Carbon Fiber Strips Research Articles

EXPERIMENTAL STUDY ON EXTERNAL STRENGTHENING OF RC COLUMNS USING CARBON FIBER REINFORCED POLYMER (CFRP) COMPOSITES

The use of Carbon fiber reinforced polymer (CFRP) materials for structural repair and strengthening has continuously increased in recent years, due to several advantages associated with these composites when compared to conventional materials like steel. This paper presents the results of an experiment at study on the structural behavior of reinforced concrete columns strengthened with carbon fiber sheets and strips in pre-cut grooves. The reinforced columns were strengthened before testing. The main tasks of these experiments were conducted to investigate the effects of additional strengthening of reinforced columns. Due to a number of benefits these composites have over more traditional materials like steel, the utilization of carbon fiber reinforced polymer (CFRP) materials for structural strengthening and repair has been steadily rising in recent years.

Experimental assessment of barely visible impact damage carbon fiber reinforced epoxy composite using ultrasound method

Background Carbon fiber reinforced epoxy (CFRP) is susceptible to impact damage which could resulted in reduction of the mechanical properties. This paper studies the architecture of barely visible impact damage (BVID) to comprehend the extent of damage on quasi-isotropic CFRP laminates of varying thickness (i.e. 16, 24 and 32-ply laminates of 3, 4 and 5 mm respectively). Methods Quasi-static indentation is chosen to produce BVID on CFRP laminates, followed by using non-destruction evaluation method, namely conventional contact-type ultrasonic testing (UT) and C-mode scanning acoustic microscopy (C-SAM) method. Results The findings revealed (1) the size and shapes of the BVID on CFRP laminates, (2) no damage was found at the center of the impact point, and (3) the bridging between the point of impact to the outer damaged diameter due to the consequence of diverse orientation of carbon fiber strips which exhibit excellent mechanical properties before structural failure. Conclusions The results concluded that the UT and C-SAM method can identify both the pristine region and the internal damaged structures in CFRP laminates.

Repairing and strengthening techniques of RC beams: a review

The purpose of this review is to present the techniques for strengthening or repairing of reinforced concrete-beams (RC). The concrete members, like RC beam are might be required to be strengthened to increase the internal strength capacity to resist additional external loads or repaired to increase the design’s structural rigidity and insulate the reinforcement from aggressive conditions. The experimental studies that related to the techniques of repairing and strengthening of RC beams using: external steel plates, fiber reinforced concrete (FRC), reinforced concrete (RC) jacketing, sprayed fiber reinforced polymer FRP, epoxy injection, mortar jackets, near-surface carbon fiber (SNSM-CFRP) strips, near-surface glass fiber (NSM-GFRP) rods, CFRP laminate and sheet; and adding an ultra high performance concrete (UHPC) layer. All the techniques that were discussed showed that there is an improvement in the general behavior of the beams that have been strengthened and repaired, as well as an increase in the maximum load and ductility.

Effectiveness of Strengthening RC Beams Using Composite Materials—An Accelerated Strengthening Method

The article analyses the results obtained from tests of preloaded reinforced concrete beams strengthened with carbon fibre strips bonded into the concrete reinforcement cover (NSMR method). Adhesive (thixotropic epoxy resin) bonding takes 7 days at 23 °C. The strengthening process was accelerated by heating the strip using a prototype heating device. Tests on the reinforced concrete members confirmed that accelerating the strengthening process is feasible and allowed the selection of the optimal heating temperature to provide the greatest strengthening level. The study primarily aimed to analyse the effectiveness of strengthening applied to the bottom of reinforced concrete beams under sustained loading throughout the adhesive curing process, simulating real conditions on site. Significantly higher strengthening efficiency was achieved with the use of strip heating, which accelerated adhesive cure time and reduced the strengthening execution time from 7 days to 1.5 h. The analysis included the evaluation of the effect of the steel and composite reinforcement ratios on strengthening effectiveness.

Experimental assessment of barely visible impact damage carbon fibre reinforced epoxy composite using ultrasound method

Background: Carbon fibre reinforced epoxy (CFRP) is susceptible to impact damage which could resulted in reduction of the mechanical properties. This paper studies the architecture of barely visible impact damage (BVID) to comprehend the extent of damage on quasi-isotropic CFRP laminates of varying thickness (i.e. 16, 24 and 32-ply laminates of 3, 4 and 5 mm respectively). Methods: Quasi-static indentation is chosen to produce BVID on CFRP laminates, followed by using non-destruction evaluation method, namely conventional contact-type ultrasonic testing (UT) and C-mode scanning acoustic microscopy (C-SAM) method. Results: The findings revealed (1) the size and shapes of the BVID on CFRP laminates, (2) no damage found at the point of damage, and (3) the bridging between the point of impact to the outer damaged diameter due to the consequence of diverse orientation of carbon fibre strips which exhibit excellent mechanical properties before structural failure. Conclusions: The results concluded that the UT and C-SAM method can identify both the pristine region and the internal damaged structures in CFRP laminates.

Studying the effect of wrapping the steel bars using carbon fiber strips on the behavior of reinforced concrete beams subject to cyclic loading

The behavior of reinforced concrete beams subjected to cyclic loading was studied in this research to determine the impact of wrapping main reinforcing bars in carbon fibre (CFRB) strips. The objective of the present work included studying the impact of length and the number of layers of CFRB strips, that are used in wrapping main bars, on the overall response of reinforced concrete beams subjected to a cyclic load. Wrapping the reinforcing bars by Carbon fibre is a helpful substitute when there is no enough space to increase the quantity and size of these bars. For this purpose, five reinforced concrete beams were prepared and tested. One of these beams was a reference beam with unwrapped main reinforcement. Two beams have main steel bars wrapped along the mid third of the span with either single or two layers of CFRB. The main reinforcement for the remaining two beams was wrapped along their entire length with either single or double layers of CFRB. A nonlinear finite element analysis of the tested beams was carried out and the predicted results are compared with the experimental outcomes. The results show that CFRB significantly and effectively contributes to increasing the flexural strength and overall behavior of the reinforced concrete beam at different rates depending on the length and number of CFRB layers that wrapped the steel bars.

Tribological Properties of Carbon Fiber-Reinforced PEEK against 304 Stainless Steel with Reticulate Surface Texture.

With the aim of improving the durability and reliability of polyetheretherketone (PEEK) composites reinforced with carbon fiber (CF) as thrust bearings without lubricants, a reticulate surface texture was fabricated by plane honing on a stainless steel (SS) counterpart to promote its tribological properties. Pin-on-disk experiments were designed, with the results showing that the reticulate surface texture effectively reduces the friction coefficient from 0.40 to 0.20 compared with the polished SS surface, within the range of the pv value from 0.185 to 1.85 MPa∙m/s. The wear mechanism of the polished SS surface against CF-PEEK, proven with SEM and EDS observations as well as AE measurements, is revealed, falling into abrasive wear with SS particles embedded in the friction interface around the CF strips, causing three-body contact. The reduction in the friction coefficient of the textured SS disk against the CF-PEEK pin can be achieved due to diminution of the CF wear debris and SS particles, which are scraped off by the groove edges and trapped by the groove valleys, reducing the three-body abrasive wear, while the honed plateau is used as a flank surface like a cutting tool to scratch more soft PEEK particles as the transferred film, owing to adhesive wear. This investigation suggests that the SS disk with a honed surface structure can be used as the counterpart of CF-PEEK bearings with a low friction coefficient and wear rate under dry friction.

Square metallic tubular sections bonded with high strength carbon fibre sheets under compression

This paper presents the strength and stiffness enhancement of square steel hollow sections wrapped by Carbon Fibre Reinforced Polymer (CFRP)strips. Main factors used were number of layers and size of the CFRP. Distances between the adjacent strips are kept constant spacing of 40 mm. According to the objective of the study, twelve hollow steel sections are wrapped by carbon fibre strips and two samples are without wrapping is kept reference for comparison. Results confirmed that the strength and stiffness are improved better for carbon fibre wrapped samples compared to unwrapped sample.

Behavior of Reinforced Concrete Beams Strengthened With Carbon Fiber Strips.(Dept.C)

Behavior of Reinforced Concrete Beams Strengthened With Carbon Fiber Strips.(Dept.C)

Effect of shear connectors on strength of structural sandwich panels

This study investigates the structural behavior of precast lightweight sandwich panels with dimensions of (500 × 500 mm) and 120 mm height. Specimens consists of three layers: concrete face wythes (with thicknesses of 45 mm and grades of (80, 70) MPa) and high-density foam (with thickness of 30 mm) as a core material. Steel and carbon fiber shear connectors (rods and strips) were used in panels with angles of (45°, 60° and 90°). Three-point flexure load test was carried out on all panels. Obtained results were studied with predicted ultimate loads from ANSYS software and the theoretical extremes capacities of 0% and full-composite cases to evaluate the effects of changing components. Strength/weight ratio and degree of composite action were obtained to can judge the panels with effective parameter. It was found that adding carbon fiber strips has a high positive effect in degree of composite action. Steel bars shear connectors were the optimum shear connectors’ type with high strength concrete. Carbon fiber strips and rods shear connectors were the best shear connectors’ type with light high strength concrete. All properties of specimens enhanced with the decrease of the angle of shear connectors with both of steel and carbon fiber shear connectors. Angle of 45° is the optimum angle that resists the flexure load, obtaining high degree of composite action and high strength/weight ratio. It also obtained the highest percent of predicted ultimate loads from ANSYS software.

Constructing hybrid gridshells using bending-active formwork

Aiming to promote a more sustainable approach to material utilization in architecture, this article presents an alternative construction method for lightweight and efficient concrete structures. The strategic focus is placed on building wide-spanning roof structures like vaults, domes, and freeform shells with the lowest possible input of raw materials and energy. To achieve this objective, the article explores the novel idea of using bending-active structures, made from millimeter-thin carbon fiber strips, as lost formwork and structural reinforcement for the production of hybrid gridshells. After a general introduction to the state-of-the-art in concrete construction, the authors discuss opportunities and challenges related to flexible formwork designs and their possible impacts on the building industry. Relying on the example of a built prototype, the authors present a promising design methodology and analyze the gridshell’s geometrical and structural characteristics throughout different stages of the construction process. The article concludes by discussing the added value of this research and identifying the key aspects that need to be considered in the further development of this construction method.

Flexural Behavior of Square Ferrocement Panels Enhanced with Recycled Tires Sim Strengthened by CFRP

This paper presents an experimental algorithm with the results of using steel fibers in ferrocement panels, which were recovered from tires scrap. Waste steel fibers were cut with the same geometrical characteristics of normal steel fibers and were used in the panels at different layers. To have a reference ferrocement specimen, a plain mixture without fibers and mixtures containing a ratio of recycled steel fiber were also prepared. Some mechanical tests, such as compressive strength, splitting tensile strength and flexural strength were determined. Furthermore, load deflection behaviors for 24 panels specimens were carried out under patch load. Test results show that the recycled steel fibers layers recovered from scrap tires affected the mechanical behavior of ferrrocement panels that are similar to the number of wire mesh layers. Depending on the distribution of R.S.F layers and wire mesh layers, the load-deflection curves were found. A comparison between these curves indicates that the R.S.F can reduce the deflection of panels, and increasing the number of wire mesh layers can increase the ability to bear stresses for panels. Rehabilitation with carbon fiber strips CFRP carried out with three forms (box network, inclined with diagonal, parallel to the diagonal and mix of diagonal and box network). The curves show that the rehabilitation with a parallel form to the diameter of the sample is a better treatment, which is characterized by resistance to stresses rather than other forms. We estimate that the recycled steel fibers increase the flexural strength and tensile strength, and 10% is the optimal ratio for increasing the flexural strength and tensile, increasing the number of wire mesh layers increases the ability to bear stresses of the panels. Recycled steel fibers can cause reduction in the deflection of ferrocement panels and can give the same bearing strength proximity (or less) to the panel containing the same number of wire mesh layers.

Structural Reinforcement of a Masonry Building

A structural reinforcement carried out on a 12th century mansion in masonry with the aim of a seismic improvement valued as a decrease in the Seismic Risk Class [4].The reinforcement technique combines the use of FRP systems with carbon fiber strips applied to the external perimeter walls and FRCM systems applied to the internal walls.The proposed solution allows the seismic improvement both in relation to local failure phenomena and in the overall behavior of the whole structure. Particular focus is given to the dimensional calculation of the reinforcements and to the combined contribution of the two techniques, highlighting the peculiarities of both. The FRP system is used to avoid overturning and to increase the resistance of the walls, while the FRCM system is used for the general improvement of the mechanical properties of the masonry. Particular attention is paid to the evaluation of the design resistance values related to the debonding failure by carrying on special technical measures in installation of aramid fiber or CFRP connectors.The intervention methodology allows an increase of the Seismic Risk Class of at least 3 levels, as deductible from the calculation of the PAM value.

3D printed continuous fibre-reinforced composites: Bio-inspired microstructures for improving the translaminar fracture toughness

Translaminar fracture toughness is a vital property governing the notch sensitivity and damage tolerance of composites. Nature has shown that incorporating material transitions can increase toughness significantly. This work presents finite element models demonstrating that such transitions can indeed increase the translaminar fracture toughness. The designed microstructures were then 3D printed using continuous glass and carbon fibres. The specimens consisted primarily of glass fibres, but with local carbon fibre strips. A new compact tension specimen with a side groove was designed to ensure proper failure. When the strips were sufficiently large, toughness improvements of 20–60% were found after the crack had grown through the strips. These results reveal a powerful strategy for locally increasing the toughness in areas where it is needed the most.

In-plane behaviour of clay brick masonry wallettes retrofitted with single-sided fabric-reinforced cementitious matrix and deep mounted carbon fibre strips

The in-plane shear behaviour of a new seismic retrofit concept which combines two standalone retrofit measures for in-plane and out-of-plane strengthening of masonry walls was investigated. The in-plane reinforcement consists of a single-sided carbon fabric-reinforced cementitious matrix (FRCM) overlay, while the out-of-plane reinforcement consists of deep mounted carbon fibre reinforced polymer strips embedded in a viscous-elastic epoxy. An experimental program was undertaken in which clay brick masonry wallettes were subjected to the diagonal compression test to assess the effectiveness of the strengthening system on the in-plane behaviour. The obtained results showed that the single-sided carbon FRCM overlay increased the shear capacity with 80%, compared to the unstrengthened control specimens. Moreover, by testing two different FRCM overlay thicknesses it was found that a thicker matrix layer does not increase the shear capacity of wallettes. However, wallettes provided with a thicker FRCM overlay did show a higher level of ductility. Furthermore, the obtained experimental results showed that the presence of only the aforementioned out-of-plane reinforcement does not affect the in-plane strength of masonry wallettes loaded under shear, and even prevented the disintegration after reaching the failure load compared to the unstrengthened control specimens. Finally, an existing analytical model as well as the Eurocode 8 design provisions were compared to the found failure mechanisms and failure loads. The analytical model developed showed good correspondence with the experimental values for both the failure mechanism and failure load, with an experimental/model ratio left( varphi right) of 0.98, while Eurocode 8 proved to lead to conservative values.

Effectiveness of strengthening pre-loaded RC beams with CFRP strips in conventional and accelerated strengthening procedures

This paper analyses the results obtained from the testing of reinforced concrete beams additionally strengthened with composite materials pressed into the concrete cover using the near-surface-mounted reinforcement (NSMR) method. The testing program comprised two series of beams with cross-sectional dimensions of 0.12 x 0.30 x 3.30 m. The series differed in the amount of longitudinal steel reinforcement, 0.51% and 1.00%. Three beams were cast in each series. One beam was assigned as the control beam, while two other beams were strengthened with carbon fibre strips. A two-component thixotropic epoxy resin was used as a bonding agent. One of the two beams was cured for 7 days (to the product information document). The bonding process in the other beam was accelerated to last 1.5 hours by heating the strip up to 70°C. As the strengthening of "new" elements is not an accepted practice in engineering, the beams were pre-loaded. The load was maintained during the strengthening procedure and curing period (for 7 days and 1.5 hours) and then the beams were monotonically loaded to failure. The comparison of load capacity results for the CFRP strengthened and control beams revealed the effectiveness of the strengthening method. The paper also presents the strengthening technique in the NSMR application with the prototype heating device.

The Rehabilitation of Structures on the National Route 10 Section 12 between Upington Km 0.0 and Nakop Km134.17

National Route 10 Section 12 is situated between Upington and Nakop at the border between South Africa and Namibia in the Northern Cape Province. As part of SANRAL’s Bridge Management System, three bridges and twenty four major in-situ cast culverts were identified to be in need of rehabilitation and/or strengthening. This paper details the condition of the existing structures as well as the methods and materials used to repair and strengthen the structures to be in a safe and serviceable condition. Due to the harsh environmental conditions, as well as the remoteness of the structures, the methods and materials for repair had to be carefully considered. In this regard, special reference is made to the use of carbon fibre strips to increase the bearing capacity of the bridgeand culvert deck slabs. The method for the strengthening of the floor slabs and internal walls of a number of culverts, for which the compressive strength of the existing concrete was found to be in the order of 1.0 MPa, is also discussed.

Numerical Analysis of Effectiveness of Strengthening Concrete Slab in Tension of the Steel-Concrete Composite Beam Using Pretensioned CFRP Strips

One of the methods to increase the load carrying capacity of the reinforced concrete (RC) structure is its strengthening by using carbon fiber (CFRP) strips. There are two methods of strengthening using CFRP strips - passive method and active method. In the passive method a strip is applied to the concrete surface without initial strains, unlike in the active method a strip is initially pretensioned before its application. In the case of a steel-concrete composite beam, strips may be used to strengthen the concrete slab located in the tension zone (in the parts of beams with negative bending moments). The finite element model has been developed and validated by experimental tests to evaluate the strengthening efficiency of the composite girder with pretensioned CFRP strips applied to concrete slab in its tension zone.

Experimental and analytical analysis for bending load capacity of old timber beams with defects when reinforced with carbon fiber strips

This paper describes a comparative experimental and analytical study of the maximum bending load in timber beams of Pinus sylvestris L. having natural defects (knots, grain deviations, fissures and wanes) that are reinforced with carbon fiber composite (CFRP). Beams extracted during rehabilitation of the roof frame of the School of Law, University of Granada, had been in service for over two hundred years. Two commercial CFRP pultruded laminates were applied as reinforcement, for comparison. Both were properly glued with epoxy resin on the tension side of the beams, partially covering the area on this side. It is clearly shown that, due to the abundance of defects, using the elastoplastic constitutive law of timber and assuming the same tension and compression elastic moduli in the cross-section equilibrium method, the analytical values for the bending load capacity will not match the experimental ones. However, this assumption has been traditionally used in most previous research on timber beams reinforced with composite materials. As an alternative, a more general model for the timber may be used, in which the two moduli are considered to be different in compression and tension stresses. Results demonstrate how this modification provides a much better match between analytical and experimental values of the bending load capacity. The improvement is especially evident for beams with natural defects and many years in service, reinforced with CFRP for rehabilitation purposes. Moreover, a better mechanical behavior of the reinforced specimens is obtained, when compared with the control ones (without reinforcement): reinforcement induced an improvement of up to 88% in bending load capacity.

Bond strength of carbon fiber composites glued to concrete surface

This paper describes an analytical study about the bond between concrete and glued carbon fiber composites (CFCs) using data of 2 experimental researches. A total of 27 double compression‐tension tests were carried out on specimens with 2 concrete cubes (fixed and movable) connected by carbon fiber strips on opposite sides. The variables were concrete strength, with the evaluation of 9 specimens with strength of 20.5 to 38.1 MPa, with monotonic loading and smooth surface for all specimens, and 18 specimens with strength of 23.2 to 40.8 MPa, with monotonic loading and loading/unloading cycles and different concrete surfaces (smooth face and rough face). The test results showed that the ultimate bond stress slightly varies according to concrete strength in the analyzed zone. The strains of CFCs and concrete were measured, allowing the calculation of bond stress and the corresponding mean strain, which were compared with the values obtained by the expression given in the international codes. The prediction of the old expression applies to steel plates strengthening method, and the results of a more recent expression of CFC glued to concrete given by fib Bulletins and Model Code 2010 are compared with test results. The experimental results provided graphs and correlation curves for bond stress vs maximum strain, energy of fracture vs bond stress and a relationship between the mean shear strain and concrete strength. The expression for fracture energy given by fib Bulletins and Model Code 2010 varies with concrete strength fc and a reasonable agreement with test data was achieved.