Glass Fiber-reinforced Polymer Tubes Research Articles

Behavior of hybrid GFRP–perforated-steel tube-encased concrete column under uniaxial compression

This study presents an experimental investigation on concrete confined by glass fiber reinforced polymer (GFRP) and perforated-steel tube subjected to uniaxial compression. The compressive behavior of this hybrid structure is compared with GFRP tube encased concrete and steel tube encased concrete. The three key experimental parameters were investigated: the layers of GFRP tube (1, 2, 3 and 4), the perforation diameter of porous steel tube (5mm and 10mm), and the grid form of perforated steel tube (axial type and helical type). The effects of these parameters on the failure mode, stress–strain relationship and ductility of the specimens were discussed. A simplified design model was proposed for the specimens and the predictions were in good agreement with the experimental results. In addition, the interactive function between steel and GFRP on the confined concrete was analyzed which considered an influence factor provided by these two confinement materials. This study showed that the hybrid GFRP–perforated steel tube exerts the full potential of these two materials, i.e. GFRP with its high tension strength enhanced the loading carrying capacity and the perforated-steel with its high elastoplasticity enhanced the deformation performance in hardening segment, softening branch and residual strength plateau of the concrete, respectively. This study therefore demonstrated that the combination of GFRP and perforated steel tubes is a new effective method to confine concrete.

Hydrostatic Implosion of GFRP Composite Tubes Studied by Digital Image Correlation

The mechanisms and pressure fields associated with the hydrostatic implosion of glass fiber reinforced polymer (GFRP) tubes with varying reinforcement are investigated using high-speed photography. Experiments are conducted in a large pressure vessel, designed to provide constant hydrostatic pressure throughout collapse. Three-dimensional (3D) digital image correlation (DIC) is used to capture full-field displacements, and dynamic pressure transducers measure the pressure pulse generated by the collapse. Results show that braided GFRP tubes release pressure waves with significantly greater impulse upon collapse as compared to filament-wound tubes, increasing their damage potential.

Impact of Tool Inserts in High Speed Machining of GFRP Composite Material

Composite materials are in-homogenous, anisotropic and cause high tool wear at high cutting speeds in machining. Industrial practices worldwide reveal a need to use high speed machining to achieve the desired material removal rate, surface finish and to reduce cost cutting. In this research work, impact of turning glass fibre reinforced polymer tube with two contrasting turning tool inserts such as titanium aluminium nitride and tungsten carbide have been analysed. The turning was conducted at low to high cutting conditions up to spindle speeds of 2000 rpm and feed rate of 0.446mm/rev. The cutting force, feed force were acquired with a strain gauge based dynamometer, the chip cross section was observed using scanning electron microscopy and the temperature was sensed with a infra red thermo sensor. The advanced titanium aluminium nitride insert shows better machining characteristics across cutting speeds.

Harsh environments effects on the axial behaviour of circular concrete-filled fibre reinforced-polymer (FRP) tubes

Concrete-filled fibre-reinforced polymer (FRP) tubes (CFFTs) are becoming an attractive system for structural elements proposed to harsh environments. FRP tube provides a corrosion resistant element, reinforcement, confinement for the concrete core, and a stay-in-place formwork. Harsh environments may affect the mechanical performance of the FRP tube, which consequently affect the structural response of the CFFT members. This project investigates the environmental degradation and the durability of concrete cylinders unconfined and confined by filament-wound glass-FRP tubes. Standard plain concrete cylinders and CFFT cylinders were immersed in pure water, salt and alkaline solutions, and exposed to 200 freeze–thaw cycles, between −40 °C and +40 °C. Then, the cylinders were tested under uniaxial compression test to evaluate their performance by comparing the stress–strain behaviour and their ultimate load capacities. Test results indicated that the FRP tube, in CFFTs, is significantly qualified as a sustainable coating material to resist the harsh environments attacks. Theoretical predictions using long term confinement models from CSA and ACI codes are presented.

Behavior of reinforced concrete-filled GFRP tubes under eccentric compression loading

This paper presents the results of experimental and theoretical study on the behavior of reinforced concrete-filled glass fiber reinforced polymer (GFRP) tubes (RCFFTs) under eccentric compression loading. A total of six RCFFT specimens were tested, the effects of the following parameters were examined: GFRP tube thickness (4.5 and 6.0 mm), longitudinal reinforcement, inserted I-shaped steel, and eccentricity (20 and 40 mm). The results of this investigation indicate that the ultimate load capacity and ductility of the RCFFT specimens are improved in terms of increasing the thickness of the GFRP tube under eccentric load. However, increasing the eccentricity significantly decreases the load capacity of RCFFT specimens. The internal steel bar could enhance the rigidity and loading capacity of RCFFT specimens. Furthermore, ultimate load capacity and ductility of the specimen are increased significantly by inserting shaped steel into concrete filled GFRP tube, Also, the simplified design equations are proposed to predict the ultimate load capacities of RCFFT specimens.

Effects of bonding in short-span rectangular concrete filled GFRP tubes

Flexural performance of concrete-filled tubes is highly dependent on the composite action between the concrete core and encasing tube. This study investigates the performance of short-span concrete-filled rectangular glass fiber reinforced polymer (GFRP) tubes with different levels of bonding between the concrete core and GFRP tube. The bonding configurations include (1) no bonding, (2) bonding of the webs, (3) bonding of the flanges, and (4) bonding of the webs and flanges. The study includes both experimental and finite element analysis results for each configuration. Comparing the performance of each configuration showed a two fold increase in stiffness and strength as a result of bonding between the concrete core and GFRP tube. Furthermore it was concluded that bonding of the flanges was most critical with web bonding providing only a slight increase in performance.

Behaviour of perforated GFRP tubes under axial compression

This study investigates the influences of various parameters on the behaviour of perforated Glass Fibre Reinforced Polymer (GFRP) tubes under axial compression. A total of 15 GFRP tubes with and without perforations were tested under axial compression. All the GFRP tubes were divided into two groups: 12 tubes with 89mm outer diameter and 6mm wall thickness and 3 tubes with 183mm outer diameter and 8mm wall thickness. The influences of hole diameter, vertical hole spacing, tube diameter, perforation pattern, transverse hole spacing, and hole reinforcement on the axial compressive behaviour of perforated GFRP tubes were experimentally investigated. Considerable decreases in the axial stiffness, axial critical load, and axial deformation capacity of perforated GFRP tubes have been observed. The hole diameter, tube diameter, perforation pattern, and transverse hole spacing significantly influence the axial compressive behaviour of perforated GFRP tubes. However, the influences of vertical hole spacing and hole reinforcement have been observed not significant. Design-oriented equations for the prediction of the axial stiffness, axial critical load and axial deformation capacity of perforated GFRP tubes under axial compression have been proposed. The proposed equations have been found to be in good agreement with experimental results and can be used for the reliable design of perforated GFRP tubes.

Behavior of Circular Glass Fiber Reinforced Polymer Tubes Under Axial Compression

This project involves an evaluation of behaviour of circular GFRP tubes under axial compression. Circular tube columns having different length and cross sections resulting in the range of combinations of global and sectional slenderness, were tested under axial load. From this study, the compressive strength, ultimate load and failure modes were determined. After experimental investigation on evaluation of behavior of GFRP tubes, numerical investigation process is started, using ANSYS. Finite element models of the circular tubes will be generated and analyzed using SHELL elements. In this process orthotropic properties has been defined to align the material direction of the composite lay-up and stacking sequence. The experimental results were compared with the analytical results. It includes the parametric study of L/D and D/t ratio of various dimensions and orientation in finite element model. It gives the best orientation angle for the compressive behavior of GFRP tubes

Experimental study on flexural behavior of splicing concrete-filled GFRP tubular composite members connected with steel bars

Based on the experiment, this paper focuses on studying flexural behavior of splicing concrete-filled glass fiber reinforced polymer (GFRP) tubular composite members connected with steel bars. The test results indicated the confinement effects of GFRP tubes on the concrete core in compression zone began to produce, when the load reached about 50%<i>P_u</i> (<i>P_u</i>-ultimate load), but the confinement effects in tensile zone was unobvious. In addition, the failure modes of composite members were influenced by the steel ratio of the joint. For splicing unreinforced composite members, the steel ratio more than 1.96% could satisfy the splicing requirements and the steel ratio 2.94% was ideal comparatively. For splicing reinforced specimen, the bearing capacity of specimen with 3.92% steel ratio was higher 21.4% than specimen with 2.94% steel ratio and the latter was higher 21.2% than the contrast non-splicing specimen, which indicated that the steel ratio more than 2.94% could satisfy the splicing requirements and both splicing ways used in the experiment were feasible. So, the optimal steel ratio 2.94% was suggested economically. The experimental results also indicated that the carrying capacity and ductility of splicing concrete-filled GFRP tubular composite members could be improved by setting internal longitudinal rebars.

Compressive Behavior of Concrete Confined with GFRP Tubes and Steel Spirals

This paper presents the experimental results and analytical modeling of the axial compressive behavior of concrete cylinders confined by both glass fiber-reinforced polymer (GFRP) tube and inner steel spiral reinforcement (SR). The concrete structure is termed as GFRP–SR confined concrete. The number of GFRP layers (1, 2, and 3 layers) and volumetric ratios of SR (1.5% and 3%) were the experimental variables. Test results indicate that both GFRP tube and SR confinement remarkably increase the ultimate compressive strength, energy dissipation capacity, and ductility of concrete. The volumetric ratio of SR has a more pronounced influence on the energy dissipation capacity of confined concrete with more GFRP layers. In addition, a stress–strain model is presented to predict the axial compressive behavior of GFRP–SR confined concrete. Comparisons between the analytical results obtained using the proposed model and experimental results are also presented.

Axial compressive behaviour of GFRP tube reinforced concrete columns

This paper presents an innovative reinforcing scheme for concrete columns using glass fibre reinforced polymer (GFRP) tubes. GFRP tubes (solid and perforated) have been placed into concrete columns to provide reinforcement in both longitudinal and transverse directions. In this study, 14 columns with 150mm diameter and 300mm height have been cast and tested under axial compression. The columns have been divided into seven groups; each group contains two columns. The first group of columns are the reference columns without any reinforcement. The other six groups of columns are reinforced with solid and perforated (axially and diagonally) GFRP tubes. The test results show that GFRP tubes are effective in improving the strength and the ductility capacity of FRP (fibre reinforced polymer) tube reinforced concrete (FTRC) columns. Also, perforated GFRP tubes have been found effective in integrating concrete core with concrete cover. However, axially perforated FTRC columns have been found most effective considering the strength and the ductility capacity of the concrete columns. In addition to the experimental investigations, numerical simulations have been carried out to assess the influence of tube perforations on the behaviour of FTRC columns. The simulation results show that reduction in the hole diameter, rather than increase in the vertical hole spacing, is the most effective in increasing the strength and the ductility capacity of FTRC columns.

Performance of Concrete-Filled FRP Tubes under Field Close-in Blast Loading

AbstractBlasts, whether deliberate or accidental, are a great concern for a society’s critical infrastructure as well as expeditionary military installations. Improvement to existing construction methods that enhance blast resilience can ultimately save lives and property. Concrete-filled FRP tubes (CFFTs) are known to improve a conventional reinforced concrete member’s resistance to traditional loads by strengthening, protecting, and confining the reinforced concrete core. Glass fibre reinforced polymer (GFRP) tubes are readily available in a variety of sizes suitable for use as a stay-in-place structural formwork for midsized reinforced concrete members, which can simplify and expedite construction. These advantages point to CFFTs’ great potential in resisting blast loads. This study aimed to quantify the advantages of encasing a reinforced concrete member with a GFRP tube subjected to close-in blast loading and to investigate the effects of the presence of the tube, the internal steel reinforcement rat...

Optimal design for the mortar-filled glass fibre-reinforced polymer tube dowels

Use of mortar-filled glass fibre-reinforced polymer (GFRP) tubes is considered as an alternative of steel dowel bars in concrete pavement. The mortar-filled GFRP tubes have two major advantages over conventional steel dowels: its stiffness is comparable to that of concrete and it has a high corrosion resistance. In the present study, five different types of mortar, made with different concrete materials and mix proportions, were used to fill up a given GFRP tube. The mechanical properties, such as flexural and shear strength, of these mortar-filled GFRP tubes were investigated. One mortar-filled GFRP tube was then selected and used as dowels in field pavement. The field performance of the mortar-filled GFRP tube dowels was evaluated. The results indicate that the GFRP tube dowels have sufficient load transfer capacity and the overall performance of the GFRP tube dowels is comparable to that of steel dowel.

Composite Action of Concrete-Filled Rectangular GFRP Tubes

AbstractThis paper investigates the composite action and performance of rectangular concrete-filled glass fiber–reinforced polymer (GFRP) tubes in four-point bending. The study compares the performance of three different concrete-filled beam configurations with different levels of adhesive bonding of the concrete core to the GFRP tube. The three different configurations include (1) unbonded, (2) bonding of the flanges, and (3) bonding of the flanges and webs. The results show low composite action for the unbonded beam configuration up to full composite action for the completely bonded beam configuration. An analytical study is presented to provide insight into the failure mechanism for the fully bonded beam configuration and to predict ultimate capacity. For evaluation, the stiffness and strength of the fully bonded concrete-filled GFRP tube considered in this study is compared with a conventional steel reinforced concrete beam, concrete-filled steel tube, and concrete-filled GFRP tube with carbon FRP (CF...

Effect of test parameters on flexural strength of circular fiber-reinforced polymer-confined concrete beams

This paper presents experimental results of a study conducted to investigate the use of filament-wound fiber-reinforced polymer tubes as a stay-in-place structural formwork for concrete beams. The experimental study was carried out on a total of seven concrete-filled fiber-reinforced polymer tube beams of 213 mm diameter and 2000 mm long. Five concrete-filled fiber-reinforced polymer tube beams and two control specimens without tube were tested under four-point bending. One control specimen was reinforced with spiral steel while the other had no transverse reinforcement. The test parameters used in this investigation include the type of internal reinforcement (steel or glass fiber-reinforced polymer bars), the type of transverse reinforcement (spiral-steel or fiber-reinforced polymer tube), fiber-reinforced polymer tube thickness and the concrete compressive strength. The fiber orientations of the tubes were mainly in the hoop direction. The test result indicated that the two control specimens failed in shear; however, using glass fiber-reinforced polymer tubes instead of transverse spiral-steel changed the mode of failure of the five concrete-filled fiber-reinforced polymer tube beams to flexural failure. The experimental cracking moments of the steel and fiber-reinforced polymer-concrete-filled fiber-reinforced polymer tube beams were compared to theoretical predictions provided by North American codes, design guidelines and the available equations in the literature. The test results indicate that the fiber-reinforced polymer tube enhances the crack and ultimate moment capacities of the test specimens, whereas it provides a longitudinal reinforcement in the tension side. In addition, improvement to the crack moment equation is suggested to account for the effect of confinement.

Seismic retrofitting of reinforced concrete frame structures using GFRP-tube-confined-concrete composite braces

This paper presents a new type of structural bracing intended for seismic retrofitting use in framed structures. This special composite brace, termed glass-fiber-reinforced-polymer (GFRP)-tube-confined-concrete composite brace, is comprised of concrete confined by a GFRP tube and an inner steel core for energy dissipation. Together with a contribution from the GFRP-tube confined concrete, the composite brace shows a substantially increased stiffness to control story drift, which is often a preferred feature in seismic retrofitting. An analysis model is established and implemented in a general finite element analysis program — OpenSees, for simulating the load-displacement behavior of the composite brace. Using this model, a parametric study of the hysteretic behavior (energy dissipation, stiffness, ductility and strength) of the composite brace was conducted under static cyclic loading and it was found that the area ratio of steel core to concrete has the greatest influence among all the parameters considered. To demonstrate the application of the composite brace in seismic retrofitting, a three-story nonductile reinforced concrete (RC) frame structure was retrofitted with the composite braces. Pushover analysis and nonlinear time-history analyses of the retrofitted RC frame structure was performed by employing a suite of 20 strong ground motion earthquake records. The analysis results show that the composite braces can effectively reduce the peak seismic responses of the RC frame structure without significantly increasing the base shear demand.

Flexural Performance and Moment Connection of Concrete-Filled GFRP Tube–Encased Steel I-Sections

A hybrid system, concrete-filled fiber-reinforced polymer (FRP) tube (CFFT)-encased steel I-section, is introduced. The embedded steel section enhances flexural strength and stiffness, and provides a pseudoductile behavior. It also facilitates connection of the CFFT member to footings or other members. Phase I of the experimental program addresses the flexural behavior of the system through ten beam specimens, including steel and CFFT control specimens. The glass fiber-reinforced polymer (GFRP) tubes varied in thickness and laminate structure. The steel section enhanced performance considerably, especially pseudoductility, in tubes with cross-ply laminates, in which a significant sustained reserved strength remains stable over large deflections on fracture of the tube. CFFTs with angle-ply tubes showed a considerable inherent ductility on their own, in which case, adding the steel section enhanced strength and stiffness only. Phase II addresses a moment connection through five cantilever tests. The connections consist of steel base plates welded to the steel sections, which are embedded into the CFFT members at various length (Ls)-to-span-length (L) ratios ranging from 0.1 to 1.0. Three distinct failure modes are observed. At (Ls/L) ratios of up to 0.17, premature bond failure occurs. At ratios of 0.17 to 0.47, the CFFT member achieves flexural tension failure of the tube just beyond the free end of the steel section. Beyond a 0.47 ratio, the full plastic hinge capacity is developed at the fixed end. A simple design-oriented model that predicts strengths at the full range of (Ls/L) ratios is developed and validated.

Cyclic Behavior of FRP Concrete Bridge Pier Frames

Concrete-filled fiber-reinforced polymer (FRP) tubes (CFFTs) were initially developed without any internal steel reinforcement as viable alternatives to conventional RC columns in nonseismic regions. Studies have shown that extending CFFT application to seismic regions requires a moderate amount of internal steel reinforcement. To date, cyclic performance of CFFTs as part of a structural frame has not been assessed. This paper describes testing of four one-sixth-scale two-column bents: a control RC, a glass FRP-concrete frame (GFF), a carbon FRP-concrete frame (CFF), and a hybrid glass/carbon FRP-concrete frame (HFF). Each frame was tested under reverse cyclic lateral loading with a constant axial load. Specimen HFF with hybrid FRP tubes demonstrated the highest moment capacity and initial stiffness, with an increase of 200 and 70%, respectively, over the control specimen. Specimen GFF showed no sign of cracking up to a drift ratio of 15% with considerable residual strength, whereas specimen CFF had the least ductility. Glass FRP tubes extended the plastic hinge length of the pier columns to twice that of the control RC frame.

PERFORMANCES OF CONCRETE-FILLED GFRP OR GFRP-STEEL CIRCULAR TUBES SUBJECTED TO FREEZE-THAW CYCLES

This paper presents an experimental investigation of the performances of concrete-filled glass fiber-reinforced polymer (GFRP) and GFRP externally wound steel circular tubes, subjected to freeze-thaw cycles ranging from -18°C to 18°C. The variation in hoop strains of the tubes during the freeze-thaw cycles was monitored by embedded fiber Bragg Grating (FBG) strain sensors in GFRP layers or between GFRP and steel tube. The residual hoop strain after each freeze-thaw cycle indicates the possible degradation of GFRP materials, such as cracks, debonding of GFRP-concrete or GFRP-steel due to mismatch of the coefficient of thermal expansion, as well as water immersion. A synergistic effect of FRP and steel tubes on the confinement of inside concrete was revealed, resulting in well-improved ductility. After 56 freeze-thaw cycles, remarkable degradation were found in the axial strength, modulus, and strain for concrete-filled GFRP tubes. However, the GFRP-steel tube system showed a negligible reduction in the ultimate axial strain by the freeze-thaw cycles with less degradation in the axial strength and modulus.

Long-Term Performance of GFRP Tubes Filled with Concrete and Subjected to Salt Solution

AbstractThis paper presents mechanical, microstructural, and physical characterization of aged glass fiber-reinforced polymer (GFRP) tubes used in the concrete-filled fiber-reinforced polymer (FRP) tube (CFFT) system for bridge columns and marine pile applications, or used hollow as tubular poles or in pipelines. The main objective of the study is to evaluate the durability and predict the long-term behavior of the filament-wound GFRP tubes. CFFTs were exposed to salt solution at 23, 40, and 50°C for 365 days to accelerate the environmental effect. Given the significance of confinement in a CFFT system, the measured hoop tensile strength of the tube before and after exposure was considered the primary indicator of durability performance of the specimens. In addition, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM) were used to characterize the aging effect on GFRP tubes. Test results showed that the GFRP tubes investigated in ...