Steel Circular Hollow Section Research Articles

Evaluation and Prediction of the Bending Behavior of Circular Hollow Steel Tube Sections Using Finite Element Analysis.

Circular hollow steel tube columns are widely used in high-rise buildings and bridges due to their ductility and lower weight compared to reinforced concrete. The use of this type of steel section has several advantages over using reinforced concrete members. The present study investigates the bending behavior of steel circular hollow sections when subjected to bending loads. The variations in material characteristics with regard to position along the cross-section of a steel tube member is first considered in this experimental study, providing for a more accurate definition of the material behavior in the model. A supported beam tested by two-point loads is the loading type that is used to study the bending performance of steel tubes. Ten circular hollow beam specimens were prepared and tested up to and post the failure stage with the following dimensions: thickness (2, 3, and 6 mm), diameter (76.2, 101.6, and 219 mm), and span (1000, 1500, and 2000 mm). A finite element analysis has been conducted for these ten specimens using the ANSYS program. The finite element model is compared to experimentally obtained data to verify that both local and global behaviors are correctly considered. The load-deflection results of this analysis showed a good agreement with the experimental results. A parametric study also was performed that considered two variables, which were the effect of the presence of circular rings and the change of opening location in the length direction on the specimens’ behavior. This study showed that the presence of the circular rings in the specimen led to an increase in its ultimate strength (of 53.24%) compared with the non-presence of these rings. In contrast, the presence of openings at 30, 40, and 50% from the specimen length reduced the strength capacity by 8.76, 14.23, and 17.88%, respectively.

Resistance of circular hollow section branch plate joints made from high strength steel

This paper presents an experimental and numerical investigation of the resistance of branch plate joints to a high-strength steel circular hollow section chord member subjected to axial compression with chord face plastification failure mode. The aim of the research was to investigate the effect of increased yield strength on joint behaviour and resistance. An experimental programme was conducted on ten specimens fabricated from S700 steel with longitudinally and transversely welded plates.

Experimental and numerical investigation of S700 high strength steel CHS beam–columns after exposure to fire

This paper presents an experimental and numerical investigation into the post-fire behaviour and residual capacity of S700 high strength steel circular hollow section (CHS) beam–columns. The experimental investigation was performed on ten S700 high strength steel CHS beam–columns and included heating and cooling of the specimens as well as post-fire material testing, initial global geometric imperfection measurements and pin-ended eccentric compression tests. A subsequent numerical investigation was conducted, where finite element models were developed and validated against the test results and then employed to carry out parametric studies to generate further numerical data over a wide range of cross-section dimensions, member lengths and loading combinations. In view of the fact that there are no specific provisions for the design of steel structures after exposure to fire, the relevant room temperature design interaction curves were evaluated, using post-fire material properties, to assess their applicability to S700 high strength steel CHS beam–columns after exposure to fire, based on the test and numerical data. The evaluation results revealed that the interaction curves provided in the American Specification and Australian Standard result in a high level of design accuracy and consistency, while the Eurocode interaction curve leads to more conservative and scattered failure load predictions. Finally, a revised Eurocode interaction curve, with more accurate end points, was proposed and shown to offer improved failure load predictions for S700 high strength steel CHS beam–columns after exposure to fire.

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.

Structural performance and design of stainless steel SHS-concrete‑carbon steel CHS double-skin stub columns

Concrete-filled double-skin steel tube (CFDST) with outer stainless steel square hollow section (SHS) and inner carbon steel circular hollow section (CHS) is introduced in this paper. The square-shaped section provides easier connection with other structural elements and the utilization of the three different materials (stainless steel, concrete and carbon steel) contributes to the advantages of their combined strength, corrosion resistance and economy. This paper reports a finite element (FE) analysis and the FE models are developed with consideration of geometric imperfection and stainless steel's non-linear material property. To validate the models, a comparison of the results of FE models and experiments is performed on the basis of ultimate section capacities, load deformation histories and failure modes. Parametric study is then carried out for the analysis of structural performance of CFDST stub columns, especially on interaction stresses between concrete and steel tubes, load deformation histories and stress distribution of each component. The failure modes and their corresponding ultimate limit states have been thoroughly discussed for the four typical types of CFDST stub column. In addition, the current international design codes including Eurocode 4, AISC and AIC are assessed with the generated ultimate section capacities from FE models. It is observed that ACI provides better predictions as compared to other codes. At last, the new design equation is proposed to predict the ultimate section capacity of the CFDST stub column which shows very good agreement with the FE analysis results.

Failure modes of bonded wrapped composite joints for steel circular hollow sections in ultimate load experiments

The concept of an innovative bonded joining technology where welding is not required is presented as an alternative to traditional welded connection for steel circular hollow section (CHS). Wrapped composite joints have potential to greatly improve fatigue endurance when applied in multi-membered truss structures, e.g. offshore jackets for wind turbines. This paper focuses on characterization of resistance and understanding of failure modes of wrapped composite joints in static experiments, as the prerequisite for harvesting its potential for high fatigue endurance. Wrapped composite joints at two scales and with two different angles of X-joint geometry are made with GFRP composite material wrapped around steel sections without welding, and tested in 3 monotonic loading cases, tensile, compression and in-plane bending, until failure. Counterpart welded joints are tested at the smaller scale for stiffness, elastic limit and ultimate load comparisons. Two general failure modes of wrapped composite joints, debonding and fracture of the composite material are identified and quantified by surface strain measurements through 3D digital image correlation (DIC) technique. Testing results indicate that wrapped composite joints have 30% to 56% larger stiffness and 3% to 68% larger ultimate load compared to welded counterparts. Debonding and final pull-out of steel brace member from the composite wrap is predominant failure mode in tensile experiments at both scales while cracking of the composite material is the governing failure mode in the bending experiment. In tensile, compressive and bending experiments failure load of wrapped composite joints exceeds the yield resistance of the steel CHS indicating opportunity to optimize the composite wrapping thickness and length.

FEM analysis for the behaviour of two-dimensional CHS joints with asymmetrical Full-Overlapped top-connection

Circular hollow section steel profiles are often used for industrial purposes, like offshore structures or for aesthetical reasons. By welding two or more steel members with different inclination angles columns with a tree-shaped structure will be formed. Designers are using this column to get a natural optic for example in representative halls. Like in nature the connected members often have asymmetrical angles. To calculate the nodes of these structures is a complex part. Due to the geometrical and material heterogeneity, different stresses arise in the microstructure. Current standards have got limitations. These limitations are there for material, geometrical options or process in welding. The vertical column is defined as chord, the connected members as braces. The inclination angle is the horizontal imperfection between braces and chord. Standards have got limitations regrading this inclination angle. There is no definition for an angle smaller than 30°. Because of aesthetical reasons, there are steel joints with two or more braces, where the inclination angles are not equal. An example is the natural optic as the ideal of a tree. Columns with an on-top connection, together with a steel plate node is not included in the current standards. However, designing engineers often have to build their own models for complex structures or design it with the help of laboratory tests. In literature, it was figured out, that the inclination angle has got a large influence on the resistance of a steel joint. Due to the geometrical heterogeneity, internal bending moments can arise, which degrades the carrying capacity of the joint. This paper is about numerical case studies of tree-shaped columns with an asymmetrical shape. The full-overlapped node is made of circular hollow section profiles (CHS), which are welded in a three-dimensional way. The aim is to figure out the influence of the inclination angles on the stability of asymmetrical shaped columns in the ultimate limit state, when the angles are not equal.

Stability and design of normal and high strength steel CHS beam-columns

An experimental and numerical study into the global buckling behaviour of structural steel circular hollow section (CHS) beam-columns with normal and high strength steel grades is presented in this paper. Two cold-formed S700 CHS profiles – 139.7×4 and 139.7×5 (diameter × thickness, in mm), were used in the beam-column testing programme. Ten CHS specimens were tested under eccentric compression, resulting in a combination of axial compressive force and uniform first-order bending moment. Digital image correlation (DIC) was used in the experiments to enable full-field monitoring of the strain and deformations in the specimens. Finite element (FE) modelling was also carried out with the aims of first replicating the test results and then generating further numerical data to complement the test data pool. Assessment of the existing EC3 design provisions was carried out against the test and FE data, which revealed that the lack of account taken for the full influence of varying yield strengths leads to inaccuracies in the EC3 resistance predictions. Improved design rules were proposed accordingly and shown to result in considerably more consistent predictions of buckling strength across a wide spectrum of steel grades. Lastly, a reliability assessment of both the EC3 and proposed design approaches was performed in accordance with EN 1990. The statistical results confirmed that the current EC3 partial safety factor is suitable for use with the new design proposals.

Strength predictions of circular hollow section T-joints of steel grade 1100 MPa

This paper presents experimental and numerical investigations of cold-formed high strength steel (CFHSS) circular hollow section (CHS) T-joints. The CFHSS CHS members have nominal 0.2% proof stress of 1100 MPa. The geometric parameters of the T-joints were designed by varying the ratios of β, 2γ and τ. A total of twelve T-joint tests were conducted by applying axial compressive load through the braces without preloading in chords. Non-linear finite element (FE) model was then developed for the CFHSS CHS T-joints. After successful validation, parametric studies were performed by using the verified FE model. The chord plastification failure of the T-joints was mainly found in both test and numerical studies. The relationship between the joint strengths and the variation of geometric ratios were investigated. The test and numerical strengths of the T-joints were used to assess the strength predictions by design equations provided in CIDECT, EN-1993-1-8 and the literature. It was found that these predictions generally provided unconservative predictions. A new equation that considers the effects of geometric ratios on the strengths was proposed based on both the test and numerical results. By adopting the newly proposed equation, the predictions are improved and provide the least scattered results when compared with other predictions.

Local buckling of thin-walled circular hollow section under uniform bending

This article presents a semi-analytical finite strip method based on Marguerre’s shallow shell theory and Kirchhoff’s assumption. The formulated finite strip is used to study the buckling behavior of thin-walled circular hollow sections (CHS) subjected to uniform bending. The shallow finite strip program of the present study is compared to the plate strip implemented in CUFSM4.05 program for demonstrating the accuracy and better convergence of the former. By varying the length of the CHS, the signature curve relating buckling stresses to half-wave lengths is established. The minimum local buckling point with critical stress and corresponding critical length can be found from the curve. Parametric studies are performed to propose approximative expressions for calculating the local critical stress and local critical length of steel and aluminum CHS.

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.

Static Behaviour of High‐Strength Steel CHS T‐Joints under In‐Plane Moment Loading

AbstractIn steel moment frames or vierendeel trusses comprised of hollow section members, T‐shaped joints are formed that are subjected to brace in‐plane bending moment (IPB). For mild steel, a large number of studies have been conducted on the behavior of tubular T‐joints subjected to IPB. However, the studies for high‐strength steel T‐joints are quite limited and mostly focused on axially loaded cases. In this paper, recent testing program conducted by the authors for high‐strength steel circular hollow section (CHS) T‐joints under IPB was presented. Supplemental numerical parametric study was conducted using the test‐validated nonlinear finite element (FE) analyses. In the FE analyses, various geometric shapes were considered such that the effect of key geometric factors and important failure modes could be identified. Based on the experimental and numerical results, a more rational deformation limit criterion under IPB loading was first proposed which can be applied to both mild and high‐strength steel joints. The chord plastification strength of high‐strength steel joints was evaluated using existing formulae and the required material factor for 700 MPa steel was suggested.

Compressive strengthening of steel columns with local corrosion using CFRP

Steel structures are damaged for a variety of reasons including accidental loads, corrosion and reduced strength ‎which need to be repaired and improved. In this investigation, local corrosion was applied to the steel circular columns ‎and the effects of Carbon Fiber Reinforced Polymer (CFRP) for ‎strengthening has been studied. 19 specimens of steel ‎Circular Hollow Section (CHS) column ‎with the same height and damage dimensions under compressive load were ‎analyzed by ABAQUS software which six cases of them were performed experimentally. In laboratory cases, ‎progressive corrosion was used to create damage on the specimens. In order to improve the accuracy of the analysis, a ‎combined ‎method was used to study the post-buckling of the plastic zone. For this purpose, the ‎specimens were first ‎subjected to elastic buckling analysis and then Riks non-linear analysis ‎with global and local imperfections was ‎conducted. The results showed that the corrosion ‎reduces the bearing capacity and rigidity of the steel columns‏ ‏and ‎complete destruction of the corroded area reduced the load bearing capacity by 40% for the column with corrosion at ‎the middle and by 21% for the damage close to the base, which shows the former is more critical. Strengthening of ‎columns retrofitted with carbon fibers restored ultimate load reduction by 33% and have a positive effect on ‎controlling fractures and reducing stresses at the damaged area. ‎

Low cycle fracture behavior of steel members with circular hollow section subjected to eccentric load

This study aims to investigate the effect of eccentric load on the seismic and fracture behavior of Q235B steel members with circular hollow section (CHS). To this end, uniaxial tension and ultra-low cycle fatigue tests on both un-notched and notched Q235B steel coupon specimens were conducted first to evaluate the material’s micromechanical fracture behavior. Next, 7 full-scale Q235B CHS steel members with different global slenderness were tested under cyclic axial loads with varying eccentricities. It is observed that: (1) the increase of the eccentricity of the axial load negatively affects the seismic and fracture resistance of CHS steel members, resulting in the deterioration of the strength, stiffness, energy dissipation, and ductility; (2) Large eccentricities lead to the reduction in the fracture life of Q235B CHS steel members; and (3) High global slenderness results in the reduction in both compression bearing capacity and energy dissipation of CHS steel members. In addition to the experimental program, finite element analyses are performed to simulate the seismic and fracture behavior of CHS steel members. The results from the finite element analyses are in good agreement with those from the experiment.

Chord plastification in high strength steel circular hollow section X-joints: Testing, modelling and strength predictions

This paper presents experimental and numerical investigations on cold-formed high strength steel (CFHSS) circular hollow section (CHS) X-joints. The CFHSS CHS members had nominal 0.2% proof stress up to 1100 MPa. The geometric parameters of the X-joints were designed by varying the ratios of β, 2γ and τ. Seventeen X-joint tests were conducted by applying axial compressive load through the braces without preloading in chords. Non-linear finite element model (FEM) was then developed for the CFHSS CHS X-joints. After successful validation of ultimate strengths, failure modes and load-deformation curves, parametric studies were performed by using the verified FEM. The chord plastification failure of the X-joints was mainly found in both test and numerical studies. The relationship between the joint strengths and the variation of geometric ratios were investigated. The strengths of the X-joints obtained in this study together with the test strengths collected from the literature were used to assess the strength predictions by CIDECT and EN-1993–1-8, as well as those from the literature. It was found that the current predictions generally provided unconservative predictions. A new equation that considers the effects of geometric ratios on the strengths was proposed based on both the test and numerical results. By adopting the newly proposed equation, the predictions are improved and provide the least scattered results when compared with the other predictions.

Design of cold-formed stainless steel circular hollow section columns using machine learning methods

Most existing design methods for the bearing capacity of stainless steel circular hollow section (CHS) columns were developed for a specific grade considering merely the global buckling failure mode. However, a variety of stainless steel grades with significant differences in material properties exist, and CHS columns may undergo local buckling, global buckling and global–local interactive buckling. To develop a unified design method suitable for various stainless steel grades and failure modes, this study adopted a machine learning based framework. First, 39 tests were conducted on cold-formed stainless steel CHS columns. Material properties, imperfections, load-deformation curves, and failure modes were reported in detail. Then, test data on stainless steel CHS columns in literature were collected and formed a database with 280 columns. Afterwards, two machine learning algorithms, Random Forest and Extreme Gradient Boosting, were used to predict the bearing capacity of column based on four types of input parameters. The Random Forest algorithm obtained the highest prediction accuracy when using all the design parameters as input. The accuracy of Random Forest algorithm based on the Comprehensive parameters (i.e., the non-dimensional slenderness of cross-section and member) is improved considerably when including the ratio of yield strength over the Young’s modulus as the input parameter. Finally, the prediction of machine learning method was compared with that of the design method in Design manual for structural stainless steel, and the proposed method shows a better accuracy.

Testing, simulation and design of eccentrically loaded austenitic stainless steel CHS stub columns after exposure to elevated temperatures

The present paper reports an in-depth testing and numerical modelling programme, to study the post-fire local buckling behaviour and residual resistances of austenitic stainless steel circular hollow section (CHS) stub columns under combined compression and bending moment. The testing programme employed twelve austenitic stainless steel CHS stub column specimens and included heating and cooling of the stub column specimens, post-fire material testing and post-fire combined loading tests. The testing programme was followed by a numerical modelling programme, where finite element models were developed and validated against the test results and then employed to perform parametric studies to generate additional numerical data. It is worth noting that there are currently no design standards established specifically for stainless steel structures after exposure to fire. In this study, the relevant design rules (i.e. cross-section interaction curves) for stainless steel CHS under combined loading at ambient temperature, as set out in the European, American and Australian/New Zealand standards and given in the continuous strength method, were assessed for their applicability to austenitic stainless steel CHS under combined loading after exposure to fire, based on the obtained test and numerical data. The results of the assessments revealed that all the codified design cross-section interaction curves have certain shortcomings, including the lack of rational exploitation of material strain hardening and the use of linear interaction, and thus yield excessively high degrees of conservatism and scatter when used for austenitic stainless steel CHS under combined loading after exposure to fire. The continuous strength method was shown to lead to accurate and consistent post-fire residual resistance predictions for austenitic stainless steel CHS under combined loading, due principally to the rational consideration of material strain hardening. Finally, the reliability of the continuous strength method was confirmed by means of statistical analyses.

A unified approach for austenitic and ferritic stainless steel CHS beam–columns subjected to eccentric loading

This paper develops a unified approach for assessing structural behaviour of austenitic and ferritic stainless steel circular hollow section (CHS) beam–columns​ under eccentric loading. This approach is based on combining a deformation-based method and collapse theory for stainless steel CHS beam–columns.A normalised M–N–Φ relationship of stainless steel CHS was derived based on a fibre model; the approach incorporated deformation capacity and strain hardening based on continuous strength method (CSM). The novelty of this paper is to present a closed-form solution for generating axial-load–end-moment interaction curves of the stainless steel CHS beam–column by combining the normalised M–N–Φ equation with a general beam–column equation. Besides, a critical normalised mid-height curvature was determined, which could be used to differentiate cross-section local buckling failure from global stability failure of stainless steel CHS beam–columns under combined loading. The proposed approach related the strengths of beam–columns to the effective column lengths by introducing a new non-dimensional slenderness ratio for stainless steel CHS beam–columns. It also provided an explicit way to consider the effect of column imperfections on the strengths of stainless steel CHS beam–columns. Accuracy of the derived normalised interaction curves was assessed by comparing the predictions against the test and numerical results for a wide range of non-dimensional slenderness ratios and different classes of CHS cross-sections for both stainless steel grades. A high level of accuracy and consistency was achieved in predicting the strengths of both short and long stainless steel CHS beam–columns for both types of steel grade.

Buckling Behavior of Non-Retrofitted and FRP-Retrofitted Steel CHS T-Joints

This paper aims to investigate the buckling behavior of circular hollow section (CHS) T-joints in retrofitted and non-retrofitted states under axial brace compressive loading. For this purpose, two types of analysis are carried out. The first one is evaluating the critical buckling load in various tubular joints, and the other one is investigating the post-buckling behavior after each buckling mode. More than 180 CHS T-joints with various normalized geometric properties were numerically modeled in non-retrofitted state to compute their governing buckling mode, i.e., chord ovalization, brace local, or global buckling. Then three joints with different buckling modes were selected to be retrofitted by fiber-reinforced polymer (FRP) patches to illustrate the improving effect of the FRP wrapping on the post-buckling performance of the retrofitted joints. In addition, FRP composite failures were investigated. The results indicate that the FRP retrofitting is able to prevent the brace local buckling, and that matrix failure is the most common composite failure in the retrofitted joints.

Experimental investigation on flexural behaviour of vertically-curved circular-hollow steel sections strengthened with externally bonded carbon fibre reinforced polymer

The behaviour of Carbon Fibre Reinforced Polymer (CFRP) strengthened vertically curved beams of Steel Circular Hollow Sections (SCHS) was studied. Sixteen numbers of curved beams with 1200 mm span having four radii of curvatures; 0 mm, 2000 mm, 4000 mm and 6000 mm were tested under three-point bending tests. A range of CFRP lengths up to 1000 mm was selected. The maximum performance was noted when the ratio between CFRP length to total length of beams is 0.625. Four types of failure modes were observed in the strengthened beams. A theoretical model was also developed and validated to predict the load–deflection behaviour of CFRP strengthened tubular vertically curved beams in the elastic region using the Maxwell-Mohr integral method.