Fiber Reinforced Polymer Tubes Research Articles

Compressive Strength Testing of Hybrid Concrete-Filled Fiber-Reinforced Plastic Tubes Confined by Filament Winding

In this study, an experiment on compressive strength of the hybrid concrete-filled fiber-reinforced polymer (FRP) tube (CFFT) confined by filament winding was conducted to improve the longitudinal strength while considering the thickness of filament winding as a variable. A maximum error of 17% was observed when the results of performing the finite element analysis (FEA) by applying the mechanical properties of the fiber-reinforced polymer (FRP) materials suggested in previous studies were compared to those of the compressive strength experiment on the hybrid-CFFT. Moreover, a maximum error of 15% was exhibited when the results derived from the strength equation proposed by analyzing the compressive strength experiment were compared. Furthermore, the compressive strength of the hybrid-CFFT increased by up to 14% when the longitudinal compressive strength of the pre-tensioned spun high strength concrete (PHC) pile and concrete-filled tube (CFT) were compared.

Ultimate Limit Design of Strengthened Steel Columns by Mortar-Filled FRP Tubes

The present study investigated the various failure modes of strengthened steel columns by mortar-filled fiber-reinforced polymer (FRP) tubes to analytically formulate the ultimate capacities of these steel columns. A simple and effective method, wherein a mortar-filled FRP tube was sleeved outside the steel member, was also formulated to enhance the buckling resistance capacity of compressed steel members. In addition, to facilitate the connection of the column to other structural members, the length of the sleeved mortar-filled FRP tubes is less than that of the original steel columns. Theoretical analyses were also performed on the critical sections of such composite columns at their ultimate states to identify their potential failure modes, such as FRP-tube splitting at the ends or on the insides of wrapped areas, local buckling at the steel ends of transition zones, and global buckling of the composite columns. The corresponding ultimate capacity of each failure mode was then analytically formulated to characterize the critical failure mode and ultimate load capacity of the columns. The current theoretical results were compared with those from literature to validate the applicability of the developed ultimate limit design approaches for FRP-mortar-steel composite columns.

Axial compressive behavior of ultra-high-strength steel fiber-reinforced concrete-filled fiber reinforced polymer (FRP) tube columns

This study presents the results of the first experimental research on the axial compressive behavior of ultra-high-strength steel (UHSS) fiber reinforced concrete-filled FRP tubes (UHSSFR-CFFT). 24 circular UHSSFR-CFFT specimens were prepared and tested under axial compression to study the influence of unconfined concrete strength and fiber type. CFFTs were manufactured with glass, carbon and basalt reinforced polymer (GFRP, CFRP and BFRP) tubes with concrete compressive strengths (f′co) ranging from 35 to 105 MPa. Axial and lateral behavior were examined closely, including variation of lateral behavior along height of specimen. The results showed that the influence of concrete compressive strength on axial compressive behavior of UHSSFR-CFFTs is dependent on fiber type. For a similar normalized lateral confining pressure of FRP jacket at ultimate (flu/f′co), axial stress enhancement ratios (k1) were observed to decrease with an increase in f′co for all three fiber types. On the other hand, the obtained axial strain enhancement ratios (k2) indicated that k2 is influenced more by flu/f′co than f′co. Comparison of the recorded values of k1 and k2 for UHSSFR-CFFT with FRP-confined plain concrete showed similar trends on the influence of (f′co) on k1, but an opposite trend was observed for k2 of BFRP-confined specimens of the current study, in which k2 increased with increasing f′co. The results showed that the shape of the lateral strain-to-axial strain curves for UHSSFR CFRP- and BFRP-confined concrete specimens were similar to those of FRP-confined plain concrete, and this relationship was not influenced noticeably by f′co. Conversely, the obtained shape of the lateral strain-to-axial strain curves for UHSSFR GFRP-confined specimens was noticeably different when compared to FRP-confined plain concrete, with this behavior influenced by f′co. Finally, the results indicated that the addition of UHSS fibers in CFRP-confined specimens did not alter the influence of f′co on strain reduction factor (kɛ) where a decrease was observed by increasing f′co. However, the converse outcome was observed for GFRP- and BFRP-confined specimens where an increase in kɛ was observed when increasing f′co.

Flexural Behavior of Post-Tensioned Normal- and High- Strength Concrete-Filled Fiber-Reinforced Polymer Tubes

Flexural Behavior of Post-Tensioned Normal- and High- Strength Concrete-Filled Fiber-Reinforced Polymer Tubes

Torsional Behavior of Circular Concrete-Filled FRP Tubes

Abstract Concrete-filled fiber-reinforced polymer (FRP) tubes (CFFTs) have been studied extensively under almost all loading conditions, except torsion. In this pioneering study, six 168-mm-diamete...

A New Torsion Testing Apparatus for Circular Members

The concrete-filled fiber-reinforced polymer tube (CFFT) is a unique structural element that is well suited for reinforced concrete applications in harsh environments due to the corrosion-resistant reinforcement. It also benefits from the stay-in-place formwork capabilities of the reinforcement and the beneficial concrete confinement offered primarily in cases of axial compression. The strength and response of the CFFT system have been studied under axial, flexural, and combined loading conditions; however, its torsional behavior has not been evaluated. Some of the challenges have been the ability to provide successful gripping of the circular cross-section as well as avoiding the undesired second-order effects when pure torsion is investigated. This paper presents a novel apparatus developed to test circular members, including CFFTs, to failure under a variety of loading conditions including pure torsion, and combined torsion, bending, and axial compression. The apparatus can accommodate a complex set of geometric nonlinearity effects associated with the deformations arising from multiple degrees of freedom. The functionality of the testing system under a state of pure torsion and combined loading was verified. The results showed that the testing apparatus effectively simulated the intended loading condition. The samples experience relatively large and complex displacements that justified the details incorporated in the design of various components of the testing configuration.

Confinement of Concrete by Fiber Reinforced Polymer Tube: A Review

Researchers studied a lot of strengthening techniques of concrete, one of which is the technology of concrete confinement. This technique is common to utilize fiber fabric impregnated with epoxy resin adhesive. Relevant applications mainly include strengthening the existing structure and new structural construction. This paper presents a review of previous studies on the confinement of concrete using fiber-reinforced polymer (FRP) tubes. Four main parameters were investigated in this study: the number of layers of FRP tubes, cross-sectional shape and slenderness ratio, material types of FRP tubes, and concrete types. The results of the investigation showed that increasing the number of FRP tubes resulting in a significant improvement in the behavior of confined specimens, circular cross-section specimens exhibited better behavior than square. Also, the behavior of confined square specimens improvement with increasing the angular radius. A carbon fiber reinforced polymer tube is better than (aramid, glass, and basalt) fibers. Finally, the concrete confining technique significantly improved the behavior of specimens regardless of the type of concrete confined, and the effect of confining decreases with the increase of compressive strength of the concrete confined.

Standing support incorporating FRP and high water-content material for underground space

The integrity and stability of underground space mainly depend upon the coordination of primary and secondary support system. This paper presents a novel secondary standing support system, termed fibre-reinforced polymer (FRP)-confined high-water content cementitious grout material column (FCCM), being an alternative structural form for underground space. The attractive feature of the FCCM is its exterior container made of FRP composite with high strength-to-weight ratio and high corrosion resistance. A total of 30 FCCM specimens were prepared and tested to demonstrate its expected structural behaviour under compression. The critical parameters covered the type and the thickness of FRP tube as well as the strength of infill material. Test results verified that the cementitious grout material in the FCCM was effectively confined by the exterior FRP tube, resulting in the significant enhancement of load carrying capacity and deformation ability. The test results also indicated that the water expulsion of confined cementitious grout material may be the other reason for the superior compressive behaviour of FCCMs. The strain hardening FCCM with large axial deformation is particularly suitable for these underground spaces where the integrity and corrosion are the main concerns.

Simulating the passive confinement of rectangular concrete prisms allowing for size effect

Tests have shown that providing passive confinement to concrete, either through the use of internal stirrups, external fibre-reinforced polymer (FRP) wraps, FRP tubes or steel tubes, can increase the concrete strength and, in particular, the concrete ductility, thereby allowing greater absorption of energy and consequently ductile failure. The problem of including the benefits of passive confinement in design is in generalising the effect of passive confinement because it varies with the member size, the configuration of the confining reinforcement and material properties. In this paper, all aspects of the complex fundamental mechanics of passive concrete confinement are explained both qualitatively and quantitatively through the use of shear–friction and bond–slip mechanics. The mechanics model was found to have a good correlation with test results. An analysis-oriented procedure is described for quantifying the passive stress–strain of concrete for rectangular sections and it is envisaged that this can be used to develop simplified rules for design, in particular for new types of members and those with new materials.

Interfacial behavior of segmental concrete-filled Basalt FRP tube under cyclic loading

A segmental concrete-filled basalt fiber-reinforced polymer (BFRP) tube was proposed, whose lightweight characteristic promoted convenient bridge column transportation and construction. A special connecting component between the adjacent BFRP segments ensured effective transfer of sectional forces. Four specimens, including three segmental specimens and one comparative integral concrete-filled BFRP tube, were tested to investigate the mechanical performance of the BFRP tube under cyclic loading. Damage patterns, load-deformation response, and strain development were observed, showing that the segmental concrete-filled BFRP tube presented satisfactory load-carrying and deformation capacities. Further, the connecting component effectively guaranteed a satisfactory hysteretic performance. Based on the test results, the overall load-carrying capacity was mainly determined by the moment resistance of the interface. Furthermore, the segmental structure weakened the confining effect on the core concrete, though applying multiple stirrups could compensate for the reduced confining effect. Finally, design methods were proposed for the connecting component.

Mechanical behaviors of GFRP tube confined recycled aggregate concrete with sea sand

An experimental program was undertaken to study the mechanical behaviors of glass fiber-reinforced polymer (GFRP) tube confined recycled aggregate concrete with sea sand (GRACSS) under the axial compression. Two different parameters were mainly considered: recycled coarse aggregates (RCA) replacement percentage (0, 100%) and type of sand (sea sand, river sand). Typical influences of RCA and sea sand on the strength, the deformation and the load–deformation curve of GRACSS were investigated. The test results showed that the failure pattern of GRACSS was similar to that of GFRP tube confined ordinary concrete (GCOC). The strength of GRACSS decreased with an increasing RCA replacement percentage, while sea sand could reduce the negative effect of RCA. It is also found that the peak deformation of GRACSS increased with the increasing RCA replacement percentage whereas with decreasing sea sand chloride ion (Cl–) content. The stiffness of the specimen was obviously influenced by the concrete type. Research findings indicated that the axial load-deformation curve of GRACSS can be divided into elastic-plastic and hardening stages. An analytical expression was proposed to calculate the load-deformation curve of GRACSS. Finally, the finite element method (FEM) was applied to study the effects of outer tube thickness, concrete strength, RCA replacement percentage and Cl– content in sea sand on the mechanical behaviors (strength and deformation) of GRACSS.

Circular fibre-reinforced polymer (FRP)-concrete-steel hybrid multitube concrete columns: Compressive behaviour

This paper presents a study on circular fibre-reinforced polymer (FRP)-concrete-steel hybrid multitube concrete columns (MTCCs), which consists of an outer FRP tube, a number of inner small steel tubes to form a “steel wall” and concrete filled in the remaining spaces. The advantages of MTCCs include excellent axial load and deformation capacities, ease of construction, elimination/mitigation of difficulties in transporting and installing large steel tubes, and possibility of optimising the arrangement of the small steel tubes to improve structural performance. A total of 7 pairs of MTCCs, 4 pairs of concrete-filled FRP tubes (CFFTs), 4 pairs of concrete-filled steel walls (CFSWs) and 3 pairs of concrete-filled steel tubes (CFSTs) were tested in the present study, with the investigated parameters covering the thickness of FRP tube, the number and type of steel inner tubes, the type of concrete and status of the steel inner tubes. The test results lead to an in-depth understanding of the behaviour of MTCCs under axial compression. Furthermore, a comparison between the test results and predictions by a model previously proposed by the authors shows that the model can reasonably well predict the axial load–strain behaviour of MTCCs but largely underestimates the ultimate strain of the specimen. This model may be used for conservative design, while further investigation is needed for the development of a more accurate model.

Behavior and modelling of FRP-concrete-steel hybrid double-skin tubular columns under repeated unloading/reloading cycles

Fiber-reinforced polymer (FRP)-concrete-steel hybrid double-skin tubular columns (hybrid DSTCs) consist of an outer FRP tube, an inner steel tube and a concrete infill between the two tubes. Extensive research has been conducted on the monotonic behavior of hybrid DSTCs, but only a limited number of studies have examined their behavior under cyclic axial compression. In particular, no systematic experimental study has been conducted on hybrid DSTCs under repeated unloading/reloading cycles. This paper first presents a systematic experimental study on hybrid DSTCs under two types of loading schemes: (a) a single unloading/reloading cycle to evaluate the relationship between the unloading strain and the plastic strain; (b) repeated unloading/reloading cycles to investigate the effect of loading history. In the present study, hybrid DSTCs were prepared using filament-wound FRP tubes of a relatively large scale (up to 300 mm in diameter), and the experimental program covered a wide range of concrete strengths (from 40.9 MPa to 104.4 MPa). The systematic experimental study with extensive instrumentation allowed the cyclic stress-strain behavior of the concrete in hybrid DSTCs to be examined in detail, clarifying the cumulative effect of the loading history on both the stress deterioration and the plastic strain of the concrete. This paper also presents a detailed comparison between the test results and the predictions of an existing cyclic stress-strain model for FRP-confined concrete in solid columns, in terms of the repeated unloading/reloading cycles. The cyclic stress-strain model is shown to provide reasonably accurate predictions, and thus can be used together with a monotonic stress-stress model for the concrete in hybrid DSTCs to predict the complete cyclic stress-strain curve of such concrete.

Behavior of Large-Scale Hybrid FRP-Concrete-Steel Multitube Concrete Columns under Axial Compression

Abstract The combined use of a fiber-reinforced polymer (FRP) tube with steel and concrete to form hybrid structural members has attracted increasing research attention. Hybrid FRP-concrete-steel m...

Confinement of concrete in double skin tubular members under axial compression loads

A hybrid double-skin tubular members (DSTM) consist of three composite materials in one section, include fiber-reinforced polymer (FRP) tube outward, steel tube inward and concrete is in between. These three materials give the member unique properties like protect member from harsh environment, reduce the amount of concrete by the presence of an inner steel tube that allowed the passage of services. Therefore, consider sustainable structure elements, as well as the rising strengthening of members and excellent corrosion resistance. This paper presents an experimental and analytical study of twenty-four circular columns with two types; concrete-filled FRP tube (CFFT) and double skin tubular column (DSTC), with a dimension of 100 × 310 mm which constructed and testing under an axial compressive load till failure, with four variables: numbers of layers of outer FRP tube, the compressive strength of concrete, thickness to diameter ratio and void ratio of inner steel tube. The experimental results showed that the concrete was effected confinement in hybrid DSTC led to very ductile behavior of stress–strain relationship and the number of outer FRP layers was the most effective parameters on DSTCs behavior. The nominal confinement ratio was affected by the thickness of outer FRP tube and compressive strength of concrete inside DSTCs.

Advances in coral aggregate concrete and its combination with FRP: A state-of-the-art review

As an economical and eco-friendly construction material, coral aggregate concrete (CAC) plays an increasingly important role in emerging marine engineering applications. CAC fully utilizes local raw materials on remote islands. Due to the porous structure and low-strength characteristics of coral aggregates, CAC exhibits unique characteristics compared to ordinary concrete. This paper presents a state-of-the-art review of the properties of CAC, including (1) the physical properties of coral aggregates; (2) the mechanical properties of CAC under uniaxial and multiaxial compression; and (3) the durability of CAC especially its chloride ion resistance and performance under drying-wetting cycles. To overcome the challenges of steel corrosion in marine environments, fiber-reinforced polymer (FRP) has been indicated to be a promising material for applications in CAC construction. The latest studies on the combination of FRP and CAC are reviewed, including the use of FRP tubes and bars.

Behaviour of FRP-confined coal rejects based backfill material under compression

This paper introduces a novel standing support incorporating fibre-reinforced polymer (FRP), termed FRP tubular standing support (FTSS). The exterior container of FTSS is the small rupture strain (SRS) GFRP tube wrapped with ultra-high molecular weight polyethylene (UHMWPE) FRP jacket with large rupture strain (LRS), while the infill is the coal rejects based backfill material (CBM). The CBM is made of industrial by-product (i.e. coal rejects) and high flowable cementitious grout material, leading to some environmental and economic benefits when it is used in underground mines. Test variables included the type of coal rejects (i.e. screened and unscreened), the thickness of SRS FRP tube (i.e. 1.5 mm and 3.0 mm) as well as the thickness of LRS FRP jacket (i.e. 2-ply, 3-ply and 4-ply). Test results showed that both the load carrying capacity and deformation ability of CBM in FTSS have been significantly enhanced attributed to the confinement provided by exterior FRP container. Existing stress–strain model for FRP-confined normal concrete can be used to reasonably predict the compressive behaviour of confined CBM in FTSS with large deformation ability. The ductile FTSS is suitable for underground spaces and infrastructures where the integrity of structure is the main concern.

Experimental and analytical investigations of the flexural behavior of hollow ±55° filament wound GFRP tubes

The behavior of ±55° filament wound glass fiber-reinforced polymer (GFRP) tubes under flexural loading was examined experimentally and analytically. A total of 15 tubes were tested under four-point bending. The main test parameter was the ratio of inner diameter (D) to wall thickness (t), (D/t) ratio. The inner diameters of the tubes were 76 and 203 mm, while their wall thicknesses varied from 1.7 to 6.7 mm, giving D/t ratios of 20–75. All tests exhibited a nonlinear load-deflection response and a similar failure mechanism, namely a progressive tensile weakening until a sudden compression failure occurs. The tests showed that the moment capacity of the tubes increased with both tube diameter and nominal pressure rating. The tubes also exhibited a prolonged post-peak behavior. An iterative cross-sectional analytical technique was developed to model both the moment-curvature and load-deflection behavior of the tubes. The model accounts for the potential failure due to local buckling as well as compression failure and was shown to accurately predict the behavior of the tubes. A parametric study was performed to find the moment capacity of tubes with ratios beyond the range tested and was used to establish a simple design equation for moment capacity.

Stress-strain behavior of FRP-confined concrete containing recycled concrete lumps

A novel method to recycle concrete is to crush demolition concrete into large pieces and then to directly mix the resulting recycled concrete lumps (RCLs) with fresh concrete to produce a new kind of recycled concrete referred to as “compound concrete”. This method avoids the complexity of recycling concrete into aggregates and enables the achievement of a higher recycling ratio and a lower recycling cost. However, due to the large sizes of RCLs and the weak interfaces between fresh concrete and RCLs, compound concrete is much more heterogeneous than normal concrete. A new technique has recently been explored to improve the properties of such compound concrete, in which the compound concrete is provided with a substantial amount of confinement from an external fiber-reinforced polymer (FRP) confining tube. This paper presents the results of an experimental program of axial compression tests on compound concrete-filled FRP tubular columns in which the FRP tubes were prefabricated using the wet lay-up method with fibers only in the hoop direction. The tubes had a negligible axial stiffness, which allows the stress-strain behavior of FRP-confined compound concrete to be clearly revealed. The test results show that, when a significant level of FRP confinement is provided, the behavior of FRP-confined compound concrete is similar to that of FRP-confined normal concrete with a strength equal to that of the fresh concrete. An existing stress-strain model previously developed for FRP-confined normal concrete is evaluated in the paper using the test results of FRP-confined compound concrete.

Polyethylene terephthalate fibre-reinforced polymer-confined concrete encased high-strength steel tube hybrid square columns: Axial compression tests

Polyethylene terephthalate (PET) fibre-reinforced polymer (FRP) composites are an emerging form of composites based on recycled PET fibres and have a large rupture strain. A novel form of hybrid columns with PET FRP tubes, i.e., square PET FRP-confined concrete encased high-strength steel (HSS) hybrid columns (referred to as PET FRP-confined concrete-steel columns or PFCCSCs), was recently proposed. The compressive behaviour of circular FCCSCs has been investigated, but there is no research on the compressive behaviour of square PFCCSCs (SPFCCSCs). In SPFCCSCs, the inner HSS tube is expected to be effective in decreasing the confinement nonuniformity in FRP-confined square columns and enhancing the ultimate axial strain and compressive strength of the core concrete. Furthermore, the axial strength of the inner HSS tube is expected to be sufficiently utilized because its buckling is delayed due to confinement from the surrounding concrete. In total, fourteen columnar specimens were tested under monotonic or cyclic axial compression, and the effects of key parameters (i.e., the steel tube yield stress and loading patterns) were investigated. The test results demonstrate that the inward and outward buckling of the inner steel tube in SPFCCSCs can be effectively suppressed or delayed by the surrounding concrete, which was well confined by the PET FRP tube. The compressive strength of a hybrid column is approximately 20% higher than the simple summation of the corresponding strengths of an FRP-confined concrete section and an HSS tube section due to the optimal combination of the three components in the hybrid columns. The SPFCCSCs with a PET FRP tube exhibit a monotonically ascending load-strain response with excellent ductility, which is of particular interest for applications in seismic engineering and underground engineering. The loading scheme has a marginal effect on the load-strain envelope response of SPFCCSCs.