Outer Fiber-reinforced Polymer Tube Research Articles

Seismic behavior of large-scale FRP-recycled aggregate concrete-steel columns with shear connectors

The application of fiber-reinforced polymer (FRP) composites for the development of high-performance composite structural systems has received significant recent research attention. A composite of FRP-recycled aggregate concrete (RAC)-steel column (FRSC), consisting of an outer FRP tube, an inner steel tube and annular RAC filled between two tubes, is proposed herein to facilitate green disposal of demolished concrete and to improve the ductility of concrete columns for earthquake resistance. To better understand the seismic behavior of FRSCs, quasi-static tests of large-scale basalt FRSCs with shear connectors were conducted. The influence of the recycled coarse aggregate (RCA) replacement percentage, shear connectors and axial loading method on the lateral load and deformation capacity, energy dissipation and cumulative damage were analyzed to evaluate the seismic behavior of FRSCs. The test results show that FRSCs have good seismic behavior, which was evidenced by high lateral loads, excellent ductility and energy dissipation capacity, indicating RAC is applicable in FRSCs. Shear connectors can significantly postpone the steel buckling and increase the lateral loads of FRSCs, but weaken the deformation capacity and energy dissipation performance.

Effect of Fiber Angles on Hybrid Double‐Tube Concrete Columns under Monotonic Axial Compression

Hybrid double‐tube concrete columns (hybrid DTCCs) are a novel form of hybrid columns that combine fiber‐reinforced polymer (FRP) composites with two traditional construction materials (i.e., concrete and steel). Hybrid DTCCs consist of an outer FRP tube and an inner steel tube aligned concentrically, with the space between the two tubes and inside of the steel tube filled with concrete. The three materials (i.e., FRP, concrete, and steel) in hybrid DTCCs are combined optimally to deliver excellent performances, such as excellent ductility and remarkable corrosion resistance. Recently, hybrid DTCCs have received increasing research attention on their compressive behavior. Existing studies, however, are focused on hybrid DTCCs with fibers of the FRP tube oriented in the hoop direction or close to the hoop direction. Against this background, this paper presents a series of monotonic axial compression tests on hybrid DTCCs with a particular focus on the effect of fiber angles (i.e., the angle of the fiber orientations to the longitudinal axis of the FRP tube). Three types of fiber angles (i.e., ±45°, ±60°, or ±80°) and two FRP tube thicknesses (i.e., 4 mm and 8 mm) were employed in the present study. Experimental results show that the concrete in hybrid DTCCs is well confined by both the FRP tube and the steel tube, leading to excellent ductility; the confinement effect of the FRP tube increases with the increase of the absolute value of fiber angles, whereas the ultimate axial strain decreases with the increase of the absolute value of fiber angles. An existing analysis‐oriented model, which considers the different confining states of the concrete between the two tubes and that inside of the steel tube, is verified using the present test results. The model is capable of providing accurate predictions for hybrid DTCCs with a ±80° FRP tube. For hybrid DTCCs with a ±45° or ±60° FRP tube, the model yields reasonable accurate predictions for the peak axial load but underestimates the ultimate axial strain consistently.

Numerical Simulation of Hybrid FRP-Concrete-Steel Double-Skin Tubular Columns under Close-Range Blast Loading

Hybrid fiber-reinforced polymer (FRP)-concrete-steel double-skin tubular columns (DSTCs) are a new form of composite columns that consist 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 DSTCs, no studies have been conducted on their behavior under blast loading. This study presents the results of a numerical study on the behavior of hybrid DSTCs under close-in blast loading. Numerical models of hybrid DSTCs are developed using finite-element code LS-DYNA, and the reliability of the developed models are validated with available testing results. With the validated models, numerical simulations are carried out to investigate the structural responses of hybrid DSTCs under blast loading. The simulation results indicate that the hybrid DSTCs behave in a ductile manner under blast loading. The outer FRP tube can effectively provide confinement to the infilled concrete, and the inner steel tube plays a key role in resisting the blast loading. Detailed parametric analyses are conducted to investigate the influences of different parameters on the blast behavior of hybrid DSTCs. The blast resistance capacities of the hybrid DSTCs, concrete-filled steel tubes (CFSTs), and concrete-filled double-skin steel tubes (CFDSTs) are compared and discussed based on the simulation results.

Compressive behavior of double-tube concrete columns with an outer square FRP tube and an inner circular high-strength steel tube

Double-tube concrete columns (DTCCs) are a novel form of hybrid columns which consist of an outer fiber-reinforced polymer (FRP) tube, an inner circular high-strength steel (HSS) tube and the concrete filled in the entire section. In a DTCC, the inner HSS tube not only effectively diminishes the non-uniformity of stress distribution of concrete in a concrete-filled square FRP tube but also enhances the confinement to the core concrete, with its buckling being effectively restrained by the surrounding concrete and the outer FRP tube. This paper presents the results of an experimental study on the axial compressive behavior of DTCCs with an outer square FRP tube. Eight square DTCC specimens were tested under axial compression. The examined column parameters included FRP tube thickness, FRP tube width, and FRP type. The experimental results show that, in square DTCCs, the concrete is well confined by both the FRP tube and the HSS tube, and the buckling of HSS tube is effectively restrained so that its high material strength can be effectively utilized, leading to an excellent column performance. The experimental results also demonstrate that square DTCCs possess considerable post peak strength, indicating excellent ductility and promising application potential of this new form of hybrid column members in earthquake prone zones.

Behavior of Hollow-Core FRP-Concrete-Steel Columns under Static Cyclic Flexural Loading

This paper presents the seismic behavior of hollow-core fiber-reinforced polymer (FRP)-concrete-steel (HC-FCS) columns comparable with the conventional RC column. The typical HC-FCS column consists of a concrete shell sandwiched between an outer FRP tube and an inner steel tube. The HC-FCS column represents a compact engineering system; the steel and FRP tubes act together as stay-in-place formworks. The steel tube acts as a flexural and shear reinforcement. This paper studies three large-scale columns—one RC column having a solid cross section and two HC-FCS columns. Each column has an outer diameter of 610 mm (24 in.) and a shear span-to-diameter ratio of 4.0. The steel tube is embedded into the reinforced concrete footing with an embedded length of 1.6 times the steel tube diameter, whereas the FRP tube only confines the concrete shell and truncates at the top of the footing. The HC-FCS columns exhibits high lateral drift reaching 15.2% and fail gradually due to concrete crushing and local steel tube buckling, followed by FRP rupture. The reference RC column fails at a drift of 10.9% due to rebar fracture. Simple beam theory overpredicts the flexural strength of the columns by an average of 9%.

Compressive Behavior of Double-Skin Tubular Columns with High-Strength Concrete and a Filament-Wound FRP Tube

AbstractHybrid fiber-reinforced polymer (FRP)–concrete–steel double-skin tubular columns (DSTCs) consist of an outer FRP tube and an inner steel tube, with the space between them filled with concre...

Compressive behavior of hybrid double-skin tubular columns with a large rupture strain FRP tube

A hybrid fiber-reinforced polymer (FRP)-concrete-steel double-skin tubular column (DSTC) consists of an outer FRP tube and an inner steel tube, with the space in between filled with concrete. This paper presents results from the first ever experimental study on hybrid DSTCs with a large rupture strain (LRS) FRP tube, namely, polyethylene terephthalate (PET) FRP tube. The experimental program involved the testing of 12 hybrid DSTC specimens with or without additional concrete inside the inner steel tube. The test results confirmed the ample ductility of hybrid DSTCs with a PET-FRP tube despite the severe local buckling of the inner steel tube at large axial deformations. The test results also suggested that the diameter-to-thickness ratio of the inner steel tube is a more critical parameter in such DSTCs than in DSTCs with a glass, carbon or aramid FRP outer tube.

Behavior and modeling of FRP-concrete-steel double-skin tubular columns made of full lightweight aggregate concrete

Fiber-reinforced polymer (FRP)-concrete-steel double-skin tubular column (DSTC) is a new type of composite columns which consist of an outer FRP tube and an inner steel tube, with concrete filled in the space between the two tubes. The composite column can be optimally designed to obtain several advantages over existing forms of columns which include high ductility, excellent corrosion resistance, and what’s more, lightweight due to the hollow cross-section. To give full play to the lightweight potentials of DSTC, the most obvious approach is to reduce the weight of concrete sandwiched between the two tubes. This paper thus develops a new type of DSTCs that is filled with full lightweight aggregate concrete (FLAC) and reports a systematic study on the compression performance of the FLAC-filled DSTCs at the first time. The results indicate that FLAC in between the FRP and steel tubes is effectively confined, resulting in an excellently ductile behavior in compression and that the ultimate strength and strain of FLAC-filled DSTCs are increased by a factor of 1.7 and 3, respectively. The void ratio has limited effect on the ultimate strength of FLAC-filled DSTC while the impact on the ultimate strain is significant. On the basis of the stress-strain model developed for FRP-confined FLAC, a stress-strain model for FLAC-filled DSTC is proposed, which provides a satisfactory agreement with the experimental results.

Structural performance of new fully and partially concrete-filled rectangular FRP-tube beams

This research introduces rectangular partially concrete-filled fiber-reinforced polymer (FRP) tube (CFFT) beams with inner voids and steel rebar. The beams contain an outer rectangular filament-wound FRP tube with an inner hollow circular or square FRP tube shifted toward the tension zone. The flexural behavior of the partially-CFFT beams was compared with a fully-CFFT beam, and another conventional steel-reinforced concrete (RC) beam having identical dimensions and flexural steel reinforcement. The results indicated that, the partially-CFFT beams had an overall strength-to-weight ratio 370% higher than that of the RC beam, while their weight was 30% lighter than the RC beam. In addition, the failure of the partially-CFFT beams was ductile in compression. The inner circular void indicated a slightly better performance than the square void in this partially-CFFT beam. Theoretical-section analysis has been conducted and compared with the experimental results.

Analytical and Finite-Element Modeling of FRP-Concrete-Steel Double-Skin Tubular Columns

AbstractThis paper presents a finite-element (FE) analysis of hybrid fiber-reinforced polymer (FRP)-concrete-steel double-skin tube (FSDT) in the form of columns. The FSDT columns that were examined consisted of a concrete wall sandwiched between an outer FRP tube and an inner steel tube. A FE software was used to develop a pushover analysis of three-dimensional FSDT models to simulate seismic loading. The FE models were validated against the experimental results gathered from seven FSDT columns tested under cyclic loading. The FE analysis results were in good agreement with the experimental backbone curves. The maximum error was 9% in predicting the bending strengths of the columns. A parametric study evaluated the effect of axial load level, concrete wall thickness, concrete strength, diameter-to-thickness ratio (D/t) of the steel tube, and number of FRP layers on the FSDT columns’ behavior. This study revealed that the behavior of FSDT columns is quite complex. It also revealed that this behavior is co...

Behavior of Hybrid FRP-Concrete-Steel Double-Skin Tubular Columns with a Square Outer Tube and a Circular Inner Tube Subjected to Axial Compression

Hybrid fiber-reinforced polymer (FRP) concrete steel, double skin tubular columns (DSTCs) are a new form of hybrid columns. The most common sectional form of hybrid DSTCs consists of a layer of concrete sandwiched between a circular inner steel tube and a circular outer FRP tube whose fiber directions are close to the hoop detection to provide effective confinement to the concrete. Much recent research has been conducted on circular hybrid DSTCs, which has demonstrated that the combination of the three constituent materials leads to several advantages not available with existing forms of columns. In practical applications, for aesthetic and other reasons, square hybrid DSTCs may be needed. This paper thus extends the existing work on circular hybrid DSTCs to square hybrid DSTCs in which the outer FRP tube is square while the inner steel tube is still circular. Results from a series of axial compression tests are presented and interpreted to examine the compressive behavior of square hybrid DSTCs. In these tests, FRP tubes formed through a wet-layup process were used instead of filament-wound FRP tubes because the latter were not readily available to the authors at the time of the study. The test results show that the concrete in these square hybrid DSTCs is effectively confined by the two tubes, and the behavior of the confined concrete is similar to that of concrete in FRP-confined solid columns. A stress-strain model for concrete in square hybrid DSTCs is also proposed and is shown to provide reasonably accurate predictions of the test results.

Stress-Strain Behavior of Concrete in Hybrid FRP-Concrete-Steel Double-Skin Tubular Columns

Hybrid fiber-reinforced polymer (FRP) concrete-steel double-skin tubular columns are a new form of hybrid columns recently proposed by the second writer. The new column consists of an inner steel tube and an outer FRP tube, with the space between them filled with concrete. The new column possesses several advantages over existing columns including excellent ductility and corrosion resistance. This paper first examines the behavior of the confined concrete between the two tubes using a finite-element model to understand the effects of the key parameters including the stiffness of the FRP tube, the stiffness of the steel tube, and the size of the inner void. Based on the available experimental observations and the results from the finite-element model, a simple stress-strain model for the confined concrete is proposed for use in practical design. Comparisons with test results show that the proposed model provides reasonably accurate and conservative predictions.