Corroded Reinforced Concrete Columns Research Articles

Fire performance of aged and corroded reinforced concrete columns

The existing guidelines for determining the fire ratings of reinforced concrete (RC) columns only take into account undamaged components, without considering any deterioration caused by age or corrosion. An experimental study was conducted to examine the effect of corrosion on the fire performance of RC columns. In this study, six full-scale RC column specimens were cast, corroded, and tested in fire conditions, consisting of two made of normal strength concrete (NSC) and four made of high-strength concrete (HSC). Out of these six, three RC columns (1-NSC and 2-HSC) were corroded using a specifically designed accelerated corrosion setup for a target mass loss of 30 %. After the completion of the accelerated corrosion exposure time, these three corroded column specimens, along with three other non-corroded control column specimens, were tested in a fire furnace, simulating the ISO-834 fire curve. It was found that due to corrosion exposure, the steel reinforcement underwent significant mass loss, and severe corrosion cracks were observed. These cracks were discovered to serve as convenient channels for heat transfer. This facilitated the earlier and more severe spalling of the concrete cover, ultimately leading to premature deterioration in the strength of the corroded RC columns during the fire. Consequently, this contributed to the catastrophic failure of the corroded RC columns, with a significant reduction in fire ratings- 44 % for NSC columns and 40.49 % for HSC columns. This paper also addresses the spalling characteristics of the corroded columns and their structural responses, including axial deformations, lateral deformations, and load variations.

Comparative study on seismic behavior of corroded RC columns strengthened by ECC combined with steel cage /fiber grid/CFRP

A method for strengthening was proposed to improve the seismic behavior of corroded reinforced concrete (RC) columns by using engineered cementitious composite (ECC) combined with a steel cage/fiber grid/carbon fibre reinforced plastics(CFRP). The corroded RC columns strengthened with ECC combined with a steel cage, fiber grid, and CFRP were subjected to low cyclic compression tests at design axial pressure ratios (n) of 0.3 and compared with corroded and uncorroded columns. Experimental results showed that ECC strengthening of corroded RC columns not only significantly improved their load-carrying capacity, displacement ductility, and energy dissipation capacity but also effectively reduced the degree of damage and stiffness degradation. The ductility coefficients of ECC/steel cage composite strengthened columns and ECC/CFRP composite strengthened columns are 35.58 % and 34.13 % higher, respectively, compared to ECC fully strengthened columns, while the ductility coefficient of ECC/fiber grid composite strengthened columns decreased by 4.33 % compared to ECC fully strengthened columns. Among them, the ECC/steel cage composite-strengthened columns exhibited the highest number of hysteresis loops, the strongest energy dissipation capacity, and the best strengthening effect. Additionally, a restoring force model for ECC-strengthened corroded RC columns was established, and its validity was verified through theoretical calculations.

A modified truss-arch model for shear strength evaluation of corroded reinforced concrete columns

Under seismic loading, corroded reinforced concrete (RC) columns are prone to brittle shear failure, which poses a significant threat to existing structures. However, due to the mechanical defects and insufficient parameters included in the equations available in codes, the literature exhibits a lack of precision in predicting the shear strength of such columns. In this paper, a shear strength equation for the RC column was established based on the truss-arch model theory. On this basis, the effect of corrosion on key parameters such as the cross-sectional area of rebar, yield strength, compressive strength of concrete, and displacement ductility was fully considered to establish the shear strength equation of corroded RC columns. To assess the accuracy and applicability of the proposed equation, a database consisting of 215 specimen parameters was compiled. Comparative analyses were conducted with existing equations from the literature. The results indicate that the mean values and coefficient of variation for the ratio of calculated values to the tested values of the equation were 1.098 and 0.601, respectively, which proves the equation’s high computational accuracy and low dispersion. Consequently, the proposed equation offers a more effective calculation method for predicting and assessing the shear strength of corroded RC columns. This method holds significant potential for enhancing the resilience of structures in seismic-prone regions.

Axial compressive behavior and model analysis of BFRP-jacketed corroded and pre-damaged circular reinforced concrete columns

Corrosion of steel reinforcements degrades the structural performance of reinforced concrete (RC) columns under static and seismic loads. Such corroded RC columns are usually retrofitted with fiber-reinforced polymer (FRP). However, existing studies on the retrofitting of RC columns with corrosion and load-induced damage are limited. To confirm the effectiveness of basalt FRP (BFRP) jacketing on the compressive behavior of corroded and pre-damaged RC columns, this study performed axial compression tests on eleven circular RC columns. The columns were fabricated, corroded, pre-damaged, and then jacketed with BFRP composites and reloaded to investigate the effects of BFRP layer number, corrosion ratio, and pre-damage degree. When jacketed by BFRP, the ultimate strength and ultimate strain of RC columns increased with BFRP layer numbers, ranging from 5% to 98% and 448% to 926%, respectively. Further, the ultimate strength and elastic modulus of the jacketed RC columns decreased with the increase in pre-damage degrees and corrosion ratios, while the ultimate strain was little affected. Buckling and corrosion of longitudinal bars significantly reduced the bar stresses at the ultimate state of BFRP-jacketed RC columns and resulted in local rupture of BFRP. This adverse effect became more pronounced as the corrosion ratio increased, but was alleviated by BFRP jacketing. On the other hand, a refined rebar stress-strain model was developed by addressing the effects of buckling, corrosion, and lateral confinement. Further, a feasible constitutive model for corroded hoop-confined columns was determined by validating the existing test results. Finally, models for the ultimate strength, ultimate strain, and stress-strain response of BFRP-jacketed corroded and pre-damaged RC columns were developed.

Time-dependent seismic fragility analysis of reinforced concrete columns subjected to chloride-induced corrosion

This paper presents a stochastic methodology to perform time-dependent seismic fragility analysis for reinforced concrete (RC) columns subjected to chloride attacks. Numerical modelling methods considering the increasing variability of reinforcement mechanical properties were proposed based on the stochastic constitutive model for corroded steel bars. Depending on the finite element model validated by test data for uncorroded and corroded RC columns, two novel stochastic cases and a traditional deterministic case were introduced and then applied to pushover analysis, incremental dynamic analysis and seismic fragility analysis. The results of damage limit states (DLSs) determined by stochastic pushover curves indicated that the seismic capacity/DLSs for columns along the service life were time-dependent and followed lognormal distributions. The incremental dynamic analysis curves and seismic fragility curves implied that chloride-induced corrosion typically led to a substantial increase in the failure probability of columns. In comparison with the correlated stochastic method, considerable underestimations of component level fragility across different damage limit states were obtained using the deterministic approach, which highlighted the importance of accounting for the variability of mechanical properties of corroded steel bars in the time-dependent seismic fragility analysis.

Exploring the shear performance and predictive shear capacity of corroded RC columns utilizing the modified compression-field theory: An investigative study

Corrosion damage substantially weakens the shear strength of reinforced concrete (RC) structures, severely compromising their seismic resistance. Therefore, developing an accurate constitutive model is imperative to investigate the impact of corrosion damage on the shear resistance of RC structures. This study presents a corroded RC shear constitutive model based on the modified compression-field theory (MCFT). To capture the flexural, shear, and slip responses of corroded RC columns accurately, a nonlinear analysis model based on OpenSees is proposed. Comparing the results from four sets of quasi-static tests reveals that the proposed constitutive model and analysis framework can well simulate the seismic performance of corroded RC columns. Based on the comparative analysis, the influence of corrosion-induced damage, reinforcement ratio, and axial load on the shear performance of RC columns is discussed. The investigation findings reveal that high corrosion levels and low reinforcement ratios remarkably weaken the shear strength of RC columns. Additionally, high axial load levels accelerate the rate of post peak shear stress degradation. Moreover, this study proposes a method for estimating the shear strength of corroded RC columns based on the MCFT. The presented approach provides a solid foundation for evaluating the shear and seismic performance of existing RC structures.

Damage prediction of RC columns with various levels of corrosion deteriorations subjected to blast loading

Coastal structures are often exposed to harsh environmental conditions such as saltwater, high humidity, and coastal winds, leading to corrosion damage to the reinforcing steel and degradation of concrete. The blast risk is characterized by a relatively low likelihood but a significant consequence. The blast resistance of structural members with deteriorated properties due to corrosion and the corresponding post-blast performance is of significance to evaluate the lifecycle structural safety facing explosion threats. In this study, the damage of reinforced concrete (RC) columns of coastal structures with various corrosion degrees subjected to blast loading is investigated. The corrosion effect was modelled by considering the deterioration of rebar diameter and yield strength, bond strength between rebar and concrete, and rust expansion pressure effect. The numerical model was validated by simulating drop weight impact tests of RC beams with different corrosion degrees. Based on the validated model, the finite element (FE) models of corroded RC columns with the maximum corrosion degree of 15% were established and their responses and damage to blast loads of various blasting scenarios were calculated. It is found that the blast response of the column increases with the degree of corrosion. The blast damage mode may change from combined shear and flexural damage to concrete spalling damage with the increment of corrosion degree. Furthermore, the residual axial loading capacity and stiffness of post-blast columns were calculated and it is found that they degrade as the corrosion degree increases. A blast damage index is defined in terms of the residual axial loading capacity of the column, which is found to increase with the corrosion degree. The damage amplification factor due to corrosion deterioration (CAF) is then proposed as a function of corrosion degree, TNT equivalent mass, standoff distance, concrete strength, and reinforcement ratio to predict the blast damage of corroded columns.

Machine learning-based prediction for residual bearing capacity and failure modes of rectangular corroded RC columns

Chloride-induced corrosion of steel reinforcement is likely to change the failure modes of reinforced concrete (RC) columns in marine environments under the combined action of vertical and seismic load. This study was aimed to predict the residual horizontal bearing capacity and failure modes of corroded RC columns based on machine learning (ML) methods. First, a database (163 flexural failure, 26 flexural-shear failure, and 35 shear failure) of rectangular corroded RC columns was established according to predefined selection criteria. Then, 6 efficient ML algorithms, including support vector machine, artificial neural network, k-nearest neighbors, convolutional neural network, random forest, and categorical boosting, were employed to establish predictive models for evaluating the residual bearing capacity and failure modes of corroded RC columns. Based on the SHapley Additive exPlanations (SHAP) method, the importance of input characteristic parameters was ranked and how the input parameters make decisions to obtain the final output results explained. Finally, influences of stirrup corrosion level (ηt), shear-span ratio (λ), and axial load ratio (n) were investigated regarding the residual bearing capacity and failure mode evolution of corroded RC columns. The results show that the proposed ML models can effectively predict the residual bearing capacity and failure modes of corroded RC columns and exhibit great potential for describing the relationship between input variables and output results.

Deformation limits of corroded reinforced concrete columns

Steel reinforcement corrosion is one of the main causes of the mechanical degradation of reinforced concrete (RC) members. Selecting proper performance indexes and quantifying their limits for structural components is an important issue in the life-cycle performance-based seismic design. In this study, the damage levels of flexure-dominated RC members are defined mainly based on the material strain. The mechanical and deformation behavior of corroded RC columns are analyzed by numerical simulation performed with Abaqus software. The corrosion ratio, the axial compression ratio, the longitudinal reinforcement ratio, the stirrup ratio and the shear-span ratio are considered in the parametric analysis. It is found that the performance of slightly corroded columns is approximate to that of noncorroded columns, although the deformation capacity significantly degrades if the column corrosion is severe. An increase in the axial compression ratio leads to a decrease in the deformation capacity of RC columns. Increases in the longitudinal reinforcement ratio and stirrup ratio are beneficial to improving the deformation capacity of slightly corroded columns but have little effect on the ultimate deformation of severely corroded columns. According to the numerical results, formulas of the yield and ultimate deformation of corroded RC columns are derived, and the deformation limit of each damage level are proposed, which can both be applied in the life-cycle performance-based seismic design and assessment of RC structures.

Investigation of Corroded Bond-Slip Effects for Corroded RC Columns

Steel bar corrosion is one of the most common causes of structural performance degradation for reinforced concrete (RC) columns subjected to extreme loads such as earthquakes. Due to the different characteristics of corrosion effects, a comprehensive and efficient finite element (FE) modeling approach is necessary for the performance assessment of corroded RC columns. To this end, this study provides an effective FE modeling approach using a recently developed geometrically nonlinear fiber-based frame element that considers bond-slip, allowing for explicit representation of corrosion-affected bonding. This aspect necessitates the use of an explicit material model for corroded bond-slip and its associated corroded properties. Since the existing models of corroded bonding properties in the literature were developed based on the highly scattered and limited experimental data, this study develops a new probabilistic model for corroded bonding properties based on more experimental data compiled from the literature and quantifies the prevailing uncertainties. To facilitate its use for modeling corroded RC structures, a cyclic corroded bond-slip model in an open-source FE software framework is implemented. In this paper, the FE modeling approach is first used to model two corroded RC columns tested in the literature, with comparison to the conventional modeling approach (i.e., assuming perfect bonding). The influence of corroded bonding on the static and dynamic behaviors of RC columns is further explored deterministically. Furthermore, the impact of uncertainty in corroded bonding properties on the static and dynamic behavior simulations of RC columns is examined. This work is concluded that (1) the FE modeling approach provided for corroded RC columns proves to be effective in capturing corrosion effects; and (2) corroded bonding plays an important role in simulating the behavior of corroded RC columns, and thus cannot be neglected. This is particularly true considering its associated uncertainty and its impact on the performance assessment of RC columns under severe corrosion conditions.

Bond-Slip Model of Corroded Reinforced Concrete and Its Application in Members

ABSTRACT The corrosion of longitudinal rebar and stirrups will cause serious degradation to the bond performance between steel bars and concrete. To investigate the impact of both longitudinal rebar and stirrup corrosion on the bond behavior, 35 reinforced concrete (RC) pull-out specimens were subjected to accelerated corrosion tests of electroosmosis-constant current-dry wet cycles and pull-out tests, and then the influence laws of the degree of corrosion of the longitudinal reinforcement, degree of corrosion of the stirrups, cover thickness, stirrup spacing and longitudinal reinforcement diameter on the bond performance were studied. The bond behavior between corroded steel bars and concrete was analyzed from the aspects of corrosion form, failure mode and bond strength. Subsequently, based on the experimental data, a modified bond-slip constitutive model that considers the design parameters, stirrup corrosion and longitudinal rebar corrosion was built and verified. Finally, based on the established modified bond-slip constitutive model, the corroded RC column was simulated, and the accuracy of the established modified bond-slip constitutive model was verified at the component level.

Structural performance deterioration of corroding reinforced concrete columns in marine environments

In aggressive marine environments, rebar corrosion caused by chloride ion ingression in concrete is a critical factor leading to premature failure of in-service reinforced concrete (RC) structures. This paper investigated the structural performance deterioration of marine RC structures affected by rebar corrosion, and proposed new analytical models for predicting the residual bearing capacity of the corroded RC columns. By analyzing the performance deterioration mechanisms of the corroded RC structures, the material degradation models and structural strength reduction models were constructed. Then, the analytical models for estimating the residual bearing capacity of the corroded RC columns under various loading conditions were proposed. From the proposed models, the moment-axial force (M-N) interaction diagrams were plotted for analyzing the influence of corrosion damage locations on the residual bearing capacity. Furthermore, the impact of marine environmental factors on the service life of the corroding RC columns under various loading conditions was investigated. Finally, a numerical example for the corroded RC columns was given to demonstrate the effectiveness of the proposed models. The results showed that the residual bearing capacity of the marine RC columns can be significantly affected by the rebar corrosion level, corrosion damage location, load condition and in-service environment.

Lifetime reliability analysis of concrete columns damaged by reinforcement corrosion

Rebar corrosion caused by chloride ion ingression is a critical factor leading to performance deterioration of in-service reinforced concrete (RC) structures exposed to aggressive environments. This paper presents a new method to evaluate the concrete crack growth, the bearing capacity degradation and the lifetime performance deterioration for the corroded RC columns under small eccentric compression. By analyzing the material degradation mechanism of the corroded RC structures, an effective method is proposed to predict the concrete crack growth and to estimate the residual bearing capacity of the corroding eccentrically loaded RC columns. Then, the concrete crack width and the load-bearing capacity deterioration rate are selected as structural performance indicators to assess the lifetime performance of the corroding RC columns. The stochastic gamma process is adopted for simulating the evolution of structural performance indicators and estimating lifetime failure probability and the remaining useful life of the corroding structures. Finally, a numerical example is given to demonstrate the effectiveness of the proposed methods for the lifetime performance assessment of the corroding columns. The obtained results show that the residual bearing capacity and the lifetime performance of the corroding RC columns can be significantly affected by rebar corrosion level, load condition and in-service environments.

Effect of Corrosion on the Hysteretic Behavior of Steel Reinforcing Bars and Corroded RC Columns

The corrosion of steel reinforcement negatively influences the mechanical performance of reinforced concrete (RC) elements reducing both their strength capacity and ductility. Especially in seismic prone areas, the degradation of the cyclic behavior of corroded RC elements is more intense, limiting the service life of structures and leading to premature failures. In the present paper, in order to study the degraded behavior of the embedded (in concrete) steel reinforcement under cyclic loading, laboratory corrosion experiments were performed on embedded steel reinforcing bars. Thereafter, mechanical tests under dynamic loadings with gradually increased deformations were carried out. From the experimental study, hysteretic models of the non-linear behavior of steel bars were extracted in non-corroded and corroded conditions, in the case of both uniform and pitting corrosion. Based on the hysteretic models of steel bars, an analysis of the cyclic response of (non-corroded and corroded) RC columns was performed using the OpenSees code. The outcomes of the present study indicated the negative consequences of corrosion on the hysteretic behavior of steel reinforcing bars, demonstrating mainly the local reduction in their cross-section (pitting corrosion) combined with the loading history and buckling phenomena as the main factors which deviate the mechanical behavior of steel bars from the classic bilinear model of monotonic loading.

Compressive behavior of GFRP partially strengthened corroded RC columns subjected to freeze-thaw erosion

The compression test of glass fiber-reinforced polymer (GFRP) partially strengthened corroded reinforced concrete (RC) columns subjected to freeze-thaw cycling was conducted in this study. A total of 45 small-scale RC columns were prepared. The columns were firstly subjected to accelerated corrosion conditioning to obtain the target level of steel loss, and then partially strengthened with 2-ply GFRP strips; finally, the strengthened RC columns were subjected to different freeze-thaw cycles. The main parameters in this experiment were reinforcement corrosion degree (0, 10%, and 20%) and number of freeze-thaw cycles (0, 25, 50, and 75). The compressive behaviors of columns were evaluated in terms of failure mode, load capacity, load-displacement response, stiffness, and ductility. Results showed that GFRP partially strengthening could significantly improve the load capacity, stiffness, and ductility of corrosion-damaged RC columns, while the ultimate load capacity and stiffness of strengthened columns decreased with the increase of freeze-thaw cycles. Moreover, a design-oriented calculation method for the ultimate load capacity of GFRP partially strengthened corroded RC columns subjected to freeze-thaw cycles was proposed and validated by the experimental results.

Numerical study and seismic design of corroded circular RC columns strengthened by C-FRCM

This study aims to numerically investigate the behaviour of corroded circular reinforced concrete (RC) columns strengthened by carbon-fabric-reinforced cementitious matrix (C-FRCM) composites. Three-dimensional finite element (FE) models of the corroded circular RC columns with and without strengthening were set up and validated against previous experimental results. Based on the validated FE models, the parametric studies were carried out to investigate the effects of axial compression ratio, degree of corrosion and layer of carbon fabrics on the behaviour of corroded RC columns under cyclic loading. It shows that the lateral load resistance increased when the axial compression ratio ranged from 0.3 to 0.4, but decreased when the axial compression ratio ranged from 0.4 to 0.6; also the ductility of the corroded RC columns reduced with increasing axial compression ratio. The ultimate capacity of corroded RC columns decreased gradually with the increasing degree of corrosion. Based on the results of parametric studies, equations were developed to estimate the ultimate capacity and displacement of the corroded RC columns repaired by the C-FRCM. The proposed equations can well estimate the ultimate lateral load resisting capacity and ultimate displacement of the corroded circular RC columns strengthened by C-FRCM.

A lumped plasticity model for corrosion-damaged reinforced concrete columns

Chloride-induced corrosion is one of the most important causes of the strength degradation of reinforced concrete (RC) bridges. As the piers of RC bridges are important elements for sustaining lateral loads, corrosion of pier columns may lead to significant degradation of the structure. It is thus necessary to have an appropriate evaluation technique to assess the effect of corrosion on the behaviour of RC columns. Numerical modelling approaches based on a concentrated plastic hinge can predict structural behaviour rapidly and with acceptable accuracy, and are highly regarded by engineers. In this study, a numerical approach was conducted to develop an empirical lumped plasticity model (LPM) for corroded RC column elements. In this study, 13 440 RC column specimens, including corroded and uncorroded columns of both rectangular and circular cross-section, were analysed under monotonic and cyclic loading. The LPM was extracted based on regression of the results of cyclic and monotonic analyses. The calibrated model, valid for corroded and uncorroded columns, was assessed using experimental results and numerical models with data out of the range of those used in the parametric study and was found to have high accuracy. The newly developed plastic hinge model can be used to model and analyse corroded bridge columns rapidly. The results are appropriate for use in further assessments such as fragility or rehabilitation analyses.

Effects of Reinforcement Corrosion and Sustained Load on Mechanical Behavior of Reinforced Concrete Columns.

The effects of reinforcement corrosion and sustained axial load on mechanical performance of reinforced concrete (RC) columns were investigated in the present study. Three different degrees of reinforcement corrosion were achieved by controlling the durations of accelerated corrosion test (i.e., 16 days, 31 days, and 63 days). Three levels of sustained axial load (i.e., 0%, 30%, and 60% of the ultimate bearing capacity) were concentrically applied on column specimens. The impressing current and the sustained load were applied on column specimens simultaneously, mimicking the degradation of RC columns in real structures. Results indicated that transverse stirrups yielded higher corrosion degree than that of the longitudinal rebar under identical duration of accelerated corrosion test. The application of sustained axial load improved the performance of corroded RC columns in terms of the reinforcement corrosion, the ultimate axial load, as well as the stiffness. Additionally, more longitudinal cracks along the main rebar were exhibited for column specimens subjected to sustained axial load. For both loaded and unloaded column specimens, corrosion of reinforcing steels exacerbated the mechanical deterioration of RC columns, lowering the ultimate load carrying capacity and the axial deformation compared to the uncorroded columns.

Experimental study on the mechanical properties of corroded RC columns repaired with large rupture strain FRP

This paper presents experimental results of the mechanical properties of corroded reinforced concrete (RC) columns repaired with large rupture strain (LRS) fiber-reinforced polymer (FRP). This work seeks to evaluate the effects of corrosion-induced damage, including concrete cracks and rebar buckling, on the confinement effectiveness of LRS-FRP. A total of sixteen RC columns were corroded to different extents by an electrochemical method and then repaired by wrapping them with FRP. A series of monotonic axial compression tests were conducted on these repaired specimens that were characterized by their corrosion conditions and FRP confinement rigidities. The test results show that LRS-FRP confinement effectively enhanced the mechanical properties of corroded RC columns. However, the existence of corrosion weakened the rebar cross-sections and further damaged the confined inner concrete, significantly influencing the compressive strength and ductility of the repaired RC columns. In addition, rebar buckling was more pronounced at higher corrosion rates, which affected the hoop strain distribution of the FRP and further reduced its confinement effectiveness. The existing ultimate condition models for confined concrete are also validated by the current test results, indicating that satisfied predictions can be made as the corrosion effects on confinement effectiveness are properly considered in these models.

Compressive Behavior of Corroded RC Columns Strengthened With Ultra-High Performance Jacket

This paper performed compressive tests on corroded reinforced concrete (RC) columns with externally confined ultra-high performance concrete (UHPC) jacket. The studied parameters in this testing program was the corrosion ratio of specimens. The influences of this parameter on the compressive behavior of concrete columns confined by UHPC jacket was reported and discussed. The test results revealed that when the rust rate was less than 20%, axial cracking was the typical failure mode of unreinforced specimens, and the cracks in the rusted area gradually increased with the increase of the rust rate. When the corrosion rate reached 30%, the concrete of the protective layer fell off significantly, and the longitudinal reinforcement also yielded. The ultimate load and peak displacement of the specimens reinforced with UHPC were significantly improved, and the improvement rates of the two were more than 80% and 30%, respectively. The failure mode of the specimen with a corrosion rate of 30% also changed to longitudinal cracking of the UHPC layer. An analytical model was proposed to predict the ultimate load of RC columns with externally strengthening UHPC jacket. The validations of the predictions against the reported test results confirmed the accuracy of the analytical model.