GFRP Tube Research Articles

Behavior of square pultruded GFRP tube filled with seawater and sea sand concrete beam

The behavior of square GFRP tube beams filled with seawater and sea sand concrete under the four-point test was studied with 48 specimens. The main test parameters of this study included cross section size, GFRP tube thickness, and sea sand replacement ratio. The failure process of the specimen during the four-point test was studied. The reslut indicated that the effect of GFRP tube strengthening core concrete on the failure process was significant. There was no apparent elastoplastic stage before the specimen failed, thus the failure mode was brittle under test, which could be found from the load-displacement curve. In addition, the effects of these test parameters on the ultimate capacity, flexural rigidity, and ductility were analyzed in this study. The test results indicated that the effects of GFRP tube thickness on the ultimate capacity and flexural rigidity were significant. The replacement of normal concrete with sea sand concrete had no obvious negative effect on the mechanical properties of the GFRP tube beams filled with concrete. Furthermore, the calculated formula of the ultimate capacity of the GFRP tube beams filled with seawater and sea sand concrete was proposed in this study. The calculated results were compared with the test results, which indicated that the calculated formula was greatly agreed with the test.

Investigation on GFRP Pultruded tube confined double skin tubular columns under axial loading

Composite construction with concrete filled steel tubes (CFT) as structural columns gained prominence in the recent construction scenario to make use of the benefits of both steel and concrete. Double skinned tubular (CFDST) filled with concrete between tubes is subjected to passive confinement pressure increasing the load carrying capacity of columns. This paper delineates the effect of confinement by outer steel and GFRP tube on the axial load capacity on CFDST short as well as slender columns made of steel inner tube. The experimental study was carried out on twenty composite columns consisting of ten numbers of double skin tubular short columns and ten numbers of double skin slender columns (with slenderness ratio 12.5). Ten short columns consist two pairs of columns with outer tube material as steel tube, two pairs of columns with outer tube materials as GFRP tube and one pair of reinforced concrete column. Diameter of the outer tube to thickness ratio (Do/t) of 21 and 30 is considered for all the columns irrespective of the length. The finite element analysis was undergone by modelling the columns in the Abaqus software, simulated the experimental work in the analytical study and the results are compared in terms of load deflection curves and failure modes of the columns. The SCFDST short columns failed by local buckling of outer tube whereas the failure of FCFDST short columns failure is characterized by rupture of the outer tube. The column with Do/t ratio 21 confines the concrete significantly than the tubes with Do/t ratio 30 irrespective of the outer tube material. The slender columns failed by global buckling and the ultimate load taken by the slender columns is reduced by 23% compared to short columns in SCFDST and 28% in FCFDST columns.

Structural Response of Circular Concrete Columns Confined with Gfrp Tubes Under Repeated and Sequential Impact Loads

Structural Response of Circular Concrete Columns Confined with Gfrp Tubes Under Repeated and Sequential Impact Loads

Investigation on various section GFRP profile strengthening concrete-filled GFRP tubular columns

Axial compression tests and numerically investigates were presented to investigate the behavior of circular winding concrete filled GFRP tubular columns with inner various section shapes of pultruded GFRP including angle section pultruded GFRP (LG-CFGT), channel section pultruded GFRP (CG-CFGT) and I section pultruded GFRP (IG-CFGT). A total of 72 columns including three groups of 24 LG-CFGT columns, 24 CG-CFGT columns and 24 IG-CFGT columns with different concrete strength, different winding GFRP tubular thickness and different column heights were tested. The failure mode, ultimate capacity, ductility, and stiffness of columns were mainly analyzed. Besides, strain development of the three groups’ columns during the test was investigated according to the strain measurement of eight columns. Based on mechanical mode and test results of core concrete being confined with GFRP tube, the calculate formula was presented in this study to predict the ultimate capacity of various section GFRP profile strengthening concrete-filled GFRP tubular columns. The calculated results were greatly consistent with the test results. In addition, the finite element model was proposed in this study, and was validated by comparing with the test results.

Seismic behavior of Double-Skin tubular E-waste concrete columns transversely confined with steel and GFRP tubes

Nowadays, FRP-confined steel tubular columns are emerging as advanced hybrid structural members due to their efficient performance under seismic loads. Such types of double-skin tubular columns (DSTCs) usually contain two different tubular systems, the first is the inner steel tube (ST) and the second is outer FRP tube, consisting of a concrete-filled space between them. The main objective of the present investigation is to examine the dynamic response of novel FRP-electronic waste (E-waste) concrete steel tubular columns (FESTCs) having an inner ST, outer glass-FRP tube (GT), and E-waste filled between the two different tubes to propose a sustainable structural column. Five FESTC elements were fabricated and tested under quasi-static loading to examine their dynamic performance under axial compressive and lateral cyclic loadings. The effect of three variables of FESTC samples on their performance was examined in the present study including ST reinforcing ratio, compressive loading ratio, and E-waste replacement ratio. The hysteretic cycles, strain spreading, ductility, skeleton curves, stiffness behavior, dissipation of energy capacity, damaging behavior, and strength reduction of fabricated samples were evaluated and deliberated. The outcomes of the present study showed that the effect of percentage replacement of E-waste aggregates on the dynamic behavior of FESTCs was low whereas compressive loading ratio portrayed a significant influence. Moreover, the capacities of the dissipation of energy and load-carrying strength of FESTCs elements were greater as compared with DSTCs elements containing natural aggregates.

Crashworthiness capability of thin-walled fibre metal laminate tubes under axial crushing

This study aims to evaluate the crushing behaviour of aluminium-glass fibre reinforced plastic (GFRP) with different layer configurations known as fibre metal laminate (FML) subject to dynamic loading conditions. The tubes were assembled to form 2/1 and 3/2 layout configurations. Resin and braided fiberglass sleeve were introduced as composite layer and sandwiched with two layers of aluminium tubes in forming 2/1 lay-up structure while a layer of composite and aluminium tube is added up alternately for 3/2 lay-up structure. These tubes were tested to evaluate the impact characteristics under low-speed axial impact loading. A finite element (FE) model was also developed and validated against the experimental results. In the numerical evaluation using a validated FE model, the internal energy of an aluminium tube was higher than the internal energy of a GFRP tube when the FML tube was progressively crushed. A series of parametric studies have shown that the increase in aluminium and GFRP wall thickness resulted higher specific energy absorption (SEA). The FML tube fold similar to the crush mode of outer tube material as when it is in its single tube form. All tube configurations were progressively crushed and unlikely to fail under catastrophic failure. FE model founds the aluminium tube layer is more dominant in energy absorption mechanism of the FML tube and increasing the number of tube layers improved crashworthiness significantly. From this discovery, a FML tube could be considered as a suitable lightweight candidate for energy absorbing applications with considerable crashworthiness capability.

Experimental Investigation and Design of Hollow Section, Centrifugal Concrete-Filled GFRP Tube Columns

The compressive response of hollow section, centrifugal concrete-filled GFRP tube (HS-CFGT) members is examined experimentally and reported analytically in this paper. A total of 17 specimens separated into two groups were tested; the specimens in each group were of four different lengths and included thirteen straight columns and four tapered columns. The details of the test rigs, procedures as well as key test observations composed of ultimate-moment capacities, load-displacement curves, and failure modes were truthfully reported. The test results were analyzed to evaluate the influence of initial eccentricity on the structural performance. Therefore, the aim of this paper is: (1) to propose a proper coefficient, φe, reflecting the effect of initial eccentricity based on the Chinese design code; and (2) to determine a new confinement coefficient, kcc = 1.10, for centrifugal concrete confined by GFRP tubes. Comparisons of the present design codes and specifications of confined concrete members with test results on 17 full-scale tube columns are also presented. Accordingly, new design equations, whose predictions generally agree well with the test results, are recommended to estimate the compressive capacity of the proposed HS-CFGT columns.

Behaviours of reinforced concrete-filled GFRP tube stub columns under low-temperature axial compression

A series of low-temperature tests on axial compression behaviours of 18 stub columns were presented in this paper, which included eight unconfined reinforced concrete columns (URCC) and ten reinforced concrete-filled GFRP tubes (RCFFTs). Regarding the compression tests on RCFFTs, axial compression load was applied to both inside confined reinforced concrete column (CRCC) and GFRP tube. The studied parameters of this paper included low temperatures of 20, −30, −60, and −80 ℃, diameter-to-thickness ratios of 20, 21, 30, 40, and 50, reinforcement ratio of 2.18% and 3.84%, and reinforcement type of steel reinforcement and GFRP bar. The failure modes, axial compression load–strain curves, and compressive stress–strain curves of RCFFTs at low temperatures have been revealed. Meanwhile, the influences of different parameters on the ultimate compression resistance, ultimate compression strength, stiffness, ultimate axial strain, and ultimate hoop rupture strain of RCFFTs at low temperatures were detailly discussed. These results indicated that low temperature generally improved the axial compression behaviours of RCFFTs. According to the test results, prediction formulae have been proposed to determine the ultimate compression resistance and ultimate axial strain of RCFFTs reasonably but conservatively at low temperatures, which considered the influence of longitudinal reinforcements and ties.

Compressive behavior of GFRP tube filled with structural polypropylene fiber reinforced seawater coral aggregates concrete

To address the challenge of shortage of concrete raw materials in the construction of reefs and islands, a novel composite column of GFRP tube filled with structural polypropylene fiber reinforced seawater coral aggregates concrete (SPFSCAC) is proposed, which not only utilizes local marine resources but also resists chloride corrosion in marine environment. The compressive behavior of SPFSCAC filled GFRP tube was investigated taking the effects of GFRP tube thickness and SPF content into account. The experimental results indicated that the usage of coral aggregates reduced the compressive performance of SCAC filled GFRP tube. After adding SPF, the compressive bearing capacity and corresponding strain of SPFSCAC filled GFRP tube were increased by 10.9 ∼ 26.9% and 11.9 ∼ 24.2% respectively compared to SCAC filled GFRP tube having an identical GFRP tube thickness, and would increase as increasing the SPF content. Adding SPF can eliminate the performance defects caused by the use of coral aggregates and enhance the core concrete. Under axial compression, the load–strain curves of SPFSCAC filled GFRP tube showed clearly four-stage characteristics. According to the transition points of experimentally obtained load–strain curves, the load–strain relationship model for SPFSCAC filled GFRP tube was proposed, and the reliability of the load–strain relationship model was verified through deviation analysis, thus providing a reference for the design and application of this new SPFSCAC filled GFRP tube.

Axial compression behaviours of seawater and sea sand concrete-filled GFRP stub tubes at arctic low temperatures

A series of low-temperature tests on axial compression behaviours of thirty stub columns were presented in this paper, which included eight hollow GFRP tubes (HFTs), six unconfined plain seawater and sea sand concrete columns (UPCCs), and sixteen seawater and sea sand concrete-filled GFRP tubes (CFFTs). Regarding the compression tests on CFFTs, axial compression load was applied to inside confined plain seawater and sea sand concrete column (CPCC) and GFRP tube concurrently. The studied parameters of this testing programme included loading schemes of monotonically or cyclically axial compression, low temperatures of 20, −30, −60, and −80 °C, and diameter-to-thickness ratios of 20, 21, 30, 40, and 50. The failure modes, axially compressive load–strain curves, and compressive stress–strain curves of all columns at low temperatures have been revealed. Meanwhile, the influences of different parameters on ultimate compression strength and ultimate axial strain of CFFTs at low temperatures were detailly discussed. These results indicated that axial compression behaviours of CFFT stub columns have been improved at low temperatures. According to the test results, prediction formulae have been proposed to determine the ultimate compression resistance and ultimate axial strain of CFFTs reasonably but conservatively at low temperatures.

Flexural behavior of hybrid GFRP-reinforced concrete-steel double-skin tubular beams

The hybrid GFRP-concrete-steel double-skin tubular beams (DSTBs) are composed of the outer GFRP tube, the inner steel tube and the sandwich concrete between both tubes. They have attracted the attention of researchers owing to the high ductility, lightweight, corrosion resistance and convenient construction. However, there are few studies on the reinforced DSTBs under bending load compared with the unreinforced DSTBs. Eight circular cross-sectional composite beams are tested in this paper to investigate the flexural behavior, including five reinforced DSTBs, two unreinforced DSTBs and one solid reinforced concrete GFRP tubular beam. The main parameters include the longitudinal steel reinforcement ratio, the inner steel tube diameter, the GFRP tube thickness, and the concrete strength. The results show that all the composite beams exhibit ductile flexural failure, and the average displacement ductility factor of the reinforced DSTBs is 3.85. The arrangement of longitudinal steel bars significantly enhances the bearing capacity and reduces the mid-span deflection of the composite beam, and it is recommended to use a reasonable low steel ratio for the excessive steel reinforcement is adverse to the ductility. Increase of the inner steel tube diameter greatly improves the flexural capacity on premise of ensuring the stiffness and ductility. The outer GFRP tube provides moderate hoop confinement on the compressive concrete in the pure bending members, which limits the increasing extent of the flexural capacity. Reasonable confinement stiffness is suggested for the reinforced DSTBs to avoid insufficient or excessive constraint. Besides, concrete with sufficient compressive strength is recommended to be used in the hybrid DSTBs for it increases both the flexural capacity and the initial stiffness of the beam.

Hybrid double skin FRP – Steel column with rubberised concrete infill under axial loading

The use of scrap tyre rubber in concrete is an effective sustainable solution that lessens the accumulation of tyres in the landfill and related environmental hazards. Extensive research on the behaviour of rubberised concrete over the past few years has outlined some excellent mechanical properties of this material such as enhanced ductility, energy dissipation, and impact resistance but also an associated weakness of having reduced strength. In this paper, a hybrid double-skin tubular column with rubberised concrete infill is proposed to provide effective lateral confinement and longitudinal reinforcement to minimize the reduced strength of rubberised concrete. This double-skin tubular column called “hybrid RuDSTC” comprises an outer filament wound CFRP or GFRP tube, inner steel tube with rubberised concrete infill. An experimental investigation on the behaviour of the proposed column under axial compressive loading is carried out. The parameters of the investigation are the type and thickness of the FRP tube and the percentage of rubber aggregates such as 0%, 15%, and 30% by weight. Axial stress, axial strain, lateral strain, and failure shapes of the columns are determined and discussed. Results show that both the filament wound CFRP or GFRP tube and steel provide effective confinement to increase the compressive strength and the peak and ultimate strain capacities of the hybrid RuDSTC columns. An increase in the amount of rubber aggregates results in lower values of brittleness index which indicates better ductility of the columns. Performance of CFRP and GFRP enclosed columns based on their diameter to thickness ratio and the steel confined double-skin tubular columns are compared. The proposed novel hybrid column provides a sustainable solution with applications in seismic-prone regions and mining infrastructure.

Influences of Slenderness and Eccentricity on the Mechanical Properties of Concrete-Filled GFRP Tube Columns.

The existence of either eccentricity or slenderness has a significant effect on the mechanical properties of a structure or member. These properties can change the working mechanism, failure mode, and bearing capacity of the structure or member. A concrete-filled, glass fibre-reinforced, polymer tube composite column has the same problem. We carried out experiments on the influences of eccentricity and slenderness on the mechanical properties of concrete-filled, glass fibre-reinforced, polymer tube composite columns. The experimentally recorded stress–strain relationships are presented graphically, and the ultimate axial stresses and strains and the FRP tube hoop strains at rupture were tabulated. The results indicate that the influences of slenderness and eccentricity on the composite columns were significant with regard to the axial strain, hoop strain, ultimate bearing capacity, lateral displacement, and failure mode. Based on the existing research literature and the results reported in this paper, the bearing capacity formula of a composite slender column under an eccentric load was established. The theoretical results were in good agreement with the experimental results.

Quasi-static and low-velocity impact behavior of the bio-inspired hybrid Al/GFRP sandwich tube with hierarchical core: Experimental and numerical investigation

Sandwich tube structures bio-mimicking horsetail and human tendons offered significant improvement over traditional single and multi-cell tubular energy absorbers. The present research aims to investigate three manufactured hybrid multi-cell aluminum and GFRP sandwich tubes subjected to quasi-static and low-velocity axial compression. The crashworthiness characteristics and axial crushing failure mechanisms of sandwich tubes are discussed and compared with the quasi-static axial behavior of single Al and GFRP tubes. Further investigations, based on the validation of an FE model versus experimental results, using the commercial finite element code LS-DYNA, on the effects of material permutation and inner tubes diameter are perceived through the full-factorial approach of FE parametric study. The quasi-static results revealed that, packing the Al and GFRP tubes in the form of multi-cell sandwich tube generally improves the crushing patterns of individual hollow tubes. Moreover, the low-velocity response of the hybrid multi-cell sandwich tubes showed that the crushing response of the GFRP components despite AL ones depends significantly on the strain rate, where Al tubes undergo irregular diamond deformation. Eventually the results of bio-inspired hybrid multi-cell sandwich tubes indicate that incorporating more GFRP tubes provided an optimal crashworthy design and conduce to a broad range of applications within aerospace, transportation.

Inclined composite guardrails/safety barriers – Numerical and experimental evaluation of their transverse stiffnesses and compliance with standards

Three-point flexure and axial torsion tests were undertaken to establish the longitudinal elastic flexural and in-plane shear moduli of pultruded GFRP tubes. They were used to define one-dimensional two-node beam elements for modelling single- and two-bay inclined guardrails with inclinations up to 60°. Subsequently, three-dimensional FE models were developed to analyse more accurately single- and two-bay 30° inclined guardrails. The results from these analyses were compared with those of full-scale load tests on 30° inclined guardrails subjected to transverse normal preload, usability, and ultimate loads applied to the handrails. It is shown that the analysis results based one-dimensional elements significantly underestimate the mean handrail deflections and over-estimate the guardrails’ transverse stiffness. By contrast, using three-dimensional elements in the FE models give more accurate predictions, with mean handrail deflections 9% and 14–16% lower than single- and two-bay test values respectively. The corresponding percentages for mean transverse stiffnesses are 10% and 12.5 – 14.3% higher respectively. It was also observed that the responses of the guardrails were linear, the residual deflections on unloading were less than permitted for the preload, usability and ultimate loads. Furthermore, neither the single- nor the two-bay 30° inclined guardrails sustained any damage.

Structural response of glass fiber reinforced polymer tubes infilled with lightweight aggregate concrete

The purpose of the study is to reduce the self-weight of column using light weight aggregate concrete (LWC). The conventional coarse aggregate in concrete was replaced with Pumice aggregate to achieve LWC (R10, R20, R30, R40, R50). The reduction in density using LWC was noticed. To enhance the structural performance of LWC, cement was partially replaced with Ground Granulated Blast Furnace Slag (GGBFS) and Metakaolin (MK) mineral admixtures. LWC without and with mineral admixtures were cast as columns (UC-NMA, UC-MA). The effect of the confinement was noticed by casting similar mixes as infill in Glass Fiber Polymer Tubes (GFRP- C-NMA, C-MA). The axial load - displacement behaviour was compared for columns. Comparison of the results showed that confinement offered by GFRP tubes has highly enhanced the performance of infilled LWC. Parametric analysis shows that R30-MA was the optimum mix to be used as infill for GFRP tubes, to have enhanced structural performance along with reduced density.

Research on square concrete filled GFRP tube columns strengthened with CFRP sheet

This paper presented a test with 108 squares pultruded concrete filled GFRP tube (CFGT) columns which were used to investigate the behavior of the columns strengthened with CFRP sheet. Categories of failure modes were grouped according to the failure characteristics of these columns under axial compressive loading. Cracks of the four edges in length directions of GFRP tube were effectively confined by CFRP sheet. The ultimate bearing capacity of the columns with CFRP sheet strengthened was greatly higher than that of the columns without the CFRP sheet strengthening. And the ultimate bearing capacity was further increased by increasing the GFRP tube thickness. The ductility coefficient and initial stiffness of the columns were greatly increased because of the strengthening of CFRP sheet. Besides, the strain development of ten square pultruded CFGT columns under axial compressive loading was investigated. Based on the mechanical mode of square pultruded GFRP tube confined by the core concrete and the test result, this paper proposed a calculated formula which was used to predict the ultimate bearing capacity of square pultruded CFGT columns strengthened with CFRP sheet, and a good agreement with the test results was achieved.

The Simple Mix Design Method and Confined Behavior Analysis for Recycled Aggregate Concrete.

For the environment protection and sustainable development in building construction, waste concrete can be processed into recycled aggregate to mix the recycled aggregate concrete (RAC). However, the existing mix design methods of RAC were complex, and the mechanical properties of RAC were more weakened than ordinary concrete. This paper presents a simple mix design method for RAC, including orthogonal test and single-factor test. Then, in order to study the behavior of confined RAC, this paper presents a comprehensive experimental study on the RAC filled in steel tube (RCFST) specimens and the RAC filled in GFRP tube (RCFST) specimens. The results show that the proposed mix design method can mix different stable strength grades of RAC promptly and efficiently. In addition, the steel tube and GFRP tube can provide a well confining effect on core RAC to improve the mechanical behavior of column. Moreover, the properties of core RAC in steel tube are the same as the common passive confined concrete, and the properties of core RAC in the GFRP tube are the same as the common active confined concrete. The study results can provide reference for other kinds of RAC mixtures as well as be a foundation for theoretical studies on confined RAC.

Effect of elevated temperatures on the compressive behavior of timber filled steel and pultruded GFRP tubes

This study examines the use of timber as a filler material for steel and pultruded GFRP tube elements and the performance of these sections is compared to solid timber columns, hollow steel and hollow pultruded GFRP tube element after exposure to elevated temperature. In total, 102 specimens were fabricated and exposure to elevated temperature ranging from 20 to 700 °C was evaluated. It was found out that filled tubes using timber could improve the compressive strength and stiffness of tubular section specimens up to 73 and 212 percent, respectively. Timber filled steel tube (TFST) and hollow steel tube specimens had a better performance at elevated temperature in comparison to other specimens such that they were able to maintain 28 and 44 percent of their compressive strength and axial stiffness at 700 °C. In contrast, timber filled pultruded GFRP tube (TFGT) and hollow pultruded GFRP tube lost more than 25 and 93 percent of their strength and initial stiffness at temperature beyond the glass transition temperature of the resin, 95 °C, and resin decomposition temperature, 288 °C, respectively. Two novel empirical models were developed which accurately predicted the compressive strength and axial stiffness of TFST and TFGT specimens at room and elevated temperature.

Accelerated curing of adhesively bonded G-FRP tube connections — Part I: Experiments

In the wake of the industry-wide trend towards lightweight construction, fibre-reinforced polymers (FRP) gradually established as an alternative to traditional materials. They are used in particular when low weight, high strength or high corrosion resistance is required. For joining FRP components, adhesive bonding is increasingly preferred to mechanical fasteners as poorer transfer of loads resulting from interrupted fibres represents problematic. Despite all the technical advantages, adhesive bonding remains a comparatively slow joining process that is usually bound to limited manufacturing temperatures. This article shows, by means of experimental investigations performed on bonded FRP tubes, that curing by inductive heating of the adhesive bond can compensate for both disadvantages. For that, particles susceptible to electromagnetic fields (EMF) were added to two adhesives, a two component epoxy (2 K-EPX) and polyurethane (2 K-PUR), and the effect thereof on the adhesive was assessed. The particles consisted of Curie material (Curie particles, CP), which relieved all requirements regarding temperature control during the induction process. Subsequently, G-FRP single lap tubular joints (SLTJ) were assembled, cured following different protocols, and subjected to tensile tests. During the process, curing temperatures were monitored using appropriate measuring techniques. Mechanical testing showed that inductively cured SLTJ achieved equal or higher shear strengths, if compared to reference sets cured following the instructions given by the adhesive manufacturers. The results showed that adhesive type as well as curing conditions, in most cases had no significant influence on joint strength, which was verified by means of an analysis of variance. Summing up, inductive heating using CP proved effective in controlling temperatures without any external control, and yielded very high joint strengths with a reduction in curing time by the factor of 100 for the epoxy and 1400 for the polyurethane.