–180%) strengthening. From this literature review, an experimental database was established, and different failure modes were identified. Finally, this research highlights current issues with UHPC and recommends some future works.

The flexural performance of RC beams strengthened with a novel high-strength and high-toughness epoxy mortar thin layer was investigated through four-point flexural tests on two contrast beams and two strengthened beams. The effects of this strengthening method on the failure modes, crack distribution, load–deflection curves, and bearing capacity of the RC beams with two reinforcement ratios were studied. The experimental results revealed that the contrast beams exhibited the typical bending failure modes where the failure mode of the reinforced beam is the yielding of the tensile reinforcement of the original beam and then fracture damage of the new epoxy mortar-reinforced thin layer. No debonding phenomenon was observed between the reinforced thin layer and the original concrete, and no visible cracks appeared before the tensile failure occurred in the thin layer. The cracks in the reinforced beams developed slowly, increased in number, and decreased significantly in width and spacing. The stiffness of the strengthened beam increased significantly, while its deformation ductility coefficient noticeably decreased. Compared to the corresponding contrast beams, the cracking load for strengthened beams A1 and B1 increased by 14% and 23%, respectively; the yield load increased by 32% and 40%, respectively; and the peak load increased by 18% and 17%, respectively. Finally, a calculation method for the flexural bearing capacity of RC beams strengthened with the novel epoxy mortar thin layer based on the flat section assumption was proposed. The calculated values showed a good agreement with the experimental values (with errors at −11.73% and 4.14%, respectively), providing a valuable reference for further research and application related to this kind of reinforcement method. [ABSTRACT FROM AUTHOR]

Although torsion is usually considered a secondary consideration in structural design, it can lead to failures, especially in structures with irregular geometry exposed to seismic forces or in unique situations. While some studies have explored the size effect on the torsional behavior of RC beams, none have addressed the impact of reinforcement. This paper investigates the size effect on the torsional behavior of RC beams with varying reinforcement ratios, including both FRP sheets and steel rebars. In this study, the torsional behavior of reinforced concrete (RC) beams with and without FRP strengthening was investigated numerically. Modeling was carried out by Finite element (FE) software ABAQUS and validated using experimental data from literature. The torsional behavior of 24 models with differences in cross-section size and reinforcement ratio were investigated. Concrete damage plasticity, Hashin damage criteria, and von Mises stress were used to investigate the damage in concrete, FRP, and steel, respectively. The cracking torsional moment, ultimate torsional moment, and torque-twist curve of the beams were evaluated and presented. The results indicated the presence of a significant size effect in the torsional strength of beams. After reinforcing the beams with FRP fabrics, the average cracking moment increased by a range of 1.72% to 36% across different groups of beams. An 8.2% increase in ultimate strength is observed with just a 0.4% rise in the FRP strengthening ratio. Post-cracking behavior was seen in 8 models with adequate steel and FRP reinforcement ratio. [ABSTRACT FROM AUTHOR]

Rebar corrosion in traditional reinforced concrete (RC) components may lead to a decrease in service life and carrying capacity. This condition is one of the reasons of the growing popularity of Fiber Reinforced Polymer (FRP) rebars as a corrosion-resistant alternative, particularly in RC infrastructure projects. Because the material properties and behavior of FRP rebar are very different from conventional steel rebar, the calculations used for reinforced concrete with conventional steel reinforcement should be updated for this material. The aim of this study is to propose a new shear strength prediction model for RC beams with transverse steel rebar in order to calculate the shear strength of RC beams with FRP transverse rebar according to TS-500, which is the Turkish Building Code. To achieve this goal, Finite Element Method (FEM) models were created for 27 RC beams with FRP transverse rebars and 9 RC beams without transverse rebars. Furthermore, for RC beams with FRP transverse rebars, a prediction model has been developed. Additionally, 13 prediction models obtained from regulations or scientific studies were compared to the proposed prediction model using a database of 105 tests obtained from previous experimental studies. It was observed that the proposed prediction model provides more consistent results with the test database from the literature compared to the models suggested by other regulations or studies. Therefore, by modifying the shear strength relations recommended in TS-500 for RC beams with transverse steel rebar, they can also be applied to RC beams with transverse FRP rebars. [ABSTRACT FROM AUTHOR]

Various methods can be employed to splice reinforcement bars, including lap splicing, welding, and mechanical splicing. Lap splicing is the most used method among these techniques. However, this study primarily focuses on evaluating the potential of mechanical splicing to replace the lap splice method. The investigation involved assessing the flexural performance of six RC beams in a series of laboratory experiments. These beams represented a control beam, an RC beam with lap-spliced rebars, and an RC beam with clamp-type mechanicalspliced rebars. The laboratory testing results indicated that the RC beam with lap-spliced rebars had the highest load-bearing capacity, resulting in the highest nominal flexural moment (Mn). In contrast, the control beam demonstrated the highest deflection, signifying a greater level of ductility. However, RC beams with mechanical splices (clamp type), while not achieving the highest flexural moment and ductilities, are still competitive, as the experiment revealed that the difference is not significant. Consequently, it can be concluded that mechanical splicing has the potential to compete with or replace lap splicing in RC beams. [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]

Reinforced concrete (RC) structures combine steel and concrete to harness their respective advantages, making them a staple in contemporary architecture. With the aging of civil engineering structures, structural health monitoring grows increasingly critical. In this context, acoustic emission technology (AE) emerges as an effective nondestructive testing method for assessing the structural damage status. Building on this foundation, the AE technology was utilized to monitor the crack growth in the RC beam under the four-point bending test. Furthermore, a visual analysis method to assess the internal damage of the RC beam, based on the spatial b value of the AE, was introduced. This method integrates the spatial b value and the AE event density distributions to develop the T value. The results indicate that as the stirrup ratio decreases, the bearing capacity of RC beams increases; however, their ductility experiences a significant reduction, and the failure mode undergoes a transformation. Throughout each failure stage of RC beams, the AE ringing number and energy exhibit unique and easily distinguishable characteristics of change. Additionally, RA-AF correlation analysis can be applied to delve deeper into the analysis of the RC beams' failure modes. Utilizing the spatial b value and T value facilitates the identification of damage locations within the RC beam, thereby offering a practical and feasible approach for structural damage analysis. [ABSTRACT FROM AUTHOR]

This is an experimental study on the flexural performance of corroded reinforced concrete (RC) beams strengthened by three different methods using Glass Fibre Reinforced Polymer (GFRP) bars. Three methods of strengthening were used: the traditional method of replacing damaged concrete covers and installing GFRP bars, the near-surface mounted (NSM) method, and a hybrid method involving mechanical fasteners and the NSM method. In total, seventeen RC beams were constructed one of which was used as a control specimen, while the remaining sixteen were divided into four groups and were exposed to accelerated corrosion to reach a theoretical mass loss of 3.5 to 30% in tensile steels. Three groups of corroded beams were strengthened using the three methods mentioned, while the other group received no strengthening. Then, all the beams were tested under four-point loading to determine their load-deflection response, stiffness, ductility, failure mode, and strain of the GFRP bars. The results showed that the conventional strengthening method using GFRP bars was relatively efficient in restoring the load-bearing capability of corrosion-damaged beams. However, sufficient anchorage length for the GFRP bars was required to achieve high ductility. The NSM method effectively improved the load-bearing capacity of beams with low corrosion levels; however, increasing the corrosion level caused the strengthened beams to fail prematurely due to concrete cover separation. It was observed that the hybrid strengthening method improved the load-bearing capacity of corroded beams while maintaining their ductility by preventing premature failure due to concrete cover separation. [ABSTRACT FROM AUTHOR]

In order to further study the shear behavior of reinforced concrete (RC) beams strengthened with ultra-high-performance concrete (UHPC) plates, an experimental study was carried out on three full scale RC beams, including a control one and two ones strengthened using UHPC plates with or without CFRP strips. The effects of UHPC plates and CFRP strips were focused. The test results show that the shear failure occurs in all the test beams, but the bearing capacity, stiffness and ductility of the reinforced beams are significantly improved. Among them, the cracking resistance of UHPC plates is improved by embedded CFRP strips, and the ultimate load and corresponding displacement are increased by 30. 8% and 28. 5%, respectively. The screw mechanical anchorage plays the role of lateral restraint and pin, which improves the contribution of UHPC plate to a certain extent. At the same time, a nonlinear finite element model is established to analyze the test beam. The simulation results are in good agreement with the test results, indicating that the constitutive relationship and related parameters selected in the model are reasonable and can be used to predict the whole process stress behavior of RC beams reinforced by UHPC plates. [ABSTRACT FROM AUTHOR]

In this study, a modified accelerated corrosion method based on the traditional galvanic method was adopted to generate non-uniform corrosion of reinforcement. The flexural performance of corroded RC beams was experimentally investigated, aiming to study the influence of longitudinal reinforcements corrosion induced by two different accelerated corrosion methods on the degradation of flexural capacity of RC beams. The corrosion-induced and load-induced cracking behaviors, as well as the degradation of flexural performance of beam specimens corroded by these two different methods were studied. The test results showed that the longitudinal reinforcements subjected to the modified accelerated corrosion method demonstrates a considerably higher circumferential and longitudinal non-uniformity, while the traditional accelerated corrosion method induces a rather uniform corrosion. For the corrosion-induced crack, the non-uniform reinforcement corrosion induced by the modified accelerated corrosion method was closer to the one after exposure to the natural environment. The non-uniformity of corrosion aggravates the propagation of both corrosion-induced and load-induced cracks, leading to the change of flexural failure mode. And the uniform corrosion induced by the traditional accelerated corrosion method underestimates the degradation of shear capacity of RC beam, especially in the cases of corrosion degree no less than 15%. [ABSTRACT FROM AUTHOR]

High temperatures during a fire can significantly degrade the structural capacity of concrete. However, in many cases, it is possible to restore and strengthen fire-damaged concrete rather than completely rebuild damaged structures. The study considered two types of concrete (normal 25 MPa and high-strength 65 MPa) with two types of strengthening techniques: carbon-fiber-reinforced polymers (CFRP) sheets with different thicknesses of 1.5 and 2.5 mm and slurry-infiltrated fibrous concrete (SIFCON) jacketing with different fiber sizes of 20 and 30 mm. The numerical simulations and analyses were conducted to capture the complex behavior of fire-damaged concrete members (beams). A fire-damaged concrete beam subjected to an extreme or critical fire Exposure time (2 hours) was evaluated and modified using a finite element simulation approach. The simulation process included three stages: the first, subjecting the concrete beam to thermal loading; the second, reflecting the fire distribution map to another model of applying mechanical loading; and the third, involving the application of strengthening to the damaged model. The results showed that the strengthening using CFRP with a thickness of 2.5 improved the load-carrying capacity compared with SIFCON in both types of concrete. 200% improvement for the normal-strength concrete beam and a 136% improvement for the high-strength concrete beam, compared to the damaged beams. [ABSTRACT FROM AUTHOR]

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

Strengthening reinforced concrete (RC) beams with fiber-reinforced polymer (FRP) grids and engineered cement composites (ECCs) can significantly enhance their shear capacity. However, the specific contributions of the components in reinforced RC beams remain unclear, necessitating further investigation into the flexural shear performance of RC beams. The numerical model was used to analyze the flexural shear performance of RC beams strengthened with an FRP grid and ECCs. Subsequently, the parameters affecting the flexural shear performance of beams were discussed. This included the compressive strength of concrete prism, the shear span ratio, the tensile strength of ECCs, the thickness of the ECC cover, the cross-sectional area of the FRP grid, and the number of FRP grid layers. Finally, a calculation formula was established to predict the shear capacity and verified by the outcomes from numerical models and experimental data. The findings indicated that the ECC-strengthened layer significantly contributed to increasing the shear capacity. Additionally, the FRP grids helped to reduce stress concentration in the flexural shear zone, thereby preventing premature concrete cracking. The max load increased by 8.06% when the ECC’s tensile strength increased from 4 MPa to 10 MPa. In addition, increasing the cover thickness from 8 mm to 20 mm caused the peak load to increase by 14.42%. The calculation formula introduced in this research accurately predicts the shear capacity of the oblique section of RC beams.

Opening in the web of reinforced concrete (RC) beams will destroy the integrity of the beam and weaken the mechanical properties of the RC beam, such as the bearing capacity and stiffness. The three-point loading test and finite element analysis were carried out on 10 RC beams with a huge rectangular opening in the web. The effects of stirrups around the holes on the shear properties of RC opening beams, such as bearing capacity, deformation capacity, and stirrup strain, were studied, and the shear transfer mechanism of RC beams at the openings was explained by using the strut-and-tie model. The finite element test results are consistent with the actual test results, as shown by the results. When the hole width is small, the reinforcement of stirrups at the hole side can significantly improve the shear capacity of the specimen, but it can also cause chord shear failure. When the hole height is small, with the strengthening of the chord stirrup, the ultimate bearing capacity of the specimen increases, but it can still result in hole-side shear failure. The curve of stiffness degradation is approximately logarithmic. Moreover, according to the finite element stress vector diagram, the shear transfer mechanism of the perforated beam based on the strut-and-tie model has been proved.

The load-deflection relationship is critical for the serviceability and structural durability of reinforced concrete (RC) structures strengthened with prestressed carbon fiber-reinforced polymer (CFRP) plates. This study aims to investigate the impact of prestressing levels and wetting/drying cycles (WDCs) on the flexural stiffness of prestressed CFRP-strengthened RC beams. A modified flexural stiffness prediction model was proposed by incorporating prestressing levels, interfacial bond slip, and softening after WDCs. Subsequently, four-point bending tests were conducted on 11 strengthened beams with different prestressing levels and WDCs to estimate flexural behavior. The results suggest that WDCs can adversely affect the flexural stiffness of the strengthened beams, particularly for the post-cracking stiffness of the non-prestressed specimens. However, prestressed strengthening can mitigate the stiffness degradation caused by WDCs. Moreover, a finite element (FE) model utilizing a traction separation model can accurately predict flexural stiffness. Finally, the flexural stiffness was computed using both the existing and proposed models and the proposed model provides the closest prediction of the flexural stiffness for CFRP-strengthened beams under WDC and prestressing.

A 3D model is established to simulate the bond performance of corroded RC beams, in which the non-uniform corrosion of tensile reinforcement and confinement conditions (characterized by the thickness-diameter ratios of 1.9–3.8 and stirrup confinement index of 0–8.3%) are investigated. In the 3D numerical model, fine modeling was adopted to consider the influences of corrosion on the steel-concrete interface and the non-uniform corrosion was considered by separating the tensile bars into two parts with inconsistent diameter loss. Meanwhile, a two-stage numerical analysis method was utilized, to reflect the corrosion-induced concrete cracking by applying forced displacement and subsequently analyzed their flexural bond performance. In comparison to the existing experiments, the proposed 3D numerical model is proved to be reasonable. In addition, the simulation results show that the increment of the (residual) bond strength generated by the increasing thickness-diameter ratio increases with the mass loss rate, while the increases of stirrup confinement index cause much more increases in the (residual) bond strength for the corroded RC beams than the un-corroded beams. Furthermore, a bond stress-slip relationship is proposed taking the non-uniform corrosion and confinement conditions into account, which correlates well with the experiments.

In this study, the reinforced concrete (RC) beams were strengthened by use of carbon fiber reinforced polymer (CFRP) and engineering cementitious composite (ECC). The flexural behavior of the strengthened RC beams was investigated experimentally, and analytical prediction methods were used to verify the experimental results. The experimental results showed that, the premature delamination between CFRP plate and concrete occurred if the beam was solely reinforced by CFRP, nevertheless, this can be effectively prevented by the composite use of CFRP and ECC. Compared with reference beam, the CFRP-ECC composite strengthened technique significantly enhanced the cracking load, yield load, and ultimate load of beams up to 23–31 %, 4–6 %, and 5–10 %, respectively, in addition, the stiffness, ductility, and energy absorption capacity (EAC) can also be enhanced upon the composite strengthening. In final, the prediction model has high accuracy, and the error variation within 5 % when comparing the predicted and tested values of flexural bearing capacity.

The implementation of steel-fiber reinforced concrete (SFRC) can improve the durability of reinforced concrete structures exposed to corrosive environments. More recently, the recycled-tire steel fibers (RTSF) impressively boosted mechanical performance and post-cracking strength of plain concrete. Unlike the engineered steel fiber (ESF), RTSF is capable of arresting both micro- and macro-cracks. Micro-crack arresting via RTSF incorporation can reduce chloride penetration in SFRC. In this study, first, the influence of low dosage of RTSF and/or ESF on mechanical properties of concrete is explored. Second, the effect of RTSF, ESF and their hybrid utilization on the corrosion development on embedded steel rebars is surveyed. Artificial corrosion procedure was implemented for inducing corrosion in rebars embedded in reinforced concrete (RC) beam. Finally, the flexural performance of corroded SFRC beam with different corrosion rates (0%, 2%, 5%, 7%, and 10%) were evaluated upon a three-point bending test setup. According to the results, the compressive strength of plain concrete improved 37% by 40 kg/m3 RTSF incorporation. Moreover, the tensile and post-cracking strengths of concrete enhanced significantly by hybrid utilization of RTSF and ESF. The residual strength of SFRC mix at both service and ultimate load was improved by the hybrid utilization of both RTSF and ESF by 25-120%. For uncorroded RC beams containing SFRC mix, the RTSF incorporation improved the shear capacity of the plain RC beam by 25%. Among different types of fibers, RTSF was more effective in decreasing the actual corrosion rate of rebars embedded in RC beams. Additionally, corrosion of embedded rebars up to 8% slightly reduced the rotation capacity of FRC beams.

In the scope of this study, the strengthening of reinforced concrete beams against to shear with different types of composite materials was investigated experimentally. A total of seventeen reinforced concrete beams, one with high shear strength and sixteen with low shear strength, were fabricated. The beam with high shear strength and one of the beams with low shear strength were chosen as reference beams. The remaining fifteen beam specimens were strengthened with textile-reinforced mortar (TRM) and carbon-fiber-reinforced polymer (CFRP). While light and heavy carbon mesh were used for strengthening with TRM, unidirectional carbon textile was used for strengthening with CFRP. Other experimental parameters were the spacing of strips, the number of layers (one or two) and the way of wrapping (strip or full). Simply supported beam specimens were tested under three-point loading. Beam specimens were compared in terms of failure mode, ultimate load capacity, ductility index and energy dissipation capacity. [ABSTRACT FROM AUTHOR]

High-strength jute fibre-reinforced polymer (JFRP) laminates have recently been introduced to strengthen RC beams against shear. In contrast to synthetic-based composites, JFRP laminates would be more ductile, compatible with steel shear rebar and effective in reducing debonding due to their lower modulus of elasticity. The prime objective of this research was providing an optimal solution to strengthen a severely deficient RC beam against shear using an externally bonded JFRP laminate with anchor. Fabrication of the JFRP laminate was carried out with the maximum fibre content of 37.5% to obtain high tensile strength. Five full-scale RC beam specimens were cast. Shear strengthening was done by an externally bonded JFRP laminate with double connector, multiple connector and embedded-bar anchor systems. The dimensions of JFRP laminate were obtained based on proposed guidelines. Based on the experimental test, the average tensile strength of the fabricated JFRP laminate was found to be 162 MPa. Results also showed that the JFRP laminate with multi-connector anchor increased the maximum shear capacity of deficient RC beams by 89% and the beams had failed by the fracture of laminate. Beams strengthened with embedded-bar anchor had shown flexural ductile failure. Both beams failed after yielding of flexural bar. The proposed guidelines could be used for shear strengthening of severely deficient beams to enhance the maximum shear capacity using full strength of JFRP laminate with anchor. [ABSTRACT FROM AUTHOR]

A three-dimensional meso-scale numerical model, which considers (1) the concrete meso-structures, (2) the bond slip between concrete internal structures and steel bars, and (3) the stripping behavior of carbon fiber reinforced polymer (CFRP) cloth from the surface of the concrete component, is established to investigate the effects of concrete strength and the CFRP cloth ratio on the shear performance of reinforced concrete (RC) beams. On the basis of verifying the rationality of the shear failure model and the feasibility of the CFRP reinforcement simulation method, 30 orthogonally designed numerical models of six kinds of concrete strength and five kinds of CFRP cloth ratios were designed and established. Based on the numerical simulation results, this paper analyzes the damage evolution of the CFRP–concrete interface, the variation trend of CFRP strain along the height direction of beam, the failure mode, and the load-displacement curve. Results show the following: (1) With the increase of concrete strength grade and CFRP cloth ratio, the shear strength of RC beams strengthened with increases in CFRP cloth ratio, the influence range of concrete strength grade is 24–50%, and the influence range of the CFRP cloth ratio is 10–25%; (2) The improvement range decreases, and the improvement range of the concrete strength grade decreases, and the reduction range is about 20%; (3) Based on the simulation results, influences of concrete strength and CFRP cloth ratio on the shear strength of CFRP cloth-strengthened RC beams are quantitatively considered. [ABSTRACT FROM AUTHOR]

During the service life of reinforced concrete beams (RC beams), they may experience impact loadings induced by various falling objects, such as falling rocks and fragments of upper floors. Therefore, the RC beam's impact resistance is important to its application in structures. This paper investigated the impact mitigation performance of polyurea coatings on RC beams by drop weight impact tests with different impact velocities and hammer shapes. According to the test results, the polyurea coatings can significantly reduce the RC beams' local damage and midspan displacement. Moreover, it was found that the RC beams' plateau impact forces were notably increased by the polyurea coatings. Besides, comparisons between impact tests with different impact loads indicated that the polyurea coatings' protection effect was not noticeably influenced by the hammer shape or impact velocity. Based on the test results, a numerical model was established and validated, and the model was used to study the mechanism and the parameter influence of polyurea coatings. By simulating the response of upper- and lower-side coated beams, it was revealed that the polyurea coating reduced the RC beam's overall damage by reducing its local damage and increasing its bending moment. Parametric studies showed that the mitigation effect increased with coating thickness and the increase rate decreased with the thickness. In addition, the effect of longitudinal coating length was also studied via numerical simulation, and it was found that the mitigation effect increased with coating length, and it became nearly identical to that of the fully coated beam when the coating length exceeded 60 cm. [ABSTRACT FROM AUTHOR]