Carbon Fiber Reinforced Polymer Research Articles

Numerical analysis of load-bearing capacity of shear-strengthened reinforced concrete beams without shear reinforcement using side-bonded CFRP sheets

As CFRP (carbon fiber-reinforced polymer) offers high retrofit efficiency for structural members in bending and shear due to its superior mechanical properties compared to steel, sheets made from this material have become ubiquitous in strengthening existing reinforced concrete (RC) structures. However, there needs to be more research on RC beams with no stirrups that have been shear-strengthened with side-bonded CFRP sheets. As such, this study aims to investigate this specific topic and assess design-related parameters that impact the load-bearing capacity of these shear-strengthened beams. To achieve this, nonlinear finite element models of four RC beams, including one control beam and three beams strengthened with side-bonded CFRP sheets, were built and verified regarding shear capacity, crack patterns, and failure mechanisms. The simulated beams demonstrated a high level of accuracy in all mentioned aspects. Numerical models were then developed to evaluate the design-oriented parameters that affect the response of shear-strengthened beams, including the concrete compressive strength, the amount of steel reinforcement, the number of CFRP layers, the CFRP bonding configuration, and the shear span-to-effective depth ratio. The results showed that not only the compressive strength of the concrete but also the amount of steel longitudinal reinforcement had a significant relationship with the load-bearing capacity of shear-strengthened beams. Meanwhile, the bonding configuration and the layer number of side-bonded CFRP sheets considerably influenced the ductility, the crack pattern, and the failure mode of shear-strengthened beams.

AHP VIKOR framework for selecting wind turbine materials with a focus on corrosion and efficiency

The research objective in the context of the study relates to the major concern of corrosion affecting the wind turbines in operation to find materials with high durability in relation to environmental conditions of operation, strength, and cost. A method is an integration of the Analytical Hierarchy Process (AHP) and VIKOR Multi-Criteria Decision Making (MCDM) techniques that will assess seven different material options on sixteen criteria that comprise corrosion resistance, mechanical properties, cost, and a negative environmental impact. From this result, the AHP method calculated the weights for the indicators and chose potential materials, and finally, the VIKOR method used these materials and compared and ranked them to obtain a compromise solution. The research novelty integrates the AHP and VIKOR MCDM methods to address corrosion in wind turbines. By evaluating seven materials against challenging sixteen criteria—including corrosion resistance, mechanical properties, cost, and toxicity, AHP ranks and weights the criteria, while VIKOR identifies the optimal material choice. This dual approach enhances the selection process, ensuring the chosen material improves turbine performance and durability, offering a significant advancement in the sustainable development of wind energy technology. In conclusion, by integrating AHP and VIKOR, it comprehensively evaluates multiple material options based on corrosion resistance, mechanical properties, cost, and environmental impact. This methodology effectively identifies materials that enhance wind turbine performance and extend their lifespan, addressing a critical industry challenge. The alternative exhibits a similarity to the positive ideal solution (Si) of 0.3704 and a relative closeness to the ideal solution (Ri) of 0.0750. Additionally, its priority ranking (Qi) is 0.001, placing it in the first rank for Carbon Fiber Reinforced Polymers (CFRP) within the selection methodology.

An Experimental Study and Result Analysis on the Dynamic Effective Bond Length of a Carbon Fiber-Reinforced Polymer Sheet Attached to a Concrete Surface

A carbon fiber-reinforced polymer (CFRP) is a common material utilized for the enhancement in reinforced concrete (RC) constructions. Previous research indicates that the bonding performance between a CFRP sheet and concrete determines whether the bonding of CFRP material is effective. However, the majority of existing research on the bonding performance of the CFRP–concrete interface is concentrated on static loading conditions. In order to clarify the effect of dynamic load on the bonding performance of the CFRP sheet–concrete interface, this study adopts the double-sided shear test method to carry out dynamic experimental research. The test findings reveal that the damage pattern of the CFRP sheet–concrete interface remains consistent across different loading rates. The ultimate bearing capacity increases as the strain rate increases. As the strain rate increases from 10−5 s−1 to 10−2 s−1, the effect of bond length on ultimate bearing capacity increases by about 7%. As the strain rate increases, both the maximum strain of CFRP and the maximum interfacial shear stress demonstrate a corresponding increase, with respective increase rates of 60% and 20%. The effective bond length decreases by about 20% when the strain rate rises from 10−5 s−1 to 10−2 s−1. Finally, a formula for calculating the dynamic effective bond length of a CFRP sheet, grounded in the Chen and Teng formula, has been proposed and verified.

Fracture toughness in SPCC/CFRP hybrid laminates: Mode I and mode II perspectives

Hybrid composites using adhesive joints are gaining popularity in various industries as their various material combinations can create certain advantages. This research focuses on examining the mode I and mode II fracture toughness characteristics of the combined laminate between Steel Plate Cold Rolled Commercial (SPCC) metal and Carbon Fiber Reinforced Polymer (CFRP) composite processed using adhesive bonding. SPCC/CFRP hybrid laminate composites were manufactured with a variety of manufacturing options (A, B, and C) to find the most optimal method using two types of epoxy and cyanoacrylate adhesives, with two different bonding processes: secondary bonding and co-bonding. Fracture toughness values were measured through the Double Cantilever Beam (DCB) test for mode I and the End Notched Flexure (ENF) test for mode II. The test results showed that epoxy adhesives in the SPCC/CFRP adhesive joints provided better fracture toughness performance, especially when combined with the co-bonding technique. Specimens from manufacturing option C showed the highest GIC and GIIC values of 83.05 and 254.94 J/m2, respectively. These values increased by 58.98 % and 80.48 % compared to manufacturing options A and B in Mode I. Additionally, the GIIC value for manufacturing option C increased by 78.00 % and 66.76 % compared to manufacturing options A and B. The SPCC/CFRP hybrid laminates showed adhesive failure on the SPCC surface when using epoxy adhesive, whereas adhesive failure occurred on the CFRP surface with cyanoacrylate adhesive for the different manufacturing options.

Axial Impact Response of Carbon Fiber-Reinforced Polymer Structures in High-Speed Trains Based on Filament Winding Process.

The continuous increase in the operating speed of rail vehicles demands higher requirements for passive safety protection and lightweight design. This paper focuses on an energy-absorbing component (circular tubes) at the end of a train. Thin-walled carbon fiber-reinforced polymer (CFRP) tubes were prepared using the filament winding process. Through a combination of sled impact tests and finite element simulations, the effects of a chamfered trigger (Tube I) and embedded trigger (Tube II) on the impact response and crashworthiness of the structure were investigated. The results showed that both triggering methods led to the progressive end failure of the tubes. Tube I exhibited a mean crush force (MCF) of 891.89 kN and specific energy absorption (SEA) of 38.69 kJ/kg. In comparison, the MCF and SEA of Tube II decreased by 21.2% and 21.9%, respectively. The reason for this reduction is that the presence of the embedded trigger in Tube II restricts the expansion of the inner plies (plies 4 to 6), thereby affecting the overall energy absorption mechanism. Based on the validated finite element model, a modeling strategy study was conducted, including the failure parameters (DFAILT/DFAILC), the friction coefficient, and the interfacial strength. It was found that the prediction results are significantly influenced by modeling methods. Specifically, as the interfacial strength decreases, the tube wall is more prone to circumferential cracking or overall buckling under axial impact.

Ultraviolet Irradiation Surface Treatment to Enhance the Bonding Strength of Polyamide-Based Carbon Fiber-Reinforced Thermoplastic Polymers.

Adhesive bonding is a suitable joining method to satisfy the increasing industrial demand for carbon fiber-reinforced polymers without the need for a machining process. However, thermoplastic-based carbon fiber-reinforced polymers have small adhesive strength with structural thermoset adhesives. In this study, an ultraviolet irradiation surface treatment was developed to improve the adhesive bonding strength for polyamide-based carbon fiber-reinforced polymer. The type of ultraviolet wavelength, irradiation distance and irradiation time were optimized. Surface treatment with simultaneous UV irradiation of 185 nm and 254 nm wavelength generated unbound N-H stretching that was capable of chemical bonding with epoxy adhesives through a photo-scission reaction of the amide bond of polyamide matrix. Therefore, ultraviolet irradiation treatment improved the wettability and functional groups of the polyamide-based carbon fiber-reinforced polymers for adhesive bonding. As a result, the adhesive strength of the polyamide-based carbon fiber-reinforced polymers was increased by more than 230%.

An in situ prepared fiber-based piezoresistive film for ultrasonic wave detection on nonplanar carbon fiber-reinforced composites

Owing to the flexibility and high-frequency responsiveness, nanocomposite piezoresistive sensors are suitable for Lamb wave detection on composite materials. Various types of nanocomposite films have been developed for this purpose. However, the inelasticity trait of commonly used electrodes for the nanocomposite films impedes their application on the nonplanar surface of composites. Herein, an in situ prepared piezoresistive film based on graphene and polymethyl methacrylate nanocomposite has been proposed for ultrasonic wave detection on nonplanar carbon fiber-reinforced composites. Electrospinning method is employed to fabricate piezoresistive fiber film onto carbon fiber-reinforced polymer (CFRP) composites, and the sensitivity along the thickness direction is utilized via employing the CFRP layer as one electrode. The fabricated sensitive films exhibit the capability to detect up to 150 kHz ultrasonic signals on curved surfaces. With the help of Hilbert energy spectrum, the precise damage localization on CFRP is achieved by the sensitive film array with a relative error of only 1%. This innovation provides a new in situ preparation method for ultrasonic sensitive film on nonplanar-shaped CFRP components for nondestructive evaluation task.

An intelligent CFRP bolt with embedded carbon nanotube eddy current sensors for damage self‐diagnosis of bolted composite joints

AbstractRecognizing the critical demand for composite bolts and the damage‐mode complexity of composite bolt joints, this study introduces the concept of an intelligent carbon fiber reinforced polymer (CFRP) bolt, which achieves self‐monitoring of damage in small and complex CFRP bolted joints. The proposed eddy current sensor (ECS) is mainly composed of a coil made of carbon nanotube film and encapsulated with epoxy resin film. This achieves homogeneous embedding of the sensor by using the same material for both sensor and bolt. The CFRP bolt is fabricated by molding process, with the proposed ECS embedded in bolt shank. The numerical simulation results indicate that hole‐edge damages impact the distribution of induced current density and eddy current flow in CFRP plates. Additionally, the impedance amplitude of the ECS effectively monitors bearing damage propagation. Shear tests confirm that the integration method of the proposed ECS within the CFRP bolt introduces negligible intrusion to the host bolt's integrity. Experimental results demonstrate that the intelligent CFRP bolt can effectively monitor the damage propagation at the hole edge, with an accuracy for bearing damage exceeding 0.5 mm. At a working frequency of 10 MHz, the sensor's sensitivity in detecting a 0.5 mm bearing damage reaches 4.20%.Highlights An intelligent CFRP bolt was fabricated using the molding method. The embedding of the ECS did not cause adverse effects on the bolt. The proposed EC sensor is composed of carbon nanotube and epoxy resin adhesive films. The eddy current distribution at the hole edge of the CFRP bolted joints is analyzed. The ability of intelligent bolts to monitor hole edge damage is verified by experiments.

Imaging and reconstruction of asymmetric wrinkles in carbon fibre composites using high-frequency eddy current and full matrix capture-based ultrasound

Ply wrinkles are a common defect found in Carbon Fiber Reinforced Polymer (CFRP) laminates that can lead to failure in composite structures if not correctly evaluated during manufacture stages. The mechanical performance of a structure depends on multiple parameters of a wrinkle, such as amplitude, wavelength, and asymmetry, which ideally need to all be measured to characterise the wrinkle properly. To address this issue, the authors designed and manufactured a set of complex wrinkles with various asymmetry offsets and amplitude and obtained raw data by testing them with a high-frequency eddy-current system. A unique trajectory in the complex Nyquist plot was found on asymmetric wrinkles, demonstrating the dominant influence of wrinkle asymmetry on electrical resistance. The authors also used full matrix capture ultrasound to characterise the wrinkles and measured the profiles by extracting texture phase randomness. The study revealed the superior capability of FMC UT for characterising and retrieving the profile in wrinkle coupons, while HF ECT was more adaptable for identifying the region of interest effectively. This work also implements a state-of-the-art deep fusion strategy to demonstrate a lightweight architecture can be easily used to combine multiple sources of wrinkle profiles and generate a more accurate prediction than traditional methods. Overall, the demonstrated work can be further applied to CFRPs with increasing geometric complexity and defects to facilitate the design efficiency and testing of CFRP components.

Fire performance of CFRP-strengthened piloti-type columns with fire-resistant materials during standard fire exposure

This paper presents a numerical investigation into the fire endurance of carbon fiber reinforced polymer (CFRP)-strengthened columns, shielded with fire-resistant materials, in piloti-type reinforced concrete buildings. The strengthened column, equipped with a fire protection system, underwent exposure to the ASTM E119 standard time-temperature curve for a duration of 4 h. To comprehensively evaluate the thermal and structural performance of the strengthened column at elevated temperatures and substantiate the effectiveness of the fire protection system, a fully coupled thermal-stress analysis was conducted. The numerical modeling approach employed in this study was rigorously validated through previous experimental studies in conjunction with adherence to the ACI design guideline, specifically ACI 440.2R-17. Using the validated structural fire model, the thermal and structural behaviors of the RC column with an insulated CFRP strengthening system were investigated based on four key performance criteria: glass transition temperature, ignition temperature of polymer matrix, critical temperature of reinforcing bars, and the design axial load capacity at elevated temperatures. Furthermore, a comparative assessment of fire endurance was performed using diverse fire-resistant materials, including Sprayed Fire-Resistive Material (SFRM) and Sikacrete®-213 F, with insulation thicknesses ranging from 10 to 30 mm, during the 4-hour fire exposure period.

In-plane crushing behavior and energy absorption of CFRP honeycombs with different core topologies

The in-plane crushing behavior and energy absorption performance of carbon fiber reinforced polymer (CFRP) honeycombs with different core topologies were experimentally investigated under uniaxial loading conditions. Three types of CFRP honeycomb core topologies (i.e. circular, square and hexagonal) with different cell wall thicknesses and heights were considered in the designs. The honeycomb samples were fabricated by the molding and bonding process, which is widely used in the easy, fast and economical manufacturing of thin-walled honeycomb structures. A total of twenty-seven sample groups were experimentally tested for each loading condition, in which honeycomb samples with different core topologies were designed to have almost the same weights for a meaningful comparison. The experimental results revealed that all honeycomb designs have higher in-plane compression strength in the expansion direction, and hexagonal honeycombs showed the highest strength and energy absorption performance in both directions due to their stable load-carrying capacity and outstanding force efficiency. In particular, the experimental findings showed that the crushing strength and the specific energy absorption of CFRP honeycomb structures can be improved up to 6.1 and 4.2 times, respectively, by properly adjusting the cell wall thickness and height parameters. The results also revealed that the proposed lightweight CFRP honeycombs with the structural densities of 155–283 kg/m3 showed better in-plane crushing performance than many competing cellular topologies.

Explainable Boosting Machine Learning for Predicting Bond Strength of FRP Rebars in Ultra High-Performance Concrete

Aiming at evaluating the bond strength of fiber-reinforced polymer (FRP) rebars in ultra-high-performance concrete (UHPC), boosting machine learning (ML) models have been developed using datasets collected from previous experiments. The considered variables in this study are rebar type and diameter, elastic modulus and tensile strength of rebars, concrete compressive strength and cover, embedment length, and test method. The dataset contains two test methods: pullout tests and beam tests. Four types of rebar, including carbon fiber-reinforced polymer (CFRP), glass fiber-reinforced polymer (GFRP), basalt, and steel rebars, were considered. The boosting ML models applied in this study include AdaBoost, CatBoost, Gradient Boosting, XGBoost, and Hist Gradient Boosting. After hyperparameter tuning, these models demonstrated significant improvements in predictive accuracy, with XGBoost achieving the highest R2 score of 0.95 and the lowest Root Mean Square Error (RMSE) of 2.21. Shapley values analysis revealed that tensile strength, elastic modulus, and embedment length are the most critical factors influencing bond strength. The findings offer valuable insights for applying ML models in predicting bond strength in FRP-reinforced UHPC, providing a practical tool for structural engineering.

Modified cure cycles for increased fatigue performance of fiber metal laminates

Modified (MOD) cure cycles that deviate from the manufacturer’s recommended cure profile can reduce the inherent thermally induced residual stresses (TRS) in fiber metal laminates (FML). Literature shows that MOD cycles do not adversely affect the material properties but enhance the quasi-static material strength. However, the literature does not comprehensively discuss the impact of MOD cycles on material performance during cyclic fatigue loading. This paper, therefore, investigates how MOD cycles influence the fatigue characteristics of different FML layups made of carbon fiber-reinforced polymer (CFRP) and steel. The experimental results confirm that the quasi-static material strength and the modulus of the FML are increased when using MOD cure cycles. The evaluation of fatigue tests with digital image correlation, thermography, and electrical resistance measurements of notched specimens shows that a reduction of TRS delays damage initiation in the metal facesheets and decreases the crack growth rate until facesheet failure. The results further show that layup-dependent parameters, the maximum stress in the metal sheets, and metal sheet thickness significantly govern the evolution of fatigue damage. In summary, modified cure cycles are an efficient tool to enhance the quasi-static and fatigue performance of CFRP-steel hybrid laminates.

Mechanical Properties of Full-Scale Wooden Beams Strengthened with Carbon-Fibre-Reinforced Polymer Sheets

The strengthening, rehabilitation and repair of wooden beams and beams made of wood-based materials are still important scientific and technical issues. This is reflected, among other things, in the number of scientific articles appearing and the involvement of research centres around the world. This is also related to society’s growing belief in the importance of ecological and sustainable development. This article presents an overview of the latest work in this field and the results of our own research on strengthening solid wooden beams with carbon-fibre-reinforced polymer (CFRP) sheets. The tests were carried out on full-size solid beams with nominal dimensions of 70 × 170 × 3300 mm. A 0.333 mm thick CFRP sheet was used for reinforcement. The research analysed various reinforcement configurations and different reinforcement ratios. For the most effective solution, a 46% increase in load capacity, 35% stiffness and 249% ductility were achieved with a reinforcement ratio of 1.7%. Generally, the higher the reinforcement ratio and coverage of the surface of the wood, the higher the strengthening effectiveness. The brittle fracture of wood in the tensile zone for unreinforced beams and the ductile crushing of wood in the compressive zone for reinforced beams were obtained. The most important achievement of this work is the description of the static work of beams in previously unanalysed configurations of strengthening and the confirmation of their effectiveness. The described solutions should extend the life of existing wooden buildings and structures and increase the competitiveness of wooden-based structures. The results indicate that, from the point of view of optimizing the cost of reinforcement, it is crucial to develop cheaper ways of combining wood and composite than to verify different types of fibres.

Upcycling end-of-life carbon fiber in high-performance CFRP composites by the material extrusion additive manufacturing process

Each year, a significant amount of waste is produced from carbon fiber polymer composites at the end of its lifecycle due to extensive use across various applications. Utilizing regenerative carbon fiber as a feedstock material offers a promising and sustainable approach to additive manufacturing based on materials. This study proposes the additive manufacturing of recycled carbon fiber with a polyamide-12 polymer composite. Filaments of recycled carbon fiber-reinforced polyamide-12 (rCF-PA12) with different recycled carbon fiber contents (0%, 10%, and 15% by weight) in the polyamide-12 matrix are developed. These filaments are utilized for 3D printing of specimens by using various infill density parameters (80% and 100%) on a fused deposition modeling 3D printer. The study examined how the fiber content and infill densities influenced the flexural performance of the printed specimens. Notably, the part containing 15 wt% recycled carbon fiber (rCF) composites showed a significant improvement in flexural performance due to enhanced interface bonding and effective fiber alignment. The results indicated that reinforcing the printed part with 10% and 15 wt% recycled carbon fiber (rCF) improved the flexural properties by 49.86% and 91.75%, respectively, compared to the unreinforced printed part under the same infill density and printing parameters. The investigation demonstrates that the additive manufacturing-based technique presents a potential approach to use carbon fiber-reinforced polymers waste and manufacture high-performance engineering, economic, and environmentally friendly industrial applications with the complicated design using different polymer matrices.

Tests of pulse interference from lightning discharges occurring in unmanned aerial vehicle housings made of carbon fibers.

The Aim of the study was to determine the effect of a carbon fiber enclosure on overvoltages induced in unmanned aerial vehicle (UAV) circuits. Carbon fiber reinforced polymer (CFRP) is characterized by a heterogeneous structure and a thorough analysis of its impact on the LEMP (Lightning ElectroMagnetic Pulse) protection of UAVs is crucial for the further development of such machines. The shorter the distance, the greater the amplitude of the EMP, the greater the value of the surges. Their maximum value determines the safe zone. This distance can be reduced by using an enclosure that can absorb or dissipate EMP. The tested object was placed between a large capacitor plates, which ensured the uniformity of the field. This article presents new results of tests on the CFRP shielding effectiveness against the electrical component of atmospheric discharge. Using described below method, an increase in the signal amplitude inside the box was achieved in relation to the input signal, thus strengthening it instead of suppressing it.

Development of an anchor system for thick CFRP plates: Experimental and numerical investigation

Carbon fiber reinforced polymer (CFRP) has been widely used in construction, rehabilitation and maintenance of civil infrastructures. Anchor system is one of the most crucial part ensuring load transfer between CFRP and the structures. However, for CFRP plate anchors, there is a contradiction between the anchor capacity and the anchor size. In this paper, a novel cylinder shaped anchor for thick CFRP plates was developed based on a detailed experimental and numerical study. The proposed anchor weighs only 6 kg and it can develop 98 % strength of the 3 mm thickness CFRP plates. The experimental and numerical results revealed that the anchor efficiency of the proposed cylinder shaped anchor system is significantly affected by wedge shape, anchor material, tooth shape, pretightening force and magnitude of interference. The proposed anchor system can significantly promote application of thick CFRP plates.

Post impact flexural behavior investigation of hybrid foam-core sandwich composites at extreme Arctic temperature

This study explores the post-impact bending behavior and failure mechanisms in hybrid sandwich composites made of Carbon Fiber Reinforced Polymer (CFRP) and Glass Fiber Reinforced Polymer (GFRP). Flexural tests conducted at both ambient room temperature and low temperature Arctic conditions reveal a significant enhancement in flexural performance when GFRP layer is incorporated on the outer side of the hybrid composite. The investigation utilizes images from testing to elucidate damage modes, including fiber and matrix cracking in the composite facesheet, as well as core shearing and debonding in the Polyvinyl Chloride (PVC) foam core. Residual flexural properties are notably influenced by stacking sequence, facesheet compressive properties, pre-existing impact damage and temperature conditions. Analytical predictions, validated experimentally, highlight the effect of stacking sequence, low temperature, and impact energy on flexural collapse modes, with competing failure modes such as indentation and core shear. Collapse maps indicate that room temperature specimens predominantly collapse through indentation, while diverse collapse mechanisms emerge due to facesheet thickness, rigidity, and degraded tensile strength. The study aims to provide fundamental insights for future composite designs tailored for Arctic applications.

Coupled thermal-electrical–mechanical characteristics of lightning damage in woven composite honeycomb sandwich structures

In this study, lightning strike damage of woven carbon fibre-reinforced polymer laminates (W-CFRPs) and woven composite honeycomb sandwich panels (W-CHSPs) are simulated using the proposed sequential thermal-electrical–mechanical finite element (FE) coupling model incorporating dielectric breakdown of materials. Surface current with an amplitude of 200 kA and corresponding lightning shockwave overpressure were applied on each composite. The FE model coupled with LaRC05 criterion was used to study the failure behaviours of intralaminar damage and interlaminar delamination of the W-CFRPs and W-CHSPs. A series of lightning strike tests were performed to validate the FE model. Detailed lightning damage assessments and mechanisms were characterized by a combination of visual inspection, image processing, ultrasonic scanning and micro computed tomography (Micro-CT) and showed good agreements with the FE-predicted results. It can be concluded that shockwave overpressure significantly impacts lightning-induced damages, thereby supporting the effectiveness of the newly proposed sequential thermal-electrical–mechanical coupling model, which demonstrates improved predictive accuracy.

Effect of CFRP strip tie configurations on the behavior of GFRP reinforced concrete columns under different loading conditions

This study presents the results of an experimental program on the behavior of concrete specimens reinforced longitudinally with glass fiber-reinforced polymer (GFRP) bars and transversely with square, square-square, and square-circular (S, SS, and SC) configurations of carbon fiber-reinforced polymer strip (CS) ties under different loading conditions. Nine specimens were tested as columns under concentric and eccentric axial loads and three specimens were tested as beams under four-point bending. The experimental results demonstrated that specimens reinforced with the SC configuration of CS ties exhibited superior load-carrying capacity and deformability compared to specimens reinforced with the S or SS configurations when subjected to concentric and eccentric axial loads. Also, the contribution of GFRP bars in the maximum axial load sustained by specimens under concentric axial load is higher for specimens reinforced with SC configuration of CS ties than for specimens reinforced with S and SS configurations of the CS ties.