Double-skin Tubular Columns Research Articles

Development of Circular Multicell Double-Skin Tubular Columns: Testing and Improved Axial Performance

Development of Circular Multicell Double-Skin Tubular Columns: Testing and Improved Axial Performance

Axial compressive behavior of hybrid CFRP-concrete-steel double-skin tubular columns

This paper investigates the axial compressive behavior of hybrid carbon fiber reinforced polymer (CFRP)-concrete-steel double-skin tubular columns (DSTCs) under core cross-section loading. A total of 18 DSTCs are tested, comprising 9 stub columns and 9 long columns. The thickness and fiber winding direction of the CFRP tube, hollow ratio, and slenderness ratio are compared. The impact of these factors is examined on failure modes, ultimate strength, and ductility of DSTCs. The tested results indicate that the failure modes of DSTCs are correlated with the fiber winding direction of the CFRP tube. Concrete confined by CFRP tubes with a fiber winding direction at 90° demonstrates minimal damage. The ultimate load of DSTCs is enhanced by increasing the thickness of CFRP tubes, whereas it is negatively influenced by both the hollow ratio and slenderness ratio. The ductility of DSTCs improves as the thickness of CFRP tubes and the hollow ratio increase. Additionally, the established FEA is utilized for stress analysis as well as parametric study of DSTC columns. The results show that the thickness of CFRP tubes, the modulus of elasticity in the circumferential direction of CFRP tubes, the slenderness ratio, and the hollow ratio have a greater effect on the axial compressive performance of DSTC long columns. The strength of concrete, the strength and thickness of steel tubes have less influence on the axial compressive performance of DSTC long columns. Typical FRP-confined concrete models are utilized to validate the axial ultimate strength. A new stability coefficient is recommended to improve the precision.

Residual Load-Carrying Capacity of Hybrid FRP-UHPC-Steel Double-Skin Tubular Column after Lateral Impact

Residual Load-Carrying Capacity of Hybrid FRP-UHPC-Steel Double-Skin Tubular Column after Lateral Impact

Durability Assessment of Hybrid Double-Skin Tubular Columns under Wet–Dry Cyclic Environments

Durability Assessment of Hybrid Double-Skin Tubular Columns under Wet–Dry Cyclic Environments

The performance of waste glass aggregate concrete GFRP-steel double-skin tubular columns under axial compression: Experimental study

In an attempt to alleviate the problem of growing waste glass and fully utilize the excellent material properties of fiber-reinforced polymer (FRP), a novel composite structure, waste glass aggregate concrete glass fiber reinforced polymer (GFRP)-steel double-skin tubular column (WGAC-DSTC), was proposed based on the FRP-concrete-steel double-skin tubular column (DSTC). In the present research, eight WGAC-DSTCs and four waste glass aggregate concrete-filled GFRP tubular columns (WGAC-CFFTs) were investigated to explore their mechanical performance under axial compression. Effects of diverse replacement ratio of waste glass aggregate, GFRP tube thickness, and hollow ratio of column on the mechanical performance of twelve columns were investigated. Meanwhile, this research analyzed and discussed the failure characteristics of columns, load-displacement relationship, ductility coefficient, stiffness coefficient, parameter analysis, ultimate bearing capacity, load-strain relationship and constraint factor. Besides, predicted formulae for estimating the ultimate bearing capacity of WGAC-CFFTs and WGAC-DSTCs were proposed. The research results indicated that (1) Failure mode of the WGAC-DSTCs displayed axial compression failure or shear failure and failure mode of WGAC-CFFTs exhibited mainly axial compression failure; (2) WGAC-DSTCs with 10 % replacement ratio of waste glass aggregate and hollow ratio of 0.4 indicated an increase in the ultimate bearing capacity by 17.24 % and 45.78 %, respectively, as the GFRP tube thickness increased from 1.5 mm to 2 mm and 3 mm. As the column's hollow ratio enhanced from 0.27 to 0.68, the column's ultimate bearing capacity significantly decreased by 7.08 %-60.55 %. The ultimate bearing capacity of WGAC-CFFTs showed a trend of first increasing by 8.33 %-9.41 % but then decreasing by 1.52 % when the replacement ratio of waste glass aggregate rose from 0 % to 30 %; (3) WGAC could replace natural aggregate concrete in traditional DSTC and the bearing capacity could be guaranteed. Besides, it's recommended to utilize 20 % replacement ratio of waste glass aggregate for the WGAC-DSTC whose ultimate bearing capacity enhanced by 15.17 % and possessing optimal mechanical performance; (4) The results calculated utilizing predicted formulae matched well with results of experiment. The application of waste glass aggregate concrete in DSTC can contribute to economic growth and environmental protection and meet the concept of sustainable development.

Machine learning and nonlinear finite element analysis of fiber‐reinforced polymer‐confined concrete‐steel double‐skin tubular columns under axial compression

AbstractFiber‐reinforced polymer (FRP)‐confined double‐skin tubular columns (DSTCs) are an innovative type of hybrid columns that consist of an outer tube made of FRP, an inner circular steel tube, and a concrete core sandwiched between them. Available literature focuses on hollow DSTCs with limited research on DSTCs made with inner steel tubes filled with concrete. Overall, DSTCs have many applications, highlighting the importance of studying the effects of concrete filling and strength on the composite system. To address this gap, finite element models (FEMs) and both traditional and innovative machine learning (ML) techniques were used to develop accurate models for predicting load‐bearing capacity and confined ultimate strain under axial loads. A comprehensive database of 60 experimental tests and 45 FEMs simulations of columns was analyzed, with five parameters selected as input variables for ML‐based models. New techniques like gradient boosting (GB), random forest (RF), convolutional neural networks, and long short‐term memory are compared with established algorithms like multiple linear regression, support vector regression (SVR), and empirical mode decomposition (EMD)‐SVR. Regression error characteristics curve, Shapley Additive Explanation analysis, and statistical metrics are used to assess the performance of these models using a database containing 105 FEMs test results that cover a range of input variables. While EMD‐SVR and GB perform well for confined ultimate strain, the suggested EMD‐SVR, GB, and RF models show superior predictive accuracy for confined ultimate load. To be more precise, for confined ultimate load prediction, EMD‐SVR, GB, and RF obtain values of 0.99, 0.989, and 0.960, respectively. The values for GB and EMD‐SVR at confined ultimate strain are 0.690 and 0.99, respectively. However, design engineers are limited by the “black‐box” nature of ML. In order to solve this, the study presents an open‐source GUI based on GB, which gives engineers the ability to precisely estimate confined ultimate load and strain under various test conditions, enabling them to make well‐informed decisions about mix proportion.

Ultimate strength and design of CFDST columns with intermittent welded plate stiffeners

This study conducts an experimental investigation and formulates a finite element model and design equation to determine the ultimate strength of concrete-filled double-skin tubular (CFDST) short columns. These columns are equipped with intermittent welded plate stiffeners, and the welding is performed on the inner surface of the outer tube through pre-drilled holes at intervals of 10 t, 20 t, 30 t, and 40 t, where “t” represents the thickness of the outer tube. The study investigates the behaviour of the CFDST column influenced by the presence of plate stiffeners, determines the axial strength of eighteen CFDST specimens and discusses the load-displacement curve, deformation and ultimate strength. The findings demonstrated that the ultimate load of the plate-stiffened CFDST columns is between 24% and 42% higher than the unstiffened CFDST columns. The plate-stiffened CFDST columns also exhibited higher ultimate strength at the smallest weld spacing of 10 t. The experimental results showed that the plate stiffeners influenced the distribution of the internal forces, which changed the effective confinement area of the concrete. The investigated force distribution provides a fundamental theoretical basis for computing the confinement area for the finite element model (FEM) and design model. This study developed a verified nonlinear FEM that employed ABAQUS to replicate the behaviour of the plate-stiffened CFDST columns. Finally, this study proposes a new design model that considers the effective cross-sectional area of the concrete confined in CFDST columns with intermittent welded plate stiffeners. The strength predictions of the plate-stiffened CFDST columns were accurate compared to the experimental results.

Performance of RC double skin tubular column confined with UPVC pipe under axial compression

Performance of RC double skin tubular column confined with UPVC pipe under axial compression

Machine-learning-based predictive models for concrete-filled double skin tubular columns

This paper aims to develop a unique artificial neural network (ANN)-based equation as well as MATLAB- and Python-based graphical user interfaces (GUIs) using the most comprehensive and up-to-date database for predicting the behaviour of axially loaded concrete-filled double skin tubular (CFDST) short and slender columns with normal- and high-strength materials. Two machine learning (ML) methods, which are ANN and extreme gradient boosting (XGBoost), are trained and tested using 1721 sets of data, with 129 of them collected from experimental studies and 1592 generated by finite element (FE) simulations. The accuracy of the developed ML models is assessed through comparing their predictions with the experimental and FE results. To demonstrate the effect of each parameter on the predicted results, the SHapley Additive exPlanations (SHAP) method is used. The developed ML models are also used to conduct parametric studies to examine the effect of geometric and material parameters on the predicted results. The accuracy of the ML models and the proposed ANN-based equation in predicting the ultimate axial capacity of CFDST columns is compared with that of six design methods including two design code provisions and four design equations proposed by researchers. A numerical example is presented to illustrate the design procedure of the CFDST column using the proposed ANN-based equation. The results indicate that the ANN model performs better on unseen data than the XGBoost model with lower root mean square error for the test set. The results also show that the ML models and the proposed ANN-based equation are superior to the other design models in prediction accuracy.

Durability assessment of hybrid double-skin tubular columns (DSTCs) under simulated marine environments

Fiber-reinforced polymer (FRP)-concrete-steel hybrid double-skin tubular columns (hybrid DSTCs), consisting of an outer FRP tube, an inner steel tube, and concrete infill between them, are a relatively new structural system. Despite DSTCs being proven to have enhanced structural capabilities over traditional concrete columns, their durability in aggressive environments remains unclear. This study presents a durability assessment of hybrid DSTCs with a glass fiber-reinforced polymer (GFRP) tube. Hybrid DSTCs were immersed in artificial seawater at different temperatures (i.e., room temperature, 40 °C, and 60 °C) for a duration of up to 540 days. The time-dependent behaviors, including axial load-strain (axial and hoop) curves, compressive strength, and ultimate axial and hoop strain, are systematically investigated at different aging times. Test results reveal that the compressive strength of DSTCs exhibits a slight reduction at room temperature and 40 °C, while an obvious reduction is observed at 60 °C. After 540 days, the compressive strengths for hybrid DSTCs with 3-mm-thick and 6-mm-thick GFRP tubes reduce to 79% and 93%, respectively. A decrease in strength is notable for DSTCs with a 3-mm-thick GFRP tube at 60 ℃. The degradation of GFRP tubes is also observed via scanning electron microscope (SEM) analysis, with greater degradation observed in 3 mm-thick GFRP tubes compared to the 6 mm-thick counterparts.

Load–Displacement Behaviour and a Parametric Study of Hybrid Rubberised Concrete Double-Skin Tubular Columns

Rubberised concrete has emerged as a material of interest to the research community with the mission of creating sustainable structural members and decreasing the burden of waste tyre rubber. The potential benefits of replacing natural aggregates with rubber particles to obtain greater energy absorption and ductility are proven in the literature. To negate the reduction in capacity due to the addition of rubber particles, single- and double-skin confinements were proposed and successfully tested by researchers. Hybrid rubberised double-skin tubular columns (RuDSTCs) were recently trialled and tested by the authors. Each of these hybrid RuDSTCs had a filament-wound carbon fibre-reinforced polymer (CFRP) outer tube and an inner steel tube with rubberised concrete as the sandwich material between the two tubes. To explore the axial behaviour of such a column, this paper develops a finite element modelling strategy and carries out a comprehensive parametric study of the hybrid RuDSTC with 0%, 15%, and 30% combined aggregates replaced with rubber particles. This methodology is validated by experimental results, and a good agreement is found. Hybrid RuDSTC models are developed in four groups with different material and geometric parameters, in addition to those corresponding to the experimentally tested column, to explore the effects of the thickness ratio, hollow ratio, steel tube yield strength, and CFRP tube diameter with a special focus on the transition of the characteristic bilinear stress–strain curve of the hybrid RuDSTCs. The results show the smooth transition of the stress–strain curve with increasing rubber content after the yielding of steel, which indicates better ductility of the rubberised columns. The novel hybrid RuDSTCs can provide a promising sustainable solution with greater capacity compared with their unconfined counterparts. Better strain and enhanced ductility of the hybrid RuDSTCs compared with non-rubberized hybrid DSTCs enable their use in seismic-prone regions and mining infrastructure.

Influence of cyclic loading on lightweight self-compacting concrete double-skin tubular columns

Self-compacting concrete (SCC) has gained prominence in recent decades due to its inherent qualities, particularly its ability to compact autonomously. SCC proves invaluable in scenarios where traditional compaction is challenging due to placement conditions or the presence of close space reinforcement. This study focuses on evaluating the structural performance of lightweight self-compacting concrete (LWSCC) columns confined with glass fiber-reinforced polymer (GFRP) and steel tube (ST) subjected to cyclic loading. The LWSCC columns, denoted as LWSTC, are designed with inner steel tubes and outer GFRP tubes, imparting corrosion resistance and reduced weight alongside enhanced ductility. Through quasi-static loading, five fabricated LWSTC columns were subjected to assess their structural response under dynamic effects. The investigation delves into three key variables: axial load ratio, reinforcement ratio, and the replacement ratio of coarse lightweight expanded clay aggregate (LECA) in the fabricated LWSTC columns. A comprehensive analysis of various parameters, including skeleton curves, ductility, hysteretic cycles, damage modes, dissipation of energy capacity, stiffness behavior, strain spreading, and strength reduction, was conducted on the LWSTC columns. The findings reveal that the replacement of LECA with natural aggregates has an insignificant impact, whereas varying the axial load ratio significantly influences the structural behavior of LWSTC. Notably, LWSTC exhibits a remarkable 121% higher horizontal load capacity compared to counterparts using natural aggregate. Furthermore, LWSTC demonstrates superior axial strength and enhanced capability for energy dissipation.

Seismic performance of GFRP-rubberized concrete-steel hybrid solid columns

The application of structured rubberized concrete offers an effective solution for recycling rubber tires. This paper proposes a novel GFRP-rubberized concrete-steel hybrid solid columns (GRSRC), which combines rubberized concrete with circular FRP-concrete-steel double-skin tubular columns (DSTCs). Quasi-static tests were carried out on 7 GRSRC specimens to investigate the influence of rubber contents, steel tube diameters, and axial load ratios on their seismic performance. The test results indicate that the GRSRC has excellent ductility, lateral displacement capacity, and energy dissipation capacity. The GRSRC exhibits slow strength degradation at large lateral displacements due to the double-tube confinement effect. Using rubberized concrete with a rubber content of 20% as a replacement for ordinary concrete has little impact on the seismic performance of the specimens. When the rubber content reaches 40%, the seismic performance decreases significantly. Furthermore, its lateral load-bearing capacity, energy dissipation capacity, and deformation capacity are also reduced with the decreasing diameter of the steel tube, resulting in brittle damage. Increasing the axial load ratio enhances the stiffness, lateral load-bearing capacity, and energy dissipation capacity but may reduce ductility, deformation capacity, and hysteretic performance. Finally, a simplified model of GRSRC restoring force is established and validated, providing a theoretical basis for practical engineering applications.

FRP-concrete-steel tubular columns with a large inner void under lateral impact loading: Experimental study and finite-element modelling

By combining two concentrically placed tubes (i.e., an FRP tube as the external sheath and a steel tube as the inner reinforcement) and a sandwiched concrete layer, FRP-concrete-steel double-skin tubular columns (DSTCs for short) are an attractive type of hollow-core columns suitable for bridge piers working in humid and corrosive environments. The very limited experimental studies on DSTCs under impact loading had one or two of the following limitations: (1) the void ratio φ was far smaller than the size with practical engineering value; (2) the column diameter Dc was too small compared with the section size used in real engineering. To supplement the existing research, DSTCs with a large inner void and a practical large column diameter (i.e., φ = 0.73 and 0.82; Dc = 300 mm) were experimentally investigated subjected to lateral impact loading, with particular research attentions on parameters including the impact velocity, the boundary conditions, as well as the void ratio of the DSTC specimen. Test results indicated that: (1) the failure mechanism was primarily controlled by the boundary condition; a bending-dominant failure mode was observed for the DSTC specimen with the top end free and the bottom end fixed; in contrast, a small global lateral displacement and severe localized dent deformation was observed for the DSTC specimen with the top end simply-supported and the bottom end fixed; (2) the peak impact force, the impact duration as well as the residual lateral displacement had a positive correlation trend with the impact velocity; (3) a DSTC specimen with a larger void ratio had a lower peak impact force and a smaller global lateral displacement. Finite element model based on ANSYS/LS-DYNA was employed to simulate DSTCs subjected to lateral impact loading, which could yield results with reasonable accuracy.

Calculation of axial compression performance and bearing capacity of hollow sandwich glass fiber-reinforced polymer-concrete-steel double-skin tubular column

To evaluate the axial compressive performance of the hollow sandwich GFRP-concrete-steel double-skin tubular columns (DSTC), 15 composite column specimens were produced to study the effect of various design variables. And the study presents a rational and accurate finite element (FE) model that provides a detailed working mechanism of the DSTCs, leading to the enrichment of parametric research and the creation of an extensive database. Based upon the unified strength theory of double shear, limit equilibrium theory, and superposition theory, the study evaluates and compares the effectiveness of different bearing capacity calculation models. With each added millimeter in the thickness of the GFRP tube, the ultimate bearing capacity of the DSTC specimen increased by 23.6% and 61.8%, respectively, compared to that of the 1.5 mm thick GFRP tube sample. The lower the hollow ratio of the DSTC section, the higher its ultimate bearing capacity. Specimens with a hollow ratio of 0.3 and 0.43 showed an ultimate bearing capacity 1.4 times and 1.25 times higher, respectively, than those with a hollow ratio of 0.6. The study observes a relatively high level of precision in the results of the ultimate equilibrium theory, with an average error rate of 20%.

Cyclic axial compressive performance of hybrid double-skin tubular square columns

This paper presents an experimental study on the cyclic axial compressive behavior of FRP-concrete-steel hybrid double-skin tubular columns. The square column specimens were cast with an external Fiber Reinforced Polymer jackets, inner steel tube and concrete in between. The height of the columns was 500 mm and the side dimension was 150 mm. The effects of loading scheme, void ratio and diameter-thickness ratio on axial compression behavior were investigated. A total of eight columns were tested under monotonic and cyclic axial compression. The experimental results show that the effect of loading scheme on axial stress-strain envelope curve and the peak load were not significant, and the ultimate state of the square columns subjected to cyclic axial compression was very similar to that of specimens subjected to monotonic axial compression. Besides, compared with void ratio, the diameter-thickness ratio of the inner steel tube has significant influence on the peak load of the columns when subjected to cyclic axial compression.

Experimental behavior of concrete-filled double-skin tubular columns with outer galvanized corrugated steel tubes under axial compression

Twelve lightweight and corrosion-resistant concrete-filled double-skin tubular (CFDST) columns with outer galvanized corrugated steel tubes (CSTs) and inner flat carbon steel tubes were subjected to monotonic axial compression tests. Compared to a traditional CFDST column, a CFDST column with a CST as the outer tube can reduce the longitudinal stress transmitted by the steel and better provide hoop confinement for the sandwiched concrete. The key parameters were the hollow ratio (χ) and inner tube thickness (ti). The failure mode, axial load capacity, strain and ductility of specimens with different parameters were analysed. There was noticeable slippage at the lock seam of the CST under axial loading, which releases the CST and results in the relatively low strength and ductility of the specimens. Keeping other parameters constant, an increase in χ and a decrease in ti led to a reduction in the peak load (Nu), strength index (SI) and ultimate strain (εcc). On the other hand, the ductility index (DI) increased as χ and ti increased. The strain development of the outer CST in one corrugation period was nonuniform. The hoop strain (εho) dominated at the crest of the CST, while the vertical strain (εvo) dominated at the trough. εvo gradually decreased from the trough to the crest, whereas εho increased from the trough to the crest. The applicability of the current standard design code formulae and axial load capacity equations for circular CFDST columns was evaluated using a newly expanded database, and a satisfactory axial load capacity model for circular CFDST columns with outer CSTs was proposed.

Axial compressive behavior of GFRP tube-reinforced concrete-steel double skin tubular columns

Hybrid FRP-reinforced concrete-steel double-skin tubular columns (DSTCs) exhibit the benefits of high bearing capacity, sufficient ductility and excellent durability. However, there are fewer studies on reinforced DSTCs under axial compression compared to unreinforced DSTCs. Eleven circular cross-section columns were tested to study the compressive behavior of GFRP-reinforced concrete-DSTCs. The main parameters considered were the thicknesses of GFRP tubes, longitudinal reinforcement ratio, hollow ratio and concrete strength. The test results showed that reinforced DSTCs had higher bearing capacity and better ductility than traditional DSTCs, and their bearing capacity could be increased by 36%–48%. The bearing capacity and initial stiffness increased with the increase of longitudinal reinforcement ratio, thicknesses of GFRP tubes and concrete strength, while they decreased with the increase of hollow ratio. When the load was within the range of 55%Pu, the restriction of the GFRP tube to the concrete was not obvious. Furthermore, an analytical model was established to predict the full load-strain curves of reinforced DSTCs, which considered the restraining effect of stirrups and the bi-axial stress state of FRP tube. The established model was in good agreement with most of the test results.

Influence of GFRP Confining Tube Parameters in Double-Skin Tubular Short Columns under Axial Loading

Abstract Composite construction with steel and concrete has become a widespread solution in modern construction practices because of its inherent properties such as high strength-to-weight ratio, good corrosion resistance, and high stiffness. Concrete-filled fiber-reinforced polymer (FRP) steel double-skin tubular compression members as vertical load–carrying members in buildings helps in optimizing the advantages of three materials: steel, concrete, and FRP. This study investigates the axial compressive behavior of short, concrete-filled glass fiber–reinforced polymer (GFRP) steel double-skin tubular (GSDST) columns and concrete-filled GFRP tubular (CFFT) columns. Parameters such as the number of FRP layers, hollow section ratio (HSR), variation of diameter of the inner steel tube, and the angle of orientation of the fibers have been examined in this investigation. The experimental study was carried out by performing a monotonic axial compressive loading condition. Three different angles of fiber orientation, 0° along the hoop direction, 45°, and 0°/90° with respect to the axis of the column, were adopted in this study. The ultimate load-carrying capacity, axial displacement, axial and horizontal strains, and failure modes were observed. The experimental results indicate that the structural performance of GSDST columns is significantly influenced by GFRP tube thickness, inner steel-tube diameter, and fiber-orientation angle. Maximum displacement was observed in the specimens with high HSR, thus showing a ductile characteristic in the axial load-displacement behavior. The load-carrying ability of the specimens decreased as the HSR increased. The load-carrying capacity of the specimens increased with the increase in outer GFRP tube thickness. This study demonstrates that GFRP tubes can be used efficiently in the construction field as vertical load–carrying components by enhancing the axial behavior of FRP steel double-skin tubular columns.

Axial compression behavior of double-skin FRP-concrete-steel tubular columns: Experimental and analytical investigations

Double-skin tubular columns (DSTCs) with fiber-reinforced polymer (FRP) confined concrete have shown promising load-bearing capacity and ductile behavior under axial loading. A new variation of DSTC with concrete sandwiched between an outer FRP tube and a stiffened inner steel tube can provide additional benefits than the traditional unstiffened column form. The first objective of this study was to experimentally investigate the behavior of square-square (SS) shaped stiffened DSTCs with concrete sandwiched between outer FRP-tube and an inner steel tube. Experimental results of 22-test specimens are discussed and then analysis-oriented stress-strain model is proposed for the FRP confined concrete, quantifying the influence of stiffened steel tubes, stiffener characteristics and unconfined concrete strength used in the tests. The proposed confined-concrete model was then used to perform the finite element (FE)-based calibration study against test results for stiffened DSTCs with square-square (SS) cross-sectional shape. The stiffener properties varied in both experimental and analytical studies include quantity, layout or configuration, and cross-sectional dimensions. Based on the proposed confined concrete model, the FE-based calibration demonstrated superior agreement with the experimental results (2 to 5% average difference at critical stages of loading, i.e. “elastic”, “peak” and “ultimate” axial loads). The experimental and numerical based results were finally used to propose a simple equation for accurately predicting the axial load capacity of stiffened SS-shaped DSTCs.