Circular Hollow Section Columns Research Articles

A component method approach for single-sided beam-to-column joints with CHS column and welded double-tee beam

This paper focuses on predicting the flexural stiffness and strength of beam-to-column joints with Circular-Hollow-Section (CHS) columns and externally welded double-tee beams using the Component Method approach. Currently, Eurocode 3 Part 1.8 lacks guidelines for assessing the stiffness of these joints, resulting in their practical modelling using extreme assumptions like pin or full restraint. Nevertheless, the literature demonstrates that these joints can exhibit semi-rigid behaviour due to the relatively high local deformability of the tube in the joint area. Another concern relates to the strength of these joints. In fact, recent studies have shown that Eurocode 3 Part 1.8 formula for predicting the yield resistance of these joints is over-conservative.Within this framework, the purpose of this study is to fill the current knowledge gaps (over-conservative strength prediction and lack of rules for determining the stiffness) by undertaking a thorough investigation involving numerical and analytical activities. Specifically, the research presents a component-based modelling approach for predicting stiffness and strength of CHS to double-tee beam connections.In this regard, the work presented in this paper has involved the selection of experimental tests from literature to validate a Finite Element (FE) model, specifically focusing on X- and T-joints and internal and external beam-to-column joints. The validated numerical models have been then employed to simulate the response under monotonic loading conditions of additional sets comprising forty T-joints and thirty external beam-to-column joints, respectively. The currently available formulations for predicting the resistance of T-joints were applied to the forty cases simulated, evaluating their accuracy. This allowed the individuation of the most accurate literature formula for the strength prediction of T-joints, showing that the recent proposal of Voth and Packer (2012) yields sufficiently accurate results. Instead, analytical formulations for predicting the stiffness of T-joints were properly derived in a closed-form solution and were validated against the results of the parametric study. Finally, drawing upon knowledge regarding the stiffness and strength of T-joints, the flexural response of external beam-to-columns connections was evaluated proposing a component model, whose accuracy was verified against the cases simulated in the parametric analysis.

Experimental and numerical investigations of S890 and S960 ultra-high strength steel circular hollow section columns

The experimental and numerical investigations of the buckling behaviour and load-carrying capacities of S890 and S960 ultra-high strength steel (UHSS) circular hollow section (CHS) columns were conducted and reported in this paper. The experimental program encompassed tensile coupon tests, initial global and local geometric imperfection measurements and pin-ended column tests. Parallelly, the numerical modelling program was carried out, where the developed finite element (FE) models were validated with reference to the experimental observations and then employed in parametric studies to result in additional numerical data, considering various cross-sectional dimensions and member lengths. Based on the obtained FE and test data, the applicability of the relevant codified design buckling curves in the current European, Australian and American specifications to S890 and S960 UHSS CHS columns was evaluated, since the aforementioned standards only cover the design rules with steel material yield strength no greater than 700 MPa. The assessment results showed that the European code and Australian standard can generally accurately predict the resistances of S890 and S960 UHSS CHS columns, but result in some unsafe data points, while the American specification yielded accurate and consistent resistance predictions. Finally, a revised Eurocode design buckling curve was proposed, accompanied by the reliability assessment through statistical analyses, with the improved design accuracy and consistency revealed.

Cyclic modelling of T-joints with CHS chord members and passing-through plates

This paper focuses on modelling the cyclic response of welded T-joints between Circular-Hollow-Section (CHS) chords and passing-through plates. Recent works have highlighted that, in practical applications, this specific joint typology can be regarded either as a standalone connection or as a component representing one of the main sources of deformability and energy dissipation capacity in more complex beam-to-column joints with CHS columns and passing-through I-beams. Currently, research efforts have primarily focused on predicting the strength and stiffness of this type of connection. However, there is a knowledge gap regarding the characterization of the cyclic response of joints with passing-through members, a crucial aspect for modelling steel structures with these connection types in seismic areas.In light of this, the paper aims to characterize the cyclic response of T-joints with CHS members and passing-through plates using a comprehensive approach that incorporates experimental, numerical, and analytical methods. Initially, the results of an experimental study examining the cyclic behaviour of T-joint specimens with passing-through plates are presented. Subsequently, models of the tested joints are implemented in Finite Element software and validated against the experimental outcomes. The validated models are used to conduct a parametric study, considering 44 different configurations to obtain their force-displacement cyclic responses. These responses are mathematically modelled using the hysteretic uniaxial material from the OpenSees library and a Genetic Algorithm based tool previously developed by the authors (MultiCal). Finally, regression analyses are performed to develop formulations for predicting the mathematical parameters of the hysteretic uniaxial material model starting directly from the geometrical and mechanical properties of the connection.This approach enables designers to model the cyclic response in structural analysis with a straightforward approach, without the need for new calibrations or tests, if the modelled joints fall within the proposed range of calibration. From the point of view of the component modelling, the approach presented aligns with the larger research strand devoted to the extension of the component method codified in Eurocode 3 part 1.8 to cyclic loading conditions.

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.

Stability and design of stainless steel hollow section columns at elevated temperatures

This paper investigates the stability and design of stainless steel circular, elliptical, square and rectangular hollow section (CHS, EHS, SHS and RHS) columns at elevated temperatures. Nonlinear shell finite element models are employed to conduct comprehensive parametric studies whereby extensive benchmark structural performance data on the behaviour and resistance of stainless steel hollow section columns at elevated temperatures is generated. In total, 26,760 cold-formed and hot-rolled austenitic, duplex and ferritic stainless steel CHS, EHS, SHS and RHS columns at elevated temperatures are taken into account, considering various member slendernesses, cross-section geometries, cross-section slendernesses and elevated temperature levels. New flexural buckling design rules are put forward for stainless steel hollow section columns in fire, which consistently considers the elevated temperature strength at 2% total strain f2,θ as the reference material strength for all cross-sections classes. The accuracy, safety and reliability of the proposed new design rules are assessed for a wide range of cases. Comparisons are also made against the results obtained through the column fire design rules of the European structural steel fire design standard EN 1993-1-2 [1]. It is demonstrated that the proposed new design rules furnish more accurate, safe-sided and reliable flexural buckling resistance predictions for stainless steel hollow section columns at elevated temperatures relative to the column fire design provisions of EN 1993-1-2 [1].

Cyclic behaviour of 3D cut welded connections with CHS columns and through I‐beams

AbstractThis paper investigates the cyclic behaviour of a novel typology of steel beam‐to‐column connection made by welding circular hollow section (CHS) columns and through I‐beams. In fact, due to the novelty of this configuration and the lack of design equations in the current codes, the application of this innovative solution is limited in common practice.The LASTEICON research project has recently investigated the main technological issues related to the manufacturing process and the joint's flexural resistance. Additionally, at the University of Salerno, studies on this joint began a few years ago, focusing on the characterisation of its bending response within the framework of the component method approach. Therefore, experimental, numerical and analytical activities have led to defining the joint's main components and proposing formulations able to predict the initial stiffness and the chord failure resistance. However, the proposed approach concerns the investigation of the monotonic behaviour of the joint, leaving the investigation of its cyclic response still unexplored.To fill this gap, the cyclic flexural response of connections with CHS columns and through I‐beams is assessed in this paper, starting from the knowledge of the monotonic and cyclic behaviour of the main components of the connection.

Structural response and design of stainless steel hollow section columns at elevated temperatures

AbstractThis paper investigates the flexural buckling behaviour and design of stainless steel circular, elliptical, square and rectangular hollow section (CHS, EHS, SHS and RHS) columns at elevated temperatures through numerical modelling. Shell finite element models are utilised to perform numerical parametric studies whereby benchmark structural performance data are generated. A large number of cold‐formed and hot‐rolled austenitic, duplex and ferritic stainless steel CHS, EHS, SHS and RHS columns at elevated temperatures are taken into account, considering various cross‐section and member slendernesses. Since the fire design provisions provided in the European fire design standard EN 1993‐1‐2 for stainless steel columns are largely based on those originally developed for carbon steel columns, they typically lead to rather inaccurate ultimate resistance predictions for stainless steel columns at elevated temperatures. To address this, in the present study, a new flexural buckling design method for stainless steel hollow section columns at elevated temperatures is put forward. The accuracy, safety and reliability of the proposed design method and the provisions in EN 1993‐1‐2 are assessed. It is observed that the proposed fire design method leads to more accurate, safe‐sided and reliable flexural buckling resistance predictions for stainless steel hollow section columns at elevated temperatures relative to the provisions in EN 1993‐1‐2.

Numerical investigation and design method of cold-formed sorbite stainless steel circular tubes under uniaxial compression

The recently developed novel high-strength sorbite stainless steel (S600E) combines the advantages of exceptional mechanical properties, high corrosion resistance, effortless weldability, and cost-effectiveness, granting remarkable competitiveness in stainless steel structures. The authors have conducted and published experiment results on S600E circular hollow section (CHS) columns under uniaxial compression, which serve as a foundation for the subsequent numerical analysis presented in this study. An extensive parametric study encompassed key variable parameters such as slenderness ratio, section size, and diameter-to-thickness ratio, culminating in 748 numerical models. Meanwhile, the ultimate strength obtained through finite element analysis (FEA) was utilized to evaluate the calculation methods prescribed by current European, Australian/New Zealand, and Chinese stainless steel structural design standards and the direct strength method (DSM) available in the literature. The result shows that the DSM can accurately predict the ultimate strength of CHS columns with an average error of 0.2%, while other specifications are slightly conservative. Then, the effective area calculation method was proposed in this paper, whose rationality was verified by meso finite element analysis. Moreover, a revised equation in Chinese code was proposed, which can improve the prediction accuracy by 9.2%. Finally, a reliability analysis was conducted to assess the safety levels of the design standards and DSM. The findings of this study can not only benefit the adoption of the high-strength stainless steel in the construction industry and therefore potentially mitigate carbon-emission-related environmental issues.

Experimental study of the behavior under axial compression of steel tube confined concrete with a circular hollow section (STCC-CHS)

A new type of steel tube confined concrete columns (STCC) in which the outer steel tube only confines the core concrete and does not directly bear the axial load. Based on this, a new type of steel tube confined concrete with a circular hollow section (STCC-CHS) column was presented in this article. It demonstrated high strength and relatively light weight, high economic efficiency and promises easy installation. Axial compression tests were conducted to quantify the effects of the diameter-thickness ratio and the hollow ratio on the failure modes, the ultimate strength in axial compression, strain and stiffness. Constraint effects and ductility were also analyzed. The test results show that the outer steel tube effectively delays local buckling failure. The smaller the hollow ratio and the smaller the diameter-thickness ratio, the greater a column's bearing capacity. The observed ultimate compressive strength is compared with STCC and CFDST components. The experimental data are used to test the utility of the recommended formulas for predicting the axial bearing capacity of such columns, with several different models of the confined concrete strength.

Numerical investigation of branch plate-to-CHS connection under eccentric shear loading

Circular Hollow Section (CHS) columns are usually used in high-rise buildings. International design specifications usually overestimate the design of the beam-to-CHS column branch plate connections. This paper numerically investigates the behavior and strength of beam-to-CHS column branch plate connections using a finite element (FE) model. The FE model is verified using different experimental results available in previous literature. A parametric study is carried out on specimens subjected to eccentric shear loading on the branch plate with a constant column length and end conditions. The parameters included the CHS column diameter, wall thickness, branch plate length and the effect of load eccentricity. A notable effect of these parameters is observed on the connection capacity. The mode of failure of the studied specimens ranged from chord plastification for small thicknesses followed by chord face punching to excessive column ovalization at the vicinity of the connection followed by either chord punching or tearing out in the weld. For CHS columns with large thicknesses, punching failure in the column face or premature weld failure is observed. Finally, the results of the parametric study indicated a prominent effect of load eccentricity on the in-plane bending capacity. Therefore, a proposed improvement to the current design guidelines for the strength of CHS column branch plate connection subjected to in-plane bending is presented in this paper.

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.

Experimental and numerical investigation on the effect of concrete infill in pultruded GFRP CHS intermediate and long columns under axial and eccentric compression

The paper presents an experimental investigation of concrete-filled (CFFT) pultruded glass fibre-reinforced (GFRP) circular tubular columns under concentric and eccentric loading. The effective slenderness ratios of the CFFTs were 33, 44 and 55 and were tested under two different eccentricities of 28.5 mm and 57 mm. The failure modes observed for the CFFTs include localised hoop rupture and longitudinal splitting of the GFRP tube with concrete crushing. The axial load-carrying capacities of the CFFTs decreased with increasing eccentricity and slenderness. The strength and the ductility of the CFFTs were compared with their circular hollow section (CHS) counterparts tested in a previous study. A P-M interaction curve was developed, and its applicability was assessed against the experimental results for different slenderness ratios. The ultimate axial load and the locus and nature of the failure modes of CFFTs predicted from the developed finite element models were in good agreement with the experimental observations. The extent of damage of the GFRP tube in the CFFTs was compared to the damage of the GFRP CHS columns using FE analysis employing the Hashin damage material model for GFRP tube.

Analytical Model for Steel Fibre-Reinforced Concrete-Filled Tubular Columns Exposed to Fire

This study proposes an analytical model for the evaluation of the mechanical behaviour of circular hollow section columns infilled with steel fibre-reinforced concrete when exposed to elevated temperatures in a fire situation. This work includes the discussion of the results from a sensitivity analysis conducted through numerical simulation and the development of an analytical model based on the prEN1994-1-2:2021 European standard for the design of reinforced concrete structures exposed to fire. The sensitivity analysis aims to compare the fire resistance of centrally and eccentrically loaded circular hollow section columns infilled with plain and steel fibre-reinforced concrete. The proposed analytical model for determining the design buckling load of composite steel fibre-reinforced concrete-filled tube columns in a ?re situation is ready to serve as an annexe or supplementary technical document to the EN1994-1-2:202x standard.

Development of design equations for ultra-high strength steel CHS columns under transient fire conditions considering thermal creep and axial restraint effects

Despite their potential for widespread structural applications, the use of ultra-high strength steel (UHSS) members in buildings is currently hindered by the lack of suitable design relationships for these components. In response to this technical gap, this paper presents design equations for Grade 1200 UHSS circular hollow section (CHS) columns under transient fire conditions. The design relationships are derived from an extensive parametric study on the in-fire behavior of UHSS tube columns using advanced finite element (FE) simulations in ABAQUS software. However, to verify the FE modeling framework, experiments are also conducted on axially-compressed UHSS tube specimens. The thermal creep of the UHSS tubes is explicitly included as a user-defined subroutine in the modeling by a robust creep model exclusively developed for the UHSS material under transient fire conditions. In addition to the utilization factor, the effects of non-dimensional slenderness, heating rate (or thermal creep), and axial restraint stiffness ratio are also studied and considered in the design equations obtained for the UHSS CHS columns. Finally, it is shown that the present design relationships can predict the columns' buckling and failure temperatures with a maximum absolute error (MAE) of 4%.

Experimental and numerical investigation of pultruded GFRP circular hollow tubular columns under concentric and eccentric loading

This paper presents an experimental investigation of pultruded glass fibre reinforced polymer (GFRP) circular hollow section (CHS) columns under concentric and eccentric compression. The member slenderness of the selected columns was in the short, intermediate, and long range, and two different eccentricities were chosen within the column's cross section. Predominant failure modes observed in the experiment include longitudinal splitting and localized delamination buckling. The load-carrying capacities of the concentric column under different slenderness values were quantified and compared with existing design rules. Under eccentric loading, the ultimate loads of the columns decrease with increasing eccentricity and slenderness, and the load–strain behaviour displayed non–linear characteristics due to geometric non-linearity. Failure modes of all the tested columns were well predicted by the FE models, and it was found that splitting material failure was due to hoop matrix tensile rupture.

Flexural Buckling of Wire Arc Additively Manufactured Tubular Columns

Wire arc additive manufacturing (WAAM) is a metal three-dimensional (3D) printing method that enables large-scale structural elements with complex geometry to be built in a relatively efficient and cost-effective manner, offering revolutionary potential to the construction industry. However, fundamental experimental data on the structural performance of WAAM elements, especially at the member level, are lacking. Hence, an experimental study into the flexural buckling response of WAAM tubular columns has been conducted and is presented in this paper. A total of 18 stainless steel square and circular hollow section (SHS and CHS) columns were tested under axial compression with pin-ended boundary conditions. Regular SHS and CHS profiles were chosen to enable direct comparisons against equivalent, conventionally manufactured sections and, hence, to isolate the influence of the additive manufacturing process, whereas the cross-section sizes and column lengths were varied to achieve a broad spectrum of member slendernesses. Given the geometric undulations inherent to the WAAM process, 3D laser scanning was used to determine the as-built geometry and global geometric imperfections of the specimens; digital image correlation (DIC) was employed to monitor the surface deformations of the specimens during testing. Full details of the column testing program, together with a detailed discussion of the experimental results, are presented. The applicability of the current column design provisions in EN 1993-1-4 and AISC 370 to WAAM stainless steel members was assessed by comparing the test results with the codified strength predictions. The comparisons emphasized the need to allow for the weakening effect of the inherent geometric variability of WAAM elements to achieve safe-sided strength predictions.

Flexural buckling of high-strength aluminium alloy CHS columns

High-strength aluminium alloys are increasingly popular and gaining more prominence in structural engineering. The global buckling behaviour and design of high-strength aluminium alloy circular hollow section (CHS) columns subjected to axial compression are investigated in this study. Ten experiments on CHS specimens with two extruded 7A04-T6 CHS profiles – 165 × 15 and 165 × 7.5 (in mm), were conducted. The material tests and initial geometric imperfection measurements were carried out prior to column tests. The test setup, procedure and results, including failure modes, ultimate resistances and load–displacement curves were comprehensively reported and analysed. Based on the developed and validated finite element (FE) models, an extensive parametric study, over a broad range of member and cross-section slenderness as well as the strain hardening exponents and proof strengths of the high-strength aluminium alloy material, was performed to complement the test data pool. The applicability of current buckling design provisions used for normal-strength aluminium alloy columns in the European, Chinese, American, Australian & New Zealand standards and the proposal of Rasmussen and Rondal to 7A04-T6 high-strength aluminium alloy CHS columns was evaluated through comparisons with the test and FE results. The results show that the European, Chinese and American standards provide conservative buckling resistance predictions, while the Australian & New Zealand standard and Rasmussen’s proposal generally yield unsafe capacity predictions. Finally, two flexural buckling curves within the framework of the EN 1999-1-1:2007 design method, featuring a revised linear imperfection term and a newly developed hybrid linear-nonlinear imperfection term, were proposed accordingly, and were shown to provide more accurate and consistent buckling resistance predictions.

Structural Response and Residual Capacity of S700 High-Strength Steel CHS Columns after Exposure to Elevated Temperatures

The structural behavior and residual capacity of S700 high-strength steel circular hollow section (CHS) columns after exposure to elevated temperatures were studied through testing and numerical modeling. The testing program was conducted on 10 S700 high-strength steel CHS columns and comprised heating and cooling of the specimens as well as postfire material testing, measurements of initial geometric imperfections, and pin-ended column tests. Numerical simulations were subsequently performed, where finite element models were built and validated with reference to the experimental results and afterward used to conduct parametric studies to obtain further numerical data. Given that there are no specific provisions for the design of steel structures after exposure to elevated temperatures, the relevant room-temperature design buckling curves were evaluated, using postfire material properties, for their applicability to S700 high-strength steel CHS columns after exposure to elevated temperatures, based on the experimental and numerical data. The evaluation results indicated that the buckling curves prescribed in the American specification and Australian standard lead to accurate and consistent residual capacity predictions for S700 high-strength steel CHS columns after exposure to elevated temperatures, while the Eurocode buckling curve yields conservative predictions of residual capacity. A revised Eurocode buckling curve was then proposed, and resulted in a higher level of accuracy than its original counterpart.

Testing, simulation and design of hot-rolled seamless austenitic stainless steel CHS columns

Stainless steel circular hollow section (CHS) members are favoured by architects and structural engineers because of their aesthetics, superior torsional resistance and corrosion resistance. Hot-rolling is one of the typical production processes for producing CHS members. Nevertheless, few research has been carried out concerning the hot-rolled stainless steel CHS members. This paper reports experimental and numerical investigations into hot-rolled seamless stainless steel CHS columns. Flexural buckling tests on eight columns were firstly carried out in the experimental investigation. This was followed by numerical modelling investigation, where the FE models were developed and validated against the test results. The validated FE models were then used to conduct a series of parametric studies to obtain more data covering a wide range of member slenderness and cross-section sizes. Based on test and FE results, three existing design approaches in the Eurocode, Chinese specification and American specification were assessed and discussed. The assessment results show that the three design approaches all provide relatively accurate strength prediction on the whole, but the design approaches in the 1993-1-4 + A2 and ANSI/AISC 370-21both give overestimated strength predictions while design approach in the CECS 410 gives a relatively conservative strength prediction when the column slenderness is small. In view of this, new column design curve has been proposed, with its advantage over the existing design approaches confirmed by quantitative and graphical comparisons.

Flexural buckling of normal and high strength steel CHS columns

This paper presents an experimental and numerical investigation into the stability of normal and high strength steel circular hollow section (CHS) columns. Two cold-formed S700 CHS profiles – 139.7×4 and 139.7×5 (in mm), were studied in the experimental programme, and twelve column tests (six on each profile), together with accompanying material tests, were performed. The load-deformation histories and key results from the tests are reported. Following the physical testing, a numerical simulation campaign was conducted. The developed finite element (FE) models for CHS columns were initially validated against the test results. Parametric studies were then carried out, where 2000 additional buckling resistance data were numerically generated for hot-finished and cold-formed CHS columns, covering steel grades from S355 to S900. The obtained test and FE results, together with existing experimental data from the literature, were used to assess the current Eurocode 3 stability design rules. It was shown that the normalised performance of CHS columns is influenced by the yield strength, which is not fully captured by the EC3 design approach. The somewhat conservative Class 3 slenderness limit for compression further worsen the accuracy for those with slender cross-sections. Improvements to the EC3 design rules were proposed to address these shortcomings, including (a) modified Ayrton-Perry formulae enabling a continuous transition of buckling curves across the yield strength spectrum and (b) a new Class 3 limit for CHS in compression. The modified EC3 approach was assessed and shown to improve the accuracy and consistency of resistance predictions over the current EC3 approach, while meeting the Eurocode structural reliability requirements.