Corroded Reinforced Concrete Beams Research Articles

Calculation Method for Flexural Damage of RC Beams Subjected to Cyclic Loads and Corrosive Actions

Fatigue constitutive laws of concrete and S-N curves of steel bars have been investigated widely. This study aims to explore the failure problems of reinforced concrete (RC) beams subjected to cyclic loads and corrosive actions. The live loads obtained from Chinese technical standards and practical surveys were adopted in experiments and numerical calculations. A series of tests were conducted to study the fatigue performance of normal and corroded RC beams. A numerical method was proposed to calculate the fatigue damage of RC beams under corrosive actions and cyclic loads. The performance of RC beams with increasing fatigue cycles were analyzed with using MATLAB software in which the global stiffness degradation was introduced to represent the properties evolutions of corroded steel bars and concrete.

Strength of Corroded RC Beams with Bond Deterioration

AbstractThe paper proposes strut and tie models for the flexure, shear, and bond strength of corroded reinforced concrete (RC) beams. The deterioration of the material properties including bond and...

Influence of reinforcement corrosion on fire performance of reinforced concrete beams

Abstract Corroded steel bars frequently exist in concrete structures under chloride exposure conditions; moreover, corroded reinforced concrete (RC) is not fireproof. This paper presents an investigation on the effects of reinforcement corrosion on the fire performance of RC beams. The corroded RC beams were prepared using an accelerated corrosion test, and the fire test was carried out according to the ISO 834 standard fire. Test results indicated that corrosion of the tensile steel bars led to premature failure of the concrete beams. During the fire tests, with the increase of the steels’ degree of corrosion, the midspan deflection of the RC beam rapidly develops, while the fire resistance obviously decreases. Because the thermal diffusion coefficient of air is higher than that of concrete, a corrosion induced crack increased the heating rate of the corroded steel bar inside the concrete, and the vertical cracks caused by the applied loading had a significant impact on the temperature field of the beam tensile zone. Notably, reinforcement corrosion may lead to brittle failure in a balanced-reinforced beam subjected to fire.

Experimental analysis of the correlation between bending strength and SMFL of corroded RC beams

Abstract Measuring the bearing capacity is critical for assessing the safety and durability of civil engineering structures. However, the existing non-destructive testing (NDT) techniques cannot estimate the bending strengths of corroded reinforced concrete (RC) beams easily. Thus, the correlation between self-magnetic flux leakage (SMFL) and bending strength of corroded RC beams was investigated in this study to estimate the bending strength. First, a theoretical model was established based on the physical properties of ferromagnetic materials and engineering mechanics. Preliminary research found that the peak-to-valley differences of the SMFL curves of corroded RC beams were strongly correlated with the bending strength. The normalized peak-to-valley differences NBP(x) and normalized bending strength NBS were defined based on this correlation. NBS of corroded RC beams can be evaluated using NBP(x) of SMFL curves. The data from 18 corroded RC beams and the theoretical model were analyzed and employed to verify the correlation between NBP(x) and NBS. The experimental results were consistent with those predicted by theory and showed the semi-quantitative correlation that NBP(x) was related to NBS exponentially (without stirrups) or approximate linearly (with stirrups). Therefore, the bending strength can be estimated semi-quantitatively via the SMFL curves. In this work, a novel correlation between the SMFL and bending strengths of corroded RC beams was established. The SMFL technique can be regarded as a new effective NDT technique for estimating the bending strength of corroded RC beams.

Flexural behaviour of corroded reinforced concrete beams repaired with ultra-high toughness cementitious composite

The repair of corroded reinforced concrete (RC) structures is necessary to improve their serviceability. Ultra-high toughness cementitious composite (UHTCC), characterised by excellent tensile behaviour, crack control capacity, and durability, shows great potential for the repair and strengthening of corroded members, especially in harsh marine environments. This paper presents an experimental study and a theoretical analysis of the flexural performance of corroded RC beams repaired with UHTCC. The experimental results indicated that macro cracks in concrete were transformed into multiple fine cracks and a slight nonlinear strain distribution was observed along the sectional depth. The replacement of damaged concrete with UHTCC can recover the initial load-carrying capacity at corrosion ratios within 11.2%. After yielding of beams, the development of UHTCC-concrete interface crack in the pure bending region was beneficial to ductility improvement. A theoretical model considering the effect of pitting corrosion was proposed for calculating flexural capacity of repaired beams.

Experimental and Analytical Investigation of the Fatigue Flexural Behavior of Corroded Reinforced Concrete Beams

The fatigue flexural behavior of corroded reinforced concrete (RC) beams was experimentally and analytically examined. Seven beams were constructed and tested, and an analytical fatigue prediction model (FPM) was proposed to assess the fatigue behavior of the corroded beams. After validating the FPM with the experimental test results, the FPM was then extended to better understand the effects of the degree of steel corrosion, the corrosion pit geometry, and the fatigue load level on the performance of corroded RC beams. The results show that the fatigue behavior of the corroded steel bars determines the fatigue behavior of the beams. Rebar corrosion has a significant detrimental effect on the fatigue performance of RC beams due to stress concentration, loss of steel cross-sectional area, and diminished bonding at the steel–concrete interface. The stress concentrations increase with increasing pit width-to-length and depth-to-diameter ratios. Differences in pit geometry and the resulting changes in stress concentrations due to corrosion should be considered when assessing fatigue performance.

Incorporation of corrosion and bond-slip effects in properties of reinforcing element embedded in concrete beams

Corrosion of rebar in reinforced concrete (RC) structures leads to a reduction in strength and durability. In this paper, the lifetime flexural behavior of the corroded RC beams is examined through a simplified modeling methodology in a finite element program. To this aim, properties of the embedded reinforcing element in the finite element analysis are changed to include the bond-slip and corrosion effects in overall structural behavior. Application of the method for corroded beams leads to acceptable results, close to experimental values. To evaluate the flexural behavior of the beam over time, a theoretical model is presented regarding the reduction of cross-section and strength of the rebar, and the moment-curvature diagram is obtained for the corroded structure. The simplified method of predicting the lifetime moment-curvature behavior in this study provides the possibility of a more efficient and economical design.

Static bearing capacity of partially corrosion-damaged reinforced concrete structures strengthened with PET FRP composites

Abstract This study evaluated the static bearing performance of partially corrosion-damaged reinforced concrete (RC) beams and columns strengthened with polyethylene terephthalate (PET) composites. According to the electrochemical corrosion method, the corrosion rate of reinforcements in the key regions of columns and beams were designed as 15%, which conformed to the actual situations of the non-uniformly corroded steel bars in the RC structures. After that, the partially corroded RC columns and beams were strengthened with PET composites. Specimens strengthened with carbon fiber reinforced plastic (CFRP) and without strengthening worked as the control groups. SEM studies showed that the good interface bonding performance between PET and concrete ensured the excellent integrity of PET-strengthened structures. Experimental results showed that the ductility and bearing capacity of columns and beams got greatly decreased due to the corrosion of reinforcements, and PET composites could effectively repair the damagement caused by corroded steel bars. The ductility improvement by PET composites was better than that of CFRP. For axial compression, the ductility index of CP-0 column improved by 334.62% compared to that of CF-0 column. Similar to the corroded RC columns, the ductility index of CP-15 column improved by 127.49% than that of CF-15 column. A calculated model was proposed to predicate the stress–strain relationship of PET composites strengthened partially corroded RC columns accurately. For flexure, PET and CFRP composites strengthened beams had the same ultimate bearing capacity. Meanwhile, PET composites could better ensure the ductility of partially corroded RC beams than that of CFRP. Compared to BF-0 beam, the ductility index of BP-0 beam increased by 93.75%. Compared to BF-15 beam, the ductility index of BP-15 increased by 69.23%. In the compression and flexure tests, the rupture strain of PET composites improved by 114.82%∼164.11% than that of CFRP, which took full advantage of the high deformation property of PET composites. The study therefore concludes that PET composites is a suitable material for external strengthening of partially corroded RC structures.

Damage Evolution of RC Beams Under Simultaneous Reinforcement Corrosion and Sustained Load.

To accurately obtain the performance of concrete structures in coastal regions, it is necessary to correctly understand the damage evolution law of reinforced concrete (RC) members under real working conditions. In this paper, four RC beams, subjected to different levels of corrosion and sustained load, are first tested. Reinforcement corrosion coupled with sustained load increases the number and width of cracks at the soffit of beams but decreases their loading capacities. Crack width of the corroded beam under 50% of designed load is two times of that under 30% of designed load. Residual loading capacities of the corroded beams subjected to 30% and 50% of designed load are 87.5% and 81.8% of the control beam. A finite element model is developed for the corroded RC beams. Due to less confinement, concrete below and at the sides of reinforcements is subjected to a higher stress, compared to concrete above the reinforcements. Corrosion expansion of reinforcements is successfully modelled by a temperature-filed method, as it properly simulates the damage evolution of the corroded RC beams. As a result, concrete cracking, caused by the reinforcement corrosion, is well captured. Coupling reinforcement corrosion with sustained load significantly increases the damage level in RC beams, particularly for those subjected to a high sustained load. The whole damage evolution process of concrete cracking due to corrosion expansion under the coupling effect of sustained loading and environment can be simulated, thus providing a reference for the durability evaluation, life prediction, and numerical simulation of concrete structure.

Corrosion fatigue life prediction for steel bar in concrete based on fatigue crack propagation and equivalent initial flaw size

A new corrosion fatigue life prediction approach for steel bar in concrete based on fatigue crack propagation and equivalent initial flaw size (EIFS) was proposed, coupling corrosion growth and fatigue crack propagation together. By using fracture mechanics method and introducing the concept of EIFS, theoretical approach for corrosion fatigue life prediction was discussed, and the corresponding mechanical model was presented. Through accelerated corrosion test of reinforced concrete (RC) beams, the quantitative relation between corrosion pit depth and corrosion degree expressed by mass loss was established. Fatigue loading test of corroded RC beams was carried out, and the quantitative relation between EIFS and corrosion degree was presented according to the test results of corrosion fatigue life. The corrosion fatigue fracture of steel bar obtained by fatigue loading test was observed, and it is found that corrosion has no substantial effect on the critical crack size. Finally, the proposed corrosion fatigue life prediction model was validated by comparing with the existing experimental results, and the predicted values were in acceptable agreement with the test results. The findings of this study can be used to predict the fatigue life of aging corroded RC beams under corrosive environment.

Research on Arch Effect and CFRP Strengthening Effect of RC Beams with Corroded Stirrups

In many cases the corrosion of steel reinforcement is considered to be the main reason that leads to the deterioration of the bond between steel reinforcement and concrete and causes the failure of members. However, stirrups with smaller diameter are more likely to get rusted and it is more difficult to find corrosion expansion cracks on the surface of concrete. Then the function of stirrups to restrict longitudinal bar from slipping will be weakened, which alters the mechanical properties and failure mode of corroded Reinforced Concrete (RC) beams. In this paper, the influence of corrosion of stirrups and the effect of strengthening corroded RC beams with Carbon Fiber Reinforced Polymer (CFRP) sheets were studied. The corrosion rate for each group varied between 0% to 18% which represented mass loss of the longitudinal steel reinforcement on the tension side. The longitudinal reinforcement of beams in Group A was not wrapped by the stirrups in order to simulate the situation that the stirrups were seriously corroded and lost their function. Beams of Group B were corroded control beams. Beams of Group C were corroded and then repaired by applying longitudinal CFRP sheets at the bottom and additional U-shaped CFRP sheets around the cross-section. Test results showed that the corrosion of stirrups had a detrimental effect on strength as well as the bond stress between steel bars and concrete. The mechanical mode of experimental beams tended to act like an arch. The greater the corrosion rate was, the more obvious the arch effect was. In addition, combining longitudinal and U-shaped CFRP sheets enhanced the ultimate load by an average of 56.5% of corroded RC beams. However, because of the longitudinal cracks, the strengthening effect of CFRP was much diminished when the corrosion rate was particularly high.

Experimental and modelling of the flexural performance degradation of corroded RC beams under fatigue load

Corrosion of reinforcing bars accelerates the fatigue damage accumulation and significantly reduces the fatigue life of aging reinforced concrete (RC) bridges. This paper experimentally investigates the effects of corrosion on the fatigue behavior of reinforced concrete beams. An accelerated corrosion test is conducted in the laboratory conditions to obtain various corroded beam specimens. The initial crack width and the crack distribution are discussed. Based on the fatigue loading test, the load-deflection, fatigue crack propagation of concrete, fatigue life and the failure modes of RC beams after different fatigue cycles are investigated. Following that, a developed flexural stiffness calculation model for the corroded beams after fatigue is proposed. This model includes the effects of fatigue, corrosion-induced cracking and fatigue modulus degradation of concrete and other influential factors. The proposed method is validated with the experimental observations from various corroded RC beams of the current paper and available in open literature.

An empirical model for the shear strength of corroded reinforced concrete beam

A total of 158 experimental tests of shear behavior of corroded reinforced concrete (CRC) beams under action of concentrated load, published in the literature were collected and compiled into a shear strength database. This database was firstly used to discuss important parameters which affect the shear strength of CRC beams. The results show that the effect of stirrups’ corrosion on shear capacity of CRC beams is greater than that of longitudinal reinforcement corrosion. The shear span-to-depth ratio is also an important factor on shear strength of CRC beams. Total 9 available empirical models for predicting the residual shear strength are evaluated and compared based on the test database. It is found that eight of the nine models underestimate the shear strength of CRC beams while the other model gives the overestimated results. It is in this regard that a new empirical model for predicting the residual shear strength of CRC beams is proposed, in which a reduction coefficient is incorporated with the consideration of the effect of stirrups’ corrosion as well as shear span-to-depth ratio. The comparison studies demonstrate that the new proposal can provide an effective and accurate prediction of the shear capacity of CRC beams with a wide range of reinforcement corrosion damages.

Finite element modeling of corroded RC beams using cohesive surface bonding approach

The modeling of loss of bond between reinforcing bars (rebars) and concrete due to corrosion is useful in studying the behavior and prediction of residual load bearing capacity of corroded reinforced concrete (RC) members. In the present work, first the possibility of using different methods to simulate the rebars-concrete bonding, which is used in three-dimensional (3D) finite element (FE) modeling of corroded RC beams, was explored. The cohesive surface interaction method was found to be most suitable for simulating the bond between rebars and concrete. Secondly, using the cohesive surface interaction approach, the 3D FE modeling of the behavior of non-corroded and corroded RC beams was carried out in an ABAQUS environment. Experimental data, reported in literature, were used to validate the models. Then using the developed models, a parametric study was conducted to examine the effects of some parameters, such as degree and location of the corrosion, on the behavior and residual capacity of the corroded beams. The results obtained from the parametric analysis using the developed model showed that corrosion in top compression rebars has very small effect on the flexural behaviors of beams with small flexural reinforcement ratio that is less than the maximum ratio specified in ACI-318-14 (singly RC beam). In addition, the reduction of steel yield strength in tension reinforcement due to corrosion is the main source of reducing the load bearing capacity of corroded RC beams. The most critical corrosion-induced damage is the complete loss of bond between rebars and the concrete as it causes sudden failure and the beam acts as un-reinforced beam.

Deterioration of shear behavior of corroded reinforced concrete beams

Steel bars in reinforced concrete (RC) structures may corrode in an aggressive environment, resulting in performance deterioration and premature failure. Stirrups begin to corrode earlier and faster than longitudinal steel bars due to their thinner concrete cover, and the shear strength decreases faster than the flexural strength. This paper presents an experimental investigation into the deterioration mechanism of shear behavior for corroded RC beams, and the prominent influencing parameters on shear behavior. The impressed current method was used to obtain corroded RC beams with different corrosion degrees in stirrups and longitudinal steel bars. Test results indicated that the beam may fail in shear instead of bending as the degrees of stirrup corrosion increases. The more severe the corrosion of stirrups was, the lower the shear strength. However, as the degree of corrosion increased in the longitudinal steel bars, the failure mode could change back to bending failure. The loss of bond strength affected the shear behavior of corroded RC beams, and the shear strength for bonded specimens was larger than unbonded ones. The shear strength decreased in beams with stirrups lacking end anchorages. Stirrups without end anchorages could still contribute to the shear strength if there was a good bond between stirrups and concrete. Otherwise, the stirrups could be ignored. With neither bond strength nor end anchorage, the beam could be treated as a beam without stirrups.

Influence of Corrosion Distribution on Estimation of Flexural Loading Capacity of Corroded RC Beams

A load carrying capacity of the reinforced concrete (RC) member is degraded by the corrosion of reinforcing steel bars due to chloride ion ingress. A lot of researches on the effect of corrosion in the longitudinal tensile reinforcing steel bars on the load carrying behavior have been available up to now. Accurate and quantitative estimation of capacity, however, is often difficult, because of the non-uniformity of corrosion in the member. Thus, a relationship between the spatial distribution of corrosion in the reinforcement including its scatter and the flexural loading capacity of RC member with such distribution of corrosion should be clarified so that the flexural capacity of corroded RC member can be estimated accurately. On the other hand, in case of the practical RC member under the corrosive environment, it should be considered that the flexural capacity often have to be derived from not a large number of inspection data on cross sectional areas of corroded reinforcements. So, in this study, a flexural loading test was performed by using RC beam specimens with the corroded tensile reinforcements provided the distribution of sectional areas. An estimation method of the flexural capacity of corroded RC beam was also shown, considering the distribution and its scatter in sectional areas of corroded reinforcements under the limited inspection data. Furthermore, the estimation of the longitudinal distribution of the cross sectional area of corroded reinforcement was performed by the spatial interpolation using Kriging method. Test results showed the yield and maximum load capacity in the corroded RC beam decreased as the corrosion rate increased. The failure mode of rupture in the reinforcement was shown in the large corrosion. The proposed estimation method was able to lead the safe evaluation of those experimental flexural capacities, determining the appropriate longitudinal characteristic value of the cross sectional area of corroded reinforcement. The flexural capacity can be also safely calculated using the characteristic value of diameters estimated by the corrosion crack width on the surface of the concrete, while the ratio of the experimental flexural capacity to the estimated one decreased as the corrosion loss increased. The distribution of bar diameters in the corroded reinforcement was able to be roughly estimated by using Kriging method. However, it was suggested that the measurement points close to the minimum bar diameter should be included to estimate the flexural capacity on the safe side.

Fatigue Assessment Model of Corroded RC Beams Strengthened with Prestressed CFRP Sheets

This paper presents a fatigue assessment model that was developed for corroded reinforced concrete (RC) beams strengthened using prestressed carbon fiber-reinforced polymer (CFRP) sheets. The proposed model considers the fatigue properties of the constituent materials as well as the section equilibrium. The model provides a rational approach that can be used to explicitly assess the failure mode, fatigue life, fatigue strength, stiffness, and post-fatigue ultimate capacity of corroded beams strengthened with prestressed CFRP. A parametric analysis demonstrated that the controlling factor for the fatigue behavior of the beams is the fatigue behavior of the corroded steel bars. Strengthening with one layer of non-prestressed CFRP sheets restored the fatigue behavior of beams with rebar at a low corrosion degree to the level of the uncorroded beams, while strengthening with 20- and 30%-prestressed CFRP sheets restored the fatigue behavior of the beams with medium and high corrosion degrees, respectively, to the values of the uncorroded beams. Under cyclic fatigue loading, the factors for the strengthening design of corroded RC beams fall in the order of stiffness, fatigue life, fatigue strength, and ultimate capacity.

Assessment of Fatigue Life for Corroded Reinforced Concrete Beams under Uniaxial Bending

An understanding of how corrosion affects fatigue behavior of reinforced concrete (RC) structures is essential for lifetime-oriented maintenance and design of existing bridges. This paper covers an experimental investigation on fatigue behavior of corroded RC beams. Corrosion in six RC beams was artificially accelerated by the impressed current method before fatigue loading was administered. All beams failed with fatigue fracturing of their tension steel bars. The fatigue test results indicated that the more severe the corrosion on steel bars was, the sooner the beams failed. The behavior of corroded steel bars determines the fatigue behavior of RC beams. This paper introduces a segmented linear model to simulate nonlinear behavior of corroded RC beams under fatigue loading, which was verified by experimental results. Of particular interest was the deterioration of corroded RC beams under fatigue loading, including the fatigue damage to concrete and corroded steel bars as well as the bond behavior between steel bars and concrete. The proposed model can simulate the development of strains in concrete and steel bars under fatigue loading, thereby permitting a fatigue life assessment. Further analysis investigated the effects of corrosion level, longitudinal variation of the cross-sectional areas, reinforcement ratio, load amplitude, and bond behavior as well. With the increasing degree of corrosion, load amplitude and longitudinal variation of the cross-sectional areas, or the decrease of the reinforcement ratio, the fatigue life of corroded RC beams decreased. The deterioration of bond behavior had little effect on fatigue life, but it led to a reduction in the flexural stiffness of beams.

Effect of Pit Distance on Failure Probability of a Corroded RC Beam

The present paper studies effect of the variation of pit distance on structural reliability of a reinforced concrete (RC) beam, with particular emphasis on the interference of localized corrosion on adjacent tensile rebars. The research question leading the inquiry of this article is how does average distance between corrosion pits in rebars affect the probability of failure in RC beams. In this paper, by using Monte Carlo Simulation (MCS), probabilities of failure in a corroded RC beam with different pit distances are quantified. Uncertainties in material properties, geometry, loads, corrosion modelling, pit distances and pit interference are taken into account. Statistical data reported in literature regarding the extent and location of corrosion is utilized to undertake a parametric study of corresponding probability distribution functions. According to results, variation of pit distance has significant influence on probabilities of failure. This influence increases if the effect of interference of localized corrosion is taking into account.

Investigation on the Flexural Behavior of Corroded Concrete Beams Repaired by CFRP Sheet Under Different Corrosion Levels

The paper presents an investigation on the flexural behavior of corroded reinforced concrete (RC) beam strengthened with Carbon Fiber Reinforced Polymer (CFRP) sheets. Different levels of corrosion are considered as a new method for classifying the corrosion levels of the corroded RC members. Twenty RC beams with five corrosion levels were fabricated by accelerated corrosion equipment, and then the CFRP were used to strengthen these members, considering the effect of different CFRP layers and different strengthened schemes, finally the static flexural load test was carried out. The test results show that the bearing capacity of the CFRP strengthening corroded RC beams is effectively enhanced, the crack width is restrained, and the flexural stiffness is improved. The ultimate flexural capacity of the specimens strengthened by one layer of CFRP sheet raises by 30% to 50% than that of the unstrengthened ones, with the increase of the corrosion level, the enhancement decreased. With the increase of the number of CFRP layers, the bearing capacity increases, while the increasing ratio reduces with the increase in the number of layers. For specimens with obvious cracks, the effectiveness of the strengthening method by bonding CFRP after cutting or chiseling off concrete method (RM1 or RM2) is higher than the method of bonding CFRP directly (DM). It is suggested that the corroded RC members with Level A, B or C1 can be strengthened by DM, while the other level members should be strengthened by RM1 or RM2. The formulae in current design code are used to predict the flexural bearing capacity of the RC beam strengthened with CFRP and their results are compared with experimental ones. A revised formula that can give a better prediction for multi-layer CFRP strengthening members is also proposed.