Fiber Reinforced Polymer Tubes Research Articles

Improvements in the lateral crushing behavior of syntactic foam‐filled glass fiber reinforced polymer tubes by the addition of straight and helical multiwalled carbon nanotubes

AbstractTo diminish the brittleness of glass fiber reinforced polymer tubes and syntactic foams, a novel composite tube filled with syntactic foam was proposed, in which thin‐walled tubes were reinforced by ribs and the syntactic foam core reinforced with multiwalled carbon nanotubes (MWCNTs). The influence of the ribs and the type and content of MWCNTs on the lateral crashworthy characteristics of composite tubes was investigated. Crushing experimental results indicated that the ribs contributed to improving the crashworthy performance for both hollow and foam‐filled tubes. The effect of the ribs on the energy absorption was more pronounced for the hollow tubes. Incorporation of straight or helical MWCNTs lead to improvement of the crush resistance and energy absorption for foam‐filled tubes. With the same MWCNT content, the peak load and absorbed energy of specimens with helical MWCNTs were nearly 14% and 13% higher than those of specimens with straight MWCNTs, respectively. Furthermore, analytical models were proposed to predict the load–displacement responses for foam‐filled tubes in the linear‐elastic, postcrushing, and foam‐compaction stages. The predicted results agreed well with experimental results. The resulting composite tubes are potential light‐weighted and crashworthy structures, which could be applied as collapsible energy absorbers in engineering fields.

Compressive performance of SWSSC-filled CFRP-stainless steel composite tube columns

The structure of concrete confined by carbon fiber-reinforced polymer (CFRP) and stainless steel tubes was investigated. The columns, which take advantage of the ductility and corrosion resistance of stainless steel, are composed of stainless steel tube, core seawater and sea sand concrete (SWSSC) and outer FRP. Forty circular SWSSC-filled FRP-stainless steel composite tube columns (SCFSSCTs) were manufactured and subjected to axial compression tests. After fracturing of the FRP, the failure modes of the specimens mainly showed extrusion expansion, with a small amount of shear failure. The increase in the thickness of the stainless steel and the number of FRP layers resulted in a significant improvement in the load capacity and deformation capacity of the structure, which was more evident in the specimens with higher steel contents. With the increase in the number of FRP layers, the increases in ultimate stress and ultimate strain were 40.4% − 130.0% and 118.6% − 282.4%, respectively, compared with the column with single stainless steel confinement. The stress–strain curves for the SCFSSCTs were similar to those of structures reinforced by FRP and carbon steel and were divided into four stages. Models were proposed to predict the full axial stress–strain curves of SCFSSCTs, including the ultimate point and the peak point.

Residual compressive strength of filament wound hybrid glass/carbon fibre reinforced polymer tubes after exposure to elevated temperature

Fibre hybridisation is used to balance the high cost of carbon fibres and the low durability performance of glass fibres. This study investigates the residual compressive mechanical properties of filament-wound hybrid glass/carbon Fibre Reinforced Polymer (FRP) tubes after exposure to elevated temperatures. Effects of temperature exposure and fibre orientation on compressive properties have been investigated. Tubes were exposed to temperatures ranging from ambient to 350 °C. Two fibre orientation configurations, including hoop (89°) and cross-ply (20% at 15°, 40% at 40°, and 40% at 75°) were used to study the effect of fibre orientation. Compression tests were carried out to study the compressive mechanical properties of FRP tubes, while Digital Scanning Calorimetry and Thermal Gravimetry Analysis were conducted to study the thermomechanical characteristics of the specimens before and after exposure to the elevated temperatures. Finally, the level of damage and its mechanisms were investigated using Scanning Electron Microscopy. The experimental test results indicate that hybrid carbon/glass FRP (C/GFRP) tubes exhibit a performance closer to the weaker tube type, i.e. CFRP tubes rather than GFRP tubes. Moreover, when subjected to elevated temperature, tubes with cross-ply fibre orientations showed slightly better compressive performance compared to the tubes with a hoop fibre orientation.

Axial compressive behavior and design of high-strength square concrete-filled steel tube short columns with embedded GFRP tubes

This paper proposed a hybrid column by embedding glass fiber-reinforced polymer (GFRP) tube into high-strength square concrete-filled steel tube (CFT), named as high-strength square steel-concrete-GFRP concrete (SCFC) column. A total of 13 high-strength square SCFC short columns were tested. The test parameters included diameter and thickness of GFRP tube, width and thickness of steel tube, yield stress of steel, and compressive strength of concrete. Results showed that high-strength square SCFC short columns exhibited post-yield strengthening behavior and stable residual strength. The axial strength, confining effect, and ductility were improved because of the embedded GFRP tube. Detailed finite element models were developed and benchmarked to investigate the strength contribution of each component and conduct parametric studies. It was shown that: (i) the concrete infill and the steel tube contributed >90% to the overall compressive strength and (ii) the strength improvement by embedding GFRP tube was closely related to the section size ratio, confinement ratio of the GFRP tube, and confinement ratio of the steel tube. Evaluation of the current equations showed that they were not accurate enough to estimate the axial compressive strength of high-strength square SCFC short columns. New equations were then proposed.

Bond-slip performance of seawater sea sand concrete filled filament wound FRP tubes under cyclic and static loads

Adequate bond strength of concrete filled tubes is required to ensure full composite action and prevent premature bond failure before ultimate bending capacity is reached. This study investigates the bond strength and bond slip mechanisms of FRP tubes filled with seawater sea sand concrete (SWSSC) under static and cyclic axial loads using a push-out test. Glass and carbon fibre reinforced polymer (FRP) and two different diameters (100 mm and 165 mm) were tested to investigate the effect of changing parameters on the bond strength. Each group of specimen was tested under static load (SL) and various different cyclic loading (CL) regimes. An ANSYS FE model was created to simulate a static pushout test for FRP SWSSC composites under varying parameters to quantify the induced tube and confinement stress. Confinement and accumulated damage were found to be the two main factors determining the change in bond strength between cyclic and static load conditions. The high active confinement of the smaller diameter GFRP tubes resulted in a slight increase in bond strength for most samples under CL. The larger diameter CFRP tubes generally exhibited a slight drop in bond strength under CL due to the more pronounced effects of accumulated interface damage.

Compressive Behavior of Concrete-Filled Filament-Wound FRP Tubes with Local Tube Damage

Concrete-filled fiber-reinforced polymer (FRP) tubes (CFFTs) are an emerging and attractive form of column for new constructions. Such a column consists of outer filament-wound FRP tubes that are filled with plain or steel-reinforced concrete. The fibers in the filament-wound FRP tube are predominantly in the hoop direction to confine the inner concrete, which leads to significantly enhanced strength and ductility in the confined concrete. Extensive studies have been conducted on the behavior of CFFTs that were subjected to various loading conditions, which confirmed the excellent performance of such members. As CFFTs become increasingly used in practice, there is a concern about the performance of CFFTs when the FRP tube is subjected to local damage that is caused by accidents, vandalism, or designed holes or cuts to accommodate connections with other structural components. Some studies have been carried out on the performance of CFFTs as flexural members with a locally damaged filament-wound FRP tube; however, the research on such CFFTs as columns remains limited. This paper presented the results of a comprehensive experimental program on the axial compressive behavior of CFFTs with a filament-wound FRP tube that was subjected to local tube damage. Two types of damage (i.e., holes and cuts) with different parameters were investigated. The test results showed that the compressive strength [i.e., peak stress (fcc′)] and the corresponding axial strain (ɛcc) of the damaged CFFTs were significantly reduced due to the local tube damage (e.g., fcc′ reduced from 12.2% to 64.8% and the corresponding ɛcc reduced from 35.2% to 77.2%). Finally, an existing model for FRP-confined concrete that considered the local FRP damage was evaluated which suggested the need for the recalibration of the model or the development of a new model for CFFTs with a locally damaged filament-wound FRP tube.

Residual compressive strength of seawater sea sand concrete filled hybrid carbon-glass fibre reinforced polymer tubes under seawater: Effects of fibre type and orientation

Despite the superior mechanical and durability properties, the higher cost of carbon, compared to other fibre options, remains a major concern in the widespread use of carbon fibre-reinforced polymer (CFRP) composites in construction applications. The hybrid formation of carbon fibres with other fibres could help reduce the cost while remaining appropriate structural properties. The present study examines the durability performance of Seawater Sea Sand Concrete (SWSSC) filled hybrid carbon-glass fibre-reinforced polymer (HFRP) tubes after exposure to seawater. Ninety-six samples filled with an alkaline solution simulating SWSSC were exposed to seawater for different durations and at different temperatures. The compressive mechanical properties of the conditioned samples were compared to the unconditioned reference samples to determine the level of mechanical degradation of the tubes. Based on Arrhenius's theory, long-term performance was predicted using the collected experimental data from short-term performance. Fibre type (i.e. carbon, glass, and hybrid carbon-glass) and fibre orientation (cross-ply and hoop) were considered as the material-based variables. When exposed to the most severe condition of 5 months at 60 °C, CFRP showed the highest average strength retention of 86.01%. The hybrid cross-ply tubes exhibited better strength retention than GFRP with strength retention of 64.84% for HFRP compared to 57.23% for GFRP. However, over the long term, the difference in performance between the two types of FRP tubes decreased and became more comparable. The onset of damage in GFRP tubes started sooner than that in HFRP. However, the long-term ultimate strength reduction of HFRP tubes was found similar to the weaker fibre type (i.e. GFRP tubes).

Dynamic Analysis and Parametric Optimization of Telescopic Tubular Mast Applied on Solar Sail

Large-scale solar sails can provide power to spacecraft for deep space exploration. A new type of telescopic tubular mast (TTM) driven by a bistable carbon fiber-reinforced polymer tube was designed in this study to solve the problem of contact between the sail membrane and the spacecraft under light pressure. Compared with the traditional TTM, it has a small size, light weight, high extension ratio, and simple structure. The anti-blossoming and self-unlocking structure of the proposed TTM was described. We aimed to simplify the TTM with a complex structure into a beam model with equal linear mass density, and the simulation results showed good consistency. The dynamic equation was derived based on the equivalent model, and the effects of different factors on the vibration characteristics of the TTM were analyzed. The performance parameters were optimized based on a multiobjective genetic algorithm, and prototype production and load experiments were conducted. The results show that the advantages of the new TTM can complete the deployment of large-scale solar sails, which is valuable for future deep space exploration.

Behavior and modeling of large-scale concrete-filled FRP tubes with longitudinal steel rebars under lateral impact loading

Fiber-reinforced polymer (FRP) has been utilized extensively as a confining material for concrete in civil engineering. Concrete-filled FRP tubes (CFFTs), consisting of a FRP tube, a concrete core and optional longitudinal rebars, are particularly attractive to be used as bridge piers in harsh environments. Most studies on CFFTs have been focused on their behaviors under static loading conditions. To extend existing studies, three identical large-scale CFFTs with longitudinal steel rebars (SR-CFFTs) were investigated experimentally, two of which were tested under lateral impact loading and one was under lateral static loading. To compare the confining behavior between FRP tube and steel stirrups, three identical large-scale reinforced concrete (RC) columns with approximately the same hoop confinement stiffness as SR-CFFTs (i.e., steel stirrups for RC columns, FRP tube for SR-CFFTs) were tested as companion specimens. The test results indicated that, (1) under lateral static loading, the RC column failed with a shear-failure manner, while the SR-CFFT specimen failed with combined bending and shear failure characteristics; (2) under lateral impact loading, the shear-dominant failure mechanism was evident for RC columns, while the failure mechanism of SR-CFFTs was flexural-dominant owing to the effective hoop confinement provided by FRP; (3) under the same impacting velocity, the SR-CFFT specimen had much less damage and much less lateral displacement than the corresponding RC column. The established FE models could provide reasonably accurate predictions for the dynamic behaviors, the impact force–time history curves and the column deformations for both RC columns and SR-CFFTs. Parameter studies were conducted to analyze the effects of the concrete strength, the longitudinal steel ratio, the impact velocity and the impact mass.

Confinement mechanism and compressive stress-strain behaviours of FRP-interlayer-steel confined concrete tubes

A fiber-reinforced polymer (FRP)-interlayer-steel confined concrete (FISC) column is formed by bonding the FRP material and a concrete-filled steel tube (CFST) with the grouting material, and it can improve the corrosion resistance and bearing capacity of CFST columns and avoid the early cracking of the epoxy resin in FRP confined concrete-filled steel tubes (CCFT). However, there are few researches on the compressive behaviours of FISC columns and the dual confinement on core concrete from the FRP tube and steel tube has not been expounded clearly. In this paper, twelve FISC specimens were tested under axial compression. The ratio of FRP and steel confining indexes and the concrete strength were the main parameters and the loading conditions (core CFST loading and whole section loading) were included. Failure patterns, load–axial shortening curves, and the strain development were analysed. In addition, the confining stresses of the FRP tube and steel tube were obtained, and it was found that the confinement on concrete could be divided into three stages of the non-confinement stage, the steel-controlling stage, and the FRP-controlling stage. In the FRP-controlling stage, the FRP confining pressure increased at a constant growth rate while the steel confinement was gradually weakened owning to the restraints of the interlayer grouting material. Furthermore, by regarding the concrete and grouting material as a whole unity, the axial stress-strain model of the confined concrete-grouting was developed, and the proposed model can predict the compressive stress-strain behaviours of an FISC column with good accuracy and simplicity.

Compressive behaviors of FRP-confined concrete prepared using spontaneous combustion gangue as coarse aggregate

Thirty-six concrete specimens composed of spontaneous combustion gangue (SCG) were tested under monotonic axial loading. To evaluate the mechanical behaviors of fiber reinforced polymer (FRP) confined SCG concrete, different concrete strengths and the glass FRP (GFRP) tube thickness were considered as variables. The compressive strength and ductility were significantly enhanced when the SCG concrete was confined with GFRP tube. In addition, SCG concrete has a specific expansion characteristic, which exhibits apparent volumetric compaction behavior during loading. Based on the existing model, a new design model of FRP-confined SCG concrete that uses piecewise functions was proposed, and its accuracy was verified.

Cyclic load tests and finite element modeling of self-centering hollow-core FRP-concrete-steel bridge columns

This paper presents experimental and numerical investigations of the seismic performance of a novel self-centering (SC) hollow-core (HC) fiber-reinforced polymer (FRP)-concrete-steel (SC-HC-FCS) bridge column. This new structure is fabricated by mounting external energy dissipators (ED) and applying unbonded post-tensioned (PT) basalt FRP (BFRP) tendon to the conventional HC-FCS column that consists of an outer FRP tube and an inner steel tube, with the space between filled with concrete. The SC-HC-FCS column combines the advantages of accelerated bridge construction and self-centering. The effects of the initial prestress force values and the configuration of the energy-dissipated aluminum bar on the column performance are studied. Based on the experimental and numerical results, it is found that the proposed SC-HC-FCS column shows adequate self-centering and energy dissipation capacities. However, it is required to properly select the configuration and material properties of the aluminum bar as energy dissipators to further refine the seismic resistance of the SC-HC-FCS column.

A New Electrical Resistance Measurement Method of Carbon Fiber-Reinforced Polymer Tubes Based on C⁴D Technique

This work introduces the capacitively coupled contactless conductivity detection ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{C}^{{4}}\text{D}$ </tex-math></inline-formula> ) technique into nondestructive testing (NDT) of carbon fiber-reinforced polymer (CFRP) and proposes a new resistance measurement method of CFRP tubes. The proposed method does not require direct contact between the electrodes and the carbon fiber. Therefore, the electrical resistance of CFRP can be measured without the treatments required by traditional electrical methods that may lead to surface or structural damage. The equivalent circuit model of the new method is established, and the challenges are analyzed. Simulation and experiment are conducted with woven fabric CFRP tubes to verify the feasibility of the proposed method, including the range of workable frequency, the effectiveness of the circuit model, and the capability of damage detection. Research results show that a relatively high working frequency is required to accurately measure the interested resistance and sense the resistance change. By selecting a workable frequency, the effectiveness of the circuit model is verified. Research results indicate that the stray capacitance between the electrodes has little effect on resistance measurement, and the capacitor–resistor–capacitor model is still applicable. Research results also verify the feasibility of the proposed method for damage detection. It is able to sense the resistance change resulted from the damage of CFRP, either the conductivity changes in simulation or actual cutting damage in experiment.

Circular concrete columns confined with GFRP tubes under repeated and sequential impact loads

The experimental work conducted in this study aims to develop more understanding of the dynamic response of concrete-filled fiber reinforced polymer (FRP) tubes (CFFTs) columns under lateral impact load by testing 16 specimens. Three different types including reinforced concrete (RC), unreinforced CFFT and steel reinforced CFFT columns were tested. The specimens were tested under both repeated and sequential impact load testing protocols. Four parameters were investigated: the cross-section size, the thickness of the FRP tube, and the presence of longitudinal reinforcement. In addition, the effect of adding polypropylene fibers (PPF) to the concrete was also studied. Based on the experimental results, the damage mechanism, impact loads, deflections and strains were monitored and discussed. The results of this investigation confirmed that steel reinforced CFFT columns exhibited superior damage control characteristics when compared to RC columns. Increasing the thickness of the FRP tube decreased the displacement by up to 18 % and the residual displacement by up to 15 %. Adding PPF delayed the failure of the specimen and slightly enhanced its response. The experimental findings showed that longitudinal internal steel reinforcement played an important role in columns’ overall behavior and increased impact capacity.

Compressive Behavior of GFRP Tubes Filled with Self-Compacting Concrete

Self-compacting concrete (SCC) features excellent flow ability without the need of vibration for compaction during casting. This makes it particularly suitable for application in hybrid fiber-reinforced polymer (FRP)-concrete–steel double-skin tubular columns (DSTCs), a high-performance structural form evolved from concrete-filled FRP tubes (CFFTs). In a DSTC, the space between the inner steel tube and the outer FRP tube for filling concrete may be narrow and the application of vibration may be difficult. However, because of the large shrinkage of SCC compared to traditional concrete of normal flow ability, the integrity and composite action of DSTCs with SCC become a major concern. To clarify this issue, an understanding of the behavior of CFFTs filled with SCC is an essential prerequisite. While a large number of studies have been published on CFFTs with normal concrete (NC), only limited studies have been carried out on CFFTs with SCC. This paper presents a comprehensive investigation on the effect of SCC on the behavior of large-scale CFFTs. Axial compression tests were carried out on concrete-filled glass FRP (GFRP) tubes with diameters of 150, 200, 300, and 400 mm. The compressive behavior of the CFFT specimens filled with NC, a nonexpansive SCC, and an expansive SCC (ESCC) was compared and discussed. The results showed that the specimens with nonexpansive SCC behaved differently compared to those with NC as a result of larger shrinkage, especially for large specimens for which the confinement level was lower. This situation, however, improved in specimens where ESCC was used. Finally, the test results were further analyzed using a theoretical model recently proposed by the authors’ group.

Tri-axial compressive behavior of expansive concrete and steel fiber-reinforced expansive concrete

Concrete is widely used with external confining devises such as fiber-reinforced polymer (FRP) tubes and steel tubes. Expansive concrete and steel fiber-reinforced expansive concrete has been proposed to prevent concrete shrinkage, and even to provide some pre-stresses in the confining devices so as to enhance confinement efficiency. However, the confinement mechanisms on expansive concrete and steel fiber-reinforced expansive concrete have not been fully understood yet. In this study, tri-axial compression tests were conducted to 52 concrete cubes with different expansive agent contents and steel fiber additions, in which 12 concrete cubes were under true tri-axial compression with different lateral confining pressures. It is found that concrete cubes under true tri-axial compression typically exhibited oblique shear failure, and their strength enhancements were limited by the magnitudes of minor principal stress. Furthermore, the effects of expansive agent content and steel fiber volume fraction on the axial stress-strain relationship were investigated. Results showed that the CaO-based expansive agent addition should be at least more than 4% to make a difference for the axial stress-strain curves. Concrete cubes with 8% expansive agent addition exhibited a steeper initial ascending slope, but the strength enhancements diminished with increasing confining pressures. Steel fiber addition could significantly enhance the peak axial stress (by 10–20%), and the enhancement effect became more prominent with increasing confining pressures. Therefore, the combined use of expansive agent and steel fiber has synergistic and complementary effects.

Nonlinear analysis of FRP-concrete-steel solid columns

In order to study the axial compression performance of the FRP (fiber reinforced polymer)-concrete-steel solid columns (FCSSC), the nonlinear analysis program of FCSSC was compiled in this paper. The program was verified by existing tests, and the impacts of FRP tube thickness, steel tube thickness, outer radius of steel tube, steel tube strength and concrete strength were examined. The outcomes showed that the calculated results agreed with the experimental results. It demonstrated the way that the program could precisely reflect the strain of FCSSC under various degrees of load and gauge a ultimate load of FCSSC. The increment of steel tube thickness, outer radius of steel tube and concrete strength on the bearing capacity of FCSSC were chiefly reflected in the increment of initial stiffness. The improvement of FRP tube thickness could provide greater constraining force. The increment of steel tube strength could expand the load at the inflection point on the load-longitudinal strain curve. The research results can give a reference to the use of the new structure.

Axial and radial crushing behaviour of thin-walled carbon fiber-reinforced polymer tubes fabricated by the real-time winding angle measurement system

This paper proposed a real-time winding angle measurement device embedded in the portable 3-axis winding machine, which was used to detect and measure the winding angle during the winding process. The device was completely designed, fabricated, tested, and divided into hardware and software sections. The hardware section was adopted Raspberry Pi 3B+ and Arducam 5MP OV5647 camera modules, and the software section was used the OpenCV software. The experimental test was carried out to validate the measurement data on ±45°, ±60°, and ±75° winding angles, and filament-wound carbon fiber-reinforced polymer tubes were performed the quasi-static radial and axial compression tests. It was found that the real-time measurement data from the system had approximately 0.45±0.02 comparative error value than the targeted winding angle, which was more accurate than traditional measurement data. Moreover, it was shown that peak crushing loading significantly increased with increasing winding angle under radial compression, which had the inverse decreasing trend under axial loading. In addition, the crushing behaviour of thin-walled CFRP tubes was studied.

Compressive behavior of PET FRP-confined concrete encased CFST columns

Environmental friendly construction materials such as polyethylene terephthalate (PET) fiber-reinforced polymer (FRP) and high-strength materials such as high-strength steel (HSS) are attracting wide attentions. In this study, a total of ten novel circular PET FRP-confined Concrete Encased Concrete-filled steel tube columns (PFCECs) with a Q690 steel tube and a PET FRP tube are tested to understand their axial compressive behavior, with the investigated variables covering the thickness of the outer PET FRP tube and the diameter ratio. The experimental results demonstrate that the load-carrying capacity of PFCECs with a given inner steel tube increase with an increase in the diameter ratio, but the ultimate axial strains and the residual axial loads do not necessarily increase with the increase of the diameter ratio. In the end, this paper compares the test results against the predictions from two existing models, and the comparisons show that the models give comparatively accurate predictions on the ultimate axial stresses/strains of the core concrete in PFCECs, but they are unable to capture complete axial stress-axial strain responses of the core concrete in PFCECs accurately.

Cyclic compressive behavior and load–strain model of FRP–concrete​ double tube composite columns

A novel fiber-reinforced polymer (FRP)–concrete double tube composite column, consisting of an outer filament winding FRP tube, an inner pultruded FRP tube and infilled core concrete and ring concrete, has been proposed and experimentally investigated under monotonic compression by the authors. It exhibited obviously improved deformability than the traditional FRP-confined concrete columns. In this study, cyclic compression tests were conducted on the composite column to examine its structural behavior under cyclic loadings. Effects of different outer and inner FRP tube thicknesses and ring concrete types were investigated. Failure modes, cyclic load–strain responses and hoop strain behavior were presented and analyzed. Cyclic load–strain model, including the envelope model, unloading and reloading models, plastic strain equation and stress deterioration equation, was proposed to predict the cyclic compressive behavior of the FRP–concrete double tube composite columns. The proposed model was verified against the test results and exhibited good performance.