Carbon Fiber Reinforced Polymer Strips Research Articles

Experimental study of shear behavior of CFRP strengthened ultra-high-performance fiber-reinforced concrete deep beams

This experimental study aims to examine the effectiveness of shear stirrups and carbon fiber-reinforced polymer (CFRP) strengthening scheme in enhancing the deep beams’ shear strength. For this purpose, a total of six deep beam specimens of 150 mm × 300 mm (depth) × 1000 mm with an effective span of 750 mm, classified into three groups of two specimens each, were prepared. The beams of the first group were of normal concrete (NC). The beams of the second group were prepared using ultra-high-performance fiber-reinforced concrete (UHPFRC). In the third group, the UHPFRC deep beams were strengthened using CFRP strips. Each group had two beams – one with no shear stirrups and another with shear stirrups. All deep beams were tested under four-point loading until failure. According to the experimental results, shear stirrups effectively contributed to enhancing shear strength, ultimate load, and deformation capacity for NC deep beam. By utilizing the UHPFRC mix, the deep beams’ shear strength was upgraded significantly compared with the NC deep beams, but the deformation capacity was reduced. The implemented strengthening scheme was effective in the enhancement of deep beams’ shear strength and deformation capacity. The improvement in the shear strength of strengthened UHPFRC deep beams was moderate (16%); however, a considerable increase was observed in the deformation capacity as the displacement and energy ductility indices were enhanced by 49% and 185%, respectively.

Predictive Capability of a Finite Element Micro-Mechanical Model for Masonry Elements Reinforced Using CFRP

Different commercial Finite Element Codes proved to be able to describe the mechanical behavior of masonry materials externally reinforced by means of Carbon Fiber Reinforced Polymers (CFRP); the behavior of fracturing materials, characterized by low tensile strength, with adhered strips can be reproduced relying on parameters based on fracture mechanics and the theories of adhesion.In this report the comparison is made of previous experimental test results with numerical analysis, carried out on masonry panels reinforced with CFRP strips and subjected to out of plane actions. The comparison is especially addressed to the evaluation of the post peak branch; in addition to the slopes of the diagram in the pre-critic phase, available kinematic ductility and energy shares both prior and after the peak load were considered in order to interpret the capability of the micro-mechanical model implemented in the FEM Code to account for the local phenomena influencing the interaction between masonry and FRP strengthening systems.

The behavior of concrete beams strengthened with NSM CFRP strips: a numerical parametric study

A non-linear finite element (NLFE) model was developed to predict the flexural response of concrete beams, strengthened with near surface-mounted (NSM) carbon fiber-reinforced polymer (CFRP) strips. The model was employed for predicting the influence of a wider spectrum of key parameters, concrete compressive strength (25–55 MPa), NSM FRP strips number (2–4) or spacing (20–35 mm), bond length (100–450 mm), FRP type (carbon, glass, and basalt) and loading pattern (four-point, three-point, and distributed load), upon the performance of these beams. The results showed a clear improvement in the performance of the CFRP-strengthened concrete beams when made at a higher-strength class of concrete. Using a higher number of NSM FRP strips of the same cross-sectional area contributed to enhancing the mechanical performance noticeably. Moreover, the model developed was capable of capturing the negative impact of using a lower spacing for a constant number of NSM CFRP strips. The impact of the FRP strips' type varied upon the mechanical property predicted and the strength grade of concrete used in the casting of the beams. The load resistance of NSM FRP-strengthened specimens was the highest under three-point load configuration, followed, in sequence, by distributed and four-point loads, respectively.

A machine‐learning‐based constitutive bond‐slip model for anchored CFRP strips externally bonded on concrete members

AbstractStrengthening is often required for reinforced concrete, steel, and masonry structures or structural elements when they possess insufficient performance against external loads such as earthquakes. Recently, the use of carbon fiber‐reinforced polymers (CFRP) has been considered a viable strengthening technique alternative to traditional methods. The major concern is premature debonding failure hindering the efficient use of CFRP systems. FRP anchor systems have been used to avoid this phenomenon. This paper employs a machine learning (ML)‐based algorithm (support vector regression) to propose predictive models to simulate the bond‐slip behavior of anchored CFRP strips externally bonded to the concrete surface. A comprehensive database was constructed using the previous reports on the bond‐slip behavior of FRP‐to‐concrete joints anchored with CFRP strips. Afterwards, the collected database was used to train and validate the proposed models. The input parameters cover all possible factors, that is, compressive strength of concrete, width of concrete block, anchor hole diameter, anchor hole depth, number of anchors at one row, number of anchors at one column; elastic modulus, width, bonding length, and thickness of CFRP strip. The output parameters are maximum shear capacity, residual shear capacity, displacement values at peak shear, and residual shear. Results imply that the proposed models have high prediction accuracies with low error rates. Proposed models are also presented in code format to be easily incorporated into analysis software for practical use.

Experimental study on the eccentric performances of high predamaged rectangular reinforced concrete columns strengthened with carbon fiber reinforced polymer

The mechanical behaviors of 12 high predamaged reinforced concrete (RC) rectangular columns strengthened with carbon fiber reinforced polymer (CFRP) under eccentric compression were experimentally investigated. The effects of the predamaged degree ( δ), CFRP strips spacing ( s f ) and eccentricity ( e) on failure mode, bearing capacity, strain behaviors of CFRP strengthened predamaged columns were examined systematically. Test results demonstrated that the strengthened RC columns with small-eccentricity were destroyed by the yielding of compressive longitudinal steel bars and the crushing of compression concrete while the transverse CFRP strips were not ruptured. The failure mode of the strengthened RC columns with large-eccentricity was distinguished by the yielding of tensile and compressive longitudinal steel bars, the rupturing of longitudinal CFRP sheet, and the crushing of compressive concrete. With the increase of predamaged degree or eccentricity, the maximum bearing capacity of specimens decreased. In contrast, CFRP strips spacing had little effect on bearing capacity. Considering the effect of predamaged degree and eccentricity, a modified model for conveniently predicting the stress–strain relationship of CFRP strengthened predamaged RC columns under eccentric compression was proposed. On the basis of experimental study, the influence coefficients of predamaged degree and eccentricity and a strain distribution coefficient of CFRP strips were introduced, a calculation formula for predicting bearing capacity of high predamaged rectangular RC columns strengthened with CFRP under eccentric compression was proposed and validated test data with good agreement.

Reinforced concrete slabs strengthened with externally bonded carbon fibre-reinforced polymer strips under long-term environmental exposure and sustained loading. Part 1: Outdoor experiments

Carbon fibre-reinforced polymers (CFRPs) can be used to increase the load-bearing capacity of concrete bridge deck slabs and their lateral cantilevers. In this study, experiments were performed to explore the long-term performances of loaded RC slabs strengthened on the top surface using non-prestressed and prestressed externally bonded (EB) CFRP strips. A real bridge application was simulated by applying mastic asphalt on the top surface. The effects of four years of outdoor exposure to elevated temperatures and solar radiation were considered. The results show that specimens strengthened with non-prestressed EB CFRP strips exhibit satisfactory behaviours, but a substantial increase in strain is shown in the CFRP strips over time. A slab strengthened with prestressed EB CFRP strips anchored with a so-called gradient anchorage experiences premature failure, owing to elevated temperatures and sustained loads.

REINFORCED CONCRETE FLAT SLABS WITH COMMON ARRANGEMENTS OF FIBRE REINFORCED POLYMER SHEETS

Retrofitting of reinforced concrete (RC) flat slabs using fibre reinforced polymer (FRP) composites has become common in recent years. Flexural retrofitting of one-way and two-way RC flat slabs using five common arrays of carbon FRP (CFRP) strips has been investigated in this paper. A comparison of the obtained results provided optimum scheme. Finite element method has been used to conduct the study using a commercial computer program. Results from the numerical analyses suggest that the use of CFRP sheets leads to improved load bearing capacities of slabs, which depends on both the type of array and the widths of FRP strips. The most optimal array of the retrofitting material (considering the effects on both strength and deflection) is the cross-like condition, which increases the capacities for one- and two-way slabs, respectively, by thirty-four percent and thirty percent while decreasing their maximum deflection by ten percent and four percent, respectively.

The behavior heated-damaged reinforced concrete beams retrofitted with different CFRP strip length and number of transverse groove

The potential of recovering the flexural performance of thermally damaged concrete beams using carbon fiber reinforced polymer (CFRP) strips with groove technique was experimentally investigated. Twenty reinforced concrete beams (150 × 200 × 1100 mm) were cast then cured for 28 days in moist burlap. A set of thirty-nine beams were heated at 250 °C, 500 °C, and 750 °C for two hours using an electrical furnace, whereas those of the second set of thirteen beams were left in laboratory air (23 °C). Nevertheless, debonding and anchoring problems remain a challenge for the success of this technique. In this study, an innovative application was implemented in which CFRP strip length with different lengths was integrated as external flexural reinforcement for reinforced concrete beams by using the groove technique. The intent was to assess the contribution of the CFRP strips to the flexural strength and thus evaluate the effectiveness of using them as primary or supplemental flexural reinforcement before and after exposing to elevated temperature. The investigated parameters include the number of transverse grooves and different elevated temperatures. The mechanical performance of other beams was evaluated under a four-point loading test setup, including measurement of strain in CFRP strips and mid-span deflection. Moreover, cracking and failure modes were monitored and characterized. Intact/strengthened and heat-damaged/strengthened beams showed improved ultimate strength, ultimate deflection, stiffness, and toughness compared to control ones. Different performance indicators revealed the good potential of strengthened heat-damaged beams using CFRP strips with grooves. Furthermore, the results showed that the grooving method performs better than surface preparation without grooves. So that the strengthening with grooves prevents premature delaminating and some of the concrete shatters in the tension side, and the weakness of beams in debonding phenomena disappeared, and flexural failure became dominant failure mode with full attachment of CFRP strips with concrete.

Experimental study on flexural behaviour of reinforced concrete beams strengthened with passive and active CFRP strips using a novel anchorage system

The paper presents the research on reinforced concrete (RC) beams strengthened with carbon fibre reinforced polymer (CFRP) strips with various configurations in terms of anchoring and tensioning. The five full-scale RC beams with the total length of 6.0 m were strengthened with passive strips, without and with mechanical anchorages at their ends, as well as with strips tensioned by the novel prestressing system with three various prestressing levels ranging from 30 to 50% of the CFRP tensile strength. All RC beams were tested under static flexural load up to failure and they were investigated in a full range of flexural behaviour, including the post-debonding phase. The main parameters considered in this study include the use of mechanical anchorages, the effect of tensioning the strips and the influence of the various prestressing levels. Several performance indicators have been established to evaluate the beams’ behaviour. The study revealed that the RC beams strengthened using tensioned CFRP strips exhibited a higher cracking, yielding and ultimate moments as compared to the beams with passively bonded CFRP strips. Moreover, increasing the beams’ prestressing level has a significant positive influence on the performance of strengthened beams. However, it did not affect the ultimate load-bearing capacity of the beams. The optimal prestressing level for the novel system has been determined as 60% of CFRP tensile strength.

Emerging anchored FRP systems bonded to steel subjected to monotonic and cyclic loading: A numerical study

Recently, the study of the bond behaviour of hybrid joints has increased due to their application in different industries. Their main purpose is to obtain lightweight but strong, durable structures. In addition, in some industries such as the automotive industry, those requirements may facilitate the construction of vehicles that have lower carbon dioxide emissions. Although the knowledge on the bond behaviour of hybrid bonded joints under monotonic loading is sufficient, the knowledge on the cyclic bond behaviour needs to be improved. The present work aims to mitigate that gap by proposing a numerical model in which the cyclic bond performance between a Carbon Fiber Reinforced Polymer (CFRP) bonded to a steel substrate can be analysed. The results provided by the Externally Bonded Reinforcement (EBR) are used as reference data. These other simulated bonding techniques cover cases where the CFRP is anchored to the substrate in different ways, which are becoming more popular, namely by: (i) linearly increasing the width of the CFRP; (ii) using the mixed adhesive concept (two solutions were considered); (iii) using a steel plate on top of the CFRP strip; and (iv) assuming no interfacial slips at the CFRP unpulled end, which is intended to simulate a perfect anchorage. Compared to the simulations carried out under monotonic loading, the simulations with the adopted cyclic loading history (loading/unloading cycles), allowed us to observe a degradation of the bond strength of the joints with the number of cycles. However, if the overlapped bonded joint is long enough, the strength of the CFRP-to-steel joints is not affected. Excluding the numerical specimens with the perfectly anchored CFRP, i.e. with an “ideal” anchorage, the length of the other adopted anchorages affected either the strength or the ductility of the joint, whether subjected to a monotonic or to the adopted cyclic loading protocol.

Deformation analysis of axially loaded weak PVC-fiber reinforced polymer confined concrete column-strong reinforced concrete beam joints reinforced with core steel tube

This paper presents an experimental study on 11 weak PVC-FRP Confined Concrete (PFCC) Column-strong Reinforced Concrete beam joints reinforced with Core Steel Tube (CST) subjected to axial load. The influences of the joint height, joint stirrup ratio, Carbon Fiber Reinforced Polymer (CFRP) strips spacing, steel ratio and CST length on the failure mode, ultimate strength, and strain behavior of specimens are analyzed and discussed. Test results indicate that the failure mode of specimens is distinguished by the cracking of PVC tube, fracture of CFRP strips, yielding of stirrups, and longitudinal steel bars in the PFCC columns. Both the longitudinal steel bars and CST yield at the joint area, while there is no obvious damage on the joint. The ultimate stress of specimens decreases with the increment of CFRP strips spacing, while the other studied variables have little impact on the ultimate stress. As the CFRP strips spacing increases, the ultimate strain of specimens decreases, and the strain development accelerates. Considering the effect of joint dimension, a modified prediction model for the stress–strain relationship of axially loaded weak PFCC column-strong RC beam joints reinforced with CST is proposed and verified with good accuracy.

Shear strengthening of high strength lightweight SCC beams internally reinforced with GFRP bars and external CFRP strips

Last few years have seen a substantial growth in the development and application of lightweight concrete (LWC) due to its enhanced mechanical properties and economic benefits in comparison to conventional normal weight concrete (NWC). The use of LWC in infrastructure has been popularised, especially in long-span bridges and high-rise bridges due to its lower density, which significantly reduces the dead load on the structure. Carbon fibre reinforced polymers (CFRP) and glass fibre reinforced polymers (GFRP) have rapidly gained acceptance in the infrastructure industry for their desirable characteristics over traditional steel. Extensive experimental research has been carried out over to years to investigate the shear performance of externally strengthened NWC beams with CFRP (carbon fibre reinforced polymer) strips. However, very limited research has been conducted on the shear performance of GFRP reinforced LWC beams externally strengthened with CFRP strips. Therefore, the main objective of this experimental study is to investigate the shear performance of high strength lightweight self-compacting concrete (HLWSCC) beams reinforced with internal GFRP bars and strengthened with external CFRP strips. HLWSCC is the latest development in concrete technology that combines the benefit of LWC and self-compacting concrete (SCC). One control specimen and two shear deficient HLSCC beams were strengthened with CFRP strips in the shear span. The test variable studied was the strip orientation (u-wrap and 45°) and all beams subjected to static four-point bending test. Load-deflection response and failure modes were observed and recorded for all the tested specimen. CFRP strips has considerably increase the load carrying capacity of HLWSCC strengthened beam specimen. The percentage increase in nominal shear strength ranged from 58.7% to 73.4% over unstrengthened control specimen.

Long-Term Performance of Seawater Sea-sand Concrete (SSC) Columns Wrapped with CFRP Strips Under Simulated Marine Environment

This article presents a durability study of carbon fiber-reinforced polymer (CFRP) partially wrapped seawater sea-sand concrete (SSC) columns exposed to natural seawater to explore the effect of exposure duration on the long-term performance of the specimens. Thirty-two cylinders were wrapped with CFRP jackets and exposed to different times of wet-dry cycles (up to 360 days) in an outdoor simulated marine environment. Test results indicate that exposure has no obvious influence on the failure process and ultimate strains of specimens, but the compressive strengths of confined columns (fcc) increase with the increment of exposure time, especially for the partially confined concrete specimens. Moreover, due to the significant variation of unconfined concrete strength fco*), the retentions of fcc and fcc/fco * exhibit an opposite trend. Therefore, the increase of fco* should be considered when using the parameter of the confined-to-unconfined ratio of strength to evaluate the long-term performance of the specimens.

Behavior of CFRP-strengthened RC beams with web openings in shear zones: Numerical simulation

The passing of service ducts and pipes often necessitates web openings in reinforced concrete (RC) beams. The strength and stiffness of the beam are reduced due to such web opening(s). Existing experimental research has shown the possibility of utilizing externally bonded Carbon Fiber-reinforced polymer (CFRP) to compensate for the strength loss of beams. However, there have been few finite element (FE) methodologies for predicting and estimating the performance of such RC beams. This paper uses nine different FE models to simulate a CFRP strengthened web opening using ABAQUS. This paper evaluates RC beam performance with web openings in the shear zone and proposed reinforcement of CFRP. Nine RC beams with openings, numerical tested under 2-loads. The models were constructed using the ABAQUS software by FE to simulate RC beams with a CFRP strengthened by two rectangular web openings. This paper studies the sequential effect of the different fundamental parameters on the strengthened RC beams' overall stiffness and shear strength response, achieving optimum utilization of the strengthened technique in load-bearing capacity and potential deflection. Results have shown no need to strengthen small web openings in the RC beams' shear zone. Beams with large openings in the shear zone need strengthening with CFRP; the beam's efficiency has been significantly improved using 2-layers of CFRP sheets around the web opening and a single-layer CFRP strip in the flexural zone bottom the chord.

Finite element modelling of RC slabs retrofitted with CFRP strips under blast loading

This paper presents nonlinear finite element (FE) simulations to predict the structural behavior of simply supported reinforced concrete (RC) slabs retrofitted with carbon fiber reinforced polymer (CFRP) as externally bonded reinforcement (EBR) and subjected to the blast loads in order to evaluate the effectiveness of using the CFRP strips as EBR for blast protection. The objective of this paper is to develop detailed numerical models in order to predict the blast response of non-retrofitted and retrofitted RC slabs during the inbound and rebound phases. A plastic material model including the strain rate effects of the material and able to predict the cracks is used to model the concrete. An elasto-plastic material model and an elastic material model are used to model the steel reinforcement and the CFRP strips, respectively. The bond interface between concrete and CFRP strip is simulated using a special contact algorithm including the strain rate effect at the interface between concrete and CFRP strip with failure criteria. The numerical results are validated by experimental tests. The maximum deflections, crack distribution and strain evolution in the steel reinforcement and in the CFRP strips found by the numerical analysis are in good agreement with the experiments. The concrete material model gives a good prediction of the blast response of the RC slab with and without EBR. Increasing the amount of the CFRP strip reduces the maximum deflection at the mid span of the slabs and the strain distribution in the steel reinforcement and in the CFRP strip. Parametric studies with respect to CFRP width and CFRP thickness are performed in order to evaluate the effects on the blast response of the RC slabs.

Non-linear analysis of one-way concrete slabs with carbon-fibre-reinforced polymer strips

Finite-element (FE) models of one-way spanning reinforced concrete slabs strengthened with carbon-fibre-reinforced polymer (CFRP) strips were constructed and analysed. The slabs, which had different-sized openings at different locations, were tested by the authors in a previous study. During the FE analysis, the effective failure modes were taken into account and the behaviour of the concrete–CFRP strip interface was modelled using a non-linear cohesive zone material model. The results of the FE analysis and experimental data were compared in terms of the ultimate load capacities of the slabs, load–displacement graphs, stress distributions and failure modes. The modelled results were found to be consistent with the experimental findings. The yield and ultimate shear force capacities, the yield and ultimate displacements and the yield stiffness of the slabs were calculated with average errors of 11.4%, 6.3%, 27.1%, 13.8% and 24.2%, respectively. After verification of the FE model, analyses of four additional slabs, not previously experimentally tested, were performed. An equation between the ultimate load capacity of a slab and opening size was developed based on the modelling results.

Structural Response of Bonded Joints between FRP Composite Strips and Steel Plates.

This paper presents the outcomes of an experimental and numerical study performed on epoxy-bonded single lap joints (SLJs) between carbon fiber-reinforced polymer (CFRP) composite strips and steel elements. For the experimental program, 34 specimens were prepared by varying the type of the composite strip and the type of adhesives and their thicknesses; all specimens were loaded in axial tension up to failure. The specific failure mechanisms were identified and commented on the basis of the performed tests, and the load–displacement curves were plotted. Additionally, the strain distributions along the bond lengths at different load stages, the shear stress–displacements (slip) variations and the stress–strain distributions for the CFRP strips were plotted and investigated. The numerical simulations, based on 3D finite element method (FEM) analysis, provided consistent results, in good agreement with the experimental ones for all parameters that were investigated and discussed in this paper.

Experimental Study of the Fatigue Performance of the Bonding Surfaces and Load-Bearing Capacity of a Large-Scale Severely Damaged Hollow Slab Strengthened by CFRP

In recent years, carbon fiber reinforced polymer (CFRP) has been widely used in bridge repair, retrofitting, rehabilitation and strengthening to improve the bearing capacity. Although many studies have been conducted to explore the strengthening efficiencies of CFRP, the test specimens were small and the results were difficult to apply to full-scale bridges. Investigations into the strengthening effects of CFRP on real life structures rely on field load tests (without damaging the structures), making it difficult to understand actual improvements in load carrying capacity and strengthening effect. Moreover, there have been few experimental studies on the fatigue performances of CFRP-strengthened structures, especially on the large-scale structures with real wheel moving loads. In this study, the feasibility and efficiency of CFRP strengthening and repair was investigated on a large-scale, prestressed concrete hollow slab decommissioned from a real-life concrete bridge. The hollow slab was first put through a destructive test to test the ultimate load-bearing capacity. Then, CFRP strips were installed on the surface of the severely damaged slab to repair and strengthen it. Fatigue load test—including the moving load test and single point sinusoidal load—and load-bearing capacity tests were conducted on the CFRP-strengthened hollow slab after the destructive test to evaluate the strengthening performance. This study could help us to understand the actual load-bearing capacities of severe damaged concrete structures strengthened by CFRP, reduce waste, save resources and improve the utilization of our infrastructures.

Analysing the Performance of Hollow Core Slabs Strengthened with CFRP

External bonding with CFRP (Carbon Fiber Reinforced Polymers) has been investigated over the last decade, as it represents a viable technique of strengthening existing prestressed concrete structures, including hollow-core slabs (HCS) with non-circular voids. The high performance of these carbon fibers has been validated through a large volume of experimental and numerical research and yet there are a few issues which remain controversial in simulating their behaviour with the finite element modelling. Although the CFRP mechanical properties are provided by the manufacturers, they are not satisfactory for a complete understanding of the analysis and design approach of HCS strengthened with CFRP. The present research is conducted on prestressed HCS with non-circular voids. The strengthening method consisted in the application of the composite material on the slab’s end internal regions of the voids, on a 500mm length: 1 layer and 2 layers. The objective of this study is to emphasize the effect of damage in the CFRP strips and moreover the interface effectiveness on the CFRP strengthened HCS. Damage is predicted using Hashin’s initiation criteria and the cohesive behaviour in the interface is used to analyse the epoxy resin which bonds the CFRP sheets to the hollow-core units. A plastic damage model was used for modelling the concrete, after a parametric study regarding the dilatancy angle and viscosity parameter was conducted for the most appropriate choice of concrete damage plasticity parameters. The overall procedure consists of numerical FE modelling in Abaqus software. Two different modelling possibilities of CFRP-to-concrete interface were studied: a tie constraint connection was first used and secondly the contact bonding was defined with the cohesive behaviour option of the contact interaction property. The results are provided in terms of load-displacement response, equivalent plastic strain and distribution of Von Misses stresses in the CFRP strips.

Performance of Reinforced Concrete Beams Strengthened with Carbon Fiber Reinforced Polymer Strips.

Carbon fiber reinforced polymers (CFRP) have shown considerable potential in the repair and rehabilitation of deficient reinforced concrete (RC) structures. To date, several CFRP strengthening schemes have been studied and employed practically. In particular, strengthening of shear damaged RC members with CFRP materials has received much attention as an effective repair and strengthening approach. Most existing studies on strengthening shear-deficient RC members have used unidirectional CFRP strips. Recent studies on strengthened T-beams demonstrated that a bidirectional CFRP layout was more effective than a unidirectional layout. As such studies are limited, in this study, the feasibility of bidirectional CFRP layouts for the shear strengthening of rectangular RC beams was experimentally evaluated. Bidirectional layout details with CFRP anchors as well as rehabilitation timing were considered and investigated. The test results showed that the members with a bidirectional CFRP layout carried less shear strength capacity than those with unidirectional layouts for the same quantity of CFRP material. Nevertheless, the bidirectional CFRP layout allowed for a uniformly distributed stirrup strain compared to the unidirectional CFRP layout at the same load level, which increased the efficiency of the transverse reinforcement. Additionally, the shear contribution of CFRP material according to the CFRP strengthening timing was verified.