Fiber Reinforced Polymer Tubes Research Articles

Compressive behavior of rectangular concrete-filled fiber-reinforced polymer and steel composite tube columns with stress-release grooves

To investigate the behavior of rectangular concrete-filled fiber-reinforced polymer (FRP) and steel composite tube (CFCT) columns with stress-release grooves under axial compression, sixty specimens were fabricated and divided into five groups for axial compression testing. The main variables were the corner radius, the number of FRP layers, the steel tube thickness and the presence of stress-release grooves. The test results indicate that steel tubes and FRPs can complement each other and discontinuous steel tubes can provide an effective confinement force on in-filled concrete. The stress–strain responses of CFCT columns with stress-release grooves consist of a linear elastic stage, a nonlinear transition stage, a linear hardening stage and a residual stage. The ultimate strength of a CFCT column is in direct proportion to the number of FRP layers, the thickness of the steel tube and the value of the corner radius. Stress-release grooves only play a positive role in specimens with relatively large values of the corner radii (r ≥ 30 mm). A new model was suggested for calculating the ultimate stress of CFCT columns with stress-release grooves. The model is applicable for CFCT and concrete-filled steel tube (CFT) specimens with stress-release grooves; the predicted results agree well with the experimental statistics.

Axial compressive behaviour of circular FRP-confined multi-tube concrete columns

A new form of hybrid structural column that has improved corrosion resistance and that can enhance the compressive strength and ultimate strain of concrete is the fibre-reinforced polymer (FRP)-confined multi-tube concrete column (MTCC) system. Existing research on MTCCs has been limited to glass FRP (GFRP) outer tubes with internal steel tubes and normal-strength concrete. This paper reports an experimental study on 22 circular MTCCs that are loaded under monotonic axial compression. Five main column parameters are investigated, namely internal tube material, internal tube configuration, concrete strength, fibre type, and FRP tube thickness. The test results show the excellent structural behaviour of MTCCs for both the normal- and high-strength concretes. The MTCCs with internal steel tubes outperformed those with aluminium internal tubes in terms of load carrying capacity. MTCCs confined with basalt FRP and GFRP jackets both performed well, while an increasing of FRP thickness improved the ultimate strength and axial strain capacity of the column. An analytical model based on the transformed section approach is also used to predict the axial load-strain behaviour of the MTCC specimens. The model provides satisfactory predictions of the test results.

Performance of Circular Concrete-Filled FRP-Grooved Steel Composite Tube Columns under Axial Compression.

A new structure termed “concrete-filled FRP-grooved steel composite tube (CFGCT) column” is proposed, which is composed of a stress-released steel tube (i.e., grooved steel tube), fiber-reinforced polymer (FRP) and concrete. Axial load tests were carried out on twenty-four specimens to investigate the constraint effect of this structure. Three main experimental variables were considered: the steel tube thickness, the FRP type, and the FRP layer. The failure modes, stress-strain relationships and the effect of the main experimental variables were discussed. The stress-strain curves of this new structure are composed of an initial linear part, a nonlinear transition part, a strengthening part and a residual part. The test results demonstrate that the bearing capacity of the structure was improved, and that the mechanical mechanism of the structure was simplified due to the stress-released grooves. Based on the test results and previous studies, formulas for calculating the ultimate stress (fcu), ultimate strain (εcu), peak stress (fcc) and peak strain (εcc) were proposed. In addition, models for predicting the stress-strain curves of CFGCT columns were put forward, and the models could precisely simulate the stress-strain curve of this new composite structure. Hence, this study indicates that a structure composed of FRP and stress-released steel tube can effectively constrain concrete.

Efficient second-order nonlinear finite-element simulation of concrete-filled FRP tubular arches

Concrete-filled fiber-reinforced polymer (FRP) tubes (CFFTs) are attractive as beams and arches in harsh environments due to their durability and ease of erection. A successful infrastructure application is the use of multiple, buried CFFT arches in short-span bridges. To effectively analyze and design CFFT arches under complex loadings, there is a need for numerical procedures that capture the structural behavior of CFFT arches including the effects of FRP confinement on the concrete core and second-order response. Here, a computationally efficient structural finite-element analysis technique for the second-order inelastic behavior of these CFFT arches is detailed. A curved, flexibility-based, layered-frame element is employed to handle geometric and material nonlinearities. A concrete constitutive model that explicitly considers the effect of dilation of the concrete core and confinement provided by the FRP tube is implemented. A bending test was performed on a CFFT arch, and experimental data compared with model predictions. Additional comparisons are made with CFFT arch and beam bending tests available in the literature. The model is shown to accurately predict the load-carrying capacity and ductility of CFFT members, and to capture arch collapse mechanisms arising from FRP rupture and concrete crushing.

Behavior of FRP-confined FRP spiral reinforced concrete square columns (FCFRCs) under axial compression

Fiber-reinforced polymer (FRP) confinement has been demonstrated to be efficient in enhancing the deformation and strength capacities of concrete, while Polyethylene terephthalate (PET) FRP-confined concrete easily exhibits a strain-softening stress-strain behavior, especially for PET FRP-confined concrete in square columns. In this study, novel PET FRP-confined FRP spiral reinforced concrete square columns (FCFRSCs) are proposed. Capitalizing the benefits of internal FRP spiral reinforcement, the strain-softening behavior of PET FRP-confined concrete is expected to be alleviated, leading to excellent mechanical performance of the proposed square columns. The axial compressive behavior of FCFRSCs, as well as square concrete-filled PET FRP tube columns (CFFTs) and FRP reinforced concrete columns (FRCs) as reference columns, were investigated via experimentation. The experimental results show that the strain softening behavior of confined concrete in FCFRSCs has been substantially enhanced with the internal FRP reinforcement, confirming the viability of the system. The strain softening behavior of FRP-confined concrete after the first peak is prevented and a hardening behavior is achieved for concrete in FCFRSCs, especially when the GFRP spiral pitch is 30 mm.

Stress–Strain Behavior of FRP-Confined Recycled Aggregate Concrete in Square Columns of Different Sizes

The application of recycled aggregate concrete (RAC) has so far mainly been limited to nonstructural components because of its inferior short- and long-term performance compared with normal concrete. Encasement of RAC with a fiber-reinforced polymer (FRP) tube has been demonstrated to be an effective technique to improve both the mechanical properties and durability of RAC. A number of studies have been carried out on FRP-confined RAC in circular columns. However, only a limited number of studies have examined the behavior of FRP-confined RAC in rectangular columns, and the existing test specimens were all small-scale. Existing studies have shown that there may exist a significant behavioral difference between small- and large-scale FRP-confined rectangular concrete columns (i.e., column size effect). Against this background, a first-ever experimental study on glass FRP (GFRP)-confined square RAC columns of three different sectional widths ranging from 200 to 400 mm was conducted and the results are presented in this paper. The same FRP confinement stiffness was adopted for the columns of different sizes so that the possible column size effect could be examined. The test results showed that the size effect indeed existed in the test FRP-confined square RAC columns and the presence of recycled aggregate amplified such effect. The size effect should be considered in the design of such columns especially when the coarse aggregate replacement ratio is relatively large. The accuracies of three existing strength models for FRP-confined normal concrete in square columns were also evaluated using the test results.

Structural Performance of Concrete-Filled GFRP Tube Slender Columns in Ambient and Standard Fire Conditions

Abstract Concrete-filled glass fiber-reinforced polymer (GFRP) tube (CFFT) columns benefit from significant concrete confinement effects that enhance its structural performance compared to conventi...

Additive Fabrication of Large-Scale Customizable Formwork Using Robotic Fiber-Reinforced Polymer Winding.

Based on the established system of concrete-filled fiber-reinforced polymer (FRP) tube (CFFT) in civil engineering and construction industry, this research presents a novel fabrication method for freeform FRP formwork through an additive process of winding FRP fabric with industrial robots. Different from the filament winding or fused deposition modeling process in additive manufacture, large-scale formwork is fabricated with layered winding of FRP fabric and simultaneously applying fast cure epoxy resin in the proposed methods. It increases the fabrication speed and material efficiency compared with the typical fabrication process of FRP formworks, and achieved the geometry flexibility from the numerically controlled additive process. The fabrication methods are developed through a series of preliminary tests, exploring the appropriate fabrication parameters, such as the overlapping height of each layer, winding speed, and epoxy resin type. Two additional prototypes addressing geometrical flexibility are also fabricated. Based on the feasibility studies, the article discussed the potential application of this system on a double-skin tubular arch (DSTA) bridge and a tree-like topological optimized column as the future outlook of this method. As developed based on the established construction systems such as CFFTs and DSTAs, not only the proposed system is compatible with current structure and construction system, but it also benefits from combining an off-shelf material with a flexible and accurate programmable robotic process. This research contributes to the scope of additive manufacturing system by targeting the fabrication of nonuniform optimized large-scale structures.

Experimental investigation of a simple shear connection to concrete-filled FRP tube (CFFT) columns

The concrete-filled fiber-reinforced polymer (FRP) tube (CFFT) system has been widely studied as a robust alternative to conventional reinforced concrete (RC) for column construction. Despite the superior structural performance of this column system in terms of durability, strength and ductility, its application in building construction is limited due to a lack of viable designs for beams-to-column connections. To address this gap, this study proposes a simple connection for a circular CFFT column and a steel I-shape beam. The connection consists of a curved end plate with a shear tab that is attached to the finished CFFT using commercially available concrete anchors. In this study, three connection assemblies with adhesive and expansion anchors were tested under half-cyclic loading. The connection assemblies varied based on the type of the anchors and installation torque. The performance was evaluated in terms of ease of construction, shear capacity, moment-rotation relationship, and observable damage. The FRP shell eliminated concrete breakout failure and the anchors exceeded the theoretical pullout capacity noted by the manufacturer. A methodology for estimating the proof load of the proposed connection detail is presented. The proposed connection provides a viable option for simple connection of steel beams to circular CFFT columns. The findings may inform future research on beam-column connections for CFFTs and lead to an increased use of CFFT systems in building construction.

The effects of elevated temperatures on the performance of concrete-filled pultruded GFRP tubular columns

Usage of concrete-filled pultruded glass fiber-reinforced polymer (GFRP) tubes (CFPGT) as columns can increase the service life of structures. However, marine structures such as oil platforms are always prone to fire because of the low resistance to the elevated temperatures. The purpose of this investigation is to evaluate the effects of concrete core strength (30 and 60 MPa), and exposure temperature (25, 100, 200, 300, and 400 °C) and time (60 and 120 min) on the compressive and bond behavior of CFPGTs. The properties of unexposed and exposed concrete core, pultruded GFRP hollow tubes, and CFPGTs were determined via compressive and disk-split tests. Also, the push-out test was used to measure bond–slip strength of partially-filled samples. The results showed that the maximum load-bearing capacity of the exposed stub columns at temperatures 100, 200, 300, and 400 °C was 8%, 22%, 34%, and 51% lower than that of the unexposed columns, respectively. Regardless of exposure conditions and the core strength, the pultruded GFRP tubes resisted about one fourth of the total load-bearing capacity. Moreover, it was observed that the ultimate axial strain (the strain corresponding to tube rupture) of column specimens was reduced with increase in concrete core strength and exposure temperature; however, the exposure time had insignificant effect on the ultimate axial strain. Dilation and load-bearing capacity of CFPGTs were considered to propose new models for predicting the experimental results. Concerning the bond strength tests, it was concluded that the exposure temperature increment led to the interlocking and coefficient of kinetic friction increase, resulting in higher bond strength. Finally, expressions were presented to estimate the bond strength of CFPGTs after exposure to elevated temperatures.

Behaviour of square concrete filled FRP tube columns under concentric, uniaxial eccentric, biaxial eccentric and four-point bending loads

This study investigated the behaviour of short square concrete filled fibre reinforced polymer tube specimens under concentric, uniaxial eccentric, biaxial eccentric and four-point bending loads. Seven concrete filled glass fibre reinforced polymer (GFRP) tube specimens (GFRP-CFFT) and seven traditional steel bar reinforced concrete (steel-RC) specimens of 200 mm x 200 mm cross-section were tested. The GFRP-CFFT specimens obtained a larger P-M interaction surface (higher maximum axial loads and higher bending moments) than the steel-RC specimens. In addition, the GFRP-CFFT specimens exhibited a lower average reduction in ductility under eccentric axial loads than the steel-RC specimens.

Numerical Modelling Of Glass Fibre Reinforced Polymer (Gfrp) Tube Subjected To Torsion

Glass Fibre Reinforced Polymer (GFRP) tubes have been used widely as cross arm of electric transmission towers to replaced old wooden cross arms. Cross arm is a part of transmission tower which is required to support conductors or electrical cables. Due to nature of assembly of these GFRP tubes, it will induce torsional force to the individual GFRP tubes of cross arm. The importance of torsional effect to the cross arm has encouraged researcher to study on torsional strength of the single tube itself in order to support a complete set cross arm. In this paper, the performance of glass fiber-reinforced polymer (GFRP) tubes under statically torsional loads was studied numerically. The specimens’ ultimate twisting angle and strain were studied through tests for validation of the numerical model. Explicit solver of ANSYS was chosen and simulation results matched experiment results well with 4 % different. There are six model were simulated and analyzed in this research. It is concluded that model 4 shown the highest ultimate strains as well as twisting angle while model 3 has the lowest ultimate strains and twisting angle. The presence of fiber orientation of 90o in model 4 has contributed to the torsional capacity of the tubes.

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.

Compressive behavior of ultra-high performance concrete confined with FRP

This paper presents an experimental study on the compressive behavior of ultra-high performance concrete (UHPC) confined with fiber-reinforced polymer (FRP) composites. A total of 18 cylindrical specimens were prepared from UHPC containing 2.5% of micro steel fibers by volume, among which 6 were unconfined and 12 were confined with carbon FRP (CFRP). They were tested to investigate the experimental compressive behavior of unconfined or CFRP-confined UHPC. The external confinement was provided by two to six plies of CFRP wraps with the confinement ratio ranging from 0.11 to 0.54. The test results obtained from this study were presented and compared with those from existing studies on unconfined and FRP-confined UHPC specimens in the form of concrete-filled FRP tubes or FRP-wrapped cylinders. Predictive equations were proposed for the compressive strength and ultimate strain of FRP-confined UHPC, based on the interpretation of test results from the present study and from the existing literature. An existing stress–strain model for FRP-confined conventional concrete has been recalibrated for FRP-confined UHPC. While the recalibrated model predicted the test results of FRP-confined UHPC reasonably well, the inadequacy of a parabolic curve for describing the stress–strain relationship of unconfined UHPC is noticed, as a result of the higher strength and more brittle behaviour of UHPC in compression.

Compound concrete-filled FRP tubular columns under cyclic axial compression

The direct use of large pieces of crushed demolition concrete (referred to as recycled concrete lumps or RCLs) for mixing with fresh concrete to create a new kind of recycled concrete (referred to as compound concrete), has obvious advantages in terms of recycling efficiency, cost-effectiveness and maximum recycling ratio compared with the recycling of concrete as aggregates. Existing research has revealed certain performance concerns with such compound concrete, including reductions in strength and durability, due to the presence of RCLs. The confinement of compound concrete with an external fiber-reinforced polymer (FRP) confining tube has recently been explored as an effective technique to improve its mechanical properties and durability. This paper presents the results of the first ever experimental study on compound concrete filled FRP tubular (CCFFT) columns aimed at the understanding and modelling of the cyclic stress–strain behavior of FRP-confined compound concrete. The effects of RCL mix ratio, FRP tube thickness, and loading scheme are examined. A monotonic stress–strain model and two cyclic stress–strain models previously developed for FRP-confined normal concrete are used to predict the test results. It is shown that the inclusion of RCLs has a marginal effect on the cyclic stress–strain behavior of FRP-confined concrete.

Flax FRP tube and steel spiral dual-confined recycled aggregate concrete: Experimental and analytical studies

Using fibre reinforced polymer (FRP) tube as outer confining material of recycled aggregate concrete (RAC) column improved its compressive strength and deformation capacity although the RAC core still behaved in a brittle failure manner. To achieve a ductile failure mode of RAC core in compression, outer flax FRP tube (FFRP) and inner steel spiral reinforcement (SR) were used in this study to confine the RAC cylinders, i.e., to form an FFRP tube-SR-confined RAC column, which is shortened as FFRP-SR-RAC. To evaluate the effects of spacing of the inner steel spiral (i.e., 25 and 50 mm), strength of RAC (i.e., 26.3 and 33.7 MPa), and the FFRP tube thickness (i.e., 3, 6 and 9 layers of FFRP) on the compressive behaviour of FFRP-SR-RAC, 36 concrete cylinders were constructed and tested in uniaxial compression. The test results indicated that comparing with unconfined RAC or FFRP tube confined RAC cylinders, the FFRP-SR-RAC specimens possessed higher compressive strength and failed in a ductile manner. When the number of FFRP layer increased and the spacing of SR decreased, the FFRP-SR-RAC cylinder gained more pronounced enhancement in the compressive strength. Based on the experimental results, stress and ultimate strain models were developed to predict the axial compressive behaviour of FFRP-SR-RAC in uniaxial compression.

Interfacial behavior of segmental concrete-filled Basalt FRP tube under compression

The joint in a segmental concrete-filled fiber-reinforced-polymer (FRP) tube deteriorates the confining strength at the interfacial section. To quantitatively investigate the interfacial load-carrying capacity and deformability of segmental concrete-filled FRP tube, this study experimentally investigated segmental concrete-filled Basalt-FRP tube (SCFBT) specimens under compression. The stirrup at the interface was considered as the main parameter and was expected to compensate for the confining strength. The SCFBT specimens underwent sudden brittle failure caused by the rapture of the Basalt FRP (BFRP) tube. The rapture was always initiated at the interface, where the confining stiffness and strength were reduced. The confined strength of the concrete in the SCFBT deteriorated owing to the discontinuous BFRP tube. However, an adequate amount of stirrup could compensate for and enhance the confining strength. With the interface, the deformability increased owing to the delayed rapture of the BFRP tube. Based on the test results, a modified confined SCFBT model was developed with consideration to supplementary stirrup.

Simulating the passive confinement of circular concrete cylinders allowing for size effect

ABSTRACT There are innumerable tests on small stocky circular cylinders with either internal passive encasement of the concrete with circular stirrups or spirals, or external passive encasement through fibre-reinforced polymer (FRP) wrapping or through the use of FRP tubes or steel tubes. These tests have shown that passive confinement can increase the strength but, in particular, can substantially increase the ductility of concrete cylinders. Because of these important benefits, the effect of passive confinement on the concrete stress/strain in a particular cylinder section is invariably derived from tests such that substantial member testing is required. In this paper, it is shown how the passive stress/strain of the concrete for a particular circular member can theoretically be determined directly from their partial-interaction shear-friction and partial-interaction bond-slip material properties for any reinforcement arrangement and geometry of the circular cylinder. This procedure provides tools for designing for the benefits of passive confinement directly without the need for member testing.

Dynamic responses of hybrid FRP-concrete-steel double-skin tubular column (DSTC) under lateral impact

Hybrid fibre-reinforced polymer (FRP)-concrete-steel double-skin tubular column (DSTC) is a new form of composite column that consists of an outer FRP tube and an inner steel tube, with the space between them filled with concrete. Although many studies have been conducted on the hybrid DSTC, studies on its lateral impact behaviour are very limited. This study numerically investigates the dynamic responses of hybrid DSTC under lateral impact. Numerical models of the hybrid DSTCs were developed and validated with existing test results. Afterwards, the dynamic responses, including the deflection-time histories and the force–time histories, were analysed. Specifically, the bending moment and shear force distributions at typical cross sections were discussed, and the impact resistance (shear and flexure) from each component (FRP tube, concrete, and steel tube) was investigated. The results indicate that the hybrid DSTC exhibits ductile behaviour under lateral impact. Even though the FRP tube cannot contribute to the impact resistance directly, it can greatly improve the impact resistance of the concrete. Moreover, parametric analyses were conducted to investigate the influences of different parameters on the lateral impact resistance of hybrid DSTC. Finally, simplified design-oriented equations were developed to predict the dynamic flexural capacity of hybrid DSTC.

Axial compressive behavior of FRP-concrete-steel double skin tubular columns with a rib-stiffened Q690 steel tube and ultra-high strength concrete

Fiber-reinforced polymer (FRP)-concrete-steel double skin tubular columns (DSTCs), which possess an outer FRP tube, an inner steel tube and sandwiched concrete between both tubes, are a kind of hybrid column with a particular merit of lightweight. It is expected that using high-strength materials (i.e., ultra-high strength concrete (UHSC) and high-strength steel (HSS) tubes) in DSTCs magnifies the merit of DSTCs. This paper presents an experimental study on axial compression behavior of DSTCs with ultra-high strength concrete and a rib-stiffened Q690 steel tube. The rib-stiffened steel tubes, which are less susceptible to local buckling compared with those without stiffeners, were used in the present study. The parameters including the quantity of stiffeners, the length of stiffeners, the FRP tube thickness, the steel tube diameter and the concrete strength were carefully designed and investigated through the experimental study. The test results demonstrate that DSTCs with UHSC and HSS tubes exhibit a ductile behavior and the axial load-axial strain curves exhibit an ascending-descending-ascending-failure behavior. Additionally, the stiffeners are beneficial in enhancing the performance of DSTCs. The comparisons between the test results and theoretical results show that the existing model of Yu et al. is inaccurate in predicting the ultimate axial stress and the ultimate axial strain of HSC and UHSC in DSTCs.