Carbon Fiber Reinforced Polymer Reinforcement Research Articles

Experimental study on the flexural performance of prestressed RC beams with post-tensioned CFRP strands

Carbon fiber reinforced polymer (CFRP) exhibits multiple advantages over conventional steel, such as high strength and corrosion resistance. By replacing prestressing steel with prestressing CFRP in new prestressed reinforced concrete (RC) structures, the corrosion issue of prestressing steel can be resolved. At present, there remains scarce research on the application of CFRP strands in the prestressed RC structures. An experimental study was conducted on prestressed RC beams with internal post-tensioned CFRP strands under flexure. The study aimed to analyze the effects of the prestress level, number of CFRP strands, layout shape of CFRP strands, bonding layer, and reinforcement ratio of steel bars on the flexural behavior. The test results indicated that all specimens experienced concrete crushing failure. After applying prestressing CFRP strands to ordinary RC beams, the cracking load increased by 50.0% to 102.2%, the yielding load increased by 20.2% to 38.6%, and the ultimate load increased by 20.3% to 41.4%. Reducing the reinforcement ratio of steel bars had a minor effect on the cracking load but resulted in a noticeable decrease in the yielding and ultimate loads of the prestressed CFRP strand-reinforced concrete beams. Moreover, the bonded specimen showed a slight increment in the cracking, yielding, and ultimate loads as well as stiffness compared to the unbonded specimen, while the deformation capacity of the unbonded specimen remained superior. The specimens with curved and straight prestressing CFRP strands exhibited very similar mechanical properties.

Bond behavior of CFRP reinforcement systems with concrete under static and fatigue loading

In this research, the single lap shear tests were used to investigate the bond behavior of carbon fiber reinforced polymer (CFRP) sheets bonded to concrete blocks under static and fatigue loads. The magnitude of the fatigue load was considered as a parameter that varied from a minimum load of 10% of Pu to a maximum load of 60%, 70% and 80% of the ultimate static load. For both loading scenarios, the applied load versus slips curves and the profiles of the interface zone strain were presented. In addition, comparisons, and analyses of the failure mode of samples subjected to static and fatigue loading are presented. The experimental results demonstrate that the loading level has a significant impact on the failure mode, fatigue life and stiffness degradation of CFRP-concrete joints during the fatigue loading.Finally, a prediction model for the fatigue life of the CFRP-concrete joint was developed as part of this investigation.

Experimental study on CFRP reinforcement and static performance of CHS KT-joints

Owing to the engineering application demands for the reinforcement of complex joints in multiplanar circular hollow section (CHS) trusses, this study investigated the reinforcement methods and static performance of KT-joints strengthened with carbon fibre-reinforced polymer (CFRP) sheets. First, CFRP reinforcement strategies for KT-joints were studied. Experimental comparisons in static performances were then conducted between bare and CFRP-strengthened CHS KT-joints. Meanwhile, CFRP reinforcement mechanisms were analysed. Finally, CFRP effective strain index η was proposed for quantitative assessment of CFRP strength utilisation. The results indicated that CFRP effectively restrained chord depression and expansion deformation, prevented local buckling of the compressive brace, and reduced strain concentration near the intersection lines. Compared with the bare joint, the ultimate load-bearing capacity and ductility of the joint reinforced with 4 layers of CFRP sheets on the chord and 3 layers on the braces increased by 24% and 25%, respectively. The initial stiffness of the joint at compressive and tensile brace locations increased by 48% and 375%, respectively. The η varied at different regions of the joint, with the maximum η found near the K-shaped gap and the intersection line of compressive brace. Based on the distribution of η, strategies for improving CFRP strength utilisation were proposed.

MODELING OF STRESS-STRAIN STATE AND STRENGTH OF DAMAGED CONCRETE BEAMS REINFORCED WITH CARBON FIBER FABRIC IN PC "LIRA-SAPR"

The study examines the problem of preserving and improving the architectural heritage in Ukraine. Many buildings and structures have a long service life or are already deteriorating due to their age and other factors. This is particularly true for reinforced concrete structures, which often have various defects and damage. Unfortunately, there are no clear methods for assessing the residual load-bearing capacity of such structures. However, the research indicates that the residual potential of damaged elements may be significantly underestimated. Therefore, it is crucial to explore and apply effective innovative solutions for strengthening these constructions. One such solution involves using composite materials (fiber-reinforced polymers, FRP) for external reinforcement of structures. Composite materials offer numerous advantages, including high strength, low weight, resistance to aggressive environments, and durability. The article presents the results of a numerical experiment aimed at investigating the influence of damage and reinforcement with carbon fiber-reinforced polymer (CFRP) on the stress-strain state and residual load-bearing capacity of concrete beams with basalt-plastic reinforcement (BFRP). For the experiment, 15 rectangular beams with dimensions of 2000×200×100 mm were prepared and nonlinearly analyzed using the "LIRA-SAPR" software, which employs the finite element method. The data obtained for each beam were compared with the results of laboratory tests, revealing that CFRP reinforcement increases the residual load-bearing capacity of the beams without significantly affecting their working deformation. Additionally, a comparative analysis was conducted on the residual load-bearing capacity and stress-strain state of the beam components: CFRP fabric, concrete, and reinforcement. The authors assert that modeling the complex stress-strain state of experimental basalt-concrete beams using nonlinear finite element calculations through the "LIRA-SAPR" software accurately reproduces experimental results, provides insight into the most likely failure mode, and reliably predicts their load-bearing capacity.

Experimental Study on Shear Performance of Concrete Beams Reinforced with Externally Unbonded Prestressed CFRP Tendons

To investigate the reinforcing effect of externally prestressed carbon-fiber-reinforced polymer (CFRP) tendons on the shear performance of reinforced concrete beams, a set of model tests was designed. Static load comparative tests were conducted on one original beam and four reinforced beams to experimentally investigate the impacts of the prestress level and damage in the shear zone on the shear reinforcement effect and analyze the reinforcement mechanism of CFRP tendons. The results show that in the beams reinforced with CFRP, the CFRP tendons could work collaboratively with the stirrups to reduce the strain on the stirrups; the increasing rate in the yield load was 28–70%. After the stirrups yielded, the CFRP tendons did not yet reach their ultimate tensile strength and could still withstand increased shear forces, resulting in an increasing rate of the ultimate load for the reinforced beams with a CFRP content of 56–78%. The enhancements in both the yield load and the ultimate load were positively correlated with the level of prestress in the CFRP tendons. This reinforcement technique efficiently restricts the growth and delays the first appearance of diagonal cracks. The prestress can close the pre-existing diagonal cracks and provide a reserve of shear capacity for the beams. The initial damage in the shear zone decreases the initial shear stiffness and increases the width of the initial diagonal cracks. However, this effect gradually diminishes as the load increases and does not significantly impact the shear capacity. Prestressing can significantly improve the strength utilization rate of the CFRP reinforcement when the reinforced beams fail. The deformation of the CFRP tendon is directly related to the shear deformation. By combining this relationship with the truss–arch model, the shear capacity for the reinforced beam can be predicted. The predicted results exhibit an error of less than 10% when compared to the test results, offering valuable design guidance for reinforced engineering composites.

Static performance of precast concrete arches with carbon fiber reinforced polymer reinforcement

In this paper, static performances of a new precast concrete arch system with carbon fiber reinforced polymer (CFRP) reinforcement were investigated. Varied concrete strengths and segment types of precast concrete arches were tested. The results show that the increase of concrete strength can improve the bearing capacity of the precast arches with CFRP reinforcement. The ultimate bearing capacity of the precast arches segmented at the arch vault with CFRP reinforcement can reach or even exceed that of complete arches, while the precast arch segmented at the shoulder had lower ultimate load. A theoretical analysis method was proposed to predict the failure and bearing capacity of the precast concrete arches with CFRP reinforcement, which were found to be in close agreement with the experimental result.

Improved Bond Stress-Slip Relationships for Carbon Fibre-Reinforced Polymer-Strengthened Masonry Triplets

Carbon fibre-reinforced polymer (CFRP) emerges as a viable solution for reinforcing unreinforced masonry (URM) walls subjected to shear loads. While masonry structures are straightforward to construct, the complexity of the construction materials, especially in terms of their mechanical properties, poses challenges for numerical studies of their structural behaviour. Walls, being fundamental components in masonry construction, play a crucial role in transferring both horizontal and vertical lateral forces. This study investigates the enhancement of masonry wall behaviour through the reinforcement of CFRP. CFRP reinforcement increases ductility and strength, reducing the risk of failure under shear conditions. Additionally, CFRP composites present a practical solution to strengthening masonry structures compared to traditional reinforcement. However, brick, mortar, and CFRP have not been thoroughly investigated. Experimental tests on the bond behaviour of different configurations of CFRP-retrofitted masonry triplets have not been performed before and are therefore presented in this paper. Triplet specimens, comprising three bricks and two mortar joints, both with and without CFRP strengthening, were subjected to bond testing. The study affirms that masonry triplets strengthened with CFRP under shear loads exhibit strength levels at least four to six times greater than those without CFRP. The experimental work was carried out with eight different CFRP configurations on triplet masonry, and each test was repeated four times. Further, the bond stress-slip relationship in the case of masonry triplets with and without CFRP was predicted with new mathematical equations based on the conducted test results. These equations were included in the commercial finite element software ANSYS and used to conduct simulations of CFRP-reinforced masonry triplets. The numerical results indicate good agreement between the finite element model and the test results. The outcome of this research improves the current knowledge on the use of CFRP to reinforce masonry walls with brick and mortar, which will contribute to the understanding of the effect of CFRP on masonry structures.

Study on the Methods of Strengthening Reinforced Concrete Beams with CFRP

After the long-term use of reinforced concrete structures, there may be structural aging and structural damage, these common engineering problems. As a result, the performance is reduced, so it is necessary to strengthen to meet the corresponding safety requirements. Carbon Fiber Reinforced Polymer (CFRP) has the advantages of lightweight, strong, high tensile strength and tensile degree. Therefore, CFRP is widely used in reinforcement. Based on CFRP reinforcement of reinforced concrete beams, this paper analyzes its reinforcement methods. The paper mainly analyzes the influence of different pasting methods of CFRP on the performance of beams and the influence of material pasting thickness on beams. Through the analysis and research, it can be concluded that CFRP has certain advantages compared with traditional reinforcement materials. Therefore, it can be used to reinforce reinforced concrete beams. This study can provide some reference value for some related projects of reinforced concrete beams reinforced by CFRP.

Enhancing tensile performance and CFRP/steel interface properties of CFRP plates with nano-SiO2 and MWCNTs

The mechanical performance of carbon fiber reinforced polymer (CFRP) is a crucial parameter influencing the effectiveness of CFRP reinforcement. The addition of nano-toughening agents to the resin matrix can effectively enhance the mechanical properties of CFRP. This paper investigates the influence of nano-SiO2 and MWCNTs content (0.2, 0.4, and 0.6 wt%) as well as their blending ratios (1:3, 1:1, 3:1) on the tensile properties of CFRP plates using the vacuum assisted resin infusion molding (VARIM) process. Additionally, an assessment is conducted to evaluate how the tensile performance of CFRP plates affects the CFRP plate/steel interface performance.The results indicate that the resin viscosity increases with the addition of nano-toughening agents, with the resin viscosity experiencing a respective increase of 32.9% and 92.7% when incorporating 0.6 wt% nano-SiO2 or MWCNTs compared to pure resin. The inclusion of nano-toughening agents enhances the tensile strength of CFRP plates, with a more pronounced effect observed when adding 0.4 wt% nano-SiO2 or MWCNTs, resulting in respective increases of 41.5% and 31.5% compared to pure CFRP plates. When nano-SiO2 and MWCNTs are mixed, the tensile performance of the CFRP plate is inferior to that of plates with the same individual nano-toughening agents content. This is attributed to the excessively high viscosity of the resin matrix during mixing, hindering complete infiltration of carbon fibers. Therefore, in the manufacturing process of CFRP plates using the VARIM technique, it is advisable to consider resins with lower viscosity. Additionally, the utilization of CFRP plates with superior tensile performance contributes to enhanced CFRP/steel interface properties, although the tensile performance of CFRP plates does not alter the bonding slip curve of CFRP/steel double-lap joint specimens.

Effects of exposure in seawater sea-sand concrete pore solution on fatigue performance of carbon FRP bars

The study aims to propose a methodology to predict the fatigue performance of carbon fiber-reinforced polymer (CFRP) bars under the seawater sea-sand concrete (SWSSC) environment. The effects of exposure in SWSSC pore solution on the fatigue damage mechanisms and fatigue performance of CFRP bars are presented. Firstly, the tensile fatigue tests of reference CFRP bars were performed under various stress levels with a constant stress ratio of 0.1. Secondly, the tensile fatigue tests of exposed CFRP bars subject to the simulated SWSSC pore solution were carried out. The tensile failure modes and fatigue damage mechanisms corresponding to different stress levels, were identified using scanning electron microscopy (SEM). Besides, the relationship between fatigue life expectancy and underlying fatigue damage mechanisms was carefully analyzed. Finally, the effective stress level method (ESLM) was proposed to evaluate the residual fatigue life of exposed CFRP bars based on the benchmark S–N curve. Combined with the degradation models (chemical etching/diffusion models) proposed in our previous research, ESLM could bridge corrosion fatigue life prediction of the exposed CFRP bars and the benchmark fatigue data of the non-exposed CFRP reinforcement. The predicted results have good correlations with the experimental data. This method can also provide valuable insight for the corrosion fatigue life prediction of other types of FRP composites.

Dowel action of textile CFRP shear reinforcement in carbon reinforced concrete

Composite structures with textile CFRP (carbon fibre reinforced polymer) reinforcement are characterised by high compressive and tensile strength and have great potential for use in thin-walled structures such as shell structures or girder webs. However, the stress transfer mechanisms activated along cracks of carbon reinforced concrete (CRC) membranes have not been sufficiently investigated yet. Especially the potential of CFRP yarns to transfer shear across sliding crack surfaces has not been thoroughly understood.For steel reinforced concrete elements, dowel action has been studied for several decades and numerous constitutive laws for the shear contribution of dowel action have been developed. In contrast, the sensitivity to transverse pressure of CFRP reinforcement is expected to have a significant influence on the activation of dowel action in cracked CRC. Neither the damage and fracture of impregnated textiles due to transverse compression nor the shear-induced delamination of reinforcement in the vicinity of cracks have been investigated in detail. Therefore, suitable constitutive laws to describe the dowel effect of CFRP reinforcement are not available.This paper presents dowel tests with textile CFRP shear reinforcement and highlights the phenomenology of dowel behaviour in carbon reinforced concrete as well as the main factors influencing the dowel behaviour.

Deformation-based design of hollow coarse-aggregate ultra-high-performance-concrete beams reinforced with CFRP bars

This study aims to develop a novel type of beams strengthened with carbon fiber-reinforced polymer (CFRP) bars and cast using ultra-high-performance concrete (UHPC) with coarse aggregates (CA-UHPC) to address issues such as poor ductility, extensive cracking, and significant deflection observed in FRP-reinforced concrete (FRP-RC) beams. Six hollow beams were fabricated and tested via a four-point-bending test under cycle loading to study the effects of parameters, including CFRP reinforcement ratios, hollow shapes, and hollow ratio on the deformation performances of the beams. The results show that the deformation of all hollow beams under service loads met the requirements of the GB50610 code for deformation. Increasing hollow ratio had a negative impact on the flexural behaviors of beams, and this effect was more pronounced in beams with higher hollow ratios than in beams with lower hollow ratios. The flexural performances of square hollow beams were better than that of circular hollow beams with the same hollow ratio. Compared to other hollow beams, square hollow beams with a hollow ratio of 44.44% demonstrated superior flexural performance and optimal cost-effectiveness. Ultimately, leveraging the computational framework for steel fiber reinforcement and residual deflection, predictive models for deflection were formulated for CFRP-CA-UHPC beams with various hollow configurations under both static and cyclic loading conditions.

Feasibility assessment of self-deicing concrete pavements with recycled CFRP reinforcement: Environmental and mechanical performance

Electrically conductive concrete (ECC) with carbonaceous conductive elements has been studied for self-deicing pavements; however, carbon fiber production is costly and resource-intensive. Therefore, mechanically recycled carbon fiber reinforced polymer (CFRP) scraps from plane manufacturing were evaluated as reinforcing and conductive elements for ECC.Evaluation of mechanical properties showed that 5%Vol rCFRP-ECC had approximately 20% higher flexural strength and twofold greater absorbed fracture energy than the reference plain concrete. In a -15 °C environment, this ECC melted ice at a heating rate of 0.05 °C/min and a 3.8 kWh/m2 power consumption.A life cycle assessment modeling of winter maintenance operations for one snowstorm in the Sierra Nevada Mountain regions in California showed that rCFRP-ECC and two other ECCs from the literature have a significantly higher global warming potential from energy consumption than snowplowing, sanding, and salting. Nevertheless, important advantages of ECCs in reducing chloride contamination in water and soil, corrosion in vehicles and infrastructure, and stronger and more durable fiber-reinforced infrastructure materials should be considered in decision-making.

Experimental study of novel wrapped CFRP-strengthened CFS-to-sheathing screw connections

Cracking damage of the sheathing wallboards in screw connections is the typical failure mode of cold formed steel (CFS) structures under seismic effects, which limits the shear capacity and weakens the hysteretic performance of CFS structures. To improve the shear performance of CFS-sheathing screw connections, a novel screw connection with carbon fiber reinforced polymer (CFRP) reinforcement is proposed in this paper. Cyclic tests were conducted on a total of 26 sets of screw connections with different configurations and wall sheathings, and the effects on the failure modes and shear performance of the connections with and without CFRP reinforcement were investigated. The strengthening effects of the sheathing material, panel thickness and end distance on the shear properties of the connections were discussed. The results indicated that (1) except for specimens with 15 mm end distance, CFRP reinforcement can effectively avoid brittle cracking failure of the connections, and the failure mode tended to ductile failure of the bearing and pull-through damage. (2) in addition to the stiffness, the shear strength, deformation capacity, ductility and energy dissipation capacity of CFRP-strengthened connections are significantly enhanced. The effect of CFRP on the shear performance improvement of connections sheathed with gypsum board (GWB) and magnesium glass board (MgO) is greater than that of oriented strand board (OSB), and the strengthening effect is not significantly influenced by the board thickness. A toughness evaluation method for CFRP-strengthened connections was proposed, and the design formulae for the shear strength of the CFRP-strengthened screw connections were recommended based on the load resistance factor design (LRFD) method and allowable strength design (ASD) method.

Experimental cyclic response of heat-damaged RC beam-column joints strengthened with CFRP strings

Reinforced concrete (RC) buildings may be subjected to high temperatures during their service life, which causes significant deterioration in the mechanical and physical characteristics of several structural members (i.e., joints), making it necessary to upgrade their overall performance to withstand the additional stresses. Therefore, the effectiveness of carbon fiber reinforced polymer (CFRP) strings used as near-surface mounted (NSM) reinforcement in restoring the structural performance and minimizing the failure mechanism of heat-damaged RC beam-column (B-C) joints is examined in this study through experimental work. The experimental research consists of twelve RC beam-column joint sub-assemblages divided into three groups: four joints were kept at room temperature, four were heated to 400 °C, and four were heated to 600 °C. Three joints from each batch were tested under a quasi-static cyclic load after adding one, two, or three strings of CFRP reinforcement. The cyclic response of joints was evaluated by determining the ultimate load capacity in pulling and pushing and its corresponding lateral displacement, energy dissipation, displacement ductility, and stiffness degradation. The experimental results showed that the upgraded joints with CFRP strings experienced a significant increase in energy dissipation, initial stiffness, displacement ductility, and ultimate load capacity in pulling and pushing over reference joints.

Analytical solution of the full-range behavior of adhesively bonded FRP-steel joints made with toughened adhesives

Fiber-reinforced polymer (FRP) composites represent an effective solution to strengthen and retrofit existing steel members. Namely, bonded or unbonded carbon FRP (CFRP) plates have been employed to improve the strength, fatigue behavior, and durability of steel bridges. In bonded solutions, the effectiveness of the CFRP reinforcement strongly depends on the adhesive employed to bond the plate, as failure usually occurs due to debonding. Within this framework, the use of toughened adhesives is particularly attractive since they may improve the load carrying capacity of the CFRP-steel interface, also providing a certain ductility. Debonding in CFRP-steel joints was previously studied using a cohesive approach. However, solutions able to describe the full-range behavior of joints with toughened adhesives and finite bonded length are not available in the literature. In this paper, a trapezoidal (trilinear) cohesive material law (CML) is employed to model the bond behavior of pultruded carbon FRP-steel joints made with a rubber-toughened epoxy adhesive, which showed cohesive debonding within the adhesive layer. The analytical solution provided is employed to study the experimental response of nine CFRP-steel joints tested using a single-lap direct shear set-up. Comparisons of analytical and experimental results of joints with three different bonded lengths confirm the effectiveness of the solution proposed.

Experimental and Numerical Study on RC Beams Strengthened by NSM Using CFRP Reinforcements

Near Surface Mounted (NSM) Carbon Fiber-Reinforced Polymer (CFRP) reinforcement technique to improve the flexural strength of reinforced concrete members has become increasingly attractive in recent years. In this study, the practical problem of concrete cover depth cutting limitation was investigated. Twelve specimens were tested by four-point bending until failure. Experimental parameters include concrete cover depth, CFRP reinforcement type, CFRP positioning, and stirrups status. Furthermore, a nonlinear FEA model was developed to simulate the tested beams and was able to predict the experimental behavior satisfactorily. A series of parametric studies were then performed using this model to understand the effect of various reinforcement parameters on the flexural performance of the beam. The results showed that Strengthening with CFRP resulted in a significant increase in yield and ultimate strengths, but a significant ductility loss was recorded due to CFRP strip debonding in the strengthened beams, this problem was addressed by using more efficient strengthening techniques utilizing the effective bond length and a proper groove depth and positioning for the NSM bars.

Flexural behaviours of pretensioned prestressed concrete-UHDC composite beams reinforced with CFRP bars

Prestressing fiber reinforced polymer (FRP) bars is widely acknowledged as an effective method for exploiting their high strength. However, compared to FRP reinforced concrete structures, prestressed FRP reinforced concrete structures exhibit weaker deformation capacity. To address this issue, ultra-high ductile concrete (UHDC) was employed to enhance the flexural behaviours of pretensioned prestressed concrete (PPC) beams reinforced with carbon fiber reinforced polymer (CFRP) bars, while additional aluminium alloy ribs (ARs) were utilized to ensure proper anchorage. A total of eight beams were designed and tested, consisting of four PPC beams and four PPC-UHDC composite beams, which featured different types of CFRP bars, reinforcement ratios and UHDC placement. The test results revealed that the CFRP-reinforced PPC-UHDC composite beams exhibited significantly improved flexural performance in terms of cracking load, ultimate load and ultimate displacement. For specimens with lower reinforcement ratio, the UHDC effectively controlled the cracks and promoted uniform strain in the CFRP bars, leading to increased ultimate load capacity and ultimate displacement. For specimens with higher reinforcement ratios, the flexural performance was comprehensively improved when the UHDC was placed in the compression zone. Numerical analysis was conducted to further investigate the flexural behaviours of PPC-UHDC composite beams under various conditions.

Woven Carbon-Fiber-Reinforced Polymer Tubular Mesh Reinforcement of Hollow High-Performance Concrete Beams.

This article presents woven carbon-fiber-reinforced polymer (CFRP) tubular mesh used as a reinforcement on the inner surface of hollow beams made of high-performance concrete (HPC). The tubular mesh was designed to serve as both the tensile and shear reinforcement of hollow beams intended for the construction of small self-supporting structures that could be assembled without mechanization. The reinforcement was prepared with a tri-axial weaving machine from carbon filament yarn and was homogenized using epoxy resin. The interaction of the composite reinforcement with the cementitious matrix was investigated, and the surface of the reinforcement was modified using silica sand and polyvinyl alcohol (PVA) fibers to improve cohesion. The sand coating enhanced bond strength, resulting in the significantly higher flexural strength of the hollow beam of 128%. The PVA fibers had a lower positive effect of 64% on the flexural strength but improved the ductility of the beam. Individual beams were connected by gluing steel parts directly inside the hollow core of the HPC beam. This procedure provides good interaction between the CFRP reinforcement and the glued steel insert and allows for the fast and simple assembly of structures. The weaving of additional layers of the CFRP reinforcement around HPC beams was also explored. A small structure made of the hollow HPC beams with inner composite reinforcement was constructed to demonstrate the possibilities of the presented technology.

Nonlinear Analysis on Torsional Strengthening Of Rc Beams Using Cfrp Laminates

This research is devoted to investigate the behavior and performance of reinforced concrete beams strengthened with externally bonded Carbon Fiber Reinforced Polymer (CFRP) laminates under the effect of torsion. In this study a theoretical analysis has been conducted using finite element code ANSYS. Six previously tested beams are used to investigate reinforced concrete beams behaviorunder torsion, two of them are solid and the rest are box-section beams. Also, two beams are without CFRP reinforcement, which are used as control beams for the strengthened one, and the other four beams are strengthened with CFRP laminates with different number of layers and spacing. Numerical investigation is conducted on these beams, and comparisons between the available experimental results for these beams and numerical results from the current study are made. Conclusions from these comparisons are presented and discussed. An increase of about 15.6% in the ultimate torque for the solid beam and of about 9.8% in the ultimate torque for the box-section beam is observed after using the CFRP strips. A parametric study is carried out to study the torsional behavior of RC beams having different number of CFRP layers and concrete compressive strength; also U-wrap for the CFRP configuration is investigated.