Carbon Fiber Reinforced Polymer Strengthening Research Articles

Behavior and Load Capacity of Concrete Slab Reinforced by CFRP Bar and Strengthening by CFRP Laminates

Abstract The most common FRP materials used are carbon fiber reinforced polymers (CFRPs), and glass fiber reinforced polymers (GFRPs). The use of CFRPs has grown rapidly in the construction industry, specifically in structural retrofitting, due to their strengthening property of CFRP. CFRPs are moreover high strength, lightweight, noncorrosive, and easy-to-install materials. In the present study, six reinforced concrete slab specimens included two control specimens reinforced by traditional steel reinforcements and the other reinforced by carbon fiber reinforced polymer CFRP bars without strengthening by laminated CFRP strips. The remaining four specimens are interiorly reinforced by CFRP bars and strengthened by CFRP laminates strips with different scheme layouts named Type 1 and Type 2. The specimens were tested under a uniformly distributed load applied at the top surface area of each specimen up to failure. The parameters considered in the present study are the amount of CFRP bars and CFRP laminates layout. Test results indicated that the strength carrying capacity and failure mode of tested specimens differ based on the steel reinforcement type and the presence of CFRP laminates layout.

Efficiency of CFRP torsional strengthening technique for L-shaped spandrel reinforced concrete beams

Abstract The present study aims to get experimentally a deeper understanding of the efficiency of carbon fiber-reinforced polymer (CFRP) sheets applied to improve the torsional behavior of L-shaped reinforced concrete spandrel beams in which their ledges were loaded in two stages under monotonic loading. An experimental program was conducted on spandrel beams considering different key parameters including the cross-sectional aspect ratio (i.e., web height/web thickness), and the availability of the CFRP strengthening system. The ledge of the spandrel beams was exposed during testing to a very high eccentric load, which was transferred to the web of the spandrel beam causing high shear, torsion, and bending moments. Consequently, the applied load resulted in in-plane and out-of-plane deformations of the web accompanied by flexural and shear cracks. This article demonstrates the advantage of using CFRP sheets to strengthen the mentioned members. The applied CFRP sheets increased the failure torsional load by about 37% compared to the identical L-spandrels without strengthening. The outcomes indicate that using CFRP sheets show improvement in restricting the deflections and rotation of L-spandrels due to increasing spandrel stiffness. The reduction in the degree of rotation attained more than 33% in comparison to the spandrel beams without strengthening. The experimental program confirmed the applicability of the proposed strengthening technique for compacted and slender L-shaped spandrel-reinforced concrete beams.

Numerical Analysis on Dynamic Response of CFRP-Wrapped RC Columns under Lateral Impact Loading

This paper presents a numerical study examining the dynamic response and resistance mechanism of reinforced concrete (RC) columns strengthened with or without carbon-fiber-reinforced polymer (CFRP) wraps under lateral impact loading by using the software LS-DYNA. First, the information of eight column models was briefly introduced as part of the laboratory experimental program from the literature. Secondly, finite element (FE) models were established in terms of the geometries of impact tests. Then, a detailed comparison between numerical results and experimental results was made, and FE models showed a relatively high simulation accuracy. Subsequently, a series of parametric analyses were carried out with a focus on the effects of axial compression ratio, the boundary condition at the column top, the layer number of CFRP wraps, and the impact velocity and impact height on the dynamic responses of plain and strengthened columns. The results demonstrated that the CFRP retrofit mechanism was not activated during the initial Stage-I when the impact force rapidly increased to the first peak and then decreased to zero. CFRP strengthening came into play in the second stage, Stage-II, and affected the response of the shear force and moment along the column height, as well as had a great influence on the control of shear damage. The dynamic response of RC columns was more sensitive to the impact velocity than to other parameters, regardless of whether CFRP wrapping was applied. The axial compression ratio would have a different influence on the column failure mode if the impact velocity was varied. The variation in impact height and boundary condition at the column top had little influence on the damage mode of strengthened columns.

CFRP contribution to load-carrying capacity of retrofitted geopolymer concrete beams

In this study, reference geopolymer concrete (GC) beams were loaded up to the failure state with a three-point bending test to obtain load–deflection behavior. These damaged reference GC beams were then repaired, strengthened with Carbon Fiber Reinforced Polymer (CFRP) in both shear and flexure. These retrofitted GC beams have been then tested in the same conditions as reference GC beams and the effect of the CFRP strengthening on the strength and behavior was investigated. The load-carrying capacities of the retrofitted GC beams were higher than the reference GC beams in all series. The increase in capacities due to CFRP strengthening was higher in retrofitted GC beams without stirrups than in retrofitted beams with stirrups. The initial stiffness of the retrofitted GC beams were lower than those of the reference GC beams. This decrease was more evident in GC beams without stirrups than in GC beams with stirrups. Strengthening with CFRP enhanced the deflection and ductility capacities of the repaired GC reference beams without stirrups compared to the reference GC beams. The experimental CFRP contribution to shear strength was tried to be estimated using the equations proposed for the CFRP contribution in reinforced concrete (RC) beams. The predicted contribution of CFRP to shear strength using all investigated equations was greater than the experimentally obtained CFRP contribution.

Prediction of fatigue crack propagation in center cracked steel plate strengthened with prestressed CFRP strip

Evaluating the fatigue behavior of steel structures strengthened with prestressed carbon fiber reinforced polymer (CFRP) is of great significance for structural repair and rehabilitation. In this paper, an analytical model based on linear elastic fracture mechanics considering the additional elongation of the steel plate caused by the central crack opening was proposed to predict the fatigue behavior of prestressed CFRP strips strengthened steel plates. The finite element model calibrated by experiments was used to verify the proposed model. The results showed that the proposed model can predict the stress state of various components, the stress intensity factor SIF amplitude, the fatigue crack growth life, and the minimum prestress of CFRP strips required for crack arrest under different strengthening conditions with high accuracy. This study will be conducive to a better application of the prestressed CFRP strengthening of thin-walled steel structures under fatigue loading.

Prediction of Ballistic Limit of Strengthened Reinforced Concrete Slabs Using Quasi-Static Punching Test

The formulas available in the literature for predicting the projectile impact response of reinforced concrete (RC) targets are generally developed based on the results of impact tests. Recently, however, in order to avoid performing involved and challenging projectile impact tests, the impact response of RC targets was predicted using the quasi-static punching response of RC slabs. In this paper, the concept is extended to concrete slabs strengthened with textile-reinforced mortar (TRM) or carbon fiber-reinforced polymer (CFRP) sheets externally bonded to the concrete surface. In 16 groups, 96 slabs of 600 × 600 × 90 mm size were cast and tested under quasi-static and impact loads. The slabs were reinforced with two types of reinforcement: ϕ8@100 mm and ϕ4@25 mm. The singly and doubly reinforced concrete slabs with rebar spacing of 100 mm were strengthened using externally bonded CFRP and TRM on the back side of the slab specimens. Two mixes of concrete, representing normal and high-strength concretes, were used. The results of the present study reveal that the CFRP and TRM strengthening of RC slabs enhanced the energy absorption in punching by 57–130% and 20–59%, respectively. The use of WWM in singly and doubly reinforced slabs also resulted in a 30–42% and 41–63% increase in energy absorption in punching, respectively. An earlier proposed model was modified to incorporate the influence of strengthening (CFRP and TRM) in the estimation of the projectile perforation energy of the strengthened RC slabs with the help of energy absorbed in their quasi-static punching. This perforation energy was then employed for predicting the ballistic limit of CFRP- and TRM-strengthened slabs. The predictions show good agreement with the experimentally observed ballistic limits.

Enhancing the Effectiveness of Strengthening RC columns with CFRP sheets

The column is the most important structural element were strengthening of columns became a demanding issue. In this paper, the effectiveness of strengthening reinforced concrete (R.C) columns with carbon fiber reinforced polymers (CFRP) wraps has been improved by increasing the contact area between the column’s surface area and CFRP. A new strengthening technique was hired for the purpose of enhancing the efficiency of CFRP jackets in improving the load capacity of R.C columns, especially columns with rectangular sections. The method is based on increasing the contact area between the CFRP jacket and the column's surface area. This was done by adjusting the profile of the col's cross-section to almost ellipsoidal. The experimental program in this research includes testing 13 columns to include all test parameters, the shape of the cross-section, and the cross-section profile. The results include axial stresses and corresponding axial strains, and lateral strains at the mid-height and quarter height of tested specimens. And also, the cracking load and maximum load with crack patterns are determined. The comparison involved the study of the effect of the traditional CFRP jacket wrapping of R.C columns with square, and rectangular sections and the newly developed strengthening technique. A theoretical study was also conducted. Where the capacity of the square and rectangular confined columns with different radius of curvature, R, of the ellipsoidal profile is determined by the predicted and design equations. The study revealed that the strengthening technique is expected to effectively enhance the efficiency of the CFRP strengthening technique, especially for columns with square and rectangular sections as the area of the well-known dead zone of these columns is reduced using the proposed technique. Also, the results proved that the efficiency of strengthening tested columns by CFRP jacket has been enhanced using the strengthening technique by about 80% of original RC columns, which exceeds the traditional method (Jacket) CFRP wrap by 60%.

Strengthening RC beams with mid-span supporting prestressed CFRP plates: An experimental investigation

This paper proposes a novel strengthening method for reinforced concrete (RC) beams using prestressed carbon fibre-reinforced polymer (CFRP) plates. In the proposed method, the CFRP plate is stressed by adjusting the position of the mid-span deviators. The strengthening process is fast and easy to apply because there is no need for hydraulic jacks or adhesives. To investigate the behaviour of the strengthened RC beams, a series of tests were conducted on both intact and damaged beams with different strengthening configurations, and the full range behaviours of the beams are reported in detail. According to the test results, the maximum stress of the CFRP plate reached 1500 MPa, and the beam strength was enhanced up to 43%. Some of the strengthening schemes achieved good ductility. As a result, the proposed strengthening method is found to be effective and can be further developed into a pseudoplastic CFRP strengthening system.

Torsional strengthening using carbon fiber reinforced polymer of reinforced concrete beams subject to combined bending, shear and torsion

The results of an experimental investigation of six large scale rectangular reinforced concrete (RC) beams subject to different ratios of combined bending, shear, and torsion strengthened with externally-bonded carbon fiber reinforced polymer (CFRP) U-wraps are presented. All beams exhibited torsion-dominated behaviour. The presence of discrete CFRP U-wrap strips controlled the cracks well and the resulting torsional cracks were observed to be oriented at about 50°. Regardless of loading ratio, strengthened beams exhibited a 70% increase in torsional capacity. Before cracking, torsion to flexure ratio had a small effect on the flexural and torsional stiffness indicating that twist and deflection have a small counteracting effect on each other. Existing beam capacities were assessed using ACI 318-19 and GB 50010-2010 while CFRP strengthening was assessed based on fib Bulletin 14. Main findings are as follows: the ACI 318-19-predicted torsional capacity was conservative while GB 50010-2010 appeared to result in better capacity-prediction of unstrengthened RC beams. Even though load capacities derived from GB 50010-2010 are consistent with torsion-dominated behaviour, neither standard-based approach addresses the complete interaction of internal forces which is necessary to determine existing in situ strength for FRP strengthening applications. The fib Bulletin 14 approach to FRP strengthening for torsion was extrapolated to U-wraps and shown to overestimate the strengthening effect of the CFRP system applied. Critically, the assumed angle of inclination of torsional cracking was increased by the presence of the U-wraps, reducing the efficacy of the CFRP application.

Estimation of Bond Strength and Effective Bond Length for the Double Strap Joint between Carbon Fiber Reinforced Polymer (CFRP) Plate and Corroded Steel Plate.

In this paper, we examine the development of the estimation models of bond strength and effective bond length for a double strap joint between carbon fiber reinforced polymer (CFRP) plate and corroded steel plate. The experimental study on the bond behavior between CFRP plate and corroded steel plate is summarized first and the analytical interfacial bond–slip model for CFRP plate externally bonded to corroded steel plate is proposed. Based on the theoretical stress analysis for the CFRP plate–corroded steel plate double-lap joint, the piecewise expressions of the interfacial shear stress and the normal peel stress of the interface between CFRP plate and corroded steel plate were established. The estimation models of the bond strength and the effective bond length for the double strap joint between the CFRP plate and the corroded steel plate were consequently developed on the basis of interfacial stress distribution equations and the stress boundary conditions. The comparison between the predicted and experimental results indicated that the proposed models could be adopted to predict the bond strength and effective bond length for the CFRP plates externally bonded to corroded steel substrates with reasonable accuracy. The proposed estimation models are expected to provide meaningful references and essential data for the reliable application of CFRP strengthening system to the performance improvement of corroded steel structures.

CFRP strengthening of fatigue cracks at U-rib to diaphragm welds in orthotropic steel bridge decks: Experimental study, optimization, and decision-making

This paper investigated fatigue strengthening of U-rib to diaphragm welds in orthotropic steel bridge decks (OSDs) using the carbon fiber-reinforced polymer (CFRP). Fatigue testing and CFRP strengthening were performed on a full-scale OSD specimen with several U-rib to diaphragm welds. A strengthening configuration was proposed during the experiment. The testing results show that the attachment of CFRP plates on the cracked U-rib wall performed well in reducing both the local fatigue stresses and the average crack growth rate. Then, a multi-objective optimization and decision-making framework was proposed to realize the optimum design of the strengthening configuration. Considered the critical factors to the strengthening efficiency and cost, the material elastic moduli, CFRP size, and strengthening timing were chosen as design variables while maximizing the strengthened fatigue performance and minimizing the total cost were together regarded as the optimization targets. Considering the uncertainty of macrocrack propagation, Monte Carlo Simulation was used to predict the lifecycle fatigue life distribution. Then, a probabilistic assessment criterion for the strengthed fatigue performance was derived by theoretical derivation. Repeated numerical simulations were conducted to obtain the strengthened stress intensity factors using a multi-scale OSD model. Based on these simulated data, a surrogate model of the optimization objective was developed by Response Surface Methodology, which successfully considered the interaction effects between multiple design variables. Finally, the optimum CFRP strengthening configurations were derived by genetic algorithm and multi-attribute decision-making. This study is convinced to not only advance our understanding of CFRP strengthening of U-rib to diaphragm welded joints but also facilitate the optimum application of CFRP material in maintaining deteriorating steel structures.

Investigation of the effectiveness of CFRP strengthening of concrete made with recycled waste PET fine plastic aggregate.

In recent decades, several studies have considered the use of plastic waste as a partial substitute for aggregate in green concrete. Such concrete has been limited to non-structural applications due to its low strength. This raises whether such concrete can be enhanced for use in some structural applications. This paper reports an attempt to develop a structural-grade concrete containing plastic waste aggregate with high proportions of substitution and confined with carbon fiber reinforced polymer (CFRP) fabrics. Experimental research was conducted involving the casting and testing 54 plain and confined concrete cylinders. A concrete mixture was designed in which the fine aggregate was partially replaced by polyethylene terephthalate (PET) waste plastic at ratios of 0%, 25%, and 50%, and with different w/c ratios of 0.40, 0.45, and 0.55. The results show that confinement has a substantial positive effect on the compressive behavior of PET concrete. The enhancement efficiency increases by 8-190%, with higher enhancement levels for higher substitution ratios. Adding one layer of CFRP fabric raises the ultimate strength of samples that have lost compressive strength to a level close to that of unconfined samples not containing PET. This confinement is accompanied by an increase in the slope of the stress-strain curve and greater axial and lateral strain values at failure. For the specimens confined by CFRP fabric, PET aggregate can be used as a partial substitute for sand at a replacement ratio of up to 50% by volume for structural applications. This paper also considers the ability of existing models to predict the strength of confined-PET concrete circular cross-sections by comparing model predictions with experimental results. The strength of confined PET concrete elements can't be accurately predicted by any of the models that are already out there. It's important to come up with a new model for these elements.

Cyclic behaviour of as-built and strengthened existing reinforced concrete columns previously damaged by fire

A structure, during its life, may be subjected to multiple hazards. These hazards are sometimes combined over a short period of time, or in some cases occur many years apart, with the first hazard influencing the structural response under a second hazard. A reinforced concrete (RC) structure previously damaged by fire and then exposed to seismic loading is one such example. To assess such structures, the effects of fire on the cyclic performance of RC elements needs to be better understood. Moreover, it is also important to develop and validate strengthening methods that can reinstate or improve the seismic performance of fire-damaged RC elements. This paper presents the results of a novel experimental campaign where six full-scale RC columns with detailing representing existing Mediterranean buildings designed to old seismic codes are subjected to fire and then cyclic loading. Four RC columns were damaged after exposure to 30 or 90 min of the ISO 834 standard fire curve in a furnace and then tested under uniaxial cyclic lateral loading up to failure. Two of these columns were repaired and strengthened post-fire with Carbon Fibre Reinforced Polymer (CFRP) wrapping. The strengthening method aimed to increase the concrete strength through confinement, and to increase the displacement ductility and energy dissipation capacity under seismic loading. Two additional control columns, one as-built and another strengthened, were cyclically tested for comparison with the fire-damaged columns. It was found that the 30 min fire exposure resulted in few concrete cracks, whilst cover spalling and general cracking was observed in the 90 min fire exposure. A significant decrease in the displacement ductility and dissipated energy of the columns was observed following fire exposure, even for the 30 min fire. The columns that had post-fire repair and CFRP strengthening, showed better cyclic performance than the control column without fire exposure. It was also found that post-fire strengthened columns may reach similar seismic performance than similarly strengthened columns without previous fire damage.

Enhancing buckling capacity of angle steel using unbonded CFRP laminates processed by Vacuum-assisted Resin Transfer Molding (VaRTM)

The carbon fiber reinforced polymer (CFRP) adhesive-bonding technique has been increasingly developed for strengthening steel structures. However, the application of this strengthening method is still considered ineffective since it requires complicated and burdensome steel surface treatments. The bonding strength of CFRP on steel, on which this method highly depends, is also prone to performance decreases due to inevitable environmental exposures. Alternatively, unbonded CFRP strengthening is proposed in this study. A total of twelve specimens are prepared and tested to evaluate the possibility of application of this strengthening method in enhancing buckling performance of angle steels. All CFRPs on the strengthened specimens are created through a process of Vacuum-assisted Resin Transfer Molding (VaRTM). It is concluded from the investigation results that the unbonded CFRP is effective in strengthening angle steels, where the buckling strength enhancements by 8.5%-54.3%. The strength increase is clearly affected by CFRP length, number of CFRP layers, and steel’s slenderness ratio. A change in the curvature of the specimens due to the presence of unbonded CFRPs can also be observed. The VaRTM process produces higher fiber content of laminates. Analytical studies carried out at the end of this paper provide a reasonable solution for strength design and a good correspond for post-buckling prediction.

Axial compressive strength of preloaded CHS stubs strengthened by CFRP

Failure process of circular hollow section (CHS) stubs strengthened by carbon fiber reinforced polymers (CFRP) at both unloading and preloading conditions was experimentally investigated. A total of 11 CHS stub specimens were tested under axial compressive loads. The specimens are divided into three categories: un-strengthened CHS stubs, CFRP-strengthened CHS stubs at no preloading condition, and CFRP-strengthened CHS stubs at preloading condition. The compressive strengths of the specimens were investigated by considering the effects of several parameters including preloading percentage, the number of CFRP laminates, the tube thickness and the configuration of CFRP laminate. For the preloaded CHS stubs, their yield strengths after CFRP strengthening reduce slightly with an increase of the preloading. However, the ultimate strengths of the CFRP-strengthened CHS stubs at different preloading percentages are almost same, i.e., the CFRP strengthening efficiency is not influenced by the preloading conditions. Finite element (FE) model was also established, and the accuracy of the FE model is verified through comparing the FE simulations with the experimental results. Using the presented FE model, parametric study is carried out to study the efficiency of CFRP strengthening technique to improve the ultimate strength of CHS stubs at preloading condition. The effects of wall thickness and diameter-to-thickness ratio of the steel tube and the CFRP wrapping method on the strengthening efficiency of CFRP to CHS stubs are also investigated.

CFRP Strengthening and Rehabilitation of Inner Corroded Steel Pipelines under External Pressure

The objective of this study was to investigate the performance of pipelines repaired with carbon-fibre-reinforced polymer (CFRP) under external pressure. The repaired pipeline experienced defects in terms of thinning of its local inner wall. The three-dimensional finite element method was used to analyse the collapse pressure of repaired pipes with internal corrosion defects. The traction–separation law and interlaminar damage criterion were applied to simulate the collapse process of repaired pipes. The results show that the collapse pressure of the composite-repaired pipe increased and the CFRP significantly reduced the strain in the defect region. It was observed that the ovality of the corrosion defect region was reduced and that the repair effectiveness mainly depended on the length, thickness, and interlayer cohesion.

Column structure strengthening with FRP (Fiber Reinforced Polymer) due to story addition

This study focuses on strengthening scheme of an existing structure with added story. The addition of a new story increases gravitational loading, which affects the seismic and wind responses of the structure and, as a consequence, the loading combination. To ensure the structure’s capacity requirement, the strengthening scheme uses CFRP (Carbon Fiber Reinforced Polymer). In order to adequately define the structure's performance, a series of structural analyses were performed. The structure's state before and after story addition, subsequently the state after CFRP strengthening, were evaluated. It is demonstrated that the additional story to the structure causes an exceedance in internal forces; however, the strengthening with CFRP is sufficient to withstand these forces, proving that the strengthening scheme is effective and beneficial.

Effectiveness and Efficiency of Externally Bonded CFRP Sheets for Shear Strengthening of RC Beam-Column Joints.

To develop feasible carbon fiber reinforced polymer (CFRP) retrofit schemes for the shear strengthening of real three-dimensional reinforced concrete (RC) beam-column joints, a series of parameters in relation to the contributions of the CFRP sheets externally bonded to joint panels was numerically investigated in this study. The parameters include CFRP reinforcement ratio, CFRP layout, transverse beam-to-joint panel width ratio, transverse beam-to-joint panel height ratio, location of transverse beam, and number of transverse beams. Strengthening efficiency, a new dimensionless index, was introduced to evaluate the residual effect of a CFRP-strengthening system weakened by the presence of transverse beams in comparison with the increase in joint shear capacity in relation to the one-way counterpart. The results obtained from 44 nonlinear finite element models, which were calibrated against experimental observations, confirmed the effectiveness of the CFRP strengthening technique with regard to the relatively wide ranges of the parameters. The significant differences among the roles of the parameters were revealed, and the reasons behind the differences were analyzed. Furthermore, the shear mechanism of the CFRP-retrofitted joint panels was discussed with the proposed strut-and-tie model.

Fatigue behavior of notched steel beams strengthened by a prestressed CFRP plate subjected to wetting/drying cycles

Prestressed carbon fiber reinforced polymer (CFRP) strengthening is effective in suppressing crack propagation of steel beams. However, the fatigue behavior of notched steel beams with prestressed CFRP under a hygrothermal environment is not fully understood. Generally, notch machining on the steel beam is an ordinary method to simulate a fatigue defect for laboratory tests. In this study, the interfacial energy release rate at the notch location was first derived for strengthened steel beams. The theoretical results show that the interfacial energy release rate can be significantly reduced by prestressed CFRP strengthening, contributing to improving the interfacial fatigue performance. In addition, notched steel beams strengthened by prestressed CFRP (with a prestress level of 25% of tensile strength of CFRP plate) were exposed to wetting/drying cycles (WDCs) and then tested under fatigue loading. The experimental results show that prestressed CFRP strengthening increases the fatigue resistance of interfacial debonding initiation and failure 3.47 times and 7.83 times, respectively, which agrees with the tendency revealed by the theoretical results. In contrast, WDC exposure reduced the fatigue lives of interfacial debonding initiation and failure by 34.6% and 27.2%, respectively. An S – N curve based on the maximum principal interfacial stress at the notch location was proposed to predict the tendency of fatigue life of debonding initiation for strengthened steel beams. Moreover, the tendency prediction for fatigue life of interfacial debonding development for the strengthened steel beams with/without WDC exposure was developed based on Paris’ law. • Theoretically reveals that the prestressed CFRP reduces the interfacial energy release rate. • Prestressed CFRP strengthening significantly improves interfacial fatigue life. • Hygrothermal exposure leads to a significant reduction of interfacial fatigue life.

Flexural behaviour of prestressed reinforced concrete beams strengthened with carbon plate

This paper presents the effect of carbon plate length on the deflection and ultimate moment of resistance of a prestressed flexural member. Numerical and experimental results are also included. Three typical failure modes were observed in the experimental programme: bending failure, end shear failure and peeling off of the carbon plate. The geometry of the beam was chosen so that three typical failure modes occurred when different carbon plate lengths were applied. The experimental results show that for the selected geometry of the prestressed concrete beam, the ultimate moment capacity of carbon-fibre-reinforced polymer (CFRP) strengthened beams is up to 3.66 times that of beams without CFRP reinforcement. However, the stiffness can be increased by as much as 52% using CFRP. Non-linear analyses of pre-tensioned beams, with and without CFRP strengthening, were compared with respect to the ultimate limit state. The experimental test results and numerical calculations showed very good agreement in terms of the yield load and ultimate load.