Double Skin Steel Tubular Columns Research Articles

Residual behaviour and damage assessment of UHPC-filled double-skin steel tubular columns after lateral impact

Ultra-high performance concrete (UHPC)-filled double-skin steel tubular (DST) column has great potential to be used in the protective structures. Although its lateral impact behaviour has been well understood, the residual behaviour after lateral impact remains unexplored. As a result, this study extensively investigated the residual behaviour and damage assessment of UHPC-filled DST columns after lateral impact. Firstly, a set of six DST columns were designed and tested under lateral impact, followed by static axial compression. In addition, two intact columns were subjected to static axial compression for comparative analysis. Secondly, the refined finite element models were developed and validated using the current test data, and the impact resistant mechanism of UHPC-filled DST columns with different impact locations was analysed. Thirdly, the suitability of different damage indexes for the damage assessment of impacted UHPC-filled DST columns was evaluated. Two damage indexes, the ratio of mid-height deflection to column height (R1), and the ratio of local deflection to the column diameter (R2), were proposed for the DST columns. Finally, two types of machine learning-based models were developed to predict the impact damage of UHPC-filled DST columns. The prediction models were interpreted locally and globally using the additive feature attribution method Shapley Additive Explanation (SHAP). The machine learning-based prediction models can rapidly evaluate the damage extent of impacted UHPC-filled DST column, which hold great significance for the selection of strengthening and retrofitting schemes.

Effects of thin-walled inner steel tubes on the compressive behavior of concrete filled double skinned steel tubular columns

Concrete-filled double skin steel tubular columns with higher hollow ratios (HHR-CFDST) have gained significant attention in recent times as essential components in offshore wind turbine structures. As these structures continue to grow, an effective strategy to reduce steel consumption is to increase the diameter-to-thickness (D/t) ratios of the steel tubes. However, there is a lack of studies exploring the performance of HHR-CFDST columns with thin-walled inner steel tubes. To address this, four HHR-CFDST columns with varyingD/t ratios of the inner tubes and one double-skin hollow steel tubular column were produced and tested under axial compression. The study investigated failure modes, local buckling behaviors, and ductility characteristics. The local buckling performance index of specimens with different D/t ratios varied by up to 16.90 %. Additionally, a finite element model was used to analyze the stress distributions of the concrete when peak loads were reached, revealing a maximum variation of 45.4 % in stress values among specimens with different D/t ratios. A multi-parameter impact analysis was then conducted to establish a reasonable limit (250) for the D/t ratio of the inner steel tube in engineering design. Finally, the findings from this investigation were integrated into existing ultimate strength formulas outlined in established specifications.

Experimental and Theoretical Studies of Hexagonal UHPC-Filled Double-Skin Steel Tubular Columns under Combined Compression and Bending

Experimental and Theoretical Studies of Hexagonal UHPC-Filled Double-Skin Steel Tubular Columns under Combined Compression and Bending

Behavior of super-sized thin-walled CFDST columns for wind turbine towers subjected to combined loads: Experiment

Concrete-filled double skin steel tubular columns with large hollow ratios (LHR-CFDST) have been commonly researched in the past few years. The excellent performance of this structure renders it promising as a novel form of wind turbine tower. Increasing the diameter-to-thickness ratio is one efficient way to reduce steel consumption as the size of this engineering structure continues to expand. There is a paucity of research on thin-walled LHR-CFDST. Meanwhile, these structures may be susceptible to local buckling without stiffening measures. Furthermore, the size effect of this type of structure is more complicated. This paper reports the first experimental investigation on super-sized thin-walled LHR-CFDST columns under combined compression-torsion-shear-bending loads. Two LHR-CFDST columns with varying stud spacings are discussed. Investigations are conducted into failure modes, local buckling behaviors, load-strain responses, and a few popular mechanical indices. According to the test results, the specimen with smaller stud spacing has an 8.1% greater ultimate bearing capacity. It is assumed that a more intensive stud arrangement can delay the onset of local buckling, thereby increasing the peak load. Besides, the arrangement of the studs leads to an obvious effect of section confinement, thus improving the overall performance of the specimens. The failure modes and load-displacement relationships simulated by the FE models agree well with the experimental results. Then, a modified method for predicting the ultimate strength of LHR-CFDST based on the previously summarized formulae for CFST under compression-bending-shear-torsion is proposed and utilized for the evaluation of two specimens in this research. Since the tested value of the specimen with narrower stud spacing is higher by 5.6% than the predicted value, it can be concluded that the large-scale thin-walled LHR-CFDST may be evaluated using this method, complemented by appropriate stiffened measures.

Compressive behavior of CFDST columns: Effects of thin-walled inner steel tubes

Concrete-filled double skin steel tubular columns with large hollow ratios (LHR-CFDST), as quintessential elements within offshore wind turbine structures, have received significant attention in contemporary times. As the scale of this type of structure continues to expand, an effective strategy to reduce steel consumption involves elevating the diameter-to-thickness (D/t) ratios of the steel tubes. Presently, there is a dearth of studies that explore the performance of LHR-CFDST columns in the case of thin-walled inner steel tubes. Four LHR-CFDST columns with varying D/t ratios of the inner tubes and one double-skin hollow steel tubular column were produced and tested under axial compression. The study encompassed an investigation into failure modes, local buckling behaviors, and ductility characteristics. The local buckling performance index of specimens with varying D/t ratios differed by up to 16.9%. Furthermore, the verified finite element model was subsequently employed for mechanistic analyses pertaining to the sandwiched concrete's stress distributions, and so on. When the peak loads were attained, the maximum variation in the stress values of the concrete of the specimens with different D/t ratios reached 50.4%. Subsequently, a multi-parameter impact analysis was applied to give a reasonable limit on the D/t ratio (225) of the inner steel tube for engineering design. Finally, the prevailing ultimate strength formulas outlined in established specifications were adapted by integrating the characteristics uncovered through this investigation.

A machine learning based interaction model to predict robustness of concrete-filled double skin steel tubular columns under fire condition

Concrete-filled double skin steel tubular (CFDST) column is a hollow composite structure component, which shows better performance than traditional reinforced concrete and steel columns due to the favorable composite action between steel and concrete. In the current study, a machine learning based interaction model combine with the extended Rankine method is developed to predict fire resistance of eccentrically loaded CFDST cylinder columns. The prediction of the reliable shear bond parameter was conducted by back propagation artificial neural network (BP-ANN) and Extreme Gradient Boosting Tree (XGBoost). To perform a reliable production, the architecture and the parametric setting of both models were constructed. Furthermore, the results of the prediction were verified by experimental results and finite element analysis. The results show that the proposed method can predict the behavior of the eccentrically load CFDST columns under fire attack with reasonable accuracy.

Hysteretic performance of circular high-strength concrete-filled double skin steel tubular columns: Experiment

In marine structures, utilizing high-strength materials in concrete-filled double skin steel tubular (CFDST) members can provide an optimized solution upon the tendency of light self-weight and high performance. The cyclic load in the marine environment usually determines the safety margin for whole offshore structures. Therefore, this paper experimentally investigated the hysteretic performance of circular high-strength concrete-filled double skin steel tubular (HCFDST) columns with out-of-code diameter-to-thickness ratios. The typical failure mode appeared with the infill material crushing, steel fracture and local buckling of outer tubes. Subsequently, the detailed analysis of hysteretic curves, skeleton curves and ductility, energy dissipation, stiffness degradation, and lateral force reduction was conducted to reflect the influences of hollow ratios, axial compression ratios, and infill types, e.g., increasing the hollow ratio from 0.54 to 0.68 and 0.82, respectively reduced the bearing capacity by 6.25% and 11.20%, and the ductility coefficient had an apparent decrease of 19.27% and 26.61%. The out-of-code HCFDST columns with reasonable design could behave with favorable hysteretic performance. A theoretical model considering the tensile strength effect of engineered cementitious composite (ECC) was finally established and verified to predict the moment-resisting capacity of HCFDST columns using ECC. The reported research on HCFDST columns can provide significant references to marine structure applications.

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.

Behaviour of polymer-filled–concrete–steel double-skin tubular columns under combined lateral impact and axial compression loading

The paper presents a study on the suitability of using a Polymer as a protective layer for critical structural elements prone to impact damage. Conventional damage mitigation methods include using an outer steel jacket with a void, protecting the inner concrete-steel composite column. Whilst it is usually found that the outer steel jacket can partially negate the impact load, the inner column still experiences a significant brunt of the impact load. In order to minimise the damage to the overall critical structural element, a concept of a Polyurethane Polymer-Filled–Concrete–Steel Double-Skin Tubular Column is proposed. Scaled-down versions of two polymer-filled double-skin column configurations were tested under low-velocity impact using a drop tower. The pre and post-damage columns were tested for their axial capacities. These polymer-filled columns were critically compared to their nominal samples without the Polyurethane fill. It was shown that the mid-span deflection and localised indentations were reduced by 17%, and the localised deformations (at the point of impact) were reduced by up to 70% overall. The columns with Polyurethane also showcased retention of 70% of axial capacity post-impact, whilst the nominal sample was only capable of retaining 48%. Finally, the intrinsic properties of Polyurethane were discussed along with a critical discussion on its ability and mechanism on how energy is dissipated by comparing mechanical and chemical properties.

Experimental study on torsional behavior of tapered high strength thin-walled concrete-filled double-skin steel tubular columns

Comparing with traditional straight concrete-filled double-skin steel tubular (CFDST) members, tapered CFDST members have been increasingly used in the domain of power industry due to esthetics and special spatial experience. In addition, the utilization of high strength materials can reduce cross-sectional area and further lower construction cost. In this paper, the torsional behavior of tapered high-strength thin-walled CFDST (THSTW-CFDST) columns with or without longitudinal stiffeners was investigated and a total of twenty tapered THSTW-CFDST specimens were tested. The failure modes, torque-torsional angle curves and torsional capacity of the THSTW-CFDST columns were investigated. The results demonstrate that the installation of stiffeners can significantly improve the local stability of thin-walled steel tubes, but reduce the torsional capacity of the members. Compared with THSTW-CFDST specimens without stiffeners, the torsional capacities of those with stiffeners have been apparently reduced. Based on the experimental results, the finite element (FE) model was developed and verified, and then utilized to ascertain the force-transfer mechanism and the stress development process of each component of THSTW-CFDST columns. In addition, the effects of the various parameters including hollow ratio, diameter-to-thickness ratio, inner steel tube strength to outer steel tube strength ratio, concrete strength the torsional behavior of THSTW-CFDST members were quantitatively assessed. Finally, the accuracy of the existing methods for predicting the torsional capacity of THSTW-CFDST members was evaluated.

Experimental study of large-scale stiffened thin-walled CFDST columns under aixal compression

Wind turbine towers offer good application potential for concrete-filled double-skin steel tubular columns with large hollow ratios (LHR-CFDST). With the increasing size of this engineering structure, the requirement to reduce construction expenses can be met by enhancing the diameter-to-thickness ratio of steel tubes. Few studies have been conducted to report on thin-walled LHR-CFDST columns. Meanwhile, local buckling and size effect shall be considered for this type of structure. Based on this, the first experimental investigation on large-scale stiffened thin-walled LHR-CFDST columns under axial compression is reported in this paper. Two large-scale thin-walled LHR-CFDST columns with different stud spacings are discussed. Failure modes, local buckling behaviours, load-strain responses, and some common mechanical indexes are investigated. According to the test results, adding studs was an effective method to increase the ultimate capacity of LHR-CFDST columns, as evidenced by the 16.6% increase in peak load for the specimen with smaller stud spacing than the other. Besides, the arrangement of studs leads to an obvious effect of section confinement, thus improving the overall compressive performance of the specimens. Then, four existing specifications all give a conservative prediction for the ultimate capacity of the specimen with smaller stud spacing, indicating that the large-scale thin-walled LHR-CFDST can be evaluated utilizing the present specifications with suitable stiffening measures.

FRP–Concrete–Steel Double-Skin Tubular Columns with UHPC/ECC: Concept and Compressive Behavior under Concentric Loading

FRP–Concrete–Steel Double-Skin Tubular Columns with UHPC/ECC: Concept and Compressive Behavior under Concentric Loading

Coupled behaviour and strength prediction of tapered CFDST columns with large hollow ratios for wind turbine towers

Concrete-filled double-skin steel tubular (CFDST) tower has emerged as a promising type of wind turbine support structure with excellent strength and stiffness. As the basic member in CFDST towers, tapered concrete-filled double-skin steel tubular columns with large hollow ratios (TLHR-CFDSTs) are frequently subjected to complex combined compression-bending-torsion loads. This paper presents a comprehensive analytical study on the coupled behaviour of the TLHR-CFDST column under combined loads and the relevant ultimate strength prediction method. A FE model was established to conduct numerical analyses and extensive parameter studies while the data from the previous experimental research was used to provide a verification basis. It is found that the column subjected to combined loads has three typical failure patterns, which are mainly governed by the bending-to-torsion ratio (mt). Columns with moderate mt undergo the bending-torsion failure and show obvious coupled performances. The load-deformation relation, the ultimate characteristics and the effects of important parameters, including axial compressive ratio (n), tapered angle (θ), hollow ratio (χ) and height-to-diameter ratio (λ) were discussed. The ultimate strength correlations of the column were revealed by analysing strength data within the parameter scopes commonly used in wind turbine towers. Lastly, a practical and accurate prediction method for the ultimate strength of the TLHR-CFDST column under combined compression-bending-torsion loads was proposed.

Experimental and analytical research on seismic performance of ECC-filled high-strength double skin steel tubular columns with out-of-code D/t ratios

Against the offshore construction requirement on light weight and high performance, using high-strength (HS) steel in concrete-filled double skin steel tubular (CFDST) members usually results in out-of-code diameter-to-thickness (D/t) ratios and performance uncertainty. A quasi-static cyclic loading test was therefore conducted to investigate the seismic performance of circular-in-circular ECC-filled high-strength double skin steel tubular (EFHDST) columns with out-of-code D/t ratios. Typical failure mode, hysteretic curves, bearing capacity and ductility were analyzed. Subsequently, the finite element (FE) model incorporating material damage effect was established and verified to conduct further parametric study. Influence of geometric parameters (e.g., wall thickness and hollow ratio), material strength and axial compression level was discussed in detail. Finally, a simplified restoring force model was developed to predict the seismic behavior of EFHDST columns. The result indicates that: the EFHDST columns fail by the ECC crushing, steel fracture and local buckling of double-skin tubes; the steel yield strength and thickness of outer tube, axial compression level and hollow ratio obviously affect the hysteretic performance (e.g., the bearing capacity and ductility) through the test and FE analysis, e.g., increasing hollow ratio from 0.54 to 0.82 the bearing capacity and ductility coefficient of test respectively decrease by 11.20% and 26.61%; the dimensionless skeleton curve, unloading stiffness degradation and hysteretic rule are proposed to form the restoring force model, where a strength model considering effect of ECC tension strength is included, and the reasonable agreement is achieved by the comparison results. The displayed research on EFHDST columns can provide significant references to its engineering applications.

Axial compression behaviour of circular concrete-filled double-skin steel tubular columns with bolted shear studs: Numerical investigation and design

The concrete-filled double-skin steel tubular (CFDST) columns have recently attracted significant attention for practical engineering constructions. The axial resistance behaviour of CFSDTs can be greatly enhanced by installing bolted shear studs as pin supports for the outer. This is a companion paper that expands on the authors' work [1]. The previous paper concentrated on full-scale experimental testing to ascertain the influence of bolted shear studs on the axial resistance of CFSDT columns, while this study focused on finite element (FE) analysis and a simplified design approach for such composite structural members. A three-dimensional FE model for predicting the axial behaviour of circular CFDST columns without and with shear studs was developed and validated using the test results of the specimens' typical failure mechanisms and load-displacement responses. The model was then employed to perform structural analysis by comparing the axial load-displacement curve, internal force distribution, longitudinal stress distribution over the sandwiched concrete, and confinement mechanism of a circular column with bolted shear studs with that of its counterpart without bolted shear studs. Parametric studies were carried out to examine the effects of bolt longitudinal spacing, diameter, length, and yield strength. It was found that the spacing of the bolts-to-width (bs/Do) ratio had significant effects on the axial resistance and ductile performance of columns. Also, a bolt spacing corresponding to bs/Do<0.44 was suggested to attain an acceptable ductile performance in practical application. Verification of the design model revealed that it led to satisfactory predictions of the ultimate strengths of circular CFDST columns without and with shear studs.

Compressive behaviour of stiffened thin-walled CFDST columns with large hollow ratio

Concrete-filled double skin steel tubular columns with large hollow ratio (LHR-CFDST) have been commonly used in recent years. With the increasing size of the engineering structures, one efficient way to decrease the consumption of steel is to increase the diameter-to-thickness ratio. Few studies have been conducted to report on thin-walled LHR-CFDST columns. At the same time, local buckling may occur in these structures in the absence of stiffening measures. Based on this, an experimental and numerical analysis was carried out for the stiffened thin-walled LHR-CFDST columns under axial compression in this paper. Five thin-walled LHR-CFDST columns with different stiffening measures (ribs, studs) were tested. The failure modes, load versus shortening curves, local buckling behaviours and ductility were investigated. The test results indicates that the stiffened measures effectively delayed the appearance of local buckling and increased the peak load. Besides, the finite element models validated by the test results were applied to the subsequent mechanical mechanism analysis of the stiffened thin-walled LHR-CFDST. It can be seen that the stiffened measures enhance the confinement of the inner and outer steel tubes on the concrete and greatly improve the ultimate strength of the concrete. Finally, the predicted peak load formulae in the existing design specifications were modified by combining the characteristics of the specimens in this paper. The peak load values obtained by the improved formulae agreed well with the test results.

Compressive Behavior of GFRP Tubes Filled with Self-Compacting Concrete

Self-compacting concrete (SCC) features excellent flow ability without the need of vibration for compaction during casting. This makes it particularly suitable for application in hybrid fiber-reinforced polymer (FRP)-concrete–steel double-skin tubular columns (DSTCs), a high-performance structural form evolved from concrete-filled FRP tubes (CFFTs). In a DSTC, the space between the inner steel tube and the outer FRP tube for filling concrete may be narrow and the application of vibration may be difficult. However, because of the large shrinkage of SCC compared to traditional concrete of normal flow ability, the integrity and composite action of DSTCs with SCC become a major concern. To clarify this issue, an understanding of the behavior of CFFTs filled with SCC is an essential prerequisite. While a large number of studies have been published on CFFTs with normal concrete (NC), only limited studies have been carried out on CFFTs with SCC. This paper presents a comprehensive investigation on the effect of SCC on the behavior of large-scale CFFTs. Axial compression tests were carried out on concrete-filled glass FRP (GFRP) tubes with diameters of 150, 200, 300, and 400 mm. The compressive behavior of the CFFT specimens filled with NC, a nonexpansive SCC, and an expansive SCC (ESCC) was compared and discussed. The results showed that the specimens with nonexpansive SCC behaved differently compared to those with NC as a result of larger shrinkage, especially for large specimens for which the confinement level was lower. This situation, however, improved in specimens where ESCC was used. Finally, the test results were further analyzed using a theoretical model recently proposed by the authors’ group.

Elliptical FRP–Concrete–Steel Double-Skin Tubular Columns: Axial Behavior, Interaction Mechanism, and Modeling

Elliptical FRP–Concrete–Steel Double-Skin Tubular Columns: Axial Behavior, Interaction Mechanism, and Modeling

Torsional behaviour of tapered concrete-filled double-skin steel tubular columns with large hollow ratios

Tapered concrete-filled double-skin steel tubular columns with large hollow ratios (LHR-CFDSTs) possess light self-weight and good lateral rigidity. They exhibit tremendous potential in lateral load-critical structures, including large-span buildings, wind turbine towers and offshore infrastructures. In these structures, in addition to axial force and bending moment, columns are also commonly subjected to considerable torque. Although the compressive/flexural behaviour of tapered LHR-CFDST columns has attracted attention from researchers, studies on the torsional performance and mechanism are limited. This paper thus presents a comprehensive analytical study on the torsional behaviour of tapered LHR-CFDST columns on the basis of previous experimental research. Numerical analyses were conducted to investigate the influence of the key parameters. Full-range torsional characteristics of the column were revealed with regard to the typical torque–torsional angle relation, the stress development of the concrete and the contact between components. Load distributions as well as the effective twist length were discussed to understand the mechanism of the column under torsion. It is found that significant torsional deformation, oblique concrete cracks and struts, the compressive stress of concrete and the contact pressure all develop concentratedly within the effective twist length, which reflects the segments of the tapered column with a relatively weak torsion-resistant ability. Lastly, a torsional capacity prediction method was proposed by refining the previous theoretical model and it exhibits favourable accuracy for tapered LHR-CFDST columns with tapered angles higher than 1.50°.

Flexural buckling behaviour of concrete-filled double skin aluminium alloy columns

Concrete-filled double skin steel tubular columns consisting of two hollow steel tubes and concrete infill between their interspace, have become popular in modern construction owing to their high ultimate load, less self-weight and good ductility. The weight of these columns can be reduced further by using lightweight aluminium alloy hollow tubes instead of steel ones. This paper experimentally and numerically studied the flexural buckling behaviour of the concrete-filled double skin aluminium tubular (CFDSAT) columns subjected to axial compression. A total of 8 CFDSAT columns were tested using a pin-ended set-up. The test results are presented in terms of failure modes, ultimate load and load versus mid-height lateral displacement curves. Non-linear finite element (FE) models of the specimens were developed and their accuracy was evaluated by comparing the FE and test results. A numerical parametric investigation was conducted to study the influence of the hollow ratio, the member slenderness, the cross-sectional slenderness of the hollow tubes and the concrete strength on the structural behaviour of CFDSAT columns. The parametric study results revealed that the cross-sectional dimensions of outer section, the member slenderness and the concrete compressive strength have a significant effect on the flexural buckling response of the columns, while the influence of the cross-sectional dimensions of inner section is less prominent. In the absence of design standards for CFDSAT members, a design methodology is proposed with a design buckling curve to predict the ultimate load of CFDSAT columns based on the Eurocode 4 framework. Moreover, a revised concrete correction factor is suggested to determine the effective flexural rigidity of CFDSAT columns according to Eurocode 4.