Corroded Reinforced Concrete Beams Research Articles

Prediction of residual performance of corroded RC beams from observed surface cracks by 3D RBSM with MPC

Corrosion of reinforcing steel in concrete structures can significantly compromise their performance. Accurately estimating this deterioration for in-service structures is challenging due to uncertainties surrounding the distribution of internal corrosion and cracking patterns, compounded by the limitations of destructive testing. This research proposes a novel approach to predict the remaining load-bearing capacity of corroded reinforced concrete (RC) structures based on the pattern of surface cracks caused by corrosion. The method integrates a model predictive control (MPC) algorithm with a three-dimensional Rigid Body Spring Model (3D RBSM) to estimate internal corrosion levels from observed cracks and a normal 3D RBSM simulation to predict the residual performance. The proposed system is validated through analysis of four corroded beam specimens based on experimental work reported in the literature. In use, the MPC algorithm first estimates a corrosion distribution in a RC beam and generates simultaneous corrosion-induced crack and stress predictions. This information is then used to predict residual load-bearing capacity. The system accurately forecasts the non-uniform corrosion distribution, flexural capacity, and load-displacement curves of a specimen, offering insight into the performance differences among the specimens and demonstrating its potential to assess the serviceability of existing RC structures with corrosion issues.

Hybrid Machine learning Techniques-Aided design of corroded reinforced concrete beams

Shear strength (SS) is an essential component in the design of reinforced concrete structural elements, particularly in severe settings where reinforcements can occur and cause a loss in SS. The purpose of this work is to develop a framework for predicting the SS and optimal design of corroded reinforced concrete (CRCo) beams by using a machine learning (ML) approach. The model employed was Gradient Boosting (CGB), optimized using three metaheuristic algorithms. By optimizing the CGB model with the Hunger Games Search (HGS) algorithm, the study achieved the best ML model for predicting the SS of CRCo beams, with an R2 value of 0.996. The proposed model outperformed five other empirical SS models for CRCo beams, and sensitivity, partial dependence analyses were also conducted to explore the impact of various variables on SS. Finally, this work provided guidance on selecting appropriate beam sizes and corrosion rates for optimal CRCo beams design solutions.

Time-dependent reliability assessment and optimal design of corroded reinforced concrete beams

It remains a significant challenge to quantitatively describe the corrosion of reinforced concrete (RC) structures under chloride penetration. Moreover, when considering uncertainties throughout the life cycle of corroded RC structures for assessing their safety, reliability, and optimal design, the complexity of the problem intensifies. To address these issues, this paper studies the time-dependent reliability analysis and optimal design of corroded RC beams. At first, the time-dependent reliability of beams is investigated by considering both the serviceability limit state (SLS), which corresponds to the corrosion initiation of the reinforced steel, and the ultimate limit state (ULS), associated with the bending failure of the beam. This analysis takes into account the time-dependent chloride diffusion coefficient and incorporates a stochastic process. The reliability is evaluated using the Monte Carlo Simulation (MCS) method and the cumulative distribution function (CDF) method. Subsequently, a time-dependent reliability-based design optimization (TRBDO) problem is formulated, and the PSO-MCS, a methodology incorporating a particle swarm optimization (PSO) algorithm and MCS is adopted to solve it. After optimization, the initial cost of the specific RC beam is reduced from 1351.879€ to 1247.075€, while the time-dependent reliability within [0, 100] years is improved from 0.6057 to 0.6508. The effectiveness of the CDF, MCS and PSO-MCS methods are demonstrated through reliability analysis and design examples of corroded RC beams.

A Novel SMFL-Based Assessment Method for Corrosion Nonuniformity of Rebar and Its Application in Reliability Analysis of Corroded RC Beam

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

Characterization and grading assessment of rebar corrosion in loaded RC beams via SMFL technology

Accurate measurement and assessment of rebar corrosion are critical for the safety and durability of reinforced concrete (RC) structures. The non-destructive self-magnetic flux leakage (SMFL) technology is often employed but still has some difficulties in achieving this goal, especially when the RC structure is under load. Therefore, an SMFL measurement experiment and corresponding finite element simulation of six loaded corroded RC beams were carried out in this study. Then, a dimensionless SMFL quantitative index Gi for assessing the corrosion degree of the loaded RC beam was proposed. The experimental and simulated index Gi has a similar linear correlation with the corrosion degree of the longitudinal tensile rebars of the RC beams. The corrosion-induced increasing ratio of index Gi was up to 500% while that of the load-induced does not exceed 10.6%, which indicates that load has little effect on the SMFL-based corrosion degree assessment of RC beams. Furthermore, a universal grading assessment standard of the corrosion degree of loaded RC beams was established based on the Bayesian model and a Gi data set extracted from 500 random simulation combinations of corrosion distribution and load. According to this standard, the corrosion level of the loaded RC beam can be directly determined via the value of Gi with an accuracy between 70% and 100%. This work is beneficial for the engineering assessment of the rebar corrosion of loaded RC beams and provides an innovative research idea for this research field.

Flexural Behavior of Corroded RC Beams Strengthened by Textile-Reinforced Concrete

The flexural behavior of corroded reinforced concrete (RC) beams strengthened with textile reinforced concrete (TRC) was analyzed and discussed in this work. Thirteen beams, including one reference beam, three corrosion-only beams, and nine TRC-strengthened corroded beams, were tested under four-point bending. The failure modes, cracks, bearing capacity, load–displacement curves and ductility of the tested beams were analyzed. The results showed that the TRC played a role in increasing the number of cracks and decreasing the width of the cracks in the corroded RC beams. In terms of improving the bearing capacity, TRC can improve the bearing capacity of corroded beams even more than the reference beams, and the strengthening after removing the concrete cover of corroded RC beams is better than direct strengthening. The corroded beams after TRC strengthening exhibited improved ductility. The energy absorption index of the TRC-strengthened corroded RC beams increased with the increase in the number of textile layers.

Flexural behavior of the corroded RC beams strengthened with BFRP grid-reinforced ECC

In marine environment, the reinforced concrete (RC) used in offshore structures is subjected to significant erosion by chloride ions, resulting in severe degradation of its mechanical performance. Therefore, it is essential to employ appropriate strengthening techniques to enhance the mechanical properties of such corroded components. To assess the effectiveness of these strengthening techniques, this study investigated the flexural behavior of corroded RC beams strengthened with Basalt Fiber Reinforced Polymer (BFRP) grid-reinforced Engineered Cementitious Composite (ECC). A series of numerical models were developed and their accuracy was verified through experimental results. Subsequently, the contributions of various components to flexural capacity, stress distribution, and the neutral axis position at different stages were investigated through numerical analysis. Additionally, the impact of key parameters on the flexural capacity of the hybrid beams was discussed. Finally, a theoretical model was proposed to predict the moment-displacement curves of the hybrid beams. The results showed that, at the point of hybrid beam failure, the stress within the BFRP grid reached 50%–70% of its maximum tensile stress. As the cross-sectional area of the BFRP grid increased, it effectively delayed the failure caused by tensile stress in the hybrid beam. The theoretical model successfully predicted the moments of the hybrid beams at three feature points.

Fracture Analysis of Short-Scale Corroded/Healthy Reinforced Concrete Beams under Bending Using Acoustic Emission.

In this work, the acoustic emission (AE) technique is used to evaluate the fracture process of corroded and healthy reinforced concrete (RC) beams subjected to a monotonic bending test. In fact, many researchers have conducted laboratory experiments considering different conditions to perform rebar corrosion monitoring in RC structures using the AE method. However, previous studies have not investigated the evolution of the bending performance of RC beams at different corrosion degrees, considering the interaction of single rebar with concrete. In this study, healthy and electrically corroded RC beams are evaluated, considering different corrosion levels. The analysis of the moving average of the AE maximum amplitudes was consistent to distinguish four stages of mechanical behavior that the healthy, and corroded specimens with low and medium corrosion levels of 0.9% and 3.2% experienced up to failure. Three damage stages were identified in the case of a high corrosion level of 9.3%. Then, the AE maximum amplitudes were suitable to establish an efficient clustering, which enabled the classification of the fractures into minor, medium, and major classes. Furthermore, the digital analysis method proposed in this study was suitable to visually reveal the influence of the preexisting corrosion-induced damages on the bending failure process of the RC beams.

Korozyona Uğramış Betonarme Kirişler için Kesme Dayanımını Belirlemeye Yönelik Basitleştirilmiş Bir Yaklaşım

Corrosion damage, which can be considered as a construction or usage defect during the life of the structure, is an important parameter for the structural elements. Strength loss is observed in reinforced concrete (RC) elements due to corrosion, which is an important parameter affecting the performance of the building. Determining the shear strength of beams with corroded reinforcement is important in terms of strength loss, design, and reinforcement criteria in the structural element. In this context, the data of the corroded RC beam experimental tests carried out in the literature were collected and the ultimate shear strength values of the beams were determined depending on the test parameters. Strength estimation was performed with machine learning regression algorithms XGBoost and AdaBoost. The results obtained were evaluated with R2, RMSE and MAE performance metrics and high estimation success was achieved. The study shows that with these systems, which can perform learning based on experimental data, it is possible to estimate the shear strength values of corroded beams with known production parameters without the need for experimental measurements.

Time-dependent reliability analysis of corroded RC beams based on the phase-type fitting method

It remains an important challenge to quantitatively describe the corrosion of reinforced concrete (RC) structures under chloride penetration. When considering the uncertainties encountered throughout the life cycle of RC structures exposed to a corrosive environment and evaluating their safety and reliability, the complexity of the problem intensifies. To address these issues, this paper focuses on the time-dependent reliability analysis of corroded RC beams, utilizing the phase-type (PH) fitting method. Initially, a model for the time-dependent reliability of corroded RC beams is established, incorporating the time-dependent chloride diffusion coefficient. Subsequently, a novel PH fitting method is proposed. The effectiveness of this new method is demonstrated through numerical examples. Furthermore, the time-dependent reliability analysis of corroded RC beams is compared using both the PH fitting method and the Monte Carlo simulation. The results reveal that the proposed method can accurately and efficiently deal with time-dependent reliability problems.

Mixed Bayesian Network for reliability assessment of RC structures subjected to environmental actions

Under environmental action, reinforced concrete (RC) structures might suffer from reinforcement corrosion caused by the surrounding environment, dramatically reducing structural reliability and threatening social development. However, most of the existing reliability assessment methods for RC structures only focused on the structural performance at the design stage given the original unchanged environment, ignoring the effects of realistic exposure conditions and inspection results on reliability evaluation. Thus, this paper develops a general reliability assessment framework based on a Mixed Bayesian network (MBN), incorporating three modules, i.e., durability assessment, load-bearing capacity analysis, and time-dependent reliability analysis. In MBN, separate sub-BNs are built based on different modules and connected by pinch point variables where probabilistic information is transmitted via soft evidence. Besides, this framework considers time-dependent environmental parameters and two-dimensional chloride transport and their effects on reliability. Meanwhile, adjustment coefficients are applied to improve the results of the analytical mechanical model with respect to different limit states through the finite element model (FEM). The proposed MBN framework is illustrated for a corroded RC beam under a marine atmospheric environment to investigate the effects of environmental modeling, chloride transport patterns, and concrete crack inspection on reliability assessment. The results indicate that under the assumed conditions in the case study, early inspection of large cracks may significantly overestimate the failure probability by about 500%. Besides, failure probability might be underestimated by about 95%, ignoring the time-variant environment and two-dimensional chloride transport.

Modelling of long-term performance of RC beams under coupling steel corrosion and bond deterioration

The steel-to-concrete bond deterioration due to corrosion in the reinforced concrete (RC) structures still needs more investigation because the existing models were established based on pull-out tests, which do not represent the real RC beams owing to the flexural cracks. This paper presents a new approach that discusses the bond deterioration of corroded steel bars embedded in RC beams. The study presents simulations for an experimental database of existing corroded RC beams from previous papers using a nonlinear finite element model. The simulated specimens were divided into two categories: accelerated and long-term (after 14,23, and 28 years) corroded beams to identify the key corrosion parameters in these two conditions. The results indicated that the behavior of the RC beams, which corroded via the accelerated method, failed by concrete crushing after steel yielding, and it could be simulated considering the reduction of both steel area and bond strength only. On the other hand, the spalling pressure is a key parameter to simulate the long-term corroded RC beams because it controls the ultimate deflection, and the failure is governed by concrete cover spalling due to concrete deterioration. As an innovative result, a novel bond-slip model was proposed to predict bond deterioration due to corrosion in the RC beams, and it showed excellent accuracy compared to the existing models.

STRENGTHENING OF CORROSION-DAMAGED RC BEAMS USING UHPFC LAYERS

In the present work, experimental and numerical investigations were carried out to examine the flexural performance of reinforced concrete (RC) beams after undergoing different degrees of accelerated reinforcement corrosion and strengthened using ultra-high-performance fiber reinforced concrete (UHPFC) layers. The strengthened RC beams were tested under flexure to evaluate the effect of the UHPFC layers (with combinations of three UHPFC layer thicknesses for both options of one-sided and three-sided strengthening) on the failure mode, flexural strength, and stiffness. The flexural strength of the RC beams was significantly enhanced by increasing the thickness of the UHPFC layer. Three-sided strengthening resulted in a higher load-carrying capacity of the RC beams as compared to that of one-sided strengthening. Minimum layer thicknesses required to fully restore the load-carrying capacity of the corroded RC beams were found to be 20 mm and 40 mm for three-sided and one-sided strengthening, respectively. At ultimate load, the mid-span deflections for the strengthened beams were about half of that of the un-strengthened beams due to an increase in the stiffness of the strengthened beams. Finally, the experiment results matched the 3D-FEM predictions, indicating the simulation's accuracy in evaluating corroded-strengthened RC beam flexural performance.

An improved method for predicting the shear strength of corroded reinforced concrete beams with experimental and numerical validation

Shear failure of reinforced concrete (RC) beams is a brittle failure without giving sufficient warning. Steel bar corrosion is one of the main deterioration phenomena for concrete structures in marine environments. However, the effect of steel bar corrosion on the shear-transfer mechanism of RC beams is not yet fully understood, and existing findings are insufficient for reasoned and accurate prediction of shear strength. Thus, the primary objective of this study was to propose and validate a revised fictitious-support-point method for better predicting the shear strength of corroded RC beams. The revised method determines the fictitious support points based on a more transparent mechanical model than previously. Finite element simulation confirms the validity of the revised method from the load-bearing mechanism point of perspective. Validation with copious previously-published test data show that the revised method predicts the shear strength of corroded RC beams more accurately and reasonably than the existing method proposed by other researchers. This study contributes to effective and reasonable maintenance of corroded RC structures.

The effect of recycled-tire steel fiber and engineered steel fiber on rebar corrosion and shear behavior of corroded RC beam

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.

Performance of corroded RC beams strengthened in flexure using UHPC: Effect of configuration and thickness of the UHPC layers

In the present paper, an experimental investigation was carried out to examine the effect of configurations and thicknesses of ultra high performance fiber reinforced concrete (UHPC) layers on the flexural performance of reinforced concrete (RC) beams strengthened using UHPC layers after undergoing different degrees of accelerated reinforcement corrosion. The beams were tested under flexure to evaluate the effect of UHPC strengthening (with combinations of three UHPC layer thicknesses and two configurations) on failure modes, flexural strengths, and stiffnesses. Statistical analysis of the flexural test results using analysis of variance (ANOVA) showed the significant effects of both configuration and thickness of the UHPC layers on the performance of corrosion-damaged RC beams in flexure, irrespective of the degree of reinforcement corrosion. The RC beams strengthened with UHPC layers applied on three sides exhibited the most significant increase in the ultimate flexural strength in the range of 6 to 63% and an increase in the stiffness in the range of 28 to 112% as compared to that of the uncorroded control beam. Furthermore, analytical models were developed to predict the flexural strength of the corroded beams strengthened using different configurations of UHPC layers. The close agreement of the ultimate flexural strength between the experimentally obtained results and analytically predicted values for the strengthened RC beams indicates the accuracy of the developed analytical models, which can be used to select an optimum strategy for strengthening the corrosion-damaged RC beams.

Flexural Behavior of Corroded Concrete Beams Strengthened with Carbon Fiber-Reinforced Polymer.

The present study investigates the flexural behavior of reinforced concrete (RC) beams; the longitudinal reinforcing rebars of the beams were corroded and then strengthened with carbon fiber-reinforced polymer (CFRP). The corrosion of the longitudinal tension reinforcing rebars in eleven beam specimens was accelerated in order to obtain different corrosion levels. Afterwards, the beam specimens were strengthened by bonding one layer of CFRP sheets to the tension side to restore the strength loss due to the corrosion. The failure modes, flexural capacity, and midspan deflection of the specimens with different corrosion levels of the longitudinal tension reinforcing rebars were obtained by the four-point bending test. It was found that the flexural capacity of the beam specimens decreased with the increase in the corrosion level of the longitudinal tension reinforcing rebars and that the relative flexural strength was only 52.5% when the corrosion level was 25.6%. The stiffness of the beam specimens decreased significantly when the corrosion level was higher than 20%. Through a regression analysis of the test results, a model for the flexural bearing capacity of the corroded RC beams strengthened with CFRP was proposed in the study.

Experimental study, numerical simulation and GRNN model for predicting the flexural loading capacity of corroded reinforced concrete beams

The present article is an effort to quantify the flexural strength of corroded reinforced concrete (RC) beams. Eight RC beams with dimensions of 150 × 200 × 2200 mm were tested in four-point bending, including six beams corroded in a chloride environment with average corrosion of longitudinal reinforcement in the range of 5% to 15%. The remaining two beams were used as control beams. The ultimate strength, failure mode and particularly the relationship between crack width and corrosion level are analyzed and discussed. A two-dimensional non-linear finite element model has been presented to simulate the steel bar corrosion considering the deterioration of concrete strength and steel-concrete bond stress. The generalised regression neural network (GRNN)-based model for the ultimate flexural strength of corroded RC beams has been established based on 123 experimental data collected from previous studies. The experimental results were used to separately validate the non-linear finite element model and novel GRNN model. Experimental results indicate that if the overall corrosion rate is used, the corrosion crack width can be a function of the percentage of section loss. The GRNN model provides superior predictive results compared to previous empirical methods with the highest correlation coefficient (r), and the smallest normalised root mean square error.

NSM and hybrid techniques for retrofitting corroded RC beams using GFRP bars

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.

Deformation Performance of CFRP-Strengthened Corroded Reinforced Concrete Beams after Fatigue Loading

To study the deformation performance of CFRP-strengthened corroded RC (reinforced concrete) beams under fatigue loading, a numerical analysis method based on the fatigue damage failure process was used, and the fatigue constitutive models of each material were used as the basis. The finite element software ABAQUS was used to model and analyze the CFRP-strengthened corroded RC beams, and the degradation of bond performance between rusted reinforcement and concrete was considered in the simulation. Then, the flexural stiffness calculation method of CFRP-strengthened corroded RC beams was analyzed. Based on the validation of the finite element model, a regression analysis was performed on the mid-span deflection data of the simulated beam to establish a formula for calculating the mid-span deflection of CFRP-strengthened corroded RC beams under fatigue loading. Finally, the collected experimental data were compared with the calculation results using the mid-span deflection formula, which was validated to confirm its accuracy and reliability. The research results show that the mean, standard deviation and coefficient of variation of the ratio of experimental to calculated values were 0.95, 0.09 and 0.10, respectively, indicating that the calculated values of the proposed mid-span deflection formulation are in good agreement with the experimental values, which proves the correctness and high accuracy of the proposed formula for calculating the mid-span deflection. The formula can provide a theoretical basis for the evaluation of the deformation performance of CFRP-strengthened corroded RC beams under fatigue loading.