Circular Hollow Section Tubes Research Articles

Plastic collapse behavior of plate to CHS connection under biaxially symmetric load

This study investigates the plastic collapse behavior of a non-diaphragm type connection with flange plates connected to a circular hollow section (CHS) column, where four flanges were joined from two orthogonal directions. The analysis was conducted using the finite element method (FEM). The focus was on determining the collapse load of the flange joint under a biaxially symmetric load from the four flanges. In an initial numerical analysis, the fundamental collapse behavior of the cylindrical wall was explored. Finite element models of CHS tubes with perfectly elasto-plastic material properties were employed. The analysis revealed that the plastic collapse mechanism of the cylindrical wall was influenced by the axial force in the transverse flanges. Prediction equations for the collapse load of the joint were formulated, assuming four representative collapse mechanisms and employing the principle of virtual work based on the numerical analysis results. Additionally, the ultimate strength of the joint, determined by the plastic collapse of the cylindrical wall, was computed using finite element models of CHS tubes with realistic hardening properties. A comparison between predictions from the equations based on perfectly elasto-plastic CHS tubes and numerical solutions through finite element analysis (FEA) of CHS tubes with realistic hardening properties validates the accuracy of the proposed prediction equations, even when applied to realistic steel tubes.

Stress Distribution Prediction of Circular Hollow Section Tube in Flexible High-Neck Flange Joints Based on the Hybrid Machine Learning Model.

The flexible high-neck flange is connected to the circular hollow section (CHS) tube through welding, and the placement of the weld seam and corresponding stress concentration factor (SCF) are crucial determinants of the joint's fatigue performance. In this study, three hybrid models combining ant colony optimization (ACO), a genetic algorithm (GA), and grey wolf optimization (GWO) with a random forest (RF) model were developed to predict the stress distribution on the inner and outer walls of the CHS tube under different flange parameter combinations. To achieve this, an automated finite element (FE) analysis program for flexible high-neck flange joints was initially developed based on ABAQUS 2020 software. Parameter combinations were randomly selected within a reasonable range to simulate the nonlinear mechanical behavior of the joint under uniform tension, generating a dataset comprising 5417 sets of data. The accuracy of the FE model was validated through experimental data from the literature. Based on this, feature importance analysis was conducted to reveal the influence of different variable parameters on the stress distribution in the tube of the joint. The flange parameters and tube stress distribution are considered as inputs and outputs, respectively. Three hybrid RF models, specifically ant colony optimization-based random forest (ACO-RF), genetic algorithm-based random forest (GA-RF), and grey wolf optimization-based random forest (GWO-RF), are trained for regression prediction. The results demonstrate that the three hybrid models outperform the original machine learning model in predictive accuracy. The ACO-RF model achieved the highest accuracy with average coefficients of determination (Rmean2) of 0.9983 and 0.9865 on the testing and training sets, respectively. Building upon this foundation, the study developed a corresponding open-source graphical user interface (GUI) as a tool for facilitating computations and visualizing results. Finally, a case study on fatigue damage assessment of a flexible high-neck flange joint in a wind-turbine tower is presented to demonstrate the application of the proposed model in this study.

Mechanical Modelling of the Strength and Stiffness of Circular Hollow Section Tube under Localised Transverse Compression and Tension

The component method is a powerful tool for designing and modelling steel beam-to-column connections. Its widespread use is ensured by several formulations currently included in Eurocode 3 part 1.8 for welded and bolted joints. However, the recent use of 3D Laser Cutting Technology (3D-LCT) in the construction market has enlarged the range of solutions, allowing the realisation of tubular columns with passing-through elements. Given the recent development, no design formulations are currently provided for this typology. At this moment, only a few research studies have developed to fill this knowledge gap. At the University of Salerno, since some years, research efforts are ongoing to characterise the flexural strength of connections between Circular Hollow Section columns and passing double-tee beams, suggesting methodologies to predict the behaviour of the resistance and stiffness of this typology and some of its elementary joint components. Within this framework, this paper aims to examine the strength and stiffness of one of the main components of this joint, which was never examined previously, that is the so-called tube under localised transverse tension/compression. Design formulations are derived from a parametric study carried out through numerical simulations of several geometric configurations.

Behavior of axially loaded high-strength steel circular hollow section tubes under low velocity lateral impact

High-strength steel has been widely used in large-span and high-rise structure engineering in recent years because it can improve the mechanical performance of building structures and reduce their self-weight. In this study, a lateral impact test using a drop hammer was conducted on 22 high-strength steel circular hollow section (CHS) tubes with axial preloading. The test parameters included the impact energy, tube diameter–thickness ratio, axial compression ratio, and shape of the hammerhead. The failure modes and entire impact process, including the impact force, displacement, strain, and axial force histories of the specimens, were obtained. A finite element (FE) model of the high-strength steel CHS tube preloaded by axial force (including compression and tension) under lateral impact was established using the nonlinear finite element analysis (FEA) software ANSYS/LS-DYNA. After verifying the accuracy of the FE model by comparison with the test results, a parameter analysis was conducted to reveal the influence of the impact energy, diameter–thickness ratio, axial compression ratio, axial force direction, and shape of the hammerhead on the dynamic response of the high-strength steel tube under lateral impact based on the test and FE results of the failure mode, impact force, displacement and energy histories, and residual stress.

Experimental analysis of BFRP strengthened short steel tube with built-in FBG sensors under axial compression

This paper presents the results of an experimental investigation of the behavior and strain-sensing characteristics of short tubes strengthened by basalt fiber-reinforced polymer (BFRP) with built-in fiber Bragg grating (FBG) sensors. This study introduces a corrugated steel with punched-in patterns to improve the buckling failure mechanism of thin-walled circular hollow section (CHS) tubes. Thirty-five specimens are tested under axial compression to investigate the effects of the BFRP strengthening and the punched-in. The self-sensing properties of the built-in FBG sensors are analyzed using wavelength shift data gathered from nine additional specimens. The results demonstrate that the punched-in patterns and the BFRP can significantly enhance the strength of CHS tubes by 98% for 0.7 mm and 36% for 1.2 mm using 2 layers of BFRP. The built-in FBG sensors fulfill the demand for intelligent monitoring of FRP strengthened steel tubes. Analysis on design rules revealed that the interaction between the punched-in patterns and the BFRP must be further considered to accurately predict the compressive capacity of the proposed tubes. Finally, the innovative tubes display potential benefits in terms of cost and weight performance to replace traditional steel tubes.

Moment Resisting Connection with Curved Endplates: Behaviour Study

This article provides a behaviour analysis of moment resisting joints with curved endplates. This is a new type of connection that can be used for joining steel beams to the circular hollow section (CHS) columns by means of bolts. Some researchers apply the Eurocode model without considering the differences in calculation schemes and assumptions, such as by using the general model of an equivalent T-stub in tension. Consequently, many of the existing behaviour studies are somewhat misleading, thus there is a need for further research. Apart from the absence of analytical methods that are devoted to predicting the initial stiffness and strength of the curved T-stub, other technical difficulties were encountered, such as gaps between the endplate and the column, as well as the initial pre-loading force of the bolts. In the previous studies, endplates were manufactured by rolling flat plates to the precise curvature which resulted in firm contact. In contrast, in this study, endplates were manufactured from a standard CHS tube, which led to significant initial gaps. Meanwhile, in terms of preloading force, it was found that it affected the moment resistance of the joint. This paper discusses problems associated with ongoing researches and presents experimental tests of the two connections. The obtained results were further used in the parametric finite element analysis (FEA) to determine the effect of the gaps and preloading force of the bolts on the moment resistance and initial rotational stiffness of the joint. The results indicate that the behaviour of curved plated connections is exceedingly complex and that the preloading force is the key factor, therefore, it should be controlled.

Flexural capacity of perforated aluminium CHS tubes–An experimental study

This paper presents the results of twelve experimental tests on the flexural capacity of perforated aluminium circular hollow section (CHS) tubes; four of which were carried out without perforations. Two heat-treated aluminium alloys were used: 6061-T6 and 6063-T5. The tests covered the size and number of perforations. The flexural capacity, failure modes, and the distribution of strains around circular perforations were determined. The experimental results were then compared against the design strengths calculated from the North American Specification (NAS) for cold-formed steel (CFS) sections with perforations, derived from modified Direct Strength Method (DSM) and modified Continuous Strength Method (CSM) for aluminium alloy members with perforations, which were found to be conservative by approximately 23%, 27% and 22%, respectively. When strength reduction factors were applied, and the unified design equations proposed by Zhou and Young were used, the reduction in strength was 6% conservative to the test strengths.

Experimental study on the behaviour and strength of high strength steel CHS T- and X-joints

This paper presents an experimental investigation on high strength steel circular hollow section (CHS) T- and X-joints. In total, seven T-joints and six X-joints were tested under axial compression in the braces and failed by chord plastification. The brace to chord diameter ratio (β) ranged from 0.60 to 0.93 and chord diameter to wall thickness ratio (2γ) varied from 42.8 to 54.3. The test specimens were composed of CHS tubes which were cold-formed from one parental steel plate with a nominal yield stress of 960 MPa. The steel plate was manufactured by the quenching and tempering (QT) technique. A robotic welding machine was employed to perform the gas metal arc welding for the fabrication of the test specimens in order to achieve consistent welding quality and a low heat input of approximately 0.38 kJ/mm. The material strength reduction of the heat affected zones (HAZ) in the CHS tube was investigated. The deformation capacity, ductility and strength of the test specimens were examined. The current CIDECT and Eurocode design rules for normal strength steel tubular joints were assessed against the obtained test results. It is shown that the material strength reduction of the HAZ was minor, and the deformation capacity and ductility of the test specimens could be considered as reasonably sufficient. The CIDECT and Eurocode mean strength predictions are unduly unconservative for the T- and X-joint specimens.

Compressive strengths of concrete-filled double-skin (circular hollow section outer and square hollow section inner) aluminium tubular sections

Experimental and numerical investigations of concrete-filled double-skin aluminium stub column with a circular hollow section as the outer skin and a square hollow section as the inner skin are presented in this article. A test program was carried out to study the influences of aluminium tube geometric dimensions and concrete strength on structural performance and strength of composite columns. A series of composite columns was tested on outer circular hollow section tubes and inner square hollow section tubes; the spaces between them had been filled with concrete of different nominal cylinder strengths of 40, 70 and 100 MPa. The tubes were fabricated by extrusion using 6061T6 heat-treated aluminium alloy having a nominal 0.2% proof stress of 240 MPa. A non-linear finite element model was developed and verified against experimental results. The test and numerical results were compared with the design strengths to evaluate the applicability of the design rules in the American specifications for aluminium and concrete structures. In addition, the proposed design equations, developed by the authors for concrete-filled double-skin aluminium tubular stub columns with circular hollow section as both outer and inner skins, were used to calculate the design strengths and compared with the experimental and numerical results obtained in this study. The proposed design equations also predicted the ultimate strengths of the concrete-filled double-skin aluminium tubular stub columns accurately with circular hollow section as the outer skin and square hollow section as the inner skin.

Experimental study on axially preloaded circular steel tubes subjected to low-velocity transverse impact

Steel circular hollow section tubes are widely used as tubular structural members, and impact accidents usually occur while these tubes are in their working states. This paper presents experimental studies on axially preloaded circular steel tubes subjected to transverse low-velocity mass impact. A total of 32 impact tests, representing four types of scenarios, are conducted to investigate the influences of preloading and the boundary condition on the structural responses of tubes. An axial force loading system is designed, and a bladder accumulator is adopted in the system to compensate for the axial compressive loading. The test processes of the tubes under transverse impact are described in detail, and four failure modes are identified. All specimens of the four scenario types deformed according to the three-hinge mechanism. Based on the test results, the influence and mechanism of axial force are proposed. The effects of axial tension, axial compression and the boundary condition on the structural behaviour of tubes are discussed. The results show that the axial tension can enhance the bending resistance and lateral collapse capacity of tubes, while the axial compression reduces the collapse capacity significantly. By comparing the responses of tubes under different boundary conditions, the lateral resistance of tubes and the structural response are shown to have a strong correlation with the axial constraint.

Flexural behavior of concrete-filled aluminum alloy circular hollow section tubes

This paper presents an experimental investigation on flexural behavior of concrete-filled aluminum alloy circular hollow section (CHS) tubes under pure in-plane bending. A total of 28 circular concrete-filled aluminum alloy tubes (CFAT) with nominal concrete cube strengths of 30 MPa and 50 MPa were tested. The flexural strengths, failure modes, flexural stiffness, ductility, bending moment versus mid-span deflection curves, overall vertical deflection curves, bending moment versus longitudinal strain curves and longitudinal strain distribution curves of circular CFAT beams are reported. It is demonstrated that the comparatively large wall thickness of aluminum alloy CHS tube enhanced the bearing capacity, the bending deformation capacity and the ductility of circular CFAT beams. Whereas, the concrete strength generally has insignificant influence on the flexural strength, flexural stiffness and ductility of circular CFAT beams. The current design specifications for the CFST are generally inappropriate for circular CFAT beams under pure in-plane bending with high scatter of predictions. Further research is still required to propose accurate design rules for circular CFAT beams.

Experimental and numerical investigations on flexural behaviour of CFRP reinforced concrete-filled stainless steel CHS tubes

An experimental investigation was conducted on CFRP reinforced concrete-filled stainless steel circular hollow section (CHS) tubes subjected to in-plane bending. A total of 36 specimens including concrete-filled stainless steel CHS tubes and CFRP reinforced concrete-filled stainless steel CHS tubes were tested. An extensive parametric study was carried out by using the verified finite element model to investigate the strengthening effect of CFRP on the flexural behaviour of concrete-filled stainless steel CHS tubes. It is shown from the comparison that the strengthening effect of CFRP improved with the increase of the strength ratio (β) of CFRP. Furthermore, the ultimate strength was enhanced proportionally with the increase of the layers of CFRP positioned in the longitudinal direction for reinforcement, but the ductility generally deteriorated. Finally, the flexural strength and flexural stiffness of concrete-filled stainless steel CHS tubes is improved by increasing the interface friction coefficient between stainless steel tubes and concrete up to 0.6.

Flexural behaviour of concrete-filled stainless steel CHS subjected to static loading

This paper presents a test program on flexural behaviour of concrete-filled stainless steel circular hollow section (CHS) tubes under in-plane bending. A total of 27 specimens including 18 concrete-filled stainless steel CHS flexural members and 9 empty stainless steel CHS flexural members were tested. The ultimate strengths, failure modes, flexural stiffness, ductility, bending moment-midspan deflection curves, overall deflection curves and strain distribution curves of test specimens are reported. It is demonstrated that the ultimate strength, initial stiffness and ductility of empty stainless steel CHS flexural members are significantly enhanced by filling the concrete in the specimen along its full length. The enhancement is increased with the increase of the thickness of the CHS tube. Furthermore, the concrete strength has little influence on the ultimate strength, initial stiffness and ductility of concrete-filled stainless steel CHS flexural members. The test flexural stiffness including both initial flexural stiffness and flexural stiffness at the serviceability limit state of concrete-filled stainless steel CHS tubes under in-plane bending were compared with the design flexural stiffness calculated using the current AIJ standard, BS 5400, Eurocode 4 and AISC specification for concrete-filled steel tubes. It is shown from the comparison that the current design rules are all unconservative for initial flexural stiffness and flexural stiffness at the serviceability limit state of concrete-filled stainless steel CHS tubes under in-plane bending with high scatter of predictions.

Flexural behaviour of CFRP strengthened concrete-filled aluminium alloy CHS tubes

This paper presents an experimental investigation on flexural behaviour of concrete-filled aluminium alloy circular hollow section (CHS) tubes reinforced by carbon fiber-reinforced polymer (CFRP). A total of 30 specimens including 20 CFRP strengthened concrete-filled aluminium alloy tubes (CFAT) and 10 traditional CFAT were tested under pure in-plane bending. The ultimate strengths, failure modes, flexural stiffness, ductility and longitudinal strains of test specimens are reported. It is demonstrated that the ultimate strength of the CFAT specimens are generally enhanced by reinforcing with the CFRP, but the ductility is generally deteriorated. Furthermore, the layer of the CFRP has little influence on the ultimate strength, flexural stiffness and ductility of the CFRP strengthened CFAT specimens. It can be generally concluded that the design equations given in the current AIJ standard for the flexural stiffness of the concrete-filled steel tubes (CFST) are appropriate for the initial flexural stiffness of the CFAT, and also appropriate for the post-yield flexural stiffness of the CFAT with a proper reduction factor. The design equations are also proposed for the CFRP strengthened CFAT based on the design rules for the CFAT by further considering the flexural stiffness of the CFRP.

Bond-slip behaviour of concrete-filled stainless steel circular hollow section tubes

This paper presents the repeated push-out tests on concrete-filled stainless steel circular hollow section (CHS) tubes with different values of height-to-diameter ratio, diameter-to-thickness ratio and concrete strengths. The bond-slip behaviour of all specimens and the strain distribution on the exterior of stainless steel tubes along the longitudinal height direction were carefully investigated. It was found that the shear failure loads of bonding slip decreased successively with more loading cycles of the repeated push-out test employed in the same direction. Hence, the mechanical interlock force and friction force of the interface elements gradually decreased. Furthermore, the bond-slip failure of the interface elements between the inner concrete and outer stainless steel tube of the specimens consists of the adhesive stage, the sliding stage and the friction resistant stage. It can be generally concluded that 70% of the shear resistance of the bonding strength is taken by the interface friction force, while the remaining 30% of the shear resistance of the bonding strength is sustained by the chemical adhesive force and the mechanical interlock force. On the other hand, it was demonstrated that the height-to-diameter ratio (H/D) and the diameter-to-thickness ratio (D/t) of the stainless steel tube as well as the concrete strength (C) have insignificant influence on the shear resistance of the bonding strength of the interface elements. It was also shown from the comparison that the current design rules of concrete-filled carbon steel CHS tubes are inapplicable to the shear resistance of the bonding strength of concrete-filled stainless steel CHS tubes.

Numerical investigation of concrete-filled multi-planar CHS Inverse-Triangular tubular truss

This paper describes a numerical investigation of concrete-filled multi-planar circular hollow section (CHS) Inverse-Triangular tubular truss using finite element analysis. The configuration of specimens is Pratt truss with symmetric geometry, loading application and boundary conditions by filling the concrete in the top chord members only. The material and geometric nonlinearities of concrete-filled tubular truss were carefully incorporated in the finite element models. The failure modes, load carrying capacities and overall deflections of all specimens were obtained from the numerical analysis. The nonlinear finite element models were calibrated against the corresponding test results for validation. Good agreement between the experimental and finite element analysis results was achieved. Therefore, an extensive parametric study of 256 specimens was carried out using the verified finite element models to evaluate the effects of main influential factors including cross-section dimensions of CHS tubes, concrete strengths filled in the top chord members and the critical non-dimensional geometric parameters on the strength and behaviour of concrete-filled multi-planar CHS Inverse-Triangular tubular truss. The optimum geometric parameters including the truss span to height ratio (L/H), the truss span to joint spacing ratio (L/S) and the truss height to width ratio (H/W) were proposed in this study for the economic design of concrete-filled multi-planar CHS Inverse-Triangular tubular truss.

EXPERIMENTAL AND COMPUTATIONAL STUDY OF CONCRET FILL ALUMINUM TUBULAR COLUMN UNDER AXIAL LOADS

This work deals with an experimental and computational study was carried out on the structural behavior of circular concrete filled aluminum tubular columns subjected to increasing axial load. Twenty four specimens were tested to investigate the effect of diameter, D/t ratio and slenderness ratio of a aluminum tube on the load carrying capacity of the concrete filled tubular columns. Diameter to wall thickness ratio between 23.3 ≤ D/t ≤ 47.8, and the length to tube diameter ratio of 3 ≤ L/D ≤ 10 was investigated. The structural performance of the concrete-filled aluminum tube columns (CFTa) was investigated using constant concrete cylinder strengths of 24.2 MPa.The main purpose of the computational study aimed to investigate the potential of using fuzzy inference system (FIS) to predict the strength of the composite columns. Fuzzy inference system (FIS) model has been provided to be very effective in predicting the ultimate strength of aluminum-concrete composite columns. The average values of ratios of experimental to predicted ultimate loads are 1.001 forthe Sugeno FIS model. The circular hollow section tubes were fabricated by extrusion using 6061-T6 heat-treated aluminum alloy

Behavior of thin-walled circular hollow section tubes subjected to bending

Thin-walled steel circular hollow sections (CHSs) are widely used in wind turbine towers. The tower tubes are mainly subjected to bending. There have been a few experimental studies on the bending behavior of thin-walled CHS steel tubes. This paper describes a series of bending tests to examine the influence of section slenderness on the inelastic and elastic bending properties of thin-walled CHS. In addition, the influence of stiffeners welded in the steel tube is considered. Sixteen bending tests were performed up to failure on different sizes of CHS with diameter-to-thickness ratio (D/t) varying from 75 to 300. The experimental results showed that the specimens with small diameter-to-thickness ratios failed by extensive plastification on the central part of the tube. With the increase of diameter-to-thickness ratio, the local buckling phenomena became more pronounced. The stiffeners in the steel tubes increased the load carrying capacity and improved the ductility of the specimens. The experimental results were compared with current design guidelines on thin-walled steel members in AISC-LRFD, AS4100 and European Specification. It was found that the test results agreed well with the results based on AS4100 design code.

Numerical analysis and design of concrete-filled aluminum circular hollow section columns

This paper presents numerical investigation and design of concrete-filled aluminum circular hollow section (CHS) columns. A non-linear finite element model is developed and verified against experimental results. An extensive parametric study was carried out to study the effects of cross-section geometries and material properties on the concrete-filled aluminum CHS column strengths. A total of 192 numerical data is presented in this study. The aluminum CHS tubes of normal strength material (T5) and high strength material (T6) using three different nominal concrete cylinder strengths of 40, 70 and 100 MPa were investigated. The nominal outer diameter-to-thickness ( D/ t) ratio of the sections ranged from 10 to 160. The test and numerical results of the concrete-filled aluminum CHS columns were compared with the design strengths to evaluate the reliability of the design rules in the American and Australian/New Zealand specifications for aluminum and concrete structures. Furthermore, the composite column design equations are proposed in this study. The proposed design equations consider the benefits of composite action between the aluminum CHS tube and the concrete infill. It is shown that the proposed design equations accurately predicted the strengths of the concrete-filled aluminum CHS columns.

Service loads in dragline tubular structures: a case study of cluster A5

Draglines are used extensively for removal of overburden in the coal mining industry. Draglines with tubular booms are among the structures most susceptible to fatigue cracking due to the large number of high load cycles to which they are subjected during operation. Circular hollow section tubes are used as both lacing and chord members. In this paper, a study was carried out to better understand the stresses in a 4-lacing cluster during operation. Strain gauges were installed on a typical dragline cluster A5 to measure strains generated while in operation. Static and dynamic (swing and digging) tests were carried out, and strains obtained during the different tests were used to calculate both nominal stresses and hot spot stresses. For cluster A5, the hot spot stresses at weld toes in the lacing members were found to be significantly larger than those at weld toes in the chord members. Bending stresses were found to form a relatively larger portion of the nominal stresses at the weld toes in the lacing members compared to chord members. The results of this work highlight a conclusion found in the authors' previous work that the high tensile residual stresses resulting from welding are an important issue not measured in hot spot stress testing, but these stresses are relevant to the levels and location of cracking observed in practice. Copyright © 2011 John Wiley & Sons, Ltd.