Carbon Fiber Reinforced Polymer Strips Research Articles

Novel fatigue strengthening solution for metallic structures using adhesively bonded Fe-SMA strips: A proof of concept study

An innovative fatigue strengthening solution for metallic structures that takes advantage of the shape memory effect of an iron-based shape memory alloy (Fe-SMA) and the bridging mechanism offered by the bonding technique has been proposed and examined. Fatigue tests on cracked steel plates with bonded carbon fiber-reinforced polymer (CFRP) and nonprestressed and prestressed Fe-SMA strips were conducted. The experimental results demonstrate that the bonded prestressed Fe-SMA strips are much more effective than CFRP strips, extending the fatigue crack growth life by a factor of 3.51. The proposed innovative solution is highly effective in retarding fatigue crack growth in metallic structures.

Novel bond-slip model between concrete and angular CFRP fan type anchoraged CFRP strip

One of the most important design approaches in the repairing/strengthening details is using CFRP (Carbon Fiber Reinforced Polymer) to delay the debonding of the CFRP strips/plates from the surface to take full advantage of the CFRP reinforcement. Compared to non-anchored strips, research studies regarding bond-slip models developed for fan type CFRP anchors and anchored CFRP strips to strengthen details are limited in the related literature review. However, in studies on this subject, anchors are placed at 90° to the axial tensile force applied to the CFRP strips. The ultimate load-bearing capacity and bond-slip models of CFRP strips with the different angled CFRP fan type anchor under axial tensile force have not been found in the literature review. Within the study's scope, 28 angled CFRP strip test specimens were produced and then tested under the effect of monotonically increasing axial tensile force with an experimental setup designed by the authors. The variables examined in this study were the concrete compressive power, the CFRP strip's width, the number of the CFRP anchor fan type, and the angle of the anchor placed on the CFRP strip. As a result of the study, an equation was proposed for calculating the ultimate load-bearing capacity of angled anchored CFRP strips and angled anchored CFRP strips. Finally, a new proposal for the bond-slip model was developed. It is thought that the new interface bond-slip model developed for CFRP strips with different angles will make an important contribution to the literature. It can be used in finite element analysis to realistically analyze the capacities and load-displacement behavior of reinforced concrete structural elements by strengthening such strips.

Retrofit of concrete columns with fibre strips using grooves and corner battens

An investigation was carried out to improve the seismic performance of concrete columns reinforced with high-strength steel bars and subsequently retrofitted with vertical and horizontal carbon-fibre-reinforced polymer (CFRP) strips. Seven columns were constructed and tested under constant axial and cyclic lateral loading. The results showed that attaching CFRP vertical strips in or over grooves outperformed conventional externally bonded reinforcement, as evidenced by greater energy dissipation and strength. Furthermore, the use of corner strip–battens for the horizontal CFRP strips was found to outperform conventional wrapping, as evidenced by greater ductility and energy dissipation. Confining stresses were also more uniformly distributed and strip rupture shifted from the edges to the mid-sides of the section.

Experimental Study on Axial Compression Behavior on Circular Timber Columns Strengthened with CFRP Strips and Near-Surface Mounted Steel Bars

To investigate the working mechanism and reinforcement effectiveness of the ancient timber columns strengthened with carbon fiber reinforced polymer (CFRP) strips and near-surface mounted steel bars, in this paper, 42 timber columns have been tested under axial compression, which considered the arrangement modes of CFRP strips, number of near-surface mounted steel bars, and different strengthening ways as the main influencing factors. Based on the test results, failure modes of specimens and materials were analyzed, compressive bearing capacity and ultimate deformation of each specimen were obtained, and load-displacement curves of timber columns were diagramed. Moreover, the load-strain curves of specimens were obtained through the data collected using an extensometer, and the deformation compatibility performance of three different materials was evaluated according to the strain comparison. The test results indicate that the wrapped CFRP strips way and near-surface mounted method can work together to mutually boost the reinforcement effectiveness. The proposed composite reinforcement method can significantly improve the bearing capacity and deformation performance of timber columns. Moreover, the increase in the number of CFRP strips and steel bars generates a marked enhancement in timber columns’ compression performance. The load-strain curves of timber, steel bars, and CFRP strips are in good agreement, and the percentage differences of three different materials’ strains are almost lower than 20%, illustrating that three types of materials have acceptable deformation compatibility performance.

Numerical analysis of one-way continuous slab with partial corrosion strengthened with deferent material

This paper investigates numerically the combined effects of a construction joint and reduction in the cross-section area of negative reinforcement in one-way continuous slab on the structural behavior and the efficiency of three types of strengthens techniques. In this paper, the modles were greated by ABAQUS (software) is used to numericaly represent the specimens and simulate the applied loading. This numerical study's models represent six one-way continuous slabs, as a part of a expermentail study. The specimen's dimensions were (2200 mm in length, 500 mm width ,and 100 mm thickness). Five of the six models had a vertical construction joint and reduced the negative reinforcement steel bars' cross-sectional area. The sixth specimen used as refreance. The proposed strengthening technique were: Carbon fiber Reinforced Polymers strips, 6 mm Carbon fiber Reinforced Polymers bars Near Surface Moutain technique and steel plates. All the proposed strengthening's applied to the tension side on the top face at the internal support. The program outcomes are represented visually as stresses distribution diagrams,load-deflection curves, and cracks pattern. The results from the numerical analysis compared to the experiment results. In the experiment, the reduction in the cross-section area resulting from partial corrosion happened in one span due to the outdoor atmosphere's exposure because of the stoppage in the concrete pouring, which also resulted in forming the construction joint. The results highlighted the construction joint's effect and the steel cross-sectional area reduction on the ultimate load and the deflection. The proposed strengthening methods improved the member's overall responses, and There was a good convergence between the numerical and experimental works that verify the specimens' observed behavior.

Hybrid system of longitudinal CFRP laminates and GFRP wraps for strengthening of existing circular concrete columns

This paper presents an investigation on the behavior of a strengthening system of longitudinal premanufactured carbon fiber-reinforced polymer (CFRP) laminates and transverse glass FRP (GFRP) wrapping for strengthening of concrete columns (here after is called a hybrid system). The idea behind using the longitudinal CFRP strips was to enhance the system by increasing the flexural stiffness of the column which is effective for the strengthening of slender columns and eccentrically loaded columns where additional flexural stiffness is required for buckling control. The study was conducted experimentally in two phases under monotonic loads. Phase I was conducted on small-scale concrete specimens to characterize the hybrid system and phase II was conducted to verify the effectiveness of the hybrid system for the strengthening of large-scale slender concrete columns. In phase I, it was observed that by applying GFRP wraps on longitudinal CFRPs, the failure mode of CFRP laminates changed from buckling/debonding to crushing to achieve the full capacity of the system. However, as expected, test results in phase I showed that the usage of wrapping without longitudinal CFRP laminates was more effective than the proposed hybrid system for the strengthening of small scale concrete columns subjected to pure axial loading. For slender columns in phase II, the hybrid system enhanced the wrapping system by adding 52%, 105%, and 94% gain for axial capacity, flexural capacity, and lateral displacement at peak load, respectively, by altering the load–deflection curve of the slender columns to achieve a higher performance level.

STRESS-STRAIN RELATIONSHIP OF SHORT CIRCULAR TIMBER COLUMNS STRENGTHENED BY A COMPOSITE METHOD IN AXIAL COMPRESSION

The composite reinforcement method with near surface mounted steel bars and wrapped CFRP (carbon fiber reinforced polymer) strips can effectively improve the strength and deformation capacity of historical timber columns. To establish the stress-strain model of strengthened timber columns, 42 timber columns strengthened by the composite reinforcement method were tested under axial compression, taking the number of wrapped CFRP strips and near surface mounted steel bars as the experimental factors. The test results indicated that the composite reinforcement method can improve the ductility and compressive strength of the timber columns. Because of the inevitable initial defects of timber, the failure of timber columns mainly occurred in the area where the initial defects concentrated. The load-strain curves of timber, CFRP strips and steel bars were consistent at the same measurement point, which showed that there were good bond properties between the timber and CFRP strips or steel bars, so that they can deform and work together. According to the existing researches, the formulas of peak stress and peak strain of the strengthened timber columns were given by fitting the experimental data. Trilinear and polynomial constitutive models of strengthened timber columns under axial compression were proposed. Considering the discreteness of timber material, the theoretical model curves were consistent with the test curves. It verified the reliability of the obtained stress-strain models.

Static and Dynamic Stiffness of Reinforced Concrete Beams Strengthened with Externally Bonded CFRP Strips.

This paper presents experimental investigations of reinforced concrete (RC) beams flexurally strengthened with carbon fiber reinforced polymer (CFRP) strips. Seven 3300 mm × 250 mm × 150 mm beams of the same design, with the tension reinforcement ratio of 1.01%, were tested. The beams differed in the way they were strengthened: one of the beams was the reference, two beams were passively strengthened as precracked (series B-I), two beams were passively strengthened as unprecracked (series B-II) and two beams were actively strengthened as unprecracked (series B-III). Moreover, the strengthening parameters differed between the particular series. The parameters were: CFRP strip cross-sectional areas (series B-I, B-II) or prestressing forces (series B-III). The beams were statically loaded, up to the assumed force value, in the three-point bending test and deflections at midspan were registered. After unloading the beams were suspended on flexible ropes (the free-free beam system) and their eigenfrequencies were measured using operational modal analysis (OMA). The static measurements (deflections) and the dynamic measurements (eigenfrequencies) were conducted for the adopted loading steps until failure. Static stiffnesses and dynamic stiffnesses were calculated on the basis of respectively the deflections and the eigenfrequencies. The qualitative and quantitative differences between the parameters are described.

Behavior and Strength of Steel Fiber Reinforced Self-compacting Concrete Columns Wrapped by Carbon Fiber Reinforced Polymers Strips

Strength capacity of reinforced concrete columns is very important to resists and transmit the external loadings. For Architects the engineerings requirements to use small cross section of reinforced concrete columns or in case of poor control quality we need to increase the compressive strength of concrete or use a strengthening technique of the structural elements such as column. In the present paper, the behavior and strength of four steel fiber reinforced self-compact concrete columns reinforced by one layer of CFRP that is wrapped around a square of reinforced concrete columns subjected to static loads is investigated. Self-compacting concrete by using limestone powder is adopted and is mixed with different percentages of steel fiber such as 1%, 1.5% and 2%. Different tests are adopted to investigate the mechanical properties of self-compacted concrete mixed with different steel fiber percentages. Test results show that there is an increase in concrete mechanical properties such as compressive strength, splitting tensile strength and modulus of rupture that reflects on the increase in load capacity of column; specimens when wrapped by CFRP. The increment in columns strength capacity is more than 50% as compared with the control column. All the test specimens are modeled using finite element analysis by ANSYS and the numerical results are compared with tested specimens.

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.

The repair of recycled crushed brick aggregate RC beams with shear deficiencies with CFRP

Repairing reinforced concrete (RC) beams using externally bonded carbon fibre reinforced polymer (CFRP) laminate has become one of the main rehabilitation techniques utilised to promote sustainability in construction. The aim of this study was thus to investigate the repair of rectangular simply supported reinforced crushed brick aggregate concrete beams with shear deficiencies in their design. The experimental work consisted of testing twelve full-scale beams (1400 x 200 x 150 mm) under two points load. The specimens were made of normal, and lightweight course aggregate concrete, four beam specimens were used as references, being tested until failure in shear to obtain the ultimate load carrying capacity, while the other specimens were loaded up to 60%-89.4% of the total load at failure, then repaired by wrapping in a layer of CFRP strips in two orientations (90°) and (45°). The variables investigated in this study were therefore the concrete type (normal and lightweight), shear span-to-effective depth ratio (a/d) with two variables (a/d=2.5) and (a/d=3), and the orientation of the CFRP. The results showed that a significant contribution was made by externally bonded CFRP in terms of repairing the beams, which not only refreshes initial shear capacity but also increases the ultimate capacity. The beams showed maximum reliability when the CFRP was oriented at 90° at a ratio of 72%.

Parametric study on buckling stability of CFRP-strengthened cylindrical shells subjected to uniform external pressure

Stability performance of cylindrical shells and providing a potential method to enhance the buckling stability of these structures are major concerns for designers. Carbon Fiber Reinforced Polymer (CFRP) composites are promising materials for application in the design and retrofit of such thin-walled structures. On this basis, this paper presents a comprehensive numerical study on the buckling behavior of CFRP-strengthened cylindrical shells under uniform external pressure and evaluates the effects of different parameters in the strengthening process. Numerous CFRP-strengthened cylindrical shells with distinct reinforcement layouts in three groups of models having different slenderness ratios are investigated through nonlinear stability analyses using the ABAQUS finite element package. The application of all considered reinforcement layouts for strengthening purposes is found to be effective in improving the buckling stability of cylindrical shells. It is demonstrated that the circumferential reinforcement of the middle region of the shell using CFRP strips with [0°] fiber angle (in the hoop direction), in particular, is the most effective approach for improving the buckling performance of the CFRP-strengthened cylindrical shells under uniform external pressure.

Impact of elevated temperature and anchored grooves on the shear behavior of reinforced concrete beams strengthened with CFRP composites

Exposure of concrete structures to elevated temperatures causes a severe deterioration because of decomposition of cement hydration products, generation of vapor pressure, and the inhomogeneous volume changes of concrete's ingredients and beyond a temperature of 500 °C. The most Retrieval the structural performance of severely heat-damaged structural concrete members would be most significantly achieved using carbon fiber-reinforced polymer (CFRP) composite materials. 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 strips were integrated as external shear reinforcement for reinforced concrete (RC) beams by using the groove technique. The intent was to assess the CFRP strips' contribution to the shear strength and thus evaluate the effectiveness of using them as main or supplemental shear reinforcement before and after exposure to elevated temperature. The investigated parameters include the area and number of layers of CFRP strips and different elevated temperatures. By demonstrating an outstanding structural performance with significant enhancement in the ultimate strength, ultimate deflection, stiffness, and toughness, this paper's findings strongly attest that CFRP strips can be effectively utilized as external shear reinforcement in reinforced concrete beams exposed to elevated temperatures. New guideline and proposed empirical model are developed to predict the damage level and shear strength of heated damaged RC beams externally reinforced with CFRP composites considering the influence of the number of CFRP strips and elevated temperature as groove technique.

Behaviour of steel beams retrofitted with anchored carbon-fibre-reinforced polymer strips

Steel bridge beams can be damaged due to increased traffic loads and environmental impacts. An experimental study on the use of bonded and mechanically anchored carbon-fibre-reinforced polymer (CFRP) strips was undertaken to assess the retrofitting of such steel beams. The number of mechanical anchors used in the ends of the bonded strips was varied from zero to eight. The steel beam samples were tested under four-point loading. Loading was applied as an increasingly high static load and a low repetitive fatigue load. The load–displacement behaviour under the effects of static and fatigue loading and the strain distributions along the strips were measured and interpreted. The results showed that retrofitting cracked steel beams with CFRP strips is an effective method. In addition, retrofitting with anchored strips increased the performance of cracked beams under the effects of both static and fatigue loading.

Shear capacity behavior of Reinforced Concrete (RC) beams strengthened with CFRP strips

Recently, reinforced concrete beams strengthened with carbon fiber reinforced polymers (CFRP) have been widespread. The objective of this research is to calculate the shear strength capacity increment of reinforced concrete beams strengthened by CFRP strips. The ABAQUS software was used to construct a model of the finite elements for beam simulation. Six beams were generated in ABAQUS software, two were control beams and the remaining four were reinforced by varying CFRP strips. All beams had the same rectangular cross-section geometry and length. The obtain results showed that CFRP can significantly increase the shear capacity of the beam. And the highest load and deflection is a little affected by the CFRP strips orientation. This study can proposes a more economical way for existing structures to improve the carrying capacity.

Numerical Analysis on Flexural Behaviors of Prestressed Reinforced Concrete Beams Strengthened with NSM CFRP Strips

This paper presents the numerical analysis of prestressed reinforced concrete (PRC) beams strengthened with near‐surface mounted (NSM) carbon fiber reinforced polymers (CFRP). ABAQUS finite element software was used to simulate the existing test beams to investigate the flexural behaviors of PRC beams strengthened with NSM CFRP strips. The finite element model of beams strengthened with NSM CFRP strips was established. The finite element calculation results were compared with the experimental results to verify the accuracy and effectiveness of the model. Based on this model, the influences of concrete strength grade and amount of CFRP strips on the flexural behaviors of directly strengthened beams and the cycle numbers and overload amplitude on the flexural behaviors of damaged strengthened beam were further analyzed, and the load‐carrying capacity calculation formula of PRC beam strengthened with NSM CFRP strips was established. The results showed that the simulation results and the theoretical calculation were consistent with the test results. With the increase of concrete strength grade and amount of CFRP strips, the ultimate load of directly strengthened beams increased significantly, with a maximum increase of 21.3% and 23.0%, respectively. When the concrete strength grade exceeded C50, the improvement of the ultimate load was limited. When the overload amplitude was less than 60% of the ultimate load, the cycle numbers (within 500 times) had little effect on the yield load, ultimate load, and deformation. When the overload amplitude was higher than 60% of the ultimate load, the deformation increased, and the ultimate load decreased with the increase of the cycle numbers. The larger the overload amplitude, the smaller the ultimate load, and the larger the deformation under the same cycle numbers.

SEISMIC RETROFITTING OF REINFORCED CONCRETE SHEAR WALL USING CARBON FIBER REINFORCED POLYMERS (CFRP)

In this paper, the experimental results of a partially retrofitted non-compliant with code concrete shear wall using uni-directional carbon fibre reinforced polymer (CFRP) are introduced. The common deficiencies in the wall were insufficient reinforcement, un-confinement at boundary zone, the lake of in-plane stiffness, and ductility. The adopted retrofitting technique consists of the CFRP strips bonded to both wall face with mesh anchors installed in the wall panel and foundation to avoid debonding. The wall was tested before and after retrofitting under a constant axial load, and the displacement control lateral cyclic load was applied to the head beam level. The retrofitted wall showed satisfactory results in terms of drift and shear strength. The test results include the failure pattern, load-displacement behaviours, and deflected shape.

Out-of-plane behavior of clay brick masonry walls retrofitted with flexible deep mounted CFRP strips

The installation of carbon fiber reinforced polymer (CFRP) strips to deep vertical slots in masonry using a flexible adhesive was developed as a minimally-invasive and cost-effective out-of-plane seismic retrofitting technique for clay brick unreinforced masonry (URM) buildings. The purpose of the current experimental campaign was primarily to investigate the out-of-plane performance of full-scale, flexible deep mounted (FDM) CFRP retrofitted masonry walls. An additional objective was to assess the validity of existing model for determining the out-of-plane capacity of FDM CFRP retrofitted walls. In the experimental testing program, nine full-scale masonry walls were tested, of which six walls were retrofitted using the FDM CFRP technique. A new six point-bending test setup was adopted for quasi-dynamic cyclic testing with loading rates up to 30 mm/s. Experimental results confirmed the significant increase for out-of-plane lateral resistance and displacement capacity for the FDM CFRP retrofitted specimens with respect to the URM specimens. By implementing multiple bed joint-crack formation and cyclic degradation of the masonry, the proposed engineering model provided a good approximation of the experimentally obtained moment – mid-span displacement relations.

Iron based shape memory alloys as shear reinforcement for bridge girders

Considerable age of a very high number of bridges conjointly with a steadily increasing amount of traffic and changes in design philosophy (e.g. earthquake engineering) have made maintenance needed and retrofitting become more and more important over the years. Retrofitting can become necessary both for flexure or shear enhancements. Existing steel solutions for shear strengthening are very laborious and complex, and the durability of the steel construction is questionable. As an alternative to steel solutions, carbon fiber reinforced polymer (CFRP) sheets or strips are used for shear strengthening of reinforced concrete beams. But, prestressing of CFRP sheets or strips is hardly applicable. However, a prestressing of a shear strengthening has the advantages that the width of existing shear cracks can be reduced and the stresses in the internal steel stirrups are reduced.Therefore, in this study, a new iron-based shape memory alloy (‘memory-steel’) in the form of U-shaped (stirrups) ribbed bars with a nominal diameter of 12 mm were used in combination with sprayed mortar for shear strengthening of reinforced concrete (RC) structures. The memory-steel bars were activated with electric resistive heating. The activation resulted in a prestress of about 300 N/mm2 in the memory-steel reinforcement and consequently in vertical compressive stresses in the web of the RC beams. Large-scale experiments on T-beams with a height of 0.75 m and a total length of 5.2 m were performed to show the practicability and efficiency of the memory-steel shear strengthening. Promising results have shown that the new strengthening system works well in practice. The shear capacity could be increased significantly. Furthermore, at the serviceability limit state, the prestressed memory-steel stirrups reduced the overall beam deflections, the stresses in the internal steel stirrups, the number of cracks, and the crack widths.

The Effect of Glue Cohesive Stiffness on the Elastic Performance of Bent Wood-CFRP Beams.

This paper presents experimental, theoretical and numerical studies of wood-CFRP beams bonded with polyurethane (PUR) adhesive. The analyses include two types of CFRP (carbon fibre-reinforced polymer) strengthening configurations and pure glue laminated timber beams as a reference. Through detailed analyses of a double-lap connection on blocks with and without CFRP strips, the authors state that neglecting the cohesive stiffness of adhesive layers may lead to an overestimation of an overall beam’s stiffness. This is significant with wood–CFRP connections, which showed values two times lower than with wood–wood connections. Theoretical modelling of the equivalent area used in a theory of composites provided much stiffer behaviour of the beams than in laboratory experiments. It proves that a PUR glue eliminates the possibility of using simple models that assume a perfect connection between bonded parts. These conclusions led the authors to use the finite element method (FEM) to take into account the cohesive stiffness. The FEM, based on the properties obtained from a double-lap joint analysis, allowed for the precise prediction of the elastic stiffness of the beams.