Steel Fiber-reinforced Polymer Research Articles

Behavior of steel plate shear walls reinforced with stiffened FRP plates

Steel plate shear walls require retrofitting due to factors such as corrosion, long–term loading and functional changes. In an effort to modernise the technology used for strengthening and retrofitting steel plate shear walls, fibre–reinforced polymer (FRP) plates with additional stiffeners are employed to enhance the shear capacity of steel structures. In this study, the static properties of steel plates reinforced with these stiffened FRP plates were experimentally investigated. The application of this strengthening methodology substantially enhanced the out–of–plane stability, shear stiffness and bearing capacity of the plates, while also reducing fatigue damage. Equations for estimating the buckling and ultimate load of steel plates reinforced with stiffened FRP plates have been derived, enabling predictions of their practical performance. Finite element models incorporating the potential failure of epoxy at the FRP–steel interface were developed for further analysis. A numerical study was performed to investigate the optimal thickness of the FRP stiffener. The analysis revealed that stiffener thicknesses exceeding 6 mm did not significantly contribute to the enhancement of the load–bearing capacity or to the prevention of debonding. When the FRP rib thickness exceeds 6 mm, the economy was poor. The aforementioned findings are of considerable engineering importance, especially in the context of improving fatigue properties and shear load–bearing capacity of thin steel plates.

Bond behavior and modeling of steel-FRP composite bars in engineered cementitious composites

The combination of the steel-FRP composite bar (SFCB) and engineered cementitious composite (ECC) holds favorable applications in terms of durable resilient structures. However, a clear understanding of the interfacial bond performance of this novel combination is currently lacking. Therefore, the bond behavior and mechanism of the SFCB-ECC interface were investigated through direct pullout tests. A total of 48 cube specimens were fabricated, with the test variables including bar type, bar diameter, embedment length, and matrix type. The experimental results indicated that the bond failure mode of SFCBs and FRP bars differed from that of deformed steel bars, attributed to the damage of resin-rich ribs in relatively high-strength ECC. The bond-slip curves revealed both the fundamental differences and similarities among steel bars, SFCBs, and FRP bars. The Poisson effect and shear lag effect increased with a decrease in bar stiffness and an increase in diameter. The combined impact of the interaction between the bar stiffness and diameter resulted in varying bond strengths for steel bars, SFCBs, and GFRP bars, despite their similar surface geometries. A theoretical model for the bond strength at the SFCB-ECC interface was derived using the thick-walled cylinder principle and subsequently validated with test data. Finally, a unified empirical model framework for predicting the bond strength of various bar-matrix combinations was proposed based on the theoretical model. The accuracy of this method was evaluated using a collected database.

Bond–Slip Performance of Steel–Fiber-Reinforced Polymer Composite Bars (SFCBs) and Glass Fiber with Expansion-Agent-Reinforced Seawater Sea-Sand Concrete (GF-EA-SSSC) under Freezing–Thawing Environment

Bond–Slip Performance of Steel–Fiber-Reinforced Polymer Composite Bars (SFCBs) and Glass Fiber with Expansion-Agent-Reinforced Seawater Sea-Sand Concrete (GF-EA-SSSC) under Freezing–Thawing Environment

Bond durability between steel-FRP composite bars and concrete under seawater corrosion environments

Steel fiber-reinforced polymer (FRP) composite bars (SFCBs) can enhance the damage-controllable features of reinforced concrete (RC) structures, offering a potential solution to corrosion issues in conventional RC structures. However, the durability of SFCBs bonded to concrete remains insufficiently studied. Seawater exposure experiments were conducted on SFCBs-concrete specimens with two diameters (12 and 16 mm) at different exposure times (30, 180, and 360 days) and temperatures (23, 40, and 60 °C) in this study. Subsequent pull-out tests were performed to assess long-term bonding behaviors. The results indicate that the hydrolysis of the glass FRP (GFRP) matrix is the primary cause for the reduction in shear capacity of SFCB ribs and the degradation of bond properties between SFCB and concrete. With increasing aging time and temperature, the bond strength of SFCB-concrete gradually decreases. Thicker GFRP layer SFCB-concrete specimens exhibit better bond strength retention rates. Moreover, a predictive model for the bond strength of SFCB-concrete was proposed. As per the model predictions, the bond strength retention after 10 years of seawater immersion is 50% for 12 mm diameter SFCB, while the 16 mm diameter SFCB achieves a retention of 70%. These findings will provide valuable references for the implementation of SFCB-reinforced concrete structures.

A study into strain sensor of cement-based material using CPW transmission lines

Abstract Based on the theory of coplanar waveguide (CPW) transmission line, a novel microwave non-destructive strain monitoring sensor specifically designed for cement-based material structures is presented in this study. The aim is to establish the relationship between the variation of the S11 phase parameter of the CPW strain sensor and the structural strain, utilizing a linear analysis. The feasibility of the strain monitoring by the CPW sensor is validated through simulations and experiments. The obtained results demonstrate a strong linear correlation between the phase change of the S11 parameter and the strain, with a goodness of fit of 0.987. The simulated strain sensor exhibits a sensitivity of 48.83 ppm/με, while the experimental measurement sensor shows a sensitivity of 65.82 ppm/με. These findings highlight the potential significance of the proposed method, offering a new approach that is characterized by high sensitivity, low cost, and simplicity for strain monitoring in concrete structures. Among them, the sensor cement mortar matrix made in this study was mixed with the recycled material made of waste glass steel FRP after a certain treatment process. The development of this method holds promise for the advancement of health monitoring in concrete structures.

Influence of GFRP Confining Tube Parameters in Double-Skin Tubular Short Columns under Axial Loading

Abstract Composite construction with steel and concrete has become a widespread solution in modern construction practices because of its inherent properties such as high strength-to-weight ratio, good corrosion resistance, and high stiffness. Concrete-filled fiber-reinforced polymer (FRP) steel double-skin tubular compression members as vertical load–carrying members in buildings helps in optimizing the advantages of three materials: steel, concrete, and FRP. This study investigates the axial compressive behavior of short, concrete-filled glass fiber–reinforced polymer (GFRP) steel double-skin tubular (GSDST) columns and concrete-filled GFRP tubular (CFFT) columns. Parameters such as the number of FRP layers, hollow section ratio (HSR), variation of diameter of the inner steel tube, and the angle of orientation of the fibers have been examined in this investigation. The experimental study was carried out by performing a monotonic axial compressive loading condition. Three different angles of fiber orientation, 0° along the hoop direction, 45°, and 0°/90° with respect to the axis of the column, were adopted in this study. The ultimate load-carrying capacity, axial displacement, axial and horizontal strains, and failure modes were observed. The experimental results indicate that the structural performance of GSDST columns is significantly influenced by GFRP tube thickness, inner steel-tube diameter, and fiber-orientation angle. Maximum displacement was observed in the specimens with high HSR, thus showing a ductile characteristic in the axial load-displacement behavior. The load-carrying ability of the specimens decreased as the HSR increased. The load-carrying capacity of the specimens increased with the increase in outer GFRP tube thickness. This study demonstrates that GFRP tubes can be used efficiently in the construction field as vertical load–carrying components by enhancing the axial behavior of FRP steel double-skin tubular columns.

Phenomenological comparison between the flexural performance of steel- and CFRP-reinforced concrete elements

In recent decades, FRP reinforcement has received increasing attention in engineering research of reinforced concrete composites due to its advantages over steel reinforcement, such as corrosion resistance and high strength. Due to brittle failure and high strength-to-stiffness ratio of the FRP reinforcement, the flexural behavior of FRP-reinforced beams exhibits a qualitative and quantitative difference compared to conventional steel-reinforced elements. In particular, understanding and improving material utilization is crucial to reduce material consumption and maximize design efficiency in view of the increasing environmental concerns. In this paper, a phenomenological comparison of the flexural behavior and material utilization for various design configurations for steel- and CFRP-reinforced elements is presented. The investigations include different concrete grades, FRP reinforcement properties, cross-section shapes, and hybrid steel–FRP reinforcement cross-sections. In order to deliver a comprehensive perspective to design efficiency in practical context, serviceability deflection limit has been derived for FRP reinforced elements and integrated into the evaluation scheme. Additionally, a general modeling framework for the investigation of the moment–curvature and load–deflection response of steel- and FRP-reinforced beams has been developed supporting the presented studies. The modeling approach is based on a numerical evaluation of the cross-section equilibrium and it supports different material laws as well as arbitrary cross-section shapes and reinforcement layouts. The obtained results show fundamental differences between the bending capacity and material utilization of steel- and FRP-reinforced elements, which can stimulate the development of resource efficient designs. A deeper understanding of the phenomenology based on the present studies can streamline the current research on innovative design concepts for FRP-reinforced concrete elements with optimal utilization of these high-performance materials.

Feasibility of bolted connectors in hybrid FRP-steel structures

Due to the low weight and excellent durability of composite materials, Fibre Reinforced Polymer (FRP) decks mounted on steel superstructures are becoming increasingly common in engineering practice. Bolted joints are generally used to facilitate connections between an FRP deck and steel girders in road bridges. The connections are subjected to both high magnitude static forces as well as fatigue loading due to overpassing vehicles. With ever increasing traffic on both road and railway bridges, fatigue performance is of critical concern. Bolted FRP joints have been extensively researched in the past under static loading, but less is known about the fatigue and creep behaviour of such joints. Furthermore, little research exists on non-pultruded FRP profiles connected using bolted connections. Therefore, the objective of this research is to investigate connectors’ feasibility by means of static, fatigue and creep experiments on four different types of bolted joints comprising mechanical connectors and injection techniques. The study focuses on application in vacuum infused GFRP panels with integrated webs made of multi-directional laminates) connected to steel bridge superstructures. In addition, experimental results are used to validate Finite Element Analyses (FEA). Based on the obtained results, the novel injected steel-reinforced resin (iSRR) connector shows promising potential in hybrid steel-FRP bridges where good fatigue endurance of the connection, are required.

Flexural behaviour of concrete beams reinforced with steel-FRP composite bars

Corrosion of steel reinforcement affects the durability of concrete structures. This led researchers to look forward to alternatives for steel reinforcement. One of these alternatives is Fiber Reinforced Polymer (FRP) reinforcement, which has high tensile strength as well as excellent corrosion resistance. However, the use of FRP reinforcement always comes at the expense of ductility. Thus, Steel Fiber Composite Bars (SFCBs), which consist of a steel core and FRP protective coating, could be a suitable alternative to conventional steel/FRP reinforcement. In the current work, fourteen concrete beams were tested to investigate the flexural performance of concrete beams reinforced with manually produced SFCBs. All beams had similar dimensions of 200 mm width, 300 mm height, and a clear span of 1700 mm. The main parameters were the reinforcement type (steel/SFCB) and the concrete compressive strength (30, 40, and 50 MPa). The experimental results were presented in terms of; crack pattern, failure modes, cracking load, ultimate load, load-crack width response, load-deflection curves, and the reinforcing bars' strain curves. The test results showed that, at the same load level, using SFCBs as tensile reinforcement increased the beams' mid-span deflection and crack width compared with those reinforced with steel bars. Finally, an analytical study was performed to predict the ultimate loads, maximum crack width and maximum deflection at service load of SFCBs reinforced beams. The results from the analytical study were very close to the test results, validating the accuracy of the suggested formulas for usage in practice.

Eccentric compression behavior of Steel-FRP composite bars RC columns under coupling action of chloride corrosion and load

In order to investigate the eccentric compression behaviors of steel-FRP composite bar (SFCB) reinforced concrete (RC) columns subjected to chloride corrosion, the mechanical experiments of chloride corroded SFCBs and SFCBs RC eccentric compression columns were conducted. The effect of reinforcement type and ratio, eccentricity, slenderness, stress level and corrosion duration on bearing capacity, deformation, crack and failure pattern were investigated. The results showed that the strength retention ratio of reinforcement decreases with the increase of corrosion duration, the ultimate strengths of steel rebar, SFCB and FRP rebar decreased by 12.2%, 9.9% and 3.6%, respectively, when compared with those of uncorroded counterparts. With the increase of steel content of reinforcement, the load bearing capacity of eccentric compression RC column increases while the deformation decreases gradually. The load bearing capacity of corroded steel, SFCB and FRP RC columns maximally decreased by 16.6%, 12.4% and 7.2%, respectively, when compared with those of uncorroded counterparts. Based on the simplified materials constitutive relations and reasonable basic assumptions, formulae for discriminate failure mode, moment magnification factor and bearing capacity were developed. The predicted failure pattern, moment magnification factor and bearing capacity are in good agreement with the test results, confirming the validity of the proposed formulae, the results can be used as a reference for engineering application.

Novel FRP interlocking multi-spiral reinforced-seawater sea-sand concrete square columns with longitudinal hybrid FRP–steel bars: Monotonic and cyclic axial compressive behaviours

• Combined uses of FRP interlocking multi-spirals, SSC and hybrid FRP–steel bars are explored. • Hybrid FRP–steel bars as longitudinal reinforcement endure structural controllability. • Reducing spacings of middle or/and corner spirals improves post-peak deformability. • Unloading/reloading cycles foster plastic deformation and load degradation in FMSSCs. • Design-oriented load-strain model based on full-section confining stress is proposed. Fibre-reinforced polymer (FRP) interlocking multi-spiral reinforced-seawater sea-sand concrete (SSC) square columns (FMSSCs) can optimize the merits of FRP and SSC while providing excellent confinement to the concrete in square columns. However, existing works on FMSSCs are limited to columns with longitudinal FRP bars, whose complex compressive properties and natural brittleness challenge the structural ductility. To this end, this paper develops a variant of FMSSCs by employing hybrid FRP–steel bars (HFSBs) as longitudinal reinforcements to break out of existing limitations. The HFSBs with the inner steel bar and outer FRP layer possess distinctive post-yield stiffness and remarkable corrosion-resistant performance. A series of monotonic and cyclic axial compression tests are conducted to investigate effects of concrete types, reinforcement configurations, and loading schemes on behaviours of FMSSCs. Test results demonstrated that the use of SSC had a negligible effect on the short-term structural performance, and the presence of longitudinal HFSBs endured FMSSCs to introduce damage controllability, especially under cyclic loading. Additionally, repeated loading/reloading cycles exerted cumulative impacts on the plastic deformation and load degradation of FMSSCs but affected cyclic envelope behaviours little. Finally, a design-oriented load–strain model was proposed to predict monotonic and cyclic axial responses of FMSSCs with longitudinal HFSBs.

Behavior of R.C. beams with lap-spliced hybrid bars under flexure

ABSTRACT The steel fiber-reinforced polymer composite bars Known as (SFCB) are new kind of reinforcement, for concrete structures. A layer of glass fibers and reinforced polymer surrounding the steel bars resulting in the (GFRP), when used as concrete reinforcement contributes for enough, serviceability strength, and durability. Increasing the elastic modulus of GFRP bar, which have function of protecting corrosion in addition to reduce the initial cost of the FRP bar, is the purpose of hybridization. SFCB has the advantages of being noncorrosive, nonmagnetic nonconductive, and light in weight, along with high strength. This study presents the behavioral characteristics of RC beams, with tensile lap-spliced steel fibers—coated bars under flexure. Ten beam specimens were tested, with concrete cross-section of (25*40*420) cm and compressive strength of 30 MPa. One beam specimen, (R) was taken as reference as it was reinforced with no lap splice. Nine beam specimens were divided into three groups. Group (A) contained three beam specimens reinforced with SFCB of diameter 16 mm and lap splice of 50φ, one with stirrups, without stirrups and with staggered lap splice. Group(B) contains three beams reinforced with SFCB of 16 mm diameter and lap splice of 55 φ one with stirrups, without stirrups and with staggered lap splice. Group(C) contains three beam specimens reinforced with SFCB of 16 mm diameter and lap splice of 60 φ one with stirrups, without stirrups and with staggered lap splice. Beams were exposed to pure flexure. Crack patterns and results are presented along with stress-strain curves. Finally, conclusions are summarized and presented.

Analysis-oriented model for partially FRP-and-steel-confined circular RC columns under compression

Even though analysis-oriented models exist to simulate the axial and dilation behavior of reinforced concrete (RC) columns strengthened with fiber-reinforced-polymer (FRP) full confinement arrangements, a reliable model developed/calibrated for FRP partially imposed confinements is not yet available, identified as a research gap. Therefore, this paper is dedicated to the development of a new analysis-oriented model generalized for fully and partially confined RC columns under compression. In addition to vertical arching action phenomenon, the influence of the concrete expansion distribution along the column height on confining stress is considered in the establishment of the combined confinement from FRP strips and steel transverse reinforcements. A new unified dilation model is proposed, where the substantial effect of additional axial deformations induced by damage evolution in unwrapped zones is formulated by considering available experimental results. This model is coupled with an axial stress-strain formulation that includes a new failure surface function for simulating the dual confinement-induced enhancements, which are strongly dependent on the confinement stiffness. The developed model considers the influence of partially imposed confinement strategy on the axial and dilation behavior of RC columns, whose validation is demonstrated by simulating several experimental tests. Lastly, a parametric study is performed to evidence the dependence of FRP-steel confinement-induced enhancements on steel hoop and FRP spacing, and on the concrete compressive strength.

Flexural Behavior of Insulated Concrete Sandwich Panels using FRP-Jacketed Steel-Composite Connectors

This study presented the experimental and theoretical results of insulated concrete Sandwich panels with innovative dumbbell-shaped steel fiber-reinforced polymer (FRP) composite bar (SFCB) connectors under flexural load. The influences of FRP thickness and raised thickness of dumbbell ends of connectors, axial compression ratio, the content of vitrified microspheres in the wythes, and loading direction were discussed. The increase in thickness of a glass FRP (GFRP) jacket on the hybrid bar from 2 to 3 mm led to increased initial cracking load, ultimate load, and flexural stiffness of the Sandwich panels by 75, 49, and 16%, respectively. The increase in the thickness of dumbbell ends from 4 to 6 mm led to increased initial cracking load, ultimate load, and flexural stiffness of the Sandwich panels of 18, 46, and 9%, respectively. The incorporation of vitrified microspheres in concrete wythes resulted in a significant increase in the load-carrying capacity of Sandwich panels but decreased ductility. Increased axial compression ratio from 0/1 to 0.2/1 contributed in improving the crack resistance and ultimate loads of Sandwich panels. Further increase of the axial compression ratio to 0.4/1 led to crushing failure of concrete wythe ends. Specimens under negative loads had higher ultimate loads than the counterparts under positive loads. Three-dimensional finite-element (FE) models were developed to simulate Sandwich panel flexural behavior and numerical results compared with the test data. Then, the verified FE model was used to analyze the influence of the arrangement of dumbbell-shaped SFCB connectors. Increased connector spacing from 550 to 650 mm was found to have an insignificant influence on load-deflection responses. Moreover, analytical solutions for deflection of Sandwich panels under combined axial-flexural load were obtained, in which the effect of slipping between the facade and structural wythes and shear deflection were considered. The predicted deflection at the ultimate load agreed well with the test results. This study provided a theoretical basis and design reference for FRP-jacketed steel-composite connectors in applications of Sandwich wall panels with large insulation layer thickness.

Simplified implementation of equivalent and ductile performance for steel-FRP composite bars reinforced seawater sea-sand concrete beams: equal-stiffness design method

To overcome the steel corrosion and shortage of river sand and freshwater, the combination of steel-FRP composite bar (SFCB) and seawater sea-sand concrete provides a promising alternative. As the stress–strain relationship of SFCB is quite different, the design method of steel bar or FRP bar reinforced concrete beam cannot be applied directly to SFCB reinforced concrete (SFCB-RC) beam. Here, a simplified equivalent design method, i.e. equal-stiffness design method, is proposed, where the total longitudinal reinforcement stiffness of SFCB-RC beam is equal to that of steel bar reinforced concrete (S-RC) beam. The flexural behavior of equal-stiffness-designed SFCB-RC beams is investigated experimentally. The results show that compared with S-RC beams, equal-stiffness-designed SFCB-RC beams have similar failure modes, equal deflection, and acceptable crack width. The post-yielding stiffness contributes to 14.3%-54.5% larger load-carrying capacity and 47.0%-189.1% higher ductility coefficient. Consequently, equal-stiffness design method contributes to a better flexural performance of SFCB-RC beams compared with S-RC beams and provides a simple and reliable way to directly refer to the design method of S-RC beams, facilitating the design and application of SFCB-RC beams. Furthermore, an analytical model to predict the load-carrying capacity, deflection, and crack width of SFCB-RC beams is preliminarily developed and evaluated.

Experimental Study on Hysteretic Behavior of Concrete- Filled Square Carbon Fiber-Reinforced Polymer Steel Tubular Beam-Column

Experimental Study on Hysteretic Behavior of Concrete- Filled Square Carbon Fiber-Reinforced Polymer Steel Tubular Beam-Column

Ductility Estimation for Flexural Concrete Beams Longitudinally Reinforced with Hybrid FRP-Steel Bars.

An experimental study was conducted to evaluate the ductility of reinforced concrete beams longitudinally reinforced with hybrid Fiber Reinforced Polymer (FRP)–steel bars. The specimens were fourteen reinforced concrete beams with and without hybrid reinforcement. The test variables were bar positions, ratio of longitudinal reinforcement, and type of FRP. The beams were loaded until failure using a four-point bending test. The performance of the tested beams was observed using the load–deflection curve obtained from the test. Numerical analysis using the fiber element model was carried out to examine the growth of neutral axis due to the effects of the test variables. The neutral axis curves were then used to estimate the neutral axis angles and displacement indices. The test results showed that the reinforcement position did not significantly affect the flexural capacity of beams with a higher ratio of hybrid reinforcement, but was quite significant in beams with a lower ratio of hybrid reinforcement. It was observed from the test that the flexural capacity of beams with hybrid reinforcement was 15–45% higher than that of beams with conventional steel bars, depending on bar positions and the ratio of longitudinal reinforcement. The ductility of beams with hybrid reinforcement was significantly increased compared to that of beams with FRP, but decreased as the hybrid reinforcement ratio (Af/As) increased. This study also showed that the developed numerical model could predict the flexural behavior of beams with hybrid reinforcement with reasonable accuracy. Based on the test results, parametric analysis, and data obtained from the literature, the use of the neutral axis angle and displacement index value to evaluate the ductility of cross-sections with hybrid reinforcement is proposed.

Shaking table test of concrete columns hybrid reinforced by steel/FRP bars

Post-earthquake residual deformation can be decreased due to the designable post-yield stiffness of concrete column reinforced by steel bars/fiber reinforced polymer (FRP) bars. Shaking table tests of three concrete columns with similar initial stiffnesses were conducted, where the longitudinal reinforcement included ordinary steel bars, steel-FRP composite bars (SFCBs) and hybrid reinforcement (steel bars and FRP bars, C–H). The measurements included acceleration response and strain development. The test results showed that the absolute and relative peak ground acceleration (PGA) responses of different columns were similar to one another. The residual strain in the anchorage region was not consistent (tension or compression) and was affected by the longitudinal reinforcement type and the amplitude of the input PGA. For ordinary reinforced concrete (RC) columns, the plastic strain of steel bars developed rapidly after the input ground motion PGA reached 100 Gal, and the corresponding residual strain also developed dramatically. For the SFCB column, even after the peak strain reached 15,000 με, the residual strain was still below 500 με. For hybrid column C–H, the residual strain of the FRP bar was similar to that of the SFCB column. Even when the input wave PGA reached 560 Gal with concrete cover spalling and steel bar buckling, no damage was observed on the FRP bars. In general, compared to ordinary RC columns, concrete columns with hybrid steel and FRP bar reinforcement can achieve a smaller residual deformation, while SFCB reinforced columns can be constructed in severe environments due to a good anti-corrosion performance, such as in offshore structures.

Reliability of Steel-Fiber Reinforced Polymer Strengthened Reinforced Concrete Bridge Columns

AbstractThe reliability of reinforced concrete (RC) bridge columns strengthened with externally bonded, steel-fiber reinforced polymer (SFRP) fabric subjected to blast loads was investigated. Colum...

Behavior of concrete-filled FRP tube columns internally reinforced with FRP-steel composite bars under axial compression

Although concrete-filled fiber-reinforced polymer (FRP) tube (CFFT) columns (CFFTs) have become increasingly popular, CFFTs has a weak bending performance as the orientation of the fibers in the FRP tube is generally close to the transverse direction. To this end, this paper proposes novel Concrete-Filled FRP Tube columns internally reinforced with FRP-steel Composite Bars (referred to as CFFT-CB columns) which consist of an external FRP tube, some longitudinal reinforcing FRP-steel composite bars (FSCBs), an FSCB spiral and concrete filled in the entire section. In this study, FSCBs are composed of separated FRP bars and steel bars due to fabrication difficulty. The axial compressive behavior CFFT-CB columns is studied experimentally in this paper. The effects of the spiral type, the spiral pitch, and the thickness of the FRP tube are carefully investigated and the test results confirm the effectiveness of the proposed columns. The ultimate condition of concrete in test columns are compared with four existing stress–strain models, with the confining stresses from both the FRP tube and the FSCB spiral being accounted for. The durable CFFT-CB columns are particularly suitable for marine and coastal structures constructed in harsh environment.