Steel Circular Hollow Section Research Articles

Designing of Steel CHS Columns Showing Maximum Compression Resistance

The paper deals with a shape optimisation procedure of steel, compressed bars. Circular hollow sections (CHS) of variable cross sections and variable wall thickness are taken into account. The proposed procedure for designing of steel rods exhibiting maximum compression resistance is effective and possible to use in engineering practice. The advantage of the proposed shape of the bar is that it allows to increase the value of its load carrying capacity, i.e. it ensures the transfer of a higher value of compressive force than similar, solid struts of the same mass and length. The extent of the increase in the load capacity relative to the load capacity of the reference solid, cylindrical bar depends on the slenderness of the reference bar and ranges from 60% to 170%. Due to this very beneficial fact, it can be used wherever it is required to maintain a certain stiffness and an increased value of compressive force is desired, as well as in constructions where it is necessary to reduce weight while maintaining the adopted mechanical parameters, e.g. values of load bearing capacity. Final results achieved in the research were presented in the form of the flow chart allowing to design the compressed columns of optimum shape.

Experimental and numerical study of hot-rolled duplex stainless steel CHS columns

Stainless steel circular hollow section (CHS) members have been widely used in building structures because of their comparable strength to structural carbon steels, attractive appearance and excellent corrosion resistance. However, research on stainless steel CHS members has been limited to cold-formed members, whereas hot-rolled CHS columns have received less attention. To this end, the flexural buckling performance of hot-rolled duplex stainless steel CHS columns was investigated by a comprehensive experimental and numerical programme. A total of seven hot-rolled duplex stainless steel CHS columns covering two cross-sectional sizes with varying lengths have been tested under compression. Based on the test results, finite element (FE) models were developed and used in parametric studies to generate data points with a wider range of geometric dimensions. Comparing the test and FE results with current design guidance, it was found that the Chinese standard, CECS 410, and North American design guidance, AISC DG 27, underestimate significantly the flexural buckling resistance of such columns, while the design method in Eurocode 3: Part 1–4 might be unsafe in predicting the resistances for low slenderness values. New column buckling curves based on the Eurocode 3 and AISC DG 27 design formulae with improved accuracy and reduced scatters were also proposed and validated through careful reliability analysis.

Strengthening of corroded steel CHS columns under axial compressive loads using CFRP

Stemming from unfavorable environmental conditions, corrosion can adversely affect the behavior of steel structures and damage them. To investigate this phenomenon and study the failure mode and load bearing capacity of corroded slender steel columns to retrofit them by Carbon Fiber Reinforced Polymer (CFRP), 8 equal-height slender Circular Hollow Section (CHS) column specimens were subjected to corrosive conditions at mid-height and near to bottom supports for 12, 18 and 24 hours, retrofitted by CFRP sheets and then all corroded and retrofitted columns were experimentally tested under axial compressive loading; damage dimensions were different. These specimens and two more were also studied numerically based on the Finite Element (FE) analyses of imperfected models using ABAQUS software. The specimens were first analyzed elastically to find their local and global buckling modes and then inelastically (with nonlinear geometry and material). Experimental and numerical results showed that the main problem with slender columns was their global buckling under compressive loading and corrosion reduced their load bearing capacity and ductility. According to these results, corrosion highly affected the buckling of the corroded area and deformed it axially. Regarding corroded columns retrofitted with CFRP, fibers increased the ultimate load capacity and ductility, delayed buckling of the corroded area, controlled fractures and reduced stresses in the damaged zone.

Experimental and numerical investigation of short GFRP- reinforced steel tubular short columns

Abstract This study presents the experimental and analytical modelling of externally bonded glass fibre-reinforced polymer (GFRP) sheets for strengthening circular steel tubular short columns. The GFRP sheets are easy to handle due to the lightweight property and the high-strength can provide a degree of restraint to delay buckling of the thin steel wall. Four short columns of cold-formed steel circular hollow section (CHS) were experimentally tested. One column is conventional (without GFRP wrap) and other 3 columns are externally bonded unidirectional (hoop) GFRP sheets which are varying with numbers of layers (1, 2 and 3 layers). In addition to the experimental studies, finite element analysis was also carried out using ABAQUS software. The experimental result shows that the steel tube is strengthened by GFRP sheets and enhances the axial section capacity. The load carrying capacity of externally bonded GFRP column increases about 17%−49% on comparison with the column without confinement. The study also concluded that the column externally warped with 3 layers of GFRP sheet is found to be optimum and it attains maximum load caring capacity. The prediction of analytical results has been found to be in good correlation with the experimented results.

Testing and analysis of additively manufactured stainless steel CHS in compression

Additive manufacturing, also referred to as 3D printing, has the potential to revolutionise the construction industry, offering opportunities for enhanced design freedom and reduced material use. There is currently, however, very limited data concerning the performance of additively manufactured metallic structural elements. To address this, an experimental and numerical investigation into the cross-sectional behaviour of circular hollow sections (CHS), produced by powder bed fusion (PBF) from Grade 316L stainless steel powder, is presented. The experimental programme comprised tensile coupon tests, initial geometric imperfection measurements and five axially loaded stub column tests on specimens with a range of diameter-to-thickness (D/t) ratios. Similar cross-sectional behaviour to that of conventionally produced stainless steel CHS was observed, with the more slender cross-sections displaying increased susceptible to local buckling. In parallel with the experimental study, numerical simulations were carried out initially to replicate the experimental results and then to conduct parametric studies to extend the cross-sectional capacity data over a wider range of D/t ratios. The generated experimental and numerical results, together with other available test data on stainless steel CHS from the literature, were used to evaluate the applicability of existing design approaches for conventionally formed sections to those produced by additive manufacturing.

Behavior and design formulation of steel CHS with sleeve connections

Structures with tubular profiles gain space in civil construction due to their excellent response under tension, compression, and torsion. They are widely used in structural trusses, especially in large lengths. The profiles have a limited size due to the manufacturing and transport process. Therefore, there is a need to use some mechanism to perform the joint of profiles and obtain the desired length. This work aims to develop a new type of bar splice in circular hollow section (CHS) connection called sleeve connection, composed of two tubes connected with another smaller diameter tube with bolts arranged in a line (staggered bolts). This research presents an experimental, numerical, and parametric study of sleeve connection in CHS under centric axial tension. A numerical model was developed using the finite element method (FEM) considering sleeve connection with staggered bolts. From the numerical results, it was possible to analyze the connection behavior and failure modes: yielding gross cross-section, fracture through the effective net area, bolt shear failure, bearing failure of the plate, and bolt bending failure. This way, formulations were proposed to predict the sleeve connections' behavior with staggered bolts as a function of the failure modes.

Structural behaviour and design of high strength steel CHS T-joints

This paper investigates the structural behaviour of high strength steel (HSS) circular hollow section (CHS) T-joints under brace axial compression. Finite element analysis on CHS T-joints using S460, S700, S900 and S1100 steel was conducted, and the chord plastification failure was examined. The effect of heat affected zones (HAZ) on the joint behaviour and influences of the steel grade, brace to chord diameter ratio (β) and chord diameter to wall thickness ratio (2γ) on the suitability of the CIDECT mean strength equations for HSS CHS T-joints were evaluated. The effect of HAZ on the initial stiffness of HSS CHS T-joints is found to be insignificant. The material softening in HAZ can lower the joint strength; however, the joint strength reduction is less pronounced. In general, the influence of β ratio on the suitability of the CIDECT mean strength equations for HSS CHS T-joints is minor. The CIDECT mean strength prediction is relatively accurate for S460 CHS T-joints and becomes increasingly unconservative for higher steel grade and larger 2γ ratio. This is because the improved yield stresses of HSS generally could not be fully utilised due to the adopted CIDECT indentation limit of 3% of chord diameter. It is suggested to tighten the range of 2γ ratio to be 2γ ≤ 40 for steel grades ranging from S460 to S700 and 2γ ≤ 30 for steel grades greater than S700 up to S1100 to allow for more effective use of HSS. The CIDECT validity range of 0.2 ≤ β ≤ 1.0 is also recommended for steel grades ranging from S460 to S1100. Mean and design strength equations modified from the CIDECT strength equations were proposed for HSS CHS T-joints with 2γ and β ratios which are within the suggested ranges.

Strength prediction of steel CHS X-joints via leveraging finite element method and machine learning solutions

This study employs high-fidelity finite element method (FEM) and machine learning (ML) solutions to determine the accurate strengths of steel circular hollow section (CHS) X-joints with minimal computational effort. FE analysis methods have helped to improve the understanding of the complex structural behavior of CHS joints. However, the routine use of FE analysis imposes high computational demands and requires a thorough verification of numerical models. Alternatively, this study explores the feasibility of using ML methods for estimating the strengths of CHS X-joints. High-fidelity FE models were first built to generate about 4000 datasets. Each dataset included seven joint parameters, namely, steel grade, chord diameter, brace-to-chord diameter ratio, chord diameter-to-thickness ratio, brace-to-chord thickness ratio, chord length-to-radius ratio, and chord stress level. Two ML models; a support vector regression (SVR) and a deep neural network regression (DNNR) were formulated, extensively trained, tested, and validated via comparison with experimental data. The validated DNNR model provided a more accurate prediction of the joint strength with an average error of 0.8%. On the basis of extensive joint strength data readily available from the proposed ML solution, the joint strength margin implied in current design equations was evaluated from various perspectives via variation of key joint parameters.

Stub Column Behavior of Cold-Formed High-Strength Steel Circular Hollow Sections under Compression

AbstractThis paper describes an experimental and numerical investigation on the stub column behavior of cold-formed high-strength steel (HSS) circular hollow sections (CHSs). A total of 16 stub col...

Investigation on the behaviour of CFRP strengthened CHS members under monotonic loading through finite element modelling

During the past several years, civil infrastructure has made extensive use of tubular hollow steel members as structural elements. However, the rehabilitation and strengthening of tubular hollow steel members is a major concern due to design errors, environmental effects, reduction in material properties over time caused by corrosion and the need to withstand increased loads. A comprehensive investigation on the strengthening of tubular hollow steel members is therefore required. Although carbon fibre reinforced polymer (CFRP) strengthening technique has shown its effectiveness to improve the structural response of different steel members, studies on the structural response of circular hollow section (CHS) steel members strengthened with CFRP is limited. In the present study, an effective finite element (FE) model is first developed by comparing the FE model simulated results with the authors' experimental results. This is followed by a parametric study on the effect of the bond length of CFRP, number of CFRP layers, ratio of CFRP thickness to CHS wall thickness, diameter to thickness ratio of CHS and steel grade of CHS on the structural behaviour of the strengthened member subjected to monotonic loading. These parameters had noteworthy effects on the behaviour of the CFRP strengthened CHS steel members under monotonic loading. The CFRP strengthened CHS steel members showed an improvement in the moment capacity, secant stiffness, energy dissipation capacity and ductility compared to their bare CHS steel members. It can be concluded that the effectiveness of the CFRP strengthening technique is enhanced with the increase in the ratio of CFRP thickness to CHS wall thickness and/or increasing the diameter to thickness ratio of CHS. In contrast, the effectiveness of the CFRP strengthening technique is decreasing with the increasing of the steel grade.

Cross-sectional behaviour of cold-formed high strength steel circular hollow sections

A comprehensive experimental and numerical study into the cross-sectional behaviour of structural steel circular hollow sections (CHS), with an emphasis on high strength steel, is presented in this paper. Six cold-formed high strength steel S700 CHS profiles – 168.3×4, 139.7×4, 139.7×5, 139.7×6, 139.7×8 and 139.7×10 (diameter × thickness, in mm), spanning from Class 1 to Class 4 in compression according to EN 1993-1-1, were experimentally examined. The test programme consisted of twelve tensile coupon tests, local geometric imperfection measurements, six stub column tests, six four-point bending tests, six three-point bending tests and fifteen short beam-column tests. In parallel with the experimental study, finite element (FE) models of CHS were established and validated against the obtained experimental results, and parametric studies were subsequently carried out using the developed models to expand the cross-sectional resistance data pool. Finally, the cross-section design provisions specified in the European code prEN 1993-1-1:2018 and the American Specification ANSI/AISC 360-16 were assessed using the freshly generated experimental and numerical results as well as the existing test data on hot-rolled and cold-formed CHS from the literature. The present study provides the basis for the development of improved cross-section design rules for normal and high strength steel CHS in future research.

Evaluation of Load Factor to Be Applied in Buckling Design of Cylindrical Lattice Shells Under Asymmetric Snow Load

The load factor is one of the keys in anti-buckling design for safety together for construction cost, and studies have been becoming demanded in a recent situation that super large and super light spatial structures have been constructed. This paper investigates the relationship between reliability index β and snow load factor γs for anti-buckling design of a simply supported cylindrical lattice shell roof under simultaneous action of both dead load and asymmetric snow load. The cylindrical lattice shell analyzed is composed of an equilateral triangle grid of which members are of steel circular hollow sections. Members are connected rigidly to nodes at their both ends. The snow distribution as a main target is assumed in a way that the snow depth on the half of the arch-like roof is half of the amount on the other half roof. The snow fall depth is here assumed 50cm evaluated as 100-year return period, and its probability is assumed as Gumbel distribution with 100-year reference period. The probability distribution of buckling strength Pcr including geometrical and material nonlinearities is approximately evaluated based on a first-order perturbation. The reliability is calculated based on AFOSM, and the relationship in a form of β to γs is finally expressed for design use.

Flexural buckling behaviour and residual strengths of stainless steel CHS columns after exposure to fire

The flexural buckling behaviour and residual strengths of stainless steel circular hollow section (CHS) columns after exposure to fire were studied, based on a thorough experimental and numerical modelling programme, and reported in this paper. The experimental programme was performed on three series of specimens, and each series contained five geometrically identical specimens, with one unheated and the other four heated to different levels of elevated temperatures (namely 300 °C, 600 °C, 800 °C and 1000 °C). The detailed heating, soaking and cooling processes, material testing and pin-ended column tests were described, with the derived key experimental results fully presented. The testing programme was supplemented by a numerical modelling programme, including a validation study where finite element models were developed and validated against the test results, and a parametric study where the validated finite element models were employed to derive further numerical results over an extended range of cross-section dimensions and member lengths. Due to the absence of existing design codes for stainless steel structures after exposure to fire, the codified design provisions for stainless steel CHS columns at ambient temperature, as established in the Europe, America and Australia/New Zealand, were assessed for their applicability to stainless steel CHS columns after exposure to fire, based on the obtained test and numerical data. The assessment results generally revealed that the design buckling curve, as adopted in the European code, and the tangent modulus method, as employed in the American specification, lead to unsafe and scattered design flexural buckling strengths for stainless steel CHS columns after exposure to fire, while the explicit approach, as used in the Australian/New Zealand standard, yields a high level of accuracy and consistency in predicting the post-fire flexural buckling strengths of stainless steel CHS columns. • The flexural buckling responses and residual strengths of stainless steel circular hollow section (CHS) columns after exposure to fire were investigated. • Three series of stainless steel CHS column specimens were tested, with each series containing one unheated specimen and four specimens heated to different levels of elevated temperatures. • Finite element models were developed and validated against test results, and then utilised to perform parametric studies. • The accuracy of the codified flexural buckling design rules for stainless steel CHS columns at ambient temperature was assessed for their post-fire counterparts.

Material properties and residual stresses of cold-formed high-strength-steel circular hollow sections

Owing to the development of material processing technologies, high strength steel plates with yield strengths exceeding 460 MPa are commercially available at present. However, experimental investigations on material properties and residual stress distributions of cold-formed high strength steel circular hollow sections (CHSs) are rather limited. This paper therefore presents an experimental investigation to advance the knowledge in this area. In total, 11 steel circular hollow sections were manufactured from steel plates with the measured yield strength varying from 546.5 MPa to 973.3 MPa. A total of 58 tensile coupons taken from parent plates and hollow tubes were tested to examine the effect of cold-forming process on material properties within the cross-section. When compared with parent metals, strength enhancements were found in Q460 sections, while yield strengths remained nearly the same as parent metal in Q690 sections, and a slight strength reduction by around 1% was noticed in Q960 sections. Basic material parameters in existing material models to obtain stress-strain curves were thoroughly calibrated against the coupon test results. Results indicate that the use of the calibrated parameters can give excellent predictions in terms of stress-strain curves. Residual stress measurements on 2 cold-formed CHSs were performed, with 57 strips extracted and 684 readings taken. The maximum tensile membrane residual stress and maximum tensile bending residual stress on the external surface were observed to be 41% and 32% of the material yield strength. A multilinear predictive model for the distribution of membrane residual stresses in cold-formed high-strength-steel CHSs was subsequently proposed.

Compressive resistance of high-strength and normal-strength steel CHS members at elevated temperatures

The compressive behaviour of hot-finished circular hollow section (CHS) steel members in fire is investigated in this paper through numerical modelling. CHS members with high-strength steel grades of S690 and S460 are taken into consideration in addition to those made up of normal-strength grades S355, S275 and S235. Numerical models of CHS structural steel members able to replicate their response in fire are validated. Using the validated finite element models, extensive parametric studies are carried out for the purpose of exploring a broad range of factors influencing the cross-section and member buckling response of CHS steel members under axial compression at elevated temperatures. The accuracy and safety of the design recommendations provided in the European structural steel fire design standard EN 1993-1-2 for the determination of the axial compression resistances of CHS steel members in fire are assessed. New design methods able to provide accurate and safe estimations of the cross-section axial compression resistances and flexural buckling resistances of CHS steel members at elevated temperatures are proposed. The higher accuracy, reliability and safety of the proposed design methods relative to the existing design provisions in EN 1993-1-2 are illustrated. • Behaviour and design of high-strength and normal-strength steel CHS members under compression in fire are investigated. • FE models able to mimic response of CHS steel columns in fire are developed and validated using results from experiments. • New design rules for cross-section and flexural buckling resistance of CHS steel columns in fire are established. • Proposed design rules lead to more accurate results relative to the current design rules in EN 1993-1-2. • Accuracy, safety and reliability of proposed design rules are verified against extensive numerical data.

Cold-formed stainless steel CHS beam-columns – Testing, simulation and design

The present work was prompted by shortcomings identified in existing design provisions for stainless steel circular hollow section (CHS) beam-columns. First, addressing a lack of existing experimental data, a series of ferritic stainless steel CHS beam-column tests was undertaken at the cross-section and member levels. In total, 26 beam-column tests, including two section sizes (a non-slender class 3 and slender class 4 cross-section), two member slenderness values for each cross-section type and a wide range of loading eccentricities were carried out to investigate the interaction between local and global buckling. Following validation of finite element (FE) models, a numerical study was then undertaken to explore the buckling response of stainless steel CHS beam-columns, covering austenitic, duplex and ferritic grades with a wide range of local and global slendernesses and applied loading eccentricities. Over 2000 numerical results were generated and used to assess new design proposals for stainless steel beam-columns, featuring improved compression and bending end points and new interaction factors. The new proposals are more consistent and more accurate in their resistance predictions than the current EN 1993-1-4 (2015) design approach. The reliability of the new proposals has been verified by means of statistical analyses according to EN 1990 (2005).

Numerical study of fire resistance of stainless steel circular hollow section columns

Stainless steel has countless desirable characteristics for a structural material. Although initially more expensive than conventional carbon steel, stainless steel structures can be competitive due to their smaller need for fire protection material and lower life-cycle cost, thus contributing to a more sustainable construction. The most common stainless steel groups used in structural applications are the austenitic, ferritic and austenitic–ferritic (also known as Duplex grades). This work presents a numerical study on the behaviour of stainless steel circular hollow section members under axial compression at elevated temperatures, with different cross-section slenderness. The numerically obtained ultimate load-bearing capacities are compared with simplified calculation formulae from Eurocode 3 for columns under fire situation. A parametric study, considering different stainless steel grades from the aforementioned groups, cross-sectional classes and slendernesses, is here presented for different elevated temperatures. The numerical analyses were performed with the finite element programme SAFIR, with material and geometric non-linear analysis considering imperfections. Comparisons between the numerical results and the Eurocode 3 rules demonstrated that a specific design approach must be developed for stainless steel columns under fire situation.

Elasto-plastic behaviour and design of semi-compact circular hollow sections

Previous research has revealed shortcomings in the current Eurocode 3 (EC3) provisions for the design of semi-compact (Class 3) cross-sections. These shortcomings arise primarily from the lack of utilisation of partial plastification in bending, leading to a step in the design resistance function at the boundary between Class 2 and 3 cross-sections and an underestimation of the available capacity. This affects the accuracy of resistance predictions in bending and under combined loading, and applies at both cross-sectional and member level. To address this issue, the use of an elasto-plastic section modulus, which lies between the plastic and elastic section moduli, has been proposed and employed in the design of semi-compact I- and box sections. The aim of the present study is to develop new cross-section and member buckling design rules incorporating the elasto-plastic section modulus for semi-compact circular hollow sections (CHS), and to assess their accuracy against existing experimental and freshly generated numerical data. Firstly, an experimental database, consisting of previous cross-section and member buckling test results on steel CHS, was established. A comprehensive numerical simulation programme was subsequently carried out; in this programme, finite element (FE) models were developed, validated and used for parametric studies, where over 600 numerical structural performance data on semi-compact CHS were generated. New sets of cross-section and member buckling design expressions featuring elasto-plastic section properties were then proposed and assessed against the test and numerical data. The proposals were shown to offer improved accuracy and design efficiency over the elastic EC3 methods. The reliability of the proposed elasto-plastic design rules was then confirmed through statistical analyses in accordance with EN 1990, demonstrating their suitability for inclusion into the next revision of EN 1993-1-1. • Existing cross-section and member buckling test data on CHS were collected. • Numerical simulation was conducted to generate further data on CHS. • New design rules were developed to capture the elasto-plastic behaviour of semi-compact CHS. • Accuracy of the current Eurocode 3 and proposed methods were assessed and compared. • Reliability of the proposed design rules was confirmed through statistical analyses.

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.

Investigation of high-strength steel CHS X-joints loaded in compression including effect of chord stresses

Internationally representative steel design standards imposed restrictions on tubular joints fabricated from high-strength steels, and this is partly due to concerns regarding their unique material characteristics, such as high yield ratio and low deformability. The joint strength equation cannot be fully utilized for steels wherein yield strength exceeds 355 or 360 MPa. However, the mechanical background of the limitations is not adequately understood. The authors recently conducted experimental testing of high-strength steel circular hollow section (CHS) X-joints and clearly indicated that the current limitations are typically unduly conservative. In this study, supplemental test-validated numerical analyses were performed to further investigate the chord plastification behavior of high-strength steel CHS X-joints subjected to brace axial compression, including the effect of chord stress. Three steel grades ranging from ordinary to very high strength steels were considered in the analyses. The results indicated that the high-strength limitations to the tubular joints in current standards can be relaxed. The assumptions underlying current chord plastification strength formula are questioned and a more consistent joint strength equation is newly proposed based on the concept of effective strain-hardening. Based on a numerical and experimental database of high-strength steel joints, the suitability of the widely accepted 3% indentation criterion is evaluated from the perspective of joint flexibility. High-strength steel joints under the effect of chord stress generally outperformed ordinary steel joints, and their strengths were conservatively predicted via current chord stress functions.