RC Beams Research Articles

Advancing Shear Capacity Estimation in Rectangular RC Beams: A Cutting-Edge Artificial Intelligence Approach for Assessing the Contribution of FRP

Shear strength prediction in FRP-bonded reinforced concrete beams is crucial for ensuring structural integrity and safety. In this extensive investigation, advanced machine learning algorithms are harnessed to achieve precise shear strength predictions for rectangular RC beams reinforced with FRP sheets. The aim of this research is to enhance the accuracy and reliability of shear strength estimation, providing valuable insights for the design and assessment of FRP-strengthened structures. The primary contributions of this study lie in the meticulous comparison of various machine learning algorithms, including Xgboost, Gradient Boosting, Random Forest, AdaBoost, K-nearest neighbors, and ElasticNet. Through comprehensive evaluation based on predictive performance, the most suitable model for accurately estimating the shear strength of FRP-reinforced rectangular RC beams is identified. Notably, Xgboost emerges as the superior performer, boasting an impressive R2 value of 0.901. It outperforms other algorithms and demonstrates the lowest RMSE, MAE, and MAPE values, establishing itself as the most accurate and reliable predictor. Furthermore, a sensitivity analysis is conducted using artificial neural networks to assess the influence of input variables. This additional research facet sheds light on the critical factors shaping shear strength outcomes. The study, as a whole, represents a substantial contribution to advancing the development of accurate and dependable prediction models. The practical implications of this work are far-reaching, particularly for engineering applications in the realm of structures reinforced with FRP. The findings have the potential to transform the approach to the design and assessment of such structures, elevating safety, efficiency, and performance to new heights.

Polymer cement mortar strengthened RC beams with/without silica fume as repair material

Polymer cement mortar (PCM) overlaying methods leads to brittle interfacial debonding before its classical failure causing a sudden decrease of the load-carrying capacity. For a reliable design procedure for the practitioner, a need exits to prevent the interfacial debonding. The proposed modified 5 % silica fume (M) PCM overlay is intended to delay debonding because it increased the concrete-PCM bond (confirmed in our previous study). Fourteen RC beams (size-150x150x1440 mm, a/d – 3.5) using C40 concrete (mix proportion – 1:2.1:2.6) were prepared and strengthened with rebar (2D6 and 2D10), CFRP grid with changing stiffness (low, medium and high), and CFRP strand sheet (50 mm and 150 mm width) as strengthening reinforcement that embedded with normal (N) PCM and MPCM overlay of thickness 20 mm to investigate the effectiveness of silica fume. Four-point bending test were made at room temperature to evaluate the flexural performance. Compared to NPCM, MPCM with all cases of strengthening reinforcement enhanced the crack numbers, ductile behavior, peak load (12–25 %) and debonding load (3–33 %), proving MPCM as ideal cementitious matrix for strengthening. The flexural strengthening configuration using MPCM and reinforcement amount (area x tensile strength) ratio of 0.5 between strengthening and main bar proved to be more efficient as this configuration delayed the debonding failure, shifted fracture to classical mode and confirmed uniform shear stress transfer at the overlay-concrete interface. Conclusively, MPCM overlay nearly achieved a full-strength composite action which is effective to prevent the debonding that benefits practitioners.

Impact of developed hybrid polypropylene fiber inclusion on the flexural performance of concrete beams reinforced with innovative hybrid bars

This paper investigates the impact of incorporating a hybrid combination of structural polypropylene fibers on the flexural behavior of concrete beams reinforced with steel, GFRP, and innovative hybrid bars. A new ductile hybrid bar with equivalent bilinear stress-strain characteristics has been developed to address steel corrosion and FRP ductility issues. Fourteen half-scale RC beams were fabricated and tested under four-point loading configuration to study the flexural response. The tensile reinforcement types (steel, GFRP, and hybrid), hybrid reinforcement ratios (0.85 %, 1.26 %, and 1.70 %), reinforcement hybridization schemes (hybrid-hybrid, hybrid-GFRP, and GFRP-steel), and hybrid fiber ratio (0.0 %, 1.0 %, and 2.0 %) are the major parameters studied. The test results were recorded and analyzed in terms of mid-span deflection, cracking load, flexural capacity, and failure mechanism. The results demonstrated that the addition of hybrid fibers and using hybrid bars significantly improved the peak strength, ductility index, and bending stiffness. Moreover, the hybrid-reinforced concrete beams exhibit large inelastic deformations similar to steel-reinforced concrete beams. The inclusion of hybrid fibers improves the post-peak response of the tested beam due to fiber bridging capabilities. For design purposes, a simplified formula proposed by ACI 544 for predicting the nominal flexural capacity of hybrid fiber concrete beams reinforced with hybrid bars was presented, compared with experimental results and validated with 44 specimens from other studies. The predicted and test results were in good agreement with a standard deviation of 0.12. Additionally, 3D nonlinear finite element analysis was developed to validate the test results, demonstrating reasonable accuracy in predicting the flexural behavior of the beams.

Structural behavior of severely corroded RC beams retrofitted with UHPC layer: an experimental study

Structural behavior of severely corroded RC beams retrofitted with UHPC layer: an experimental study

Debond Identification in GFRP Strengthened RC Beam Using Surface Guided Wave Mode Generated by Angle Beam Transducer

Debond Identification in GFRP Strengthened RC Beam Using Surface Guided Wave Mode Generated by Angle Beam Transducer

Behavior of reinforced recycled aggregate concrete beams and slabs strengthened in flexure and punching with CFRP composites

Recycling of concrete generated from construction and demolition waste as coarse aggregates in concrete has been a focus of several studies for the evolution of the green concrete and conservation of natural resources. This investigation, therefore, focusses on the study of the behavior of RC beams strengthened with externally bonded CFRP wraps, cast with both natural and recycled aggregates concrete. Furthermore, one-way slabs were strengthened with Near Surface Mounted (NSM) bars, while two-way slabs were strengthened with CFRP strips. One-way and two-way slabs used in the study were cast with both natural and recycled aggregate concrete (RAC). In RAC, natural aggregates were replaced by 30% recycled concrete aggregates. All beams and slabs were cast with concrete mix design of 1:1.24:2.6 and w/c ratio of 0.43. Beams and one-way slabs, control and strengthened, were tested under four-point bending. Whereas, two-way slabs were tested in punching. A significant increase in the load-carrying capacity was observed for both natural and recycled aggregates concrete beams without shear reinforcement and two-way slabs, indicating the effectiveness of strengthening scheme. Increase of 20.5% and 12.6%, respectively, was found in the load-carrying capacities for the cases of both and natural and RAC beams with natural aggregate concrete (NAC) and RAC beams when results were compared for the case of shear deficient control and strengthened RC beams with CFRP wraps. Furthermore, increase of 27 − 37% was noted in load-carrying capacities of both natural and RAC two-way slabs when results were compared for the case of control and strengthened NAC and RAC slabs.

Structural reliability of a RC beam considering different preliminary designs

In the last decades, most of the structural designs around the world have been made by employing semi-probabilistic approaches based on partial safety factors. These practical methods allow the engineer to deal with the safety of structures without the need to directly address the uncertainties involved. The simplicity of these approaches depends on the fact that the same values of the safety factors must be applicable to a large number of different cases; this typically leads to dispersion in the structural reliability levels. The present paper aims at quantifying such dispersion within a specific scenario, regarding RC structures, in a way different from those found in the literature. It focuses on a simple residential building, for which seven preliminary design solutions are proposed by different engineers, and seven different structures are obtained from these solutions, considering the specifications given by the Brazilian structural design code ABNT NBR 6118:2014. The structural reliability indexes of a continuous beam, common to all solutions, are assessed and compared. The results indicate that, even in this specific case, the variability related to the safety levels is significant. Furthermore, in some cases the reliability index is found to be below the target levels provided by international structural standards.

Strain based damage indicators for finite element analysis of reinforced concrete structures

Numerical analysis conducted using a finite element model provides a quantitative and detailed evaluation of damage in concrete. As a result, the performance verification based on the local damage obtained numerically is considered an effective method for achieving a rational design of RC structures. Stresses and strains computed from numerical analysis are suited to indicators for representing local damage in concrete instead of sectional forces calculated from design equations; however, the performance evaluation using stresses and strains lack versatility owing to their dependency on constitutive equations and mesh discretization in numerical models. This study presents two types of strain-based damage indicators for performance verification in the design of RC structures using nonlinear finite element analysis. The second strain invariant of the deviatoric strain tensor is used to assess tensile damage, such as the opening of flexural cracks and the development of shear cracking in concrete, whereas the normalized accumulated strain energy is used to evaluate compressive damage, i.e., concrete crushing. These scalar indicators have high general usefulness, with calculation as non-local values by a weighted average, to reduce their mesh dependency. Furthermore, numerical analyses were performed to evaluate the damage condition and failure modes of RC beams, and the proposed damage indicators helped accurately understand flexure and shear failure. Lastly, we propose threshold values of the damage indicators for the performance verification of safety, represented by the load-carrying capacity in the design of RC structures.

The performance of Strengthened Lightweight RC Beams with different Techniques upon Exposure to Fire

Introduction: Reinforced concrete beams are used in a wide range of applications. In addition, reducing the weight of the concrete used increases the advantages of the beams. The main objective of this work is to study the performance of structurally strengthened lightweight reinforced concrete beams with different techniques with or without exposure to fire under concentric load and the efficacy of the fire protection system. Methods: The experimental specimens included eight half-scale tested rectangle beams with typical dimensions of 300 mm depth, 1700 mm total length, 150 mm total width, 50 mm cover, and 1500 mm span. The density of the lightweight polystyrene foam concrete was 1820kg/m3. The main parameters were fire resistance, different types of strengthening material for lightweight concrete beams, shape of the ferrocement layer on the lightweight concrete surface, and ferrocement thickness. Results: The results were analyzed in terms of crack patterns, failure modes, load deflection, load-strain behavior, stiffness, ductility, deformability, and absorbed energy. Conclusion: From the analysis of the results, the strength of LWC beams increased the strength and stiffness of the tested beam, and the fire protection system was found effective in protecting CFRP limitation from deterioration. In a theoretical study, the conservatism degree for calculating the maximum allowable flexure force was evaluated according to the ECP203, ACI-318, and BS-8110 codes.

Investigations into the Shear Load-Capacity of Strengthened Reinforced Concrete Structures with Carbon-Reinforced Concrete

As part of the experiments, 4-point-bending tests to investigate the shear capacity of strengthened T-beams were carried out. Thereby, 5 reference beams and 25 T-beams with carbon reinforced concrete strengthening were tested. Two different impregnated carbon grids in various strengthening configurations at the beams’ webs were checked. The number of strengthening layers was varied as well as the orientation of the grid in the strengthening layer. Furthermore, the influence of pre-damage of the RC beam before strengthening and two different shear slendernesses were investigated. A load increase of 25% to 42% compared to the unstrengthened reference specimens demonstrates the capability of carbon concrete for shear strengthening. In addition to the presentation of tested large-scale specimens, a test analysis will also be conducted, along with the derivation of a limit value for the maximum possible strengthening ratio using carbon-reinforced concrete based on the observed failure modes.

Experimental study on the effect of different shear reinforcement shapes and arrangement on 3D crack propagation and shear failure mechanism in RC beams

Surface crack patterns have been considered to determine the shear failure behavior of RC beams but the effect of three-dimensional crack propagation on shear crack development and shear strength of RC beams is still debatable. In this study, a three-dimensional crack evaluation was carried out to investigate the shear failure mechanism of RC beams with different shapes and arrangement of shear reinforcement (close shape shear reinforcement, rod shape reinforcement with mechanical anchorage, combination of close shape reinforcement and rod shape reinforcement, rod shape reinforcement and transverse distribution rebar) using three-point loading test by keeping the amount of shear reinforcement same in all beams. The load displacement relationships, 3D crack maps, stirrup strain and concrete strain relationships with displacement and shear resistance components were discussed in detail and these information’s are useful for designing and shear strengthening of existing beams. It was clarified that a clear difference in three-dimensional cracking pattern, shear resistance components of concrete and shear reinforcement contribution was observed in RC beams. This was due to the shear reinforcement shapes and arrangement of rod shape reinforcement, which influenced the shear strength of RC beams.

Flexural Behavior of RC Beam According to the Change in Adhesion Between Rebar and Concrete Due to Complex Deterioration

Flexural Behavior of RC Beam According to the Change in Adhesion Between Rebar and Concrete Due to Complex Deterioration

The Efficacy of Electromechanical Impedance Monitoring of Embedded Piezoelectric Ceramic Lead Zirconium Titanate Sensors in Different Orientations for Hybrid Fiber-Reinforced Concrete Structures Hydration

Abstract In this study, the influence of the orientation of embedded piezoelectric ceramic lead zirconium titanate (PZT) on the mechanical performance of hybrid fiber-reinforced (polypropylene and glass fiber) concrete beams was evaluated. The performance of concrete was evaluated under self-weight, followed by assessing the mechanical property using the electromechanical impedance (EMI) technique after optimization of M30 grade concrete with polypropylene fiber and glass fiber. PZT patches are embedded at different orientations, i.e., 0 deg, 45 deg, and 90 deg, with the axis of the structure for monitoring the hydration of the RC beam. The change in stiffness due to heat hydration in the concrete structure after 5, 7, 14, 21, and 28 days was observed by curing hybrid concrete beams and examining them after 5, 7, 14, 21, and 28 days. On the fifth day, beams were simply supported and allowed to deflect under their weight, and measurements of heat hydration in terms of conductance at frequencies ranging between 1 and 1000 kHz were done. Similarly, days 7, 14, 21, and 28 were done. Day 5 was considered the baseline. It is noted that the PZT sensor placed at an angle of 45 deg is the least effective in recording the incremental changes in hydration that occurred in the concrete beam. The highest quality results were obtained at 90 deg, which is further demonstrated by statistically quantifying the changes using the root-mean-square deviation (RMSD) percentage method and proves to be the most optimized orientation to obtain the stiffness of the hybrid reinforced beam in terms of conductance.

Shear capacity prediction for FRCM-strengthened RC beams using Hybrid ReLU-Activated BPNN model

This study presents a robust Hybrid ReLU-Activated Backpropagation Neural Network (BPNN) model for predicting shear strength (VFRCM) in RC beams reinforced with Fiber-Reinforced Cementitious Matrix (FRCM) composites. The model demonstrates exceptional accuracy, boasting a coefficient of determination (R2) of 0.924 and a mean root mean squared error (RMSE) of 10.611 kN on the test set. Leveraging k-fold cross-validation, the model's performance is rigorously assessed across ten data splits, emphasizing its reliable predictive capabilities. Hyperparameter optimization, guided by Particle Swarm Optimization (PSO), reveals an optimal value of α = 0.5757, minimizing the Mean Squared Error (MSE) to 74.53 for the dataset. Feature importance analysis underscores the significant role of critical parameters in shear strength prediction, with the longitudinal reinforcement ratio (ρl) emerging as the most influential feature, contributing 37.55 % to the model's predictive power. Additionally, the effective beam depth (d) is identified as the second most influential feature, providing approximately 16 % to the accurate prediction of VFRCM in RC beams strengthened with FRCM composites.

Experimental and analytical studies on residual flexural behaviour of reinforced alkali-activated slag-based concrete beams after exposure to fire

Understanding the flexural behaviour of reinforced alkali-activated slag-based concrete beams after exposure to a fire is imperative to ensure their safety use and develop adequate retrofitting measures. However, up to this point in time, no relevant investigations on this specific subject have been reported. This paper presents an experimental study comparing the flexural behaviour of alkali-activated slag-based concrete (AAC) and Portland cement concrete (PCC) beams exposed to the standard ISO 834 fire curve. The research considers concrete strength and heating duration as research parameters. The test results revealed that AAC beams displayed a lower temperature field and experienced less mid-span deflection increase compared to PCC beams during heating. Normal-strength AAC and PCC beams exhibited comparable losses in flexural capacity after being heated for 1 h or 1.5 h. However, PCC beam with a concrete strength over 80 MPa experienced more capacity loss due to severe spalling during heating. On the other hand, compared with PCC counterparts, AAC beams exhibited lower residual flexural stiffness and experienced greater stiffness loss, mainly due to the formation of more cracks induced by thermal shrinkage of AAC. The flexural capacity and stiffness loss of AAC beams increased with increasing concrete strength and heating duration after fire exposure. The residual flexural capacities of RC beams were predicted using a simplified analytical model that incorporates heat transfer analysis and the 500 ℃ isotherm method. The predictions demonstrated excellent agreement with the test results.

Potential change of failure modes and time-dependent behavior of RC beams under a marine atmospheric environment

Stirrups always corrode earlier than the longitudinal steel bars in RC beams, and the corrosion degree is higher. Stirrups will lose their bearing capacity due to corrosion, leading to a decrease in shear strength. Thus, the failure mode may change from bending to shear failure. Previous studies have proposed models to predict corroded RC beams' flexural and shear behavior, respectively. The missing link in these models was the absence of the change of failure modes on the structural behavior. This paper covers the authors' study of corroded RC beams, investigating the effects of reinforcement corrosion on the transformation of failure modes. A numerical simulation was performed to analyze RC beams' time-dependent behavior and failure modes. The effects of the concrete cover thickness, the corrosion initiation time, the concrete strength, and the reinforcement configuration were also investigated. The analysis showed that the stirrups corroded earlier than longitudinal steel bars, leading to potential shear failure rather than bending failure. The larger diameter of stirrups could be adopted in the design to delay the deterioration of structural behavior and the transformation of failure mode. Prolonging the corrosion initiation time using thicker concrete cover thickness and higher strength of concrete is also effective.

Experimental and theoretical study on shear behavior of HRB600 reinforced concrete beams after high temperature exposure

To investigate the variation pattern of shear performance in HRB600 RC beams after exposure to high temperatures (i.e., 200 °C, 400 °C, 600 °C, and 800 °C), 4 plain concrete beams were tested for temperature field. Additionally, 15 RC beams with shear span-to-depth (a/d) ratios of 1.2, 2, and 3 were subjected to four-point bending tests at room temperature and after high temperatures. The test results analysis focused on the effects of temperature and shear span-to-depth ratio on the failure pattern, concrete strain, load–deflection curve, and shear bearing capacity of the RC beams. The results demonstrated that increasing the shear span-to-depth ratio from 1.2 to 3 resulted in approximately 61.6 %, 51.8 %, 57.9 %, 53.0 %, and 55.5 % decreases in the ultimate bearing capacity of RC beams at 25 °C, 200 °C, 400 °C, 600 °C, and 800 °C, respectively. The load capacity of the test beam only decreased when the exposure temperature exceeded 600 °C, with the beam (a/d = 2) exposed at 800 °C exhibiting the most significant decrease of 32.4 % compared to room temperature. Finally, a method for determining the material parameters for the structure after exposure to high temperature is proposed. This method considers the sectional temperature field and is applied to the shear resistance calculation model at room temperature. The results indicate a strong agreement between the experimental and calculated values for both heated and unheated beams.

Flexural Performance Study of Basalt-Fiber-Reinforced Polymer Bar Basalt-Fiber-Reinforced Concrete Beams

The utilization of Fiber-Reinforced Polymer (FRP) rods to strengthen concrete beam structures can enhance their ultimate load-carrying capacity and mitigate steel reinforcement corrosion damage. However, a prominent issue with BFRP (Basalt FRP) rod reinforcement in flexural members is its lack of yielding behavior, which can lead to catastrophic brittle failure without any preventive measures. Therefore, this study aims to enhance the ductility of concrete by introducing a specific quantity of basalt fiber, thereby reducing the hazards associated with the brittle failure of this composite structure. This experiment focuses on two main variables: the inclusion rate of basalt fiber and the type of longitudinal reinforcement and conducts four-point static bending tests on four BFRP bar BFRC (Basalt-Fiber-Reinforced Concrete) beams. Results showed that the inclusion of fibers resulted in a delayed initiation of vertical cracks and a reduction in the severity of beam failure, thereby enhancing structural safety and reliability. When the basalt fiber inclusion rate was 0.2%, the cracking load and ultimate load of the beam increased by 18.42% and 8.27%, respectively. Furthermore, compared to traditional RC beams, BFRP bar BFRC beams showed a 58.27% increase in ultimate load capacity. A cracking moment calculation model for BFRP beams is proposed and subsequently validated through the utilization of existing experimental data.

Investigation on influence of corrosion and protective coating on steel rebars on flexural performance of RC beams

Investigation on influence of corrosion and protective coating on steel rebars on flexural performance of RC beams

Research on meso-equivalence simulation method of freeze–thaw concrete under multiaxial loading

In view of the influence of freeze–thaw cycles (FTCs) on the spatial strength of principal stress was not considered, a meso-equivalence simulation method was developed, considering the heterogeneous characteristics of FT concrete, to accurately depict frost damage behavior, which can be used to simulate the spatial strength distribution on principal stress of concrete with FTCs. Additionally, a meso-calculation method was employed to verify the loading boundary conditions and material constitutive models. Subsequently, the effectiveness of the meso-equivalence simulation method was established by its application to the mechanical analysis of FT concrete under multiaxial loads, alongside the formulation of meso-equivalence calculation models for FT-reinforced concrete (RC) beams. The results underscore the efficacy of the meso-calculation and meso-equivalence models in capturing damage mode within concrete, subjected to FTCs under multiaxial loads. Importantly, the strength envelope derived from the calculation model and the corresponding strength criterion for the multiaxial loading limit state of FTC-affected concrete aligns consistently with test findings. Moreover, the validation of the meso-equivalence simulation method is established by comparative analysis of the mechanical behavior of RC beams under FTCs, compared with test results, which not only enhances understanding of FT response but also contributes to the advancement of durability assessment.