RC Beams Research Articles

Bending Behavior of RC Beams with Regular Web Openings and Non-corroding GFRP Reinforcement

The present study pertains to the flexural behavior of RC beams with openings and non-metallic (GFRP) reinforcement. The main goal of preferring GFRP reinforcement over the conventional steel reinforcement was to safeguard the beams against the reinforcement corrosion. The presence of multiple regular transverse openings throughout the beam length increases the susceptibility of reinforcing bars to corrosion as the larger contact area in these beams with the outside environment increases the ingress of corrosive agents. Within the scope of the study, a total of 8 RC beams, including two reference beams without web openings, were tested under four-point bending. The test parameters were the flexural reinforcement ratio, the presence of short stirrups in the chords, and the presence of diagonal reinforcement spiraling around the openings. Since GFRP stirrups are difficult to bend, each stirrups was formed by connecting four individual FRP bars around the longitudinal bars. The opening circular geometry was adopted to avoid stress concentrations around the sharp corners of opening and to facilitate the placement and fixing of different schemes of reinforcement in the beams. The present tests depicted that the diagonal reinforcement around the openings have considerable contribution to the flexural behavior of RC beams with GFRP reinforcement and with multiple regular transverse openings. The RC beams with openings were able to approach their analytical flexural capacities in the presence of diagonal reinforcement for both moderately and heavily reinforced beam groups. The analytical deflection predictions of GFRP-RC beams with openings showed a good agreement with experimental data.

Flexural reliability of corroded RC beams strengthened with CFRP sheets considering longitudinal corrosion non-uniformity of steel bars

The corrosion of steel bars in RC beams along the longitudinal direction is usually non-uniform, thereby increasing the variabilities of failure mode and flexural behavior of corroded RC beams strengthened by CFRP sheets. This paper analyzed the flexural reliabilities of CFRP sheet-strengthened corroded RC beams, which considered the corrosion non-uniformities of longitudinal steel bars along the beam length. Based on the failure mode-based calculation method and Monte-Carlo simulation, the beams were discretized into a series of units along the beam length and the failure probabilities of the beams were considered as the failure probabilities of the serial units. Meanwhile, the occurrence probabilities of failure modes at bending failure were also studied. Parametric analysis results showed that the occurrence probabilities of failure modes were affected by steel reinforcement corrosion degrees, CFRP strengthening ratios and initial strains at concrete tensile edge. Meanwhile, the longitudinal corrosion non-uniformity could significantly affect the occurrence probabilities of different failure modes and degrade the flexural reliabilities; e.g., for RC beams under third-point bending, when the corrosion degree is 0.3, the predicted reliability index with considering longitudinal corrosion non-uniformity can be 28.3% lower than that without. The proposed reliability calculation method could accurately assess the impacts of longitudinal corrosion non-uniformity on flexural reliabilities and lay a solid foundation for calibrating design factors used in CFRP sheet-based strengthening designs, thereby contributing to both evaluating the safety of existing CFRP sheet-strengthened corroded RC beams and designing the strengthening CFRP sheets for existing corroded RC beams, which improve the safety and maintenance of existing RC structures in corrosive environments.

Response of Overhanging RC Beams Strengthened with Various Schemes of Externally Bonded CFRP Strips

Response of Overhanging RC Beams Strengthened with Various Schemes of Externally Bonded CFRP Strips

Development of high strength light weight concrete for RC beams by using optimum replacement level of pumice aggregate

Development of high strength light weight concrete for RC beams by using optimum replacement level of pumice aggregate

A simplified calculation model for maximum diagonal crack width of UHPC-NC composite beams

The study on precast UHPC-NC composite beams investigated the effects of shear span ratio, stirrup reinforcement ratio, and NC strength on cracking shear force and diagonal crack width. Tests on eight UHPC-NC beams and one RC beam revealed that increasing the shear span ratio reduced the cracking shear force and widened diagonal cracks. U-shaped UHPC formwork enhanced cracking shear force and delayed crack development. While stirrup ratio had minimal impact on cracking force, it helped delay crack growth. A proposed model accurately estimated cracking shear force and maximum diagonal crack width, offering valuable insights for engineering applications.

Shear Strength of RC Beams without and with Stirrups: Analytical Expressions and Comparison with Experimental Data

Shear Strength of RC Beams without and with Stirrups: Analytical Expressions and Comparison with Experimental Data

A model for predicting flexural capacity of PVC‐CFRP tube confined reinforced concrete beams

AbstractThis paper presents an experimental study on 18 specimens, including 15 polyvinyl chloride (PVC)‐carbon fiber‐reinforced polymer (CFRP) tube confined reinforced concrete beams with longitudinal CFRP sheets (PCT‐RCBs‐LCS) and 3 PVC‐CFRP tube confined reinforced concrete beams (PCT‐RCBs). The effects of five studied parameters, such as longitudinal reinforcement rate (), concrete strength grade (), width () and number () of longitudinal CFRP sheet, and specimen dimensions (), on the failure mode and flexural capacity are investigated. The PCT‐RCBs‐LCS with lower and fail by the breakage of the PVC tube and the fracture of longitudinal CFRP sheets. Conversely, the cracking of PVC tube dominates the damage of the PCT‐RCBs‐LCS with higher and , while the longitudinal CFRP sheets are not broken. The introduction of longitudinal CFRP sheets can significantly improve the flexural capacity. The ultimate flexural capacity of the PCT‐RCBs‐LCS increases as the , , , or increases. In addition. considering the influence of RC beam section shape, a model for predicting the ultimate flexural capacity of the PCT‐RCBs‐LCS is proposed based on the limit equilibrium theory and cross‐sectional strain relationship. The predicted results of the proposed model agree well with test data.

Ductility and cracking behavior of UHPC-RC composite beam under bending test based on acoustic emission parameters

Ultrahigh-performance concrete (UHPC) possesses improved mechanical properties due to its high strength, durability, and toughness. Currently, there is a single method for detecting the cracking behavior and evaluating the ductility of the UHPC-reinforced concrete (RC) composite beam. As an important part of structural non-destructive monitoring techniques, the acoustic emission (AE) technique can be used to analyze the damage pattern of the structure by the variation characteristics of its individual parameters. On this basis, four-point bending tests were carried out on the RC beam and UHPC-RC composite beam, and the AE technique was used for ductility analysis and cracking behavior monitoring. The results showed that the UHPC material enhanced the flexural capacity of the UHPC-RC composite beam. The AE ring counts and energy parameters could be used to analyze the cracking process of the UHPC-RC composite beam during flexural damage. The proposed new ductility indices, AE ring counts ductility index (ARD) and AE energy ductility index (AED), differed from the displacement ductility indices within the range of 2 %, providing a new method for calculating ductility indices of concrete structures. During the failure stage, the UHPC-RC composite beam produced more tensile cracks at the early stage of cracking and the stage of damage compared to the RC beam. In addition, the b value of the RC beam had a large range of fluctuations during the failure stage, indicating that the RC beam produced more micro-cracks and macro-cracks and more damage compared to the UHPC-RC composite beam.

Finite elemental assessment of torsional behavior of RC beams having different shear reinforcement

In this paper, the torsional behavior of 8 beams in 4 categories with 2 different ultimate concrete compressive strengths (22.92 MPa and 43.47 MPa) was evaluated, and the best alternative of shear reinforcement pattern compared to the conventional non-welded rectangular stirrup beam (NRSB) was determined. 4 types of beams were modeled using SolidWorks, namely—Non-welded Rectangular Stirrup Beam (NRSB), Welded Rectangular Stirrup Beam (WRSB), Normal Welded Warren Truss-shaped Beam (NWWTB), and Flipped Welded Warren Truss-shaped Beam (FWWTB). The dimension and weight of reinforcement were kept the same for all beams. After simulating using ANSYS, it was seen that WRSB specimens had the largest torsional moment capacity, while NWWTB in normal orientation showed marginal improvement compared to NRSB.

Analysing Flexural Response in RC Beams: A Closed-Form Solution Designer Perspective from Detailed to Simplified Modelling

This paper presents a detailed analytical approach for the bending analysis of reinforced concrete beams, integrating both structural mechanics principles and Eurocode 2 provisions. The general analytical expressions derived for the curvature were applied for the transverse displacement analysis of a simply supported reinforced concrete beam under four-point loading, focusing on key limit states: the initiation of cracking, the yielding of tensile reinforcement and the compressive failure of concrete. The displacement’s results were validated through experimental testing, showing a high degree of accuracy in the elastic and crack propagation phases. Deviations in the yielding phase were attributed to the conservative material assumptions within the Eurocode 2 framework, though the analytical model remained reliable overall. To streamline the computational process for more complex structures, a simplified model utilising a non-linear rotational spring was further developed. This model effectively captures the influence of cracking with significantly reduced computational effort, making it suitable for serviceability limit state analyses in complex loading scenarios, such as seismic impacts. The results demonstrate that combining detailed analytical methods with this simplified model provides an efficient and practical solution for the analysis of reinforced concrete beams, balancing precision with computational efficiency.

Ductility assessment of GFRP reinforced concrete beams with a wedge-based mechanical model accounting for discrete fibers and confinement

Glass fiber-reinforced polymer (GFRP) bars for internal reinforcement for concrete have gained attention due to their non-corrosive properties, high resistance, and electromagnetic transparency. On the other hand, the brittle behavior and low modulus of elasticity of FRP bars limit their application and diffusion in the civil construction market. From this perspective, this work investigates the influence of three components on the increase of ductility of GFRP beams: i) discrete alkali-resistant glass fibers added to the concrete; ii) confinement of the concrete with GFRP stirrups; and iii) use of longitudinal reinforcement on the compression zone. An experimental program including four over-reinforced beams with different reinforcement configurations was conducted. The beams were tested in four-point bending configuration and the use of fibers, stirrups and compression reinforcement contributed to substantially increasing the beam ductility index. Finally, a concrete wedge model was developed to obtain equivalent stress-strain relationships for the concrete in compression. The model was successfully validated against experiments and proved to be a useful tool for rationally evaluating GFRP RC beams’ ductility.

Negative bending behavior of prestressed hollow core slab with cast-in-place RC layer in the RC beam-slab joint area

To study the negative bending behavior of the prestressed hollow core slab (HCS) with cast-in-place (CIP) RC layer (HCSPR) in the beam-slab joint area, eight full-scale tests were conducted, covering the following parameters: support length (S), longitudinal reinforcement ratio (ρr), HCS height (h1), and CIP concrete layer height (h2). The mechanical properties of specimens were evaluated including load-deflection relationship, cracking behavior, and strain development. Two distinct failure modes of flexure and shear were observed. An extensive parametric study was also conducted to study the effects of h2, h1, prestressing degree, ρr, and span on negative bending performance. The results from the tests and parametric study indicate that h1, ρr, and h2 significantly affect the failure modes, bearing capacity, and ductility. To ensure robustness, S values no less than 30 mm are recommended for the connection between HCS and RC beam. Moreover, to avoid shear failure of HCS with CIP RC layer (HCSPR) in the joint area under negative moment, the shear span-to-depth ratio [L0/(h1 +h2)] should be restricted to be larger than 4. Lastly, both flexural and shear capacity formulas based on GB50010, EN1168, and ACI318 were compared. The calculated results were compared with the test and parametric analysis results. This research is of great significance for the application of simplified RC beam-HCS connection.

The confinement effect of basalt fibers for reinforced geopolymer composites: Flexural, shear and torsion capability for ductility and failure

Geopolymer concrete is a promising candidate to replace conventional concrete (CC), as geopolymer concrete is based on alkali-activated binders instead of Portland cement. The elimination of cement in the mix leads to a reduction in the release of greenhouse gases. It is known from the literature that the microscale properties of geopolymer concrete are similar to those of its counterparts. However, the structural performance of geopolymer elements should be investigated in detail. Therefore, in this study, the effect of basalt fiber ratio (%0 and %1), geopolymer mix type and stirrup (with and without stirrup) on flexural (four-point test), shear (overhanging test) and torsional (pure torsion test) behavior of RC beam were investigated. In these experiments, slag based geopolymer concrete with waste marble, geopolymer concrete with fly ash and geopolymer concrete with quartz powder were used in order to manufactured to the RC beams. The mechanical performances of RC beams were assessed by using load-deflection curves, stiffness, ductility, failure mode and crack propagations. Test results revealed that the use of basalt fiber tolerated the decrease in strength, although the shear, flexural and torsion capacity decreased if stirrups were not used in the beams. The use of fly ash in the mixture was more effective on the strength than other materials in terms of the aluminate and silicate it contained.

Flexural Behavior of an RC Beam Externally Strengthened with a Steel- and CFRP-Based Method

Flexural Behavior of an RC Beam Externally Strengthened with a Steel- and CFRP-Based Method

An experimental study on RC beams externally strengthened by anchored CFRP sheets monitored by Digital Image Correlation

During the past few decades, strengthening and rehabilitation of reinforced concrete (RC) structures using fiber-reinforced polymer (FRP) composites have been considered one of the most promising techniques to achieve the required strengthening and structure life span. This paper analyzes the effects of different anchorage increments using the Externally Bonded Reinforcement (EBR) strengthening technique with CFRP on the mechanical properties and deformability capacity of reinforced concrete beams subjected to bending. Axial compression, ultrasonic pulse velocity, and elastic modulus tests were carried out on cylindrical concrete specimens, and the Digital Image Correlation (DIC) technique was used to monitor the total surface deformation and track the development of cracks in the reinforced concrete beams. Strain Gauges (SGs) were used to monitor the tensile reinforcement, the compressed concrete, and the CFRP strain. Experiments on twelve beams are carried out, and the measured data from the monitoring devices are compared. The accuracy of DIC for strain and displacement monitoring matches the performance of traditional methods, with the added benefit of providing full-field monitoring.

An interpretable machine learning-based model for shear resistance prediction of CFRP-strengthened RC beams using experimental and synthetic dataset

Existing analytical models for predicting the shear resistance of RC beams strengthened with externally bonded CFRP reinforcements exhibit deficient performance due to their inability to accurately capture the complex resisting mechanisms. Combined with significant statistical uncertainties in shear failure, driven by its brittle nature, this further undermines the reliability of these models. To address these limitations, this study leverages Machine Learning (ML) to develop more robust and reliable predictive tool. A rigorous feature-selection process identified eight predictors as the most influential. Subsequently, nine ML-algorithms were trained on a refined experimental dataset comprising 239 beams, with XGBoost emerging as the top performer. This model also outperformed established models likefib Bulletin-90 and ACI 2023 models. However, the limited scope of the experimental dataset constrained the model’s predictive performance especially when separately evaluated on beams strengthened with U-wraps, full wraps or side-bonded FRP configurations. Therefore, to achieve a more reliable model a synthetic dataset was generated using Tabular Variational Auto-Encoder. The XGBoost model trained with the synthetic dataset significantly improved the performance of the former model and exhibited better predictions for all strengthening configurations. Finally, to ensure the physical consistency of predictions, values obtained from the SHapley Additive exPlanations method were analysed.

A deformability-based mechanical model for predicting shear strength of FRP-strengthened RC beams failed in concrete cover separation

Concrete cover separation (CCS) is frequently happened prior to the yielding of steel stirrups in FRP-strengthened RC beams. However, the debonding mechanism and criterion have not been fully understood. In this study, the typical crack types associated with CCS are comprehensively summarized and investigated in terms of profiles and kinematics of crack. The dowel action and dowelling cracks are proved to be the dominant factors causing CCS. Based on the cracking features, the simplified local debonding strength and average shear strength of fracture interface, which constitutes the contribution of concrete to shear capacity of strengthened RC beams, are analytically derived and verified against the available experiments and code provisions. Through regression analysis of 179 collected shear tests, a formulation based on the Critical Shear Crack Theory (CSCT) is presented to assess the deformability of strengthened RC beams governed by CCS. The commonly overlooked actual stress level in steel stirrups is considered as a function of the rotation capacity of beams and assessed based on the Modified Compression Field Theory (MCFT). Validation of this analytical approach, involving comparison against the empirical models and experimental results from 107 specimens, confirms its superior effectiveness and consistency in predicting CCS and shear strength.

Performance of RC Beams reinforced with Steel Fibers under Pure Torsion

Performance of RC Beams reinforced with Steel Fibers under Pure Torsion

Study on Flexural Performance of Reinforced Concrete Beams Strengthened with FRP Grid–PCM Composite Reinforcement

To study the flexural performance of fiber-reinforced polymer (FRP) grid–polymer cement mortar (PCM)-composite-strengthened RC beams, the finite element numerical simulation of FRP grid–PCM composite RC beams is carried out using ABAQUS to analyze the effects of the amount of FRP grid reinforcement, the type of FRP grid material, and the geometry of FRP grid on the flexural performance of reinforced concrete beams and to establish the flexural capacity calculation formula of FRP grid–PCM-reinforced RC beams in case of debonding failure, based on analysis of the influencing factors. The results show that increasing the reinforcement of the FRP grid and increasing the stiffness of the FRP grid can improve the flexural bearing capacity of RC beams, and the change of FRP grid geometry has little effect on the flexural bearing capacity of RC beams. The established formula for calculating the flexural bearing capacity of FRP grid-reinforced concrete beams can better predict the flexural capacity of reinforced concrete beams under peeling failure.

Experimental and numerical investigation of low‐velocity impact behavior and failure mode of shear deficient RC beam strengthened with CFRP strips

AbstractIt 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.