CFRP shear strengthening of reinforced-concrete T-beams with corroded shear links

This paper investigates the structural behavior of uncorroded as well as corroded RC T-beams strengthened in shear with either externally bonded (EB) carbon fiber–reinforced polymer (CFRP) sheets or embedded CFRP rods. Nine tests were carried out on RC T-beams having an effective depth of 295 mm and a shear span to effective depth ratio of 3.05. The investigated parameters are the shear link corrosion level (uncorroded, 7% corroded, or 12% corroded) and type of CFRP strengthening system (EB CFRP sheets or embedded CFRP rods). The unstrengthened beams with shear link corrosion levels of 7 and 12% had shear strengths that were 11 and 14%, respectively, less than the shear strength of the uncorroded unstrengthened beam. Both the embedded CFRP rods and EB CFRP sheets were effective in enhancing the shear strength of tested beams but the effectiveness of both strengthening systems decreased with increasing shear link corrosion level. The shear strength enhancement provided by the embedded CFRP rods and EB CFRP sheets decreased from 19 and 15%, respectively, to 12 and 11%, respectively, with an increase in shear link corrosion level from 7 to 12%. Corrosion of the shear links did not have a significant effect on the beam stiffness. Premature debonding limited the effectiveness of the EB CFRP sheets whereas the embedded CFRP rods did not exhibit signs of debonding and therefore showed higher effectiveness.The authors would like to thank Fyfe Europe for supplying the CFRP sheets and epoxy laminating resin used in this study. The first author acknowledges the financial support of the UK Engineering and Physical Sciences Research Council.This is the author accepted manuscript. The final version is available from American Society of Civil Engineers via http://dx.doi.org/10.1061/(ASCE)CC.1943-5614.000054

Structural effects of steel reinforcement corrosion on statically indeterminate reinforced concrete members

The final publication is available at Springer via http://dx.doi.org/10.1617/s11527-016-0836-2Steel corrosion in reinforced concrete structures produces loss of reinforcement area and damage in the surrounding concrete. As a consequence, increases in deflections, crack widths and stresses may take place, as well as a reduction of the bearing capacity, which depends on the structural scheme and redundancy. In this paper an experimental study of twelve statically indeterminate beams subjected to different levels of forced reinforcement corrosion is presented. Different sustained loads were applied during the corrosion phase to assess their influence on the effects of corrosion. An important increase in deflections was registered in all corroded beams, especially in those subject to higher load levels. It was also found that the rate of corrosion was affected by the load level. Internal forces redistributions due to induced damage were measured. Finally, the experimental results were compared with those predicted by a non-linear time-dependent segmental analysis model developed by the authors, obtaining in general good agreement.Peer ReviewedPostprint (author's final draft

Effects of reinforcement corrosion on the structural performance of reinforced concrete beams

This dissertation is an investigation into the effect of reinforcement corrosion on the structural performance of reinforced concrete beams. Two types of specimens are investigated, the first without any stirrups and the second with stirrups. The specimens were corroded galvanostatically as well as by subjecting them to alternate cycles of wetting and drying with a saline water. An attempt is made at classifying the extent of corrosion of the reinforcing steel and its effects on the concrete. The effect of the corrosion on the structural performance is measured by establishing its effect on the maximum load carrying capacity, the deflections, energy requirements and ductility ratio. The main conclusions made in respect of the effect of reinforcement corrosion are that it causes: a decrease in the load carrying capacity; an increase in the deflections at the equivalent load level; a decrease in the energy requirements to reach the maximum load; and a smoothing of the load-deflection relationship. A limited literature review is also presented to provide background information of corrosion in concrete and general structural behaviour. Guidelines for the development of an analytical model to predict the load carrying capacity of corrosion affected reinforced concrete beams are also given

A proposal to modify the moment coefficient in Eurocode 2 for predicting the residual strength of corroded reinforced concrete beams

Ultimate limit state (ULS) criteria are used to design reinforced concrete beams which give a ductile behaviour at failure. This means the resisting moment, M t , is less than the resisting moment in compression, M c . Since steel reinforcement is susceptible to corrosion, the ultimate capacity can be seriously affected as the degree of corrosion increases. The impact of corrosion to the main steel reinforcement on the flexural performance of reinforced concrete beams is investigated. Beams measuring 100 mm wide × 150 mm deep with differing levels of under-reinforcement (M t /M c ratios) were tested under four-point bending. Although the design code for reinforced concrete beam design has gone through various changes over the years, the fundamentals for design has broadly remained the same in that the beam is designed with an ultimate moment-coefficient (K=M/f c bd 2 ) with sufficient capacity to be able to easily carry the service loads it is exposed to. However, the long term influence of corrosion on the steel reinforcement is not considered at the design stage although a manufacturing factor of safety is applied. The analysis in this paper uses a modified-moment coefficient (K corr =M corr /f ck bd 2 ) based on EC 2 ultimate limit state design guidelines to predict the residual flexural strength of reinforced concrete beams suffering from main steel corrosion. Two grades of concrete (>C35/45 and C35/45. The analysis is then extended to include test data from other researchers to develop a similar simplified empirical analytical expression for beams with concrete grades <C35/45, thereby enabling a prediction of residual strength due to corrosion to be made for any beam size or concrete strength grade

The fatigue performance assessment of corrosion damaged RC beams, patch repaired and externally strengthened using CFRP

Includes bibliographical references.The focus of the dissertation was to provide an in depth investigation towards the fatigue performance of Carbon Fiber Reinforced Polymers (CFRP) which were externally bonded onto concrete beams as a repair and strengthening technique for internally corrosion damaged RC beams. It was identified that more research concerning the fatigue performance of externally bonded CFRP laminates used as a composite material for originally damaged concrete structures was required. Therefore, there was a need to study the failure mechanisms between the externally bonded CFRP, corrosion damaged internal steel, and patch repaired section and the original substrate concrete with respect to the long term performance, whilst treating the system (CFRP, substrate concrete, patch repair and bonding agents) as a composite material. The methodology of the dissertation included the introduction of accelerated corrosion techniques to degrade the internal steel reinforcement. The damaged RC beams were repaired by removing the damaged concrete, treating the corroded internal steel reinforcement, replacing the damaged concre te section removed with a rapid-hardening high strength patch repair mortar, and finally externally bonding CFRP laminates along the patch repaired section and entire tensile face to restore the bending capacity lost due to the reduction of internal steel and subsequent patch repair. Two of the six RC beams which were patch repaired and CFRP strengthened, were subjected to a monotonic load in order to establish the ultimate static load at failure for the RC beams. The ultimate static load at failure was then used to derive the maximum imposed cyclic fatigue loading that was applied. The remaining four RC beams were then subjected to constant sinusoidal cyclic loads at varying amplitudes, the range of amplitude dependent on the corresponding static load at failure for the identical RC beam. The aim of the cyclic load tests was to determine the long term behaviour of the repaired and strengthened RC beams at different degrees of loadings . The test specimens were tested until fatigue failure was reached. At utimate fatigue failure, the RC beams exhibited excessive concrete cracking, but eventual fatigue failure was determined when the CFRP finally delaminated along a portion or the entire length of the tensile face. It was evident that once fatigue failure occurred due to concrete cracking, the fully laminated CFRP would then withstand a large majority of the tensile stresses still being applied. The CFRP momentarily restored the overall strength of the repaired and strengthened RC beam until ultimate failure occurred at the point of CFRP delamination. The outcome of the dissertation observes and describes the failure mechanisms during RC beam and CFRP fatigue failure. The results obtained from the extensive testing plot a failure curve for each RC beam which had been corroded, patch repaired and finally CFRP strengthened. The cumulative results captured display a predicted failure curve graph. This graph indicates the percentage of ultimate cyclic load applied which was a function of the corresponding ultimate static load applied for an identical RC beam versus the number of cycles applied until failure. This curve can be used as a guideline to predict the number of cycles until failure for a repaired and CFRP strengthened RC beam of similar dimensions for a specific percentage of static loading, this loading being dependent on the increased ultimate static load at failure for a patch repaired and externally strengthened CFRP reinforced concrete beam. The predicted failure curve clearly indicates that for repaired and CFRP strengthened RC beams experiencing low fatigue cyclic amplitudes equaling 45% of the corresponding total static loading at failure, the fatigue performance is significantly increased versus the identical test specimens with increased loading of approximately 55 % and 67% of the corresponding ultimate static loads, these beams exhibit considerably decreased long term performance. The static load tests also indicated that the influence of the accelerated corrosion on the ultimate capacity of the RC beam is minimal since the addition of the externally bonded CFRP doubled the ultimate static capacity of the identical RC damaged beams. The experimentation was also able to capture the failure mechanisms for each tested beam throughout the cyclic loading phase. Identifying the failure mechanisms was useful when conducting on site investigations which focused on the long term performance of either the reinforced concrete beams that were patch repaired and strengthened or not As expected, the combination of combining a high strength patch repair mortar and external CFRP strengthening scheme significantly increased the long term performance of the RC structure. Finally, due to the investigations performed in this dissertation, the increased long-term performance of a patch repaired and CFRP strengthened RC beam can now be empirically quantified and the failure mechanisms physically observed

Limit Equilibrium Method-Based Shear Strength Prediction for Corroded Reinforced Concrete Beam with Inclined Bars

Shear strength is a widely investigated parameter for reinforced concrete structures. The corrosion of reinforcement results in shear strength reduction. Corrosion has become one of the main deterioration factors in reinforced concrete beam. This paper proposes a shear strength model for beams with inclined bars based on a limit equilibrium method. The proposed model can be applied to both corroded and uncorroded reinforced concrete beams. Besides the tensile strength of longitudinal steel bars, the shear capacity provided by the concrete on the top of the diagonal crack, the tensile force of the shear steel at the diagonal crack, the degradation of the cross-sectional area and strength of the reinforcements induced by corrosion are all considered. An experimental work on two groups accelerated corroded beams was performed. Good agreements were found between the proposed theoretical predictions and experimental observations

Simulation of the Behavior of Corrosion Damaged Reinforced Concrete Beams with/without CFRP Retrofit

Harsh environmental conditions along with aggressive chemical agents are known as one of the main reasons behind damages observed in reinforced concrete members. Corrosion of reinforcement worldwide is one of the leading causes of damages occurred in reinforced concrete over the lifespan. There are many critical energy and transportation infrastructures located on coastal regions exposed to high humidity and chloride content where they are highly prone to reinforcement corrosion. This calls for retrofit methods, which safeguard not only the strength but also the durability of corrosion deteriorated reinforced concrete structures. Carbon fiber polymers considering their mechanical and chemical properties are recognized as one of the main retrofit techniques. In this study, the influence of different levels of corrosion on the structural behavior of reinforced concrete beams is studied. ABAQUS software package is employed to simulate the nonlinear behavior of reinforced concrete beams with tensile reinforcements and stir-ups corrosion degrees of 20% and 40%. The structural behavior of original damaged specimen as well as the same specimen strengthen with carbon fiber reinforced polymer (CFRP) is studied. The purpose of the retrofit is compensate for the loss of shear and flexural capacity of the member due to corrosion. Different variants for the arrangement of CFRP strips are studied and compared. The result of the current research further uncaps the efficiency of fiber polymers to secure strength and durability of corrosion damaged reinforced concrete members

Simulation of the Behavior of Corrosion Damaged Reinforced Concrete Beams with/without CFRP Retrofit

Harsh environmental conditions along with aggressive chemical agents are known as one of the main reasons behind damages observed in reinforced concrete members. Corrosion of reinforcement worldwide is one of the leading causes of damages occurred in reinforced concrete over the lifespan. There are many critical energy and transportation infrastructures located on coastal regions exposed to high humidity and chloride content where they are highly prone to reinforcement corrosion. This calls for retrofit methods, which safeguard not only the strength but also the durability of corrosion deteriorated reinforced concrete structures. Carbon fiber polymers considering their mechanical and chemical properties are recognized as one of the main retrofit techniques. In this study, the influence of different levels of corrosion on the structural behavior of reinforced concrete beams is studied. ABAQUS software package is employed to simulate the nonlinear behavior of reinforced concrete beams with tensile reinforcements and stir-ups corrosion degrees of 20% and 40%. The structural behavior of original damaged specimen as well as the same specimen strengthen with carbon fiber reinforced polymer (CFRP) is studied. The purpose of the retrofit is compensate for the loss of shear and flexural capacity of the member due to corrosion. Different variants for the arrangement of CFRP strips are studied and compared. The result of the current research further uncaps the efficiency of fiber polymers to secure strength and durability of corrosion damaged reinforced concrete members

Limit Equilibrium Method-Based Shear Strength Prediction for Corroded Reinforced Concrete Beam with Inclined Bars

Shear strength is a widely investigated parameter for reinforced concrete structures. The corrosion of reinforcement results in shear strength reduction. Corrosion has become one of the main deterioration factors in reinforced concrete beam. This paper proposes a shear strength model for beams with inclined bars based on a limit equilibrium method. The proposed model can be applied to both corroded and uncorroded reinforced concrete beams. Besides the tensile strength of longitudinal steel bars, the shear capacity provided by the concrete on the top of the diagonal crack, the tensile force of the shear steel at the diagonal crack, the degradation of the cross-sectional area and strength of the reinforcements induced by corrosion are all considered. An experimental work on two groups accelerated corroded beams was performed. Good agreements were found between the proposed theoretical predictions and experimental observations

Development of Fibre Reinforced Geopolymer Concrete (FRGC) cured under ambient temperature for strengthening and repair of existing structures

Most of the previous research on plain and fibre reinforced geopolymer concrete (FRGC) has concerned on the properties of geopolymer mixtures hardened under heat curing conditions, which is a severe limitation for on-site, cast-in-place applications. This study focuses on the material and structural properties of novel fibre reinforced geopolymer concretes cured under ambient temperature. The overall aim of the study was to develop and test a more environmentally sustainable concrete material with improved structural characteristics, which utilises waste rather than primary mineral products, suitable for cast-in-place applications and for the structural strengthening of existing buildings. In the first part of this thesis, the material behaviour of FRGC cured under ambient temperature was examined. Initially, the work identified the role of various parameters which may affect material compressive strength, in order to enhance overall performance. In addition, the mechanical and microstructural properties of geopolymer mortar with different slag contents and variant silica fume types (densified, undensified and slurry) were assessed. Following this, the effect of slag content and silica fume particle size on the properties of steel fibre reinforced geopolymer composites (SFRGC) was examined. The optimum FRGC mixtures were further investigated in term of its durability characteristics and mechanical properties, in order to provide strain hardening characteristics. In the examined mixes, different fibre types, aspect ratios, and volume fractions, and its comparison with Portland cement based conventional concrete, have been assessed and appropriate mixtures have been identified with multiple fine cracks and strain hardening in tension. In the final part of the thesis, the structural behaviour of FRGC is examined at larger scale application. PVA and steel fibre reinforced geopolymer concrete mixtures were used as strengthening and repair materials for the protection of steel bars in a new material layer, and for subsequent improvement of the flexural strength of existing beams. Large scale beams strengthened with additional FRGC layers reinforced with steel bars have been examined. Also, an additional investigation was conducted in beams where part of the concrete cover at various depths was replaced by FRGC. In all the examined cases respective beams with conventional concrete were examined in order to evaluate the efficiency of the proposed technique. Accelerated corrosion tests were performed using the induced current technique by applying a nominal 300 mA constant anodic current. The results of this investigation showed significant improvements in the structural performance of the examined beams following strengthening or repair with FRGC. The outcomes of the experimental work indicate that FRGC considerably enhanced both the flexural strength capacity and the durability of strengthened and repaired reinforced concrete elements