Near Surface Mounted Fiber Reinforced Polymer Research Articles

Bond performance of NSM FRP–concrete interfaces with epoxy under chloride‐salt conditioned environments

AbstractConcrete in coastal areas is susceptible to structural damage caused by corrosion and expansion of reinforcement. Near‐surface mounted (NSM) fiber‐reinforced polymer (FRP) bars have become effective for strengthening damaged reinforced concrete structures. The bonding performance of NSM FRP bars in concrete is a key factor limiting their application and promotion in civil engineering. In this study, the influences of the conditioned environment, such as the chloride salt concentration, immersion time, and bond length of the FRP bar, on the bonding performance were investigated experimentally. First, material properties in a conditioned environment were studied. Subsequently, the failure mode, bond stress–slip curve, and bond strength of the NSM FRP bar in concrete were investigated. Finally, the microstructure and chemical composition of the materials were revealed using scanning electron microscopy and energy‐dispersive spectroscopy (EDS) images of the materials under environmental conditions. The transfer mechanism of NSM FRP bars in concrete with epoxy was revealed. The results showed that the failure modes of the pullout specimens can be divided into epoxy splitting failure and basalt fiber‐reinforced polymer (BFRP) pulling failure. The chloride‐salt concentration was a critical factor affecting the bond properties, and the longer the bond length, the lower the bond strength. The microstructure clearly shows that the degradation of the bonding behavior at the interface of the NSM FRP bar in concrete in a conditioned environment is attributable primarily to the resin damage of the epoxy, resulting in pit corrosion. There was no significant damage to the fibers in the FRP bar, and the degradation was primarily due to resin matrix damage and interfacial debonding. The EDS results showed that the degradation of the epoxy resin and BFRP bars was caused by CO bond and SiO bond fractures, respectively.

A new bond-slip model for NSM FRP systems using cement-based adhesives through artificial neural networks (ANN)

This paper introduced a novel Artificial Neural Networks (ANN)-based bond–slip model for the Near-surface mounted (NSM) FRP system using cement-based adhesives, as an alternative to epoxy adhesives due to their high-temperature resistance and moisture-durability problems, employing experimental data. Therefore, closed-form formulas were presented for key components of the bond-slip law, including maximum bond stress, corresponding slip, fracture energy, and post-peak branch, while taking important factors into account. Compared to available bond-slip laws, this innovative model demonstrates promising potential in predicting the bond behaviour, thereby enabling more efficient and reliable designs for the NSM FRP strengthening applications using cement-based adhesives.

Strength models of near-surface mounted (NSM) fibre-reinforced polymer (FRP) shear-strengthened RC beams based on machine learning approaches

The shear strengthening of reinforced concrete (RC) beams using near-surface mounted (NSM) fibre-reinforced polymer (FRP) bars/strips has gained substantial research attention worldwide. However, owing to the complex failure mechanisms and many influencing parameters, the shear capacities of NSM FRP shear-strengthened beams are difficult to predict. Accordingly, this study adopted machine learning approaches to predict the shear capacity of strengthened beams. An experimental database was constructed comprising 130 rectangular/T-shaped beams and their 15 parameters, collected from the existing literature. Subsequently, a genetic-algorithm-improved back propagation neural network (GA-BPNN) trained with a Bayesian regularisation (BR) algorithm was employed, which was capable of giving accurate predictions on shear capacities of strengthened beams and own good generalisation ability. Furthermore, the GA-BPNN was used for parametric studies to investigate the parameter effects on the contributions of concrete, steel stirrups, and NSM FRP to the shear capacity. Finally, with reference to the GA-BPNN parametric analyses and existing models, a design-oriented strength model for calculating the shear capacities of NSM FRP shear-strengthened beams was proposed and optimised using the genetic algorithm. A comparison with existing models proved the higher prediction accuracy of the proposed strength model.

Experimental and numerical investigation of the flexural behavior of one–way RC slabs strengthened with near–surface mounted and externally bonded systems

This study investigated the flexural performance of one-way reinforced concrete (RC) slabs strengthened with two distinct strengthening systems: near–surface mounted (NSM) bars and externally bonded (EB) carbon fiber-reinforced polymer (FRP) strips. The NSM bars comprised four types: carbon FRP (CFRP), basalt FRP (BFRP), glass FRP (GFRP), and stainless–steel (SS) bars. The NSM–strengthened slabs showcased substantial enhancements in yield and ultimate load capacity, ranging from 20 % to 55 % and 59–123 %, respectively. In comparison, those strengthened with EB–CFRP strips displayed increases from 46 % to 107 % and 45–177 %, respectively, depending on the axial stiffness ratio of the strengthening system provided. Furthermore, the slabs reinforced with NSM–BFRP bars showed an 11–25 % improvement in their ductility indices. In contrast, the slabs reinforced with EB experienced a decrease in ductility ranging from 38 % to 50 %. This reduction was attributed to the differences in the modes of failure observed in both strengthening systems. The rupture of the NSM–FRP bars and the strain readings associated at the end of testing confirmed that the tensile strength of the NSM–FRP bars was fully exploited whereas the EB–CFRP strips utilized only 29–36 % of their ultimate tensile strain due to debonding. A finite element (FE) model was formulated to anticipate the behavior of the strengthened slabs. A strong correlation between the numerical predictions and the experimental outcomes was observed. The experimental–to–numerical ratios of the ultimate load ranged between 1.0 and 1.08 for the NSM–strengthened slabs and between 0.98 and 1.38 for the EB–strengthened slabs. This validated the FE models’ ability to capture the nonlinear performance of the strengthened slabs.

Flexural performance of reinforced concrete beams strengthened using near-surface-mounted carbon-fiber-reinforced polymer bars: Effects of bonding patterns

The near-surface-mounted (NSM) fiber-reinforced polymer (FRP) technique is effective for enhancing the load carrying capacity of strengthened reinforced concrete (RC) beams. However, this technique significantly reduces the deformability of strengthened RC beams. To overcome this, the present study combines the NSM strengthening method with the partial bonding technique: the strengthening FRP reinforcement is partially bonded onto the concrete substrate). Six full-scale 4.3 m long RC beams strengthened with NSM FRPs using various bonding patterns were tested. The results indicated that mechanical interlocking grooves slightly improve the load carrying capacity, but have a negligible effect on the deformability of the strengthened beams. A decrease in the bond length increased deformability by 27.2 %, with only a 7.6 % drop in load capacity compared to that of the beam with full bonding. An advanced finite element model was developed and validated to confirm an optimal bond length of 930 mm for maximum flexural performance.

Experimental Assessment of NSM FRP Systems with Inorganic Adhesives for Concrete Strengthening

Abstract: This study explores the application of various inorganic resins in the Near-Surface Mounted (NSM) strengthening technique, aiming to provide alternatives to traditional organic resins. The research centers on sixty single lap-shear concrete blocks, employing four distinct adhesives—ordinary mortar, Ultra-High-Performance Concrete (UHPC), geopolymer, and polyester-silica—for bonding Carbon Fiber-Reinforced Polymer (CFRP) strips to the concrete blocks. Conducted under monotonic loading, the investigation assesses the bond characteristics between the inorganic resins and both CFRP composites and the concrete substrate. Interfacial behaviour, bond strength, and failure modes are meticulously analyzed, shedding light on the performance of each adhesive. The study reveals insights into the efficiency of the NSM system, emphasizing the significance of the bond between FRP composites and concrete for optimal strengthening. The findings underscore the limited research on NSM systems using inorganic resins, providing a foundation for further exploration in this domain.

Reinforced concrete columns strengthened with near-surface mounted and hybrid FRP under compression with or without eccentricity: Experimental study and finite element modeling

The utilization of FRP in strengthening of reinforced concrete (RC) columns has garnered significant attention in the past two decades. Researchers have proposed the use of near-surface mounted (NSM) FRP bars with (hybrid) or without FRP jackets alongside the conventional approach of column strengthening through jacketing particularly in the presence of load eccentricity. In the realm of static loading scenarios, a significant focus has been directed toward the evaluation of the NSM, jacketing, and hybrid methodologies, while comparatively less attention has been given to the impact of various parameters on the capacity. In this article, a total of 22 RC column specimens with medium slenderness were tested under axial compressive loads with or without eccentricity to study the effect of the parameters the number and type of NSM FRP bar, the number of layers and type of FRP jacket, and the groove size for FRP bar mounting. The experimental results reveal the beneficial effects of using FRP jackets, increasing their layers and groove dimensions, and augmenting the number of NSM FRP bars on column capacity and ductility up to 36% and 197% respectively. Additionally, an accurate Finite element model has been developed and role of corbel in eccentricity application is investigated. The results showed that the corbel is not capable of transmitting the desired eccentricity.

Numerical Analysis of an Innovative Double-Strap Joint for the Splicing of Near-Surface Mounted Fiber-Reinforced Polymer Bars for Reinforced Concrete Beam Strengthening

The issue of the cut-off splicing of an additional fiber-reinforced polymer (FRP) bar in the near-surface mounted (NSM) technique for reinforced concrete (RC) beam strengthening exposed dominantly to bending is insufficiently investigated. A possible solution of this issue is a new proposed technique: a double-strap joint. It implies the widening of the groove at the cut-off location and the symmetrical installing of additional supplements of FRP reinforcement. In this research, beam strength has been determined for the following cases: additional NSM FRP reinforcement without a cut-off, with a cut-off, and without overlapping, and with different lengths of splice overlapping. A nonlinear analysis based on the finite element method (FEM) has been applied. The length of the cut-off splice of the additional FRP reinforcement with glass fibers (GFRP) was 20Ø, 40Ø, and 60Ø. The validation of the numerical model and a comparison of the results were conducted by using the authors’ experiments. It has been shown that, in the case of a cut-off of NSM GFRP bars, a significant loss in strengthening efficiency occurs, and that, with an increase in the overlapping length, this loss decreases. An overlapping length of 60Ø provides full strengthening. An efficiency assessment was carried out via the use of a parametric study, varying the FRP bar material type and its diameter for a constant splicing length.

An experimental study on structural performance of reinforced concrete beams strengthened for combined flexure and shear by using NSM-GFRP strips

Near surface mounted fiber reinforced polymer (NSM-FRP) technique is the latest & most effective techniques used in strengthening the existing structural components, which requires strengthening against increased service loads, faulty design, environmental effects, etc. In the past, many researches on NSM technique have been carried out by using different cross-sectional shapes & dimensions of FRP materials to strengthen for shear & flexure. In the present experimental study, the behaviour of R.C. beams strengthened for combined flexure & shear studied. The beams of 150x150x700 mm size with M30 grade of concrete & Fe500 steel were considered. The control beams (unstrengthened) & strengthened beams using GFRP (Glass fibre reinforced polymer) strips were subjected to three point loading to study the behaviour of beams in combined shear & flexure. The main objectives were to assess the behaviour of strengthened beams with control beams & to study the influence of the orientation of shear strips. The beams were studied for the failure characteristics, yield & ultimate load carrying capacity, stress-strain behaviour, deflection, & crack patterns. From the test results, it’s been observed that, the load carrying capacity of the strengthened beams were increased, the improved in deflection, when compared to the control beams. The ultimate load carrying capacity of beams with shear strip orientation of 45°, 60° & 90° were increased by 50.3%, 39.3% & 25% respectively, compared to the control beams. This NSM strengthening technique can be advantageous & suitably adopted to enhance the load carrying capacity of the beams.

Numerical modelling of RC beams strengthened in shear using NSM FRP and cement based adhesives

Cement based adhesives (CBAs) are currently emerging as a suitable replacement for epoxy resins in the strengthening of reinforced concrete (RC) elements using near surface mounted (NSM) fiber reinforced polymers (FRP). However, large scale experimental testing on RC beams strengthened in shear using NSM FRP and CBA has been limited to date and there is currently an absence of strength prediction models and design guidelines to enable engineers to design and detail such strengthening systems. This paper expands the theoretical understanding of RC beams strengthened in shear using NSM FRP and CBA using 2D finite element modelling by developing an experimentally validated modelling approach. Later, parametric studies into five concrete strengths (25, 32, 40, 45 and 50 MPa) and three FRP spacings (100, 150 and 200 mm) were conducted to generate a database of results which can later be used to inform the development of design guidelines. Data on maximum FRP strains at failure were combined with existing shear strength prediction models based on the modified compression field theory (MCFT) and national design standards to propose a strength prediction modelling approach.

Torsional behaviour of RC beams strengthened by NSM GFRP bars

Near-surface mounted (NSM) fiber-reinforced polymer (FRP) reinforcement is an innovative, serviceable, and beneficial method for strengthening reinforced concrete (RC) structures. Previous studies have proven that the epoxy-resin bonded NSM FRP method effectively achieved shear and flexural strengthening. However, only a few researches have employed this technique for improving torsion but, no research has been conducted on the use of NSM with GFRP bars and epoxy adhesives. This study investigates the behavior of RC beams subjected to combined torsion when they have been enhanced with NSM GFRP U-shaped and closed stirrups with different overlap sites. Four RC beams with dimensions of (150×250×2000) mm (width X depth X length) were considered in the experimental tests. One RC beam is not strengthened and used as a control beam (CB), while three beams are enhanced with NSM GFRP bars in different shapes and overlap configurations. The findings of the tests in terms of twist angle_applied torque curves, the torque of initial cracking, the ultimate torsional carrying capacity, and the ultimate angle of twist were all recorded and evaluated. It has also been shown that a considerable improvement in the performance of RC beams in twisting can be achieved by using NSM GFRP stirrups. From the different NSM strengthening configurations used in the tests, results have demonstrated that beams strengthened by closed GFRP stirrups at the opposite overlap with 100 cm spacing outperformed other strengthened beams of about 181.5% compared to the CB. In contrast, the beam, strengthened by U-shaped GFRP stirrups with spacing at 200 cm, had the lowest torsional strength of about 48.1% relative to the CB.

Experimental and FE analysis of NSM FRP bond in low- and normal-strength natural and recycled aggregate concretes

Poor mechanical properties of construction materials constitute one of the major reasons for structural deterioration. Since the extent of the weakening in the material quality could reach an alarming threshold, their suitability for strengthening needs assessment prior to adopting any strengthening strategy. This paper experimentally investigates the bond behavior between near-surface mounted (NSM) fiber-reinforced polymer (FRP) strengthening in low- and normal-strength concrete with compressive strength in the range of 11.6 – 14.8 MPa for the former and 39.4 MPa for the latter. The use of two aggregate types – natural and recycled aggregates – was also investigated in the low-strength concretes. Steel fiber reinforcement was used in some of the mixes to check whether some enhancement is possible in low-quality concrete that can result from inferior recycled material, compromised workmanship, or material deterioration due to durability challenges. Ultimately, the variables of the study include recycled coarse aggregate incorporation ratio of 0%, 30%, 60%, and 100% replacement of the natural aggregate for each of the steel fiber’s percentages of 0%, 0.5%, and 1% of the specimen’s volume. The control NSM FRP-concrete specimen made from normal-strength concrete (39.4 MPa) was prepared and tested as a reference. The low-strength concrete mixtures demonstrated a decrease in the NSM FRP-concrete bond strength with an increase in the RCA incorporation. However, the addition of steel fibers marginally increased the bond failure capacity. Compared to the reference specimen of normal-strength concrete, at least, a 44% reduction in the NSM-concrete bond failure load was observed. Because some design guides (including the ACI 440) suggest a minimum concrete compressive strength for NSM FRP strengthening, a finite element model (FEM) was used to check the full spectrum of the mixture’s quality (both low and high-strength materials) and other key parameters affecting the NSM FRP-concrete bond behavior. The so-developed model is first validated against the experimental observations, followed by using it to run a series of parametric studies using the bar diameter, concrete compressive strength, FRP modulus, and steel fiber content as variables.

Finite Element Analysis of Flexural Strengthening of Reinforced Concrete Beams Using Near-Surface Mounted CFRP Rebars

Most of the standing structures today have already deteriorated or are on the verge of deterioration due to an increase in their age and harsh environmental conditions. For this very reason, the structures are in need of being upgraded or replaced. Retrofitting using near-surface mounted (NSM) fiber-reinforced polymer (FRP) rods has now emerged as a promising technique for strengthening the reinforced concrete members by increasing their flexural strength. This study aims to numerically investigate the efficiency of the NSM technique for flexural strengthening of RC beams by using finite element (FE) software, ABAQUS, and also evaluate the impact of variables such as concrete strength, embedded length of FRP rods, filler material used for the FRP rods, and the number of FRP rods provided. Validation of the finite element model was confirmed by first making a comparison with the experimental study presented in the literature for an un-strengthened beam. Thereafter, the validated model was used to simulate reinforced concrete beams strengthened with the NSM technique. The numerical results of the cracking moment, steel yielding moment, ultimate bending moment, and deflection at failure were reported and the impact of the variables was evaluated. The FE analysis results indicated that for the RC beams strengthened with NSM FRP rods, the flexural capacity significantly increased compared to the control beam, while the mid-span deflections of strengthened beams at failure decreased compared to the control beam.

Predicting shear behavior of reinforced-concrete beams shear-strengthened using near-surface mounted fiber-reinforced polymer method

This paper presents analytical research results to predict the shear behavior of reinforced concrete (RC) beams shear-strengthened with near-surface mounted (NSM) FRP. In this study, a section analysis method based on the modified compressive field theory (MCFT) was proposed to predict the shear behavior of RC beams shear-strengthened with NSM FRP reinforcement. The analytical method was applied to derive the analytical effective strain of the FRP shear reinforcement of 71 specimens collected from the existing literature. Then, the correlation between this analytical FRP effective strain and the major variables for shear strengthening design was analyzed through nonlinear regression analysis. From the results, a model capable of predicting the effective strain of NSM FRP reinforcement was finally proposed. This FRP effective strain model predicted the effective strain of NSM FRP reinforcement more accurately compared to models proposed by other researchers. In addition, the section analysis method using this model predicted the shear behaviour of other researchers beams shear-strengthened with NSM FRP reinforcement very well.

Shear strengthening of RC beams with NSM FRP strips: Concept and behaviour of novel FRP anchors

The high efficiency of the near-surface mounted (NSM) fibre-reinforced polymer (FRP) technique for improving the shear capacities of reinforced concrete (RC) beams has been proved by numerous studies. However, premature debonding failures including interfacial debonding and concrete cover separation, which could largely limit the utilization of FRP strength, were frequently observed in RC beams strengthened in shear with NSM FRP. Proper anchoring measures of NSM FRPs can mitigate or even prevent such debonding failures and thus enhance the FRP strengthening efficiency, but relevant research on anchoring measures for NSM FRP shear-strengthened beams is still limited. Against the above background, a novel FRP anchor for NSM FRP shear-strengthened beams is proposed in this paper. A test program consisting of eight full-scale RC beams is carried out to investigate the effectiveness of the proposed FRP anchor system. It can be seen from the test results that the proposed FRP anchor is capable of mitigating or preventing the FRP debonding failures and thus significantly enhancing the load-carrying and deformation capacities of RC beams strengthened in shear with NSM FRP strips, and the configuration of the anchor can largely influence the performance of strengthened beams.

Novel Embedded FRP Anchor for RC Beams Strengthened in Flexure with NSM FRP Bars: Concept and Behavior

The near-surface-mounted (NSM) fiber-reinforced polymer (FRP) strengthening technique for reinforced-concrete (RC) beams has attracted worldwide research attention and application in the past two decades. In spite of improved bond strength between the NSM FRP and concrete, compared with the externally bonded (EB) FRP method, premature debonding failure still occurs, and, hence, the efficiency of the NSM FRP intervention is limited. An intuitive means to enhance efficiency is to apply anchorage devices to the RC beam; however, the availability of viable anchorage is limited for NSM applications. A novel anchorage device is therefore presented in this paper, which is referred to as an embedded FRP anchor (EFA). The concept, manufacture, and installation of the EFAs were initially presented. The effectiveness of EFAs in NSM FRP-strengthened RC beams was then ascertained through full-scale beam tests and comparison with an NSM FRP-strengthened beam anchored with a U-jacket. Moreover, the effects of EFA parameters on the behavior of anchored beam were also investigated. The test results not only prove the high anchoring efficiency of EFA but also reveal the significant effects of EFA parameters on the failure mode, load–deflection response, and NSM FRP strain of the EFA anchored beam.

Bond-slip Behaviour of NSM GFRP Bars in Reinforced Recycled-Aggregate Concrete: Experiments and a Modified Model

Bond-slip behaviour of glass fiber-reinforced polymer (GFRP) bars embedded in conventional concrete has been widely investigated. In contrast, the bond-slip behaviour of near-surface mounted (NSM) GFRP bars bonded in reinforced recycled aggregate concrete (RAC) seems to be less explored, while recycled materials have been increasingly used due to reasons of environmental pollution and resource exhaustion. This study aimed to experimentally and theoretically examine the bond-slip behaviour of NSM GFRP bars in reinforced RAC under monotonic and cyclic loadings. To achieve this aim, twenty-four tests were performed, which were divided into two groups by monotonic and cyclic loadings. In each group, twelve tests were performed on ten reinforced RAC specimens and two reinforced normal aggregate concrete (NAC) specimens. The test results confirmed the brittle shear failure of concrete in the proximity of a resin-concrete surface. Bond-slip behaviour can be characterized by nonlinear and linear branches, in which the linear branch dominates the behaviour. Under monotonic and cyclic loadings, the average slips of GFRP bars in reinforced RAC were 0.238 and 0.284 mm, and their coefficients of variation (COV) were relatively large at 0.142 and 0.130, respectively. In contrast, ultimate loads had a relatively low COV of around 0.038. The effect of cyclic loading significantly increased the ultimate slip by 19.3%, whereas it negligibly reduced the ultimate load; consequently, the stiffness was reduced by 19.4%. A modified smooth model was proposed to predict the bond-slip behaviour of NSM GFRP bars in reinforced RAC under monotonic and cyclic loadings. The simplicity and accuracy of the model can be useful for engineers in structural retrofitting using NSM FRP technique. Doi: 10.28991/CEJ-2023-09-02-01 Full Text: PDF

Shear strengthening of RC beams with NSM FRP. II: Assessment of strength models

The application of near-surface mounted (NSM) fiber-reinforced polymer (FRP) for shear strengthening of RC beams has attracted abundant research in the past few decades, and a number of strength models for predicting the contribution of NSM FRPs to the shear capacity of strengthened beam have been proposed. In the first of these two companion papers, a total of 12 strength models of NSM FRP shear strengthened RC beams collected from the existing literature have been comprehensively reviewed, while the present paper aims to provide an objective assessment of these models. To this end, the experimental results of 196 RC beams strengthened in shear with NSM FRP bars/strips are collected from the existing literature, as the database for the assessment. The comparisons between the experimental results and predictions by these strength models reveal that the existing strength models all fail to give accurate predictions. The reasons for the inaccurate predictions of these models are also analyzed.

Shear strengthening of RC beams with NSM FRP. I: Review of strength models

Near-surface mounted (NSM) fiber-reinforced polymer (FRP) technique is known as a promising alternative to the externally bonded (EB) FRP technique for strengthening reinforced concrete (RC) members, on account of its many advantages such as high bond efficiency with concrete and good durability. Shear strengthening of RC beams by near-surface mounting the FRP bars/strips into the concrete cover on beam sides is one of the most prevalent applications of NSM FRP. Abundant experimental studies have been conducted to investigate the behaviour of NSM FRP shear strengthened beams, and many strength models for predicting the contribution of NSM FRPs to the shear capacity of the beam have been proposed. The present paper presents a comprehensive review of these strength models, in which all the models collected from the existing literature are first classified into three categories based on their used approach and then summarized and discussed. This paper not only aims to bring a deep understanding of the existing strength models for NSM FRP shear strengthened RC beams, but also provides a background and basis for the assessment of these models by using the newly-generated experimental database in the companion paper.

Improving the flexural behavior of RC beams strengthening by near-surface mounting

Abstract This article presents the experimental investigations undertaken to evaluate the strengthening and enhancement characteristics of near-surface mounted (NSM) devices using different types of bars. A total of 4 concrete beams (150 mm × 300 mm × 1,500 mm) were reinforced in flexure. Three beams strengthened with different embedments of NSM (carbon fiber-reinforced polymer [CFRP], Glass fiber-reinforced polymer [GFRP], and steel) bars, and one unstrengthened beam used as a control beam were tested under monotonic static loading to determine the enhancing influence of the fiber-reinforced polymer (FRP) reinforcement. The performance of different bars used to establish the concrete is examined. A general methodology to evaluate the improving flexural behavior of RC beams strengthened with NSM–FRP bars is presented. A quantitative criterion governing debonding failure is established. The proposed bond model assumes linear elastic behavior for the concrete, adhesive, and NSM–FRP bars, following the same philosophy as the American concrete institute [ACI] provisions for bond analysis and design to control the cracks. So FRP reinforcements show substantial deformation before failure when the cross-sectional area is based on a permissible strain during service, so there is no need to check the deformability. The results of the tests show that using NSM–CFRP bars improves the flexural capacity and stiffness of the strengthened concrete beams of other types.