Repair of shear-deficient normal weight concrete beams damaged by thermal shock using advanced composite materials

The use of advanced composite materials such as Fiber Reinforced Polymers (FRPs) in repairing and strengthening reinforced concrete structural elements has been increased in the last two decades. Repairing and strengthening damage structures is a relatively new technique. The aims of this study was to investigate the efficiency and effectiveness of using Carbon Fiber Reinforced Polymer (CFRP) to regain shear capacity of shear-deficient normal weight high strength RC beams after being damaged by thermal shock. Sixteen high strength normal weight RC beams (100 × 150 × 1400 mm) were cast, heated at 500 °C for 2 h and then cooled rapidly by immersion in water, repaired, and then tested under four-point loading until failure. The composite materials used are carbon fiber reinforced polymer plates and sheets. The experimental results indicated that upon heating then cooling rapidly, the reinforced concrete (RC) beams exhibited extensive map cracking without spalling. Load carrying capacity and stiffness of RC beams decreased about 68% and 64%, respectively, as compared with reference beams. Repairing the thermal damaged RC beams allowed recovering the original load carrying without achieving the original stiffness. Repaired beams with CFRP plates with 90° and 45° regained from 90% to 99% of the original load capacity with a corresponding stiffness from 79% to 95%, whereas those repaired with CFRP sheet on the web sides and a combination of CFRP plates and sheet regained from 102% to 107% of the original load capacity with a corresponding stiffness from 81% to 93%, respectively. Finally, finite element analysis model is developed and validated with the experimental results. The finite element analysis showed good agreement as compared with the experimental results in terms of load–deflection and load–CFRP strain curves.     

Repairing corroded RC beam with near-surface mounted CFRP rods

This experimental program investigates the possibility of using Carbon-Fiber-Reinforced Polymer (CFRP) rods to repair RC beams damaged by steel corrosion. The 6-mm-diameter carbon-epoxy pultruded FRP rods were implemented in undamaged areas of the concrete cover by using the Near Surface Mounted reinforcement (NSM) technique. The corroded beam tested was stored in a chloride environment under service loading for 23 years, which was representative of real structural conditions. The corroded beam showed longitudinal corrosion cracks more than 3 mm in width along the tension reinforcing bars. The repaired corroded beam was tested in three-point flexure up to failure. Then, concrete was removed around the reinforcing bars in order to measure the real local steel cross-section distribution. The maximum reduction in steel cross-section measured in the tension area was about 36% and was located at mid-span. In spite of this heavy corrosion, the bearing capacity measured on the repaired beam was equal to that of the uncorroded control beam. In our experimental conditions, the NSM technique was applicable for repairing corroded concrete structural members.     

Bond analysis of corroded reinforced concrete beams under monotonic and fatigue loads

This study investigated the fatigue bond behaviour of corroded steel reinforced concrete beams. Nine beams (152 × 254 × 2000 mm [6 × 10 × 78.74 in.]) were constructed and tested. Bond failure occurred in all the beams. The variables in this test series were: the type of load applied (monotonic or repeated loading), the repeated load range, whether the reinforcement inside the beam was corroded or not, and whether a carbon fibre reinforced polymer (CFRP) repair method was used or not. The fatigue life of the beams varied linearly with the range of applied load with a very shallow slope. Corroding the beams to a low corrosion level decreased the fatigue bond strength by about 30%. Corrosion caused the concrete in between the lugs of the reinforcing bars to be partially crushed due to the formation of the rust products from the corrosion process. This reduced the strength of the concrete keys and increased the rate of slip in the bar under repeated loading.     

Structural performance of shear-critical RC deep beams with corroded longitudinal steel reinforcement

The effect of corrosion of longitudinal reinforcement on the structural performance of shear-critical reinforced concrete (RC) deep beams was experimentally investigated. A total of eight medium-scale reinforced concrete beams were constructed. The beams measured 150 mm wide, 350 mm deep and 1400 mm in length. The test variables included: corrosion levels (0%, 5%, and 7.5%), existence of stirrups and FRP repair. Six beams were subjected to artificial corrosion whereas two beams acted as control un-corroded. Following the corrosion phase, all beams were tested to failure in three point bending. The test results revealed that corrosion of properly anchored longitudinal steel reinforcement does not have any adverse effect on the behaviour of shear critical RC deep beams. Corrosion changed the load transfer mechanism to a pure arch action and as a result the load carrying capacity was improved. A strut and tie model was proposed to predict the failure loads of shear-critical RC deep beams with corroded longitudinal steel reinforcement. The predicted results correlated well with the experimental results.     

Near surface mounted CFRP laminates for shear strengthening of concrete beams

A Near Surface Mounted (NSM) strengthening technique was developed to increase the shear resistance of concrete beams. The NSM technique is based on fixing, by epoxy adhesive, Carbon Fiber Reinforced Polymer (CFRP) laminates into pre-cut slits opened in the concrete cover of lateral surfaces of the beams. To assess the efficacy of this technique, an experimental program of four-point bending tests was carried out with reinforced concrete beams failing in shear. Each of the four tested series was composed of five beams: without any shear reinforcement; reinforced with steel stirrups; strengthened with strips of wet lay-up CFRP sheets, applied according to the externally bonded reinforcement (EBR) technique; and two beams strengthened with NSM precured laminates of CFRP, one of them with laminates positioned at 90° and the other with laminates positioned at 45° in relation to the beam axis. Influences of the laminate inclination, beam depth and longitudinal tensile steel reinforcement ratio on the efficacy of the strengthening techniques were analyzed. Amongst the CFRP strengthening techniques, the NSM with laminates at 45° was the most effective, not only in terms of increasing beam shear resistance but also in assuring larger deformation capacity at beam failure. The NSM was also faster and easier to apply than the EBR technique. The performance of the ACI and fib analytical formulations for the EBR shear strengthening was appraised. In general, the contribution of the CFRP systems predicted by the analytical formulations was slightly larger than the values registered experimentally. Performance of the formulation by Nanni et al. for NSM strengthening technique was also appraised. Using bond stress and CFRP effective strain values obtained in pullout bending tests with NSM CFRP laminate system, the formulation by Nanni et al. predicted a contribution of this CFRP system for the beam shear resistance of 72% the experimentally recorded values.     

Prediction of ductility factor of corroded reinforced concrete beams exposed to long term aging in chloride environment

An experimental study using a three-point bending test on RC beams with dimensions of 150 × 280 × 3000 mm, naturally corroded over many years was conducted to evaluate the influence of steel corrosion on structural performance and, in particular, to better understand the change in ultimate deflection in bending and then in ductility. Some previous works by different authors are also discussed. The results show that the conventional ductility factor hardly applies to the assessment of ductile behaviour of corroded beams. A new ductility factor, based on the ratio between ultimate deflection of corroded and non-corroded beams, is proposed. In addition, the relation between ductility factor of corroded beams and cross-section loss in the corroded reinforcing steels was studied on the RC beams tested. The service life of corroded structures appears to be limited by the reduction of ductility in bending behaviour, which is more pronounced on the reduction of load-bearing capacity. This was linked to the change in mechanical properties of corroded steel bars in comparison with non-corroded steel bars.     

A new ductility model of reinforced concrete beams strengthened using Fiber Reinforced Polymer reinforcement

Despite the superior performance of Fiber Reinforced Polymer (FRP) as compared with conventional steel bars in terms of high strength-to-weight ratio, corrosion resistance, and high fatigue performance, FRP strengthened beams exhibit lower ductility due to the linear elastic response of the FRP reinforcement. Several ductility and deformability models were developed in order to account for the elastic behavior, i.e. high elastic energy, of FRP when used for strengthening existing steel reinforced concrete or for new construction. In this paper, a new ductility expression that relates the deformability of a reinforced concrete (RC) structure strengthened using FRP to the energy dissipated, was developed. The developed expression also considers the type of loading, static or fatigue. The new expression was validated against experimental test results of RC beams strengthened using prestressed Near Surface Mounted (NSM) carbon FRP un-fatigued and fatigued beams. Furthermore, the ductility index at which the deformability of the structure equals the ratio of total energy dissipated to elastic energy, defined as the optimum ductility index, was investigated for both the un-fatigued and fatigued beams. The prestress strain corresponding to the optimum ductility index was found to be 2830 με (the strain value can be determined using an accepted arbitrary test such as monotonic test) while no optimum ductility was achieved for the case of the un-fatigued beams. It is noteworthy that the optimum ductility index is subject to the variability of design, beam geometry, and prestressing level. Therefore, the ductility evaluation of the NSM CFRP strengthened beams was meant to give only an insight into the problem and not to propose certain limits.     

Behavior of full-scale reinforced concrete beams retrofitted for shear and flexural with FRP laminates

Four full-scale reinforced concrete beams were replicated from an existing bridge. The original beams were substantially deficient in shear strength, particularly for projected increase of traffic loads. Of the four replicate beams, one served as a control and the remaining three were implemented with varying configurations of carbon fiber reinforced polymers (CFRP) and glass FRP (GFRP) composites to simulate the retrofit of the existing structure. CFRP unidirectional sheets were placed to increase flexural capacity and GFRP unidirectional sheets were utilized to mitigate shear failure. Four-point bending tests were conducted. Load, deflection and strain data were collected. Fiber optic gauges were utilized in high flexural and shear regions and conventional resistive gauges were placed in eighteen locations to provide behavioral understanding of the composite material strengthening. Fiber optic readings were compared to conventional gauges.Results from this study show that the use of fiber reinforced polymers (FRP) composites for structural strengthening provides significant static capacity increases approximately 150% when compared to unstrengthened sections. Load at first crack and post cracking stiffness of all beams was increased primarily due to flexural CFRP. Test results suggest that beams retrofit with both the designed GFRP and CFRP should well exceed the static demand of 658 kN m sustaining up to 868 kN m applied moment. The addition of GFRP alone for shear was sufficient to offset the lack of steel stirrups and allow conventional RC beam failure by yielding of the tension steel. This allowed ultimate deflections to be 200% higher than the pre-existing shear deficient beam. If bridge beams were retrofit with only the designed CFRP failure would still result from diagonal tension cracks, albeit at a 31% greater load. Beams retrofit with only the designed shear GFRP would fail in flexure at the mid-span at an equivalent 31% gain over the control specimen, failing mechanism in this case being yielding of the tension steel. Successful monitoring of strain using fiber optics was achieved. However, careful planning tempered by engineering judgement is necessary as the location and gauge length of the fiber optic gauge will determine the usefulness of the collected data.     

Characteristics of aluminum/CFRP short square hollow section beam under transverse quasi-static loading

Energy absorption capability and bending collapse behavior of an aluminum (Al)/carbon fiber reinforced plastic (CFRP) short square hollow section (SHS) beam were investigated under transverse quasi-static loading. The Al SHS beam was reinforced by CFRP, and the specimen was co-cured via an autoclave curing process. Three-point bending test was performed with five different lay-up sequences and three different laminate thicknesses. Stable bending collapse accompanying plastic hinge was observed in all specimens. Individual bending collapse behaviors were different depending on the lay-up sequences. The specific energy absorbed (SEA) was improved by up to 29.6% in the Al/CFRP SHS beam specimen with a [0/+45°/90°/−45°]_n lay-up sequence and laminate thickness of 1.168 mm (thickness ratio of Al: CFRP = 1: 0.87, 8 plies of prepreg) compared to the Al SHS beam. The SEA was not related with damage area of the Al/CFRP SHS beam. Finite element analysis and theoretical analysis based on Kecman’s model were performed to investigate the effect of reinforcement by CFRP on the Al SHS beam.     

Flexural strengthening of concrete beams with CFRP laminates bonded into slits

Near surface mounted (NSM) strengthening technique using carbon fibre reinforced polymer (CFRP) laminate strips was applied for doubling the load carrying capacity of concrete beams failing in bending. This objective was attained and the deformational capacity of the strengthened beams was similar to the corresponding reference beams. The NSM technique has provided a significant increment of the load at serviceability limit state, as well as, the stiffness after concrete cracking. The maximum strain in the CFRP laminates has attained values between 62% and 91% of its ultimate strain. A numerical strategy was developed to simulate the deformational behaviour of RC beams strengthened by NSM technique. Not only the load carrying capacity of the tested beams was well predicted, but also the corresponding deflection.     

Effect of damaged concrete cover on the behavior of corroded concrete beams repaired with CFRP sheets

Fiber reinforced polymer matrix composites are being increasingly considered for use in civil infrastructure. These materials have found the maximum current use as materials for rapid and cost-effective rehabilitation (retrofit, repair and strengthening) of deteriorating and under-strength structural concrete components. This paper presents the experimental results of damaged/repaired reinforced concrete (RC) beams. The experimental program consisted of RC rectangular beam specimens exposed to accelerated corrosion. The corrosion rate was varied from 5% to 15% which represents loss in cross-sectional area of the steel reinforcement in the tension side. Half of the damaged beams were repaired by bonding Carbon Fiber Reinforced Polymer (CFRP) sheets to the tension side to restore the strength loss due to corrosion. The other half of the beams was first cleaned by removing spalled concrete cover and rusted bars were thoroughly cleaned. A new layer of concrete was cast to replace the removed spalled concrete cover. Then the CFRP sheets were attached to the new concrete layer. Corroded beams showed lower stiffness and strength than control (uncorroded) beams. Strength of damaged beams due to corrosion was restored to the undamaged state when repaired with CFRP sheets for all repaired beams, but the stiffness was almost unchanged. However, the repaired beams with replaced concrete cover layer resisted higher loads on average of 13% compared to damaged beams repaired without replacing the concrete cover layer.     

Structural performance of corroded RC beams repaired with CFRP sheets

Corrosion of reinforcement is a serious problem and is the main cause of concrete structures deterioration costing millions of dollars even though the majority of such structures are at the early age of their expected service life. This paper presents the experimental results of damaged/repaired reinforced concrete beams. The experimental program consisted of reinforced concrete rectangular beam specimens exposed to accelerated corrosion. The corrosion rate was varied between 5% and 15% which represents loss in cross-sectional area of the steel reinforcement in the tension side. Corroded beams were repaired by bonding carbon fiber reinforced polymer (CFRP) sheets to the tension side to restore the strength loss due to corrosion. Different strengthening schemes were used to repair the damaged beams. Test results showed detrimental effect of corrosion on strength as well as the bond between steel reinforcement and the surrounding concrete. Corroded beams showed lower stiffness and strength than control (uncorroded) beams. However, strength of damaged beams due to corrosion was restored to the undamaged state when strengthened with CFRP sheets. On the other hand, the ultimate deflection of strengthened beams was less than ultimate deflection of un-strengthened beams.     

Strengthening steel bridge sections using CFRP laminates

This paper presents results from an experimental investigation to determine the feasibility of using carbon fiber reinforced polymer (CFRP) epoxy laminates to repair steel composite bridge members. Six specimens, each consisting of a 6.1 m long W8×24 wide flange A36 steel beam acting compositely with a 0.114 m thick by 0.71 m wide reinforced concrete slab, were first loaded past yield of the tension flange to simulate severe service distress. The damaged specimens were then repaired using 3.65 m lengths of 2 or 5 mm thick CFRP laminates bonded to the tension flange and tested to failure. The results indicated significant ultimate strength gains but more modest improvement in the elastic response. Non-linear finite element analyses were in good agreement with the experimental results. The study suggests that it is feasible to strengthen steel composite members using CFRP laminates.     

Analytical approach for the flexural analysis of RC beams strengthened with prestressed CFRP

The objective of this paper is to propose a simplified analytical approach to predict the flexural behavior of simply supported reinforced-concrete (RC) beams flexurally strengthened with prestressed carbon fiber reinforced polymer (CFRP) reinforcements using either externally bonded reinforcing (EBR) or near surface mounted (NSM) techniques. This design methodology also considers the ultimate flexural capacity of NSM CFRP strengthened beams when concrete cover delamination is the governing failure mode. A moment–curvature (M–χ) relationship formed by three linear branches corresponding to the precracking, postcracking, and postyielding stages is established by considering the four critical M–χ points that characterize the flexural behavior of CFRP strengthened beams. Two additional M–χ points, namely, concrete decompression and steel decompression, are also defined to assess the initial effects of the prestress force applied by the FRP reinforcement. The mid-span deflection of the beams is predicted based on the curvature approach, assuming a linear curvature variation between the critical points along the beam length. The good predictive performance of the analytical model is appraised by simulating the force–deflection response registered in experimental programs composed of RC beams strengthened with prestressed NSM CFRP reinforcements.     

Efficacy of CFRP-based techniques for the flexural and shear strengthening of concrete beams

Near surface mounted (NSM) and externally bonded reinforcement (EBR) strengthening techniques are based on the use of carbon fiber reinforced polymer (CFRP) materials and have been used for the structural rehabilitation of concrete structures. In the present work, the efficacies of the NSM and EBR techniques for the flexural and shear strengthening of reinforced concrete beams are compared carrying out two experimental groups of tests. For the flexural strengthening, the efficacy of applying CFRP laminates according to NSM is compared to those resulting from applying CFRP laminates and wet lay-up CFRP sheets according to EBR technique. The influences of the equivalent reinforcement ratio (steel and laminates) and spacing of the laminates on the efficiency of the NSM technique for the flexural strengthening is also investigated. A numerical strategy is implemented to analyze the applicability of the FRP effective strain concept, proposed by ACI and fib in the design of FRP systems for the flexural strengthening. To assess the efficacy of the NSM technique for the shear strengthening of concrete beams, four beam series of distinct depth and longitudinal tensile steel reinforcement ratio are tested. Each series is composed of one beam without any shear reinforcement and one beam using the following shear reinforcing systems: conventional steel stirrups; strips of wet lay-up CFRP sheet of U configuration applied according to EBR technique; and laminates of CFRP embedded into vertical or inclined (45°) pre-cut slits on the concrete cover of the beam lateral faces, according to the NSM technique. Using the obtained experimental results, the performance of the analytical formulations proposed by ACI, fib and Italian guidelines is appraised.     

Mechanical behaviour of corroded reinforced concrete beams—Part 1: Experimental study of corroded beams

Steel corrosion in reinforced concrete leads to crack occurrence along the reinforcement (secondary cracks), to a reduction in bond strength and a reduction in steel cross section. The purpose of this study is to determine the effect of these deteriorations on the global behaviour of reinforced concrete structural elements in their service and ultimate states. Mechanical experimentation was carried out on fourteen-year-old reinforced concrete beams, on two control elements and two corroded beams. A comparative analysis of the results obtained on the beams showed that concrete cracking in the compressive area had no significant influence on the behaviour in service of the corroded elements. However, significant modifications of service behaviour were observed, due to the degradations in the tensile zone, namely: loss of bending stiffness, dissymmetrical behaviour. Finally, the measure of the residual steel cross-section of the corroded re-bars showed that the loss of bending stiffnes due to steel corrosion cannot be merely explained in terms of steel cross-section reduction. Concerning the ultimate behaviour, the loss of steel cross-section is the main parameter which leads to a reduction of bearing capacity and ductility. Another part will explain the separate and coupling effects of bond strength and steel cross-section loss on the mechanical behaviour of corroded beams.     

Experimental and analytical study of corroded shear-critical reinforced concrete beams

This paper presents the experimental results of two highly corroded shear-critical deep beams subjected to a chloride environment to assess the shear behavior of long-term-corrosion damaged beams. A 26-year-old reinforced concrete beam corroded by exposure to a chloride environment was cut into two small short-shear-span beams, or deep beams, which were tested under three point bending until failure, along with a control beam of the same age, same length and same cross-section (115 × 28 × 15 cm). Cracking and corrosion maps were drawn for the corroded beams in order to assess the corrosion. Force displacement curves were drawn for the corroded and control beams. After testing the beams until failure, the main steel bars and the stirrups were extracted from the beams and loss of mass was measured and plotted for both longitudinal and transverse reinforcement. It was noted that the loss of mass of transverse and longitudinal reinforcements had not had an important influence on the failure mode and it had not affected the load-bearing capacity of the beam. It was found that the stirrups came into action after the failure of the compression strut and thus decreased the ductility of the corroded beams. Analytical investigations were made to compare the experimental shear capacity with the theoretical value. Strut and tie model predictions were more accurate than the conventional sectional methods provided for in ACI 318-08 and Eurocode 2.     

Performance of reinforced concrete slabs strengthened with different types and configurations of CFRP

A total of eight reinforced concrete slabs, 2440 × 600 × 125 mm strengthened with different layers and configurations of CFRP sheets were fabricated and tested. In addition, nonlinear finite element analysis (NLFEA) using ANSYS package was used to simulate the behavior of the test specimens. After reasonable validation of NLFEA with the experimental test results of companion slabs, NLFEA was expanded to provide a parametric study of eighteen slabs. The load–deflection, load strain, and failure modes obtained from the experimental test results and the NLFEA evidently confirmed that strengthening of under-reinforced concrete slabs with CFRP improves the flexural strength capacity and reduce the ductility. This was observed for both types of CFRP. The increase in the flexural strength and the reduction in the ductility increased with the increase in the number of CFRP layers. It was concluded that CFRP strengthening of slabs could be categorized as effective, economical, and successful only if substantial increase in the flexural strength capacity is achieved without changing the failure mode to a shear failure mode at the face of the supports or to a compression failure mode. Comparison between the two CFRP types, for almost equivalent applied area of CFRP, showed that the type of CFRP has significant influence on the behavior of the strengthened slabs. The difference is attributed to the difference in the mechanical properties and the bonding quality of the CFRP material.     

CFRP筋增强ECC梁弯曲性能试验研究

为研究碳纤维增强树脂复合材料(Carbon fiber reinforced polymer,CFRP)筋/超高韧性纤维增强水泥基复合材料(Engineered cementitious composite,ECC)梁的抗弯性能,对3根CFRP筋/ECC梁、1根玻璃纤维增强树脂复合材料(Glass fiber reinforced polymer,GFRP)筋/梁和1根CFRP筋混凝土梁进行了四点弯曲试验,分析了配筋率、纤维增强树脂复合材料(Fiber reinforced polymer,FRP)筋类型和基体类型对梁抗弯性能的影响。试验结果表明:CFRP筋/ECC梁与GFRP筋/ECC梁和CFRP筋混凝土梁类似,均经历了弹性阶段、带裂缝工作阶段和破坏阶段;配筋率对CFRP筋/ECC梁的受弯性能影响较大。随着配筋率的增加,CFRP筋/ECC梁的承载能力不断提高,延性性能逐渐减弱;ECC材料优异的应变硬化能力和受压延性,使得CFRP筋/ECC梁的极限承载能力和变形能力均优于CFRP筋混凝土梁;由于ECC材料多裂缝开裂能力,CFRP筋/ECC梁开裂后,纵筋表面应变分布比CFRP筋混凝土梁更均匀; 由于聚乙烯醇(Polyvinyl alcohol,PVA)纤维的桥联作用,CFRP筋/ECC梁破坏时,其表面出现了大量的细密裂缝,且能保持较好的完整性和自复位能力;正常使用阶段,CFRP筋/ECC梁的最大弯曲裂缝宽度均小于CFRP筋混凝土梁。最后,根据试验结果,建立了基于等效应力图的CFRP筋/ECC梁弯曲承载力简化计算模型,确定模型中的相关系数。由简化模型计算的极限承载力与试验结果具有较好的相关性。      

Fatigue behavior of RC T-beams strengthened in shear with EB CFRP L-shaped laminates

The use of externally bonded carbon fiber-reinforced polymer (EB-CFRP) to strengthen deficient reinforced concrete (RC) beams has gained in popularity and has become a viable and cost-effective method. Fatigue behavior of RC beams strengthened with FRP is a complex issue due to the multiple variables that affect it (applied load range, frequency, number of cycles). Very few research studies have been conducted in shear under cyclic loading. The use of prefabricated CFRP L-shaped laminates (plates) for strengthening RC beams under static loading has proven to be technically feasible and very efficient. This study aimed to examine the fatigue performance of RC T-beams strengthened in shear for increased service load using prefabricated CFRP L-shaped laminates. The investigation involved six laboratory tests performed on full-size 4520 mm-long T-beams. The specimens were subjected to fatigue loading up to six million load cycles at a rate of 3 Hz. Two categories of specimens (unstrengthened and strengthened) and three different transverse-steel reinforcement ratios (Series S0, S1, and S3) were considered. Test results were compared with the upper fatigue limits specified by codes and standards. The specimens that did not fail in fatigue were then subjected to static loading up to failure. The test results confirmed the feasibility of using CFRP L-shaped laminates to extend the service life of RC T-beams subjected to fatigue loading. The overall response was characterized by an accelerated rate of damage accumulation during the early cycles, followed by a stable phase in which the rate slowed significantly. In addition, the strains in the stirrups decreased after the specimens were strengthened with CFRP, despite the higher applied fatigue loading. Moreover, the addition of L-shaped laminates enhanced the shear capacity of the specimens and changed the failure mode from brittle to ductile under static loading. Finally, the presence of transverse steel in strengthened beams resulted in a substantially reduced gain in shear resistance due to CFRP, confirming the existence of an interaction between the transverse steel and the CFRP.