Circular Hollow Section Research Articles

Analysis of Flexural Buckling Capacity of Stainless Steel Columns under Axial Compression

In order to provide a basis for the compilation of the bending buckling stability part of axially compressed columns in the technical code for stainless steel structures, the design methods and experimental research data of similar components are collected and compared. The results showed that there are some deficiencies in the current European code for the design of stainless steel structures and the American code for the design of cold‐formed stainless steel structures. According to the collected test data of square tube, rectangular tube, circular tube, elliptical tube, welded H‐shaped steel, and cold‐formed C‐shaped steel for 199 section columns and according to the influence of cold‐formed effect and residual stress on the stability of axial compression members, the members are divided into three categories: A, B, and C according to the section form, in which the columns with cold‐formed square, rectangular hollow section, and lipped C‐section were included in A, columns with circular and oval hollow section were sorted into B, columns with welded H‐section were separated into C, and the three categories of axial compression stability curves are expressed in the form of Perry formula. The comparison with the test data shows that the three kinds of curves can well estimate the stability bearing capacity of members, and the discreteness is small. The reliability of the proposed formula is analyzed, and the results show that its reliability index β meets the requirements of the GB 50068 standard.

Comparison of Ultimate Capacities of RC Chimney Sections under Wind Loading

Diffusion of gaseous and particulate pollutants from tall stacks has formed an important element in the control of air pollution since the industrial revolution began. These tall reinforced concrete chimneys are considered to be cantilever columns subjected to axial load resulted from the self-weight of the shell, linings and other accessories and bending moments which are resulted from the lateral loads like wind forces and earthquake forces.
 The recently published IS: 4998 – 2015 adopted a limit state design concept which requires well defined stress-strain relationship for concrete and steel. It has been seen that there are many disparities lies between the stress-strain relationships of constituent materials adopted by IS: 4998 – 2015 and other design standards.
 This paper discusses various methods pertaining to the estimation of the ultimate strength of thin-walled hollow circular sections of reinforced concrete chimneys, subjected to wind loading. A comparative study of various methods based on the prevalent codes reveals considerable disparity in the predicted ultimate strength values. These differences have been critically analyzed and results are discussed in this paper in terms of ultimate strength along with the contribution of concrete and steel, ultimate curvature and depth of neutral axis. For the comparison of above-mentioned parameters, design recommendations of IS 4998 – 2015, CICIND 2011, ACI 307 – 08 are used.
 HIGHLIGHTS
 
 The recently published IS: 4998 – 2015 adopted a limit state design concept which requires well defined stress-strain relationship for concrete and steel which differs in terms of strain and stress limits when compared with other well established RC chimney design codes
 Various methods pertaining to the estimation of the ultimate strength of thin-walled hollow circular sections of reinforced concrete chimneys, subjected to wind loading are discussed using a comparative study with different parameters of RC chimney
 For the comparison of above-mentioned parameters, design recommendations of IS 4998 – 2015, CICIND 2011, ACI 307 – 08 are used
 Stress-strain relationship of concrete and steel also discussed with the bases of the same is also discussed in detail for each of the above codes
 
 GRAPHICAL ABSTRACT

Comparative Analysis and Design of Bridge Pier for various Geometries along height

Abstract: Slender member is subjected to axial load and biaxial bending moment and fails due to buckling. This buckling is caused due to slenderness effect also known as ‘P∆’ effect. This buckling gives rise to excessive bending moment occurring at a point of maximum deflection. This additional bending moment is considered in second order analysis. The objective of the research reported in this paper is to formulate bending moment equation by using beam column theory and to study the behaviour of solid circular section and hollow circular section of bridge pier. The optimization in area of cross section is done by providing a combination of solid and hollow circular section in place of a solid circular section of pier within permissible limits. A comparative study on behaviour for all three conditions is been carried out. Keywords: slender column, buckling, ‘P∆’ effect, beam-column, second order analysis, bridge pier.

Comparative Analysis and Design of Bridge Pier for Various Geometries Along Height Comparing the Parameters Deflection and Bending Stresses

Abstract: Slender member is subjected to axial load and biaxial bending moment and fails due to buckling. This buckling is caused due to slenderness effect also known as ‘P∆’ effect. This buckling gives rise to excessive bending moment occurring at a point of maximum deflection. This additional bending moment is considered in second order analysis. The objective of the research reported in this paper is to formulate bending moment equation by using beam column theory and to study the behaviour of solid circular section and hollow circular section of bridge pier. The optimization in area of cross section is done by providing a combination of solid and hollow circular section in place of a solid circular section of pier within permissible limits. A comparative study on behaviour for all three conditions is been carried out. Keywords: slender column, buckling, ‘P∆’ effect, beam-column, second order analysis, bridge pier.

Development of a probability distribution model for the SCFs in tubular X-connections retrofitted with FRP

In this study, results of performing 324 FE analyses on 108 circular hollow section (CHS) X-connections with fiber reinforced polymer (FRP) have been used to derive a probability distribution model for SCFs in the retrofitted joints under axial, IPB, and OPB loads. As far as the authors are aware, no study has been conducted on the probability distribution of SCFs in X-connections with FRP. However, the probability distribution models are essential for the reliability-based analysis and design of offshore structures. Therefore, based on the retrofitted X-connection FE models which were verified with several experimental tests, a set of SCF sample databases was generated. In these SCF sample databases, different FRP properties (layer number and material) and connection geometry (β, τ, and γ) are included. 10 various probability density functions (PDFs) were fitted to the relative frequency histograms of the SCF samples. For obtaining the parameters of each distribution, the maximum likelihood method was used. Assessing the goodness-of-fit based on the Chi-squared and Kolmogorov-Smirnov tests shown that the Log-normal distribution is the best one for the maximum SCF values in CHS X-connections retrofitted with FRP subjected to axial load. In addition, the Log-logistic and Generalized Extreme Value distributions were set as the governing probability function for the retrofitted X-connections under IPB and OPB loads, respectively. In the last step, five fully defined PDFs were established for the maximum SCFs in CHS X-joints retrofitted with FRP under three various types of loadings.

A Quantitative Weld Sizing Criterion and Applications in Load Capacity Evaluation of Hollow Structural Section Joints

Existing weld sizing procedures for hollow structural section (HSS) connections in Codes and Standards are empirical in nature, often resulting in oversized welds. There is a growing interest in quantitative weld sizing for ensuring both structural safety and cost-effective construction of lightweight hollow section structures. In this study, a mesh-insensitive traction stress method is introduced for evaluating strength of fillet-welded HSS joints. The results are then generalized into a closed-form expression with a clearly defined mechanics basis. This expression relates weld throat shear stress to fillet weld size and remote load, with its dimensional geometric parameters being determined through a detailed parametric finite element analysis (FEA) of circular hollow section (CHS) and rectangular hollow section (RHS) connections with various dimensions. The effectiveness of the closed-form expression is demonstrated by comparing the predicted failure loads with those measured from a large number of HSS test data available from literature. Furthermore, the proposed quantitative weld sizing criterion can lead to as much as 20% weld size reduction from those determined using existing empirical-based weld sizing criteria, which can be very beneficial for welding-induced distortion control in construction of lightweight thin-walled structures.

Effect of chord length on CHS-RHS T-joints with slender sections

The chord length is an essential geometric property that must be defined in the analysis of isolated joints composed of hollow steel sections, as well as the boundary conditions of the test. The analysis of these parameters’ effect on the behavior of joints has been addressed by other studies, mostly with joints between circular hollow sections with compact or semi-compact cross-sections. Recent research about tubular joints has addressed cases with slender sections, where the design of joints containing these sections is still in development. In this context, this study aimed to evaluate the effect of the chord length in the behavior of T-joints between circular hollow section braces and slender rectangular hollow section chords through experimental tests and a numerical study considering the application of axial compression at the braces. The joint behavior was examined through the load-strain and load-deformation curves and the von Mises stress distribution, which allowed the failure mode's determination and the joint resistance value. Chord face failure was observed in the prototypes. It was concluded that a minimum chord length of 0.6m would be the adequate value for the study of the T-joints containing the geometric properties used in this study, which would be equivalent to a chord length five times higher than the width of the cross-section (5b0).

Fire resistance of stainless steel slender elliptical hollow section beam-columns

PurposeStainless steel has different advantages when compared to conventional carbon steel. The corrosion resistance and aesthetic appearance are the most known; however, its better behaviour under elevated temperatures can also be important in buildings design. In spite of the initial cost, stainless-steel application as a structural material has been increasing. Elliptical hollow sections integrate the architectural attributes of the circular hollow sections and the structural advantages of the rectangular hollow sections (RHSs). Hence, the application of stainless-steel material combined with elliptical hollow profiles stands as an interesting design option. The purpose of the paper is to better understand the resistance of stainless-steel-beam columns in case of fireDesign/methodology/approachThe research presents a numerical study on the behaviour of stainless-steel members with slender elliptical hollow section (EHS) subjected to axial compression and bending about the strong axis at elevated temperatures. A parametric numerical study is presented here considering with and without out-of-plane buckling different stainless-steel grades, cross-section and member slenderness, bending moment diagrams and elevated temperatures.FindingsThe tested design methodologies proved to be inadequate for the EHS members being in some situations too conservative.Originality/valueThe safety and accuracy of Eurocode 3 (EC3) design methodology and of a recent design proposal developed for I-sections and cold-formed RHSs are analysed applying material and geometric non-linear analysis considering imperfections with the finite element software SAFIR.

Application of radial basis function-based meshless method for torsional analysis of elliptical and bone shaped-irregular sections

This article presents a torsional analysis of solid elliptical, hollow circular, and actual bone sections of orthotropic and functionally graded material. The formulation of the governing equation is done using the Saint-Venant torsion theory. A classical power law is considered for the modelling of functionally graded material. Five different radial basis functions-based meshless methods are used for the discretization of the governing differential equations. MATLAB code is developed to solve the discretized partial differential equations. A convergence and validation study has been carried out to demonstrate the effectiveness and accuracy of the present method. Numerical examples for torsional rigidity and shear stresses are presented for circular, elliptical, and bone-shaped irregular sections made up of orthotropic and functionally graded materials. Finally, the proposed radial basis function-based meshless method is applied to the modelling and torsional analysis of an actual bone cross-section.

Full-scale tests on laterally loaded railway overhead line equipment mast foundations

Pile foundations for masts supporting overhead line equipment (OLE) on railways in Western Europe have traditionally been designed using empirical formulae derived from tests carried out in the 1950s under the auspices of the Union Internationale des Chemins de fer (UIC). Recent application in the UK of ostensibly more analytical approaches led to significantly increased pile lengths, which contributed to the high-profile cost over-run on the Great Western electrification programme. Further, the loads associated with some newer designs of mast are greater than those covered by the original field tests, and hence are outside the evidence base for the empirical approach. To address this, full-scale field tests were carried out on three, 610 mm dia. circular hollow-section steel piles installed in a railway embankment at the High Marnham test track (Nottinghamshire, UK). Each pile was designed according to the empirical OLE master index (OLEMI) method for a different form of modern OLE mast, and instrumented using Shape accelerometer arrays (SAAs) to determine pile deformations. The results provide valuable insights into the mechanisms of deformation of piles of different lengths, both at and beyond the expected in-service loads. p–y curves derived from the SAA measurements compare reasonably well with curves constructed using the American Petroleum Institute method for undrained clay soils. The tests also demonstrate the suitability of the OLEMI approach for large structures and loads; and that the Eurocode 7 partial factors on load and undrained shear strength applied to an undrained (total stress) limit equilibrium calculation are likely to be sufficient to meet serviceability requirements for standard single-and twin-track cantilever structures.

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.

Experiment and numerical investigation on the buckling behavior of 7A04-T6 aluminum alloy columns under eccentric load

In this study, experimental and numerical analysis were performed to investigate the stability of 16 circular hollow section (CHS) 7A04-T6 extruded aluminum alloy columns under eccentric load. The analyzed parameters included cross section size, eccentric distance and slenderness ratio. The ultimate strength, mid-span displacement and strain were recorded, and the results showed that all specimens failed due to overall flexural buckling. The experimentally-validated finite element model was established by ABAQUS considering the impact of initial imperfections. A large number of parametric analyses were carried out via this model to investigate the effects of cross section size, eccentric ratio and slenderness ratio on ultimate strength. The results of experiment and parametric analyses were compared with the design strengths predicted by EN 1999-1-1, the results showed that EN 1999-1-1 was conservative in predicting the ultimate strength of specimens with an eccentricity ratio above 0.6, however, when the eccentricity ratio was lower than 0.4 and the slenderness ratio was higher than 60, the EN 1999-1-1 would overestimate the strength.

Optimization and modeling of axial strength of concrete-filled double skin steel tubular columns using response surface and neural-network methods

The main objective of this study is to optimize and model the ultimate strength of axially loaded concrete-filled double skin steel tubular (CFDST) composite columns having a circular hollow section . By performing the multi-objective optimization analysis through the response surface methodology (RSM), an ultimate strength-based optimal design solution for CFDST composite columns was proposed. Besides, artificial neural networks (ANN) together with RSM techniques were used to develop design formulations that can be involved in the prediction of the ultimate axial strength of such types of composite columns. An experiment data repository compiled from the studies available in the literature was used in both optimization and modeling analysis. The aim of the optimization was to achieve the optimum values for the design parameters based on the maximum capacity. However, in the modeling, attaining a design formula having an accurate and reliable prediction performance was the purpose. Furthermore, a verification study in which the developed models were compared with the modified design formulas of the AISC and Eurocode 4 and some existing models proposed by the researchers was carried out. It was observed that the generated models gave a good estimation capability with a considerably high R-squared value and fewer errors. After statistically analyzing the outputs of the models, it was proved that the models proposed in the current study yielded more reliable, accurate, and consistent prediction performance than the existing formulas. Besides, it was indicated the optimization analysis has a desirability value of 0.942, meaning an almost perfect optimization. • The CFDST composite columns were optimized based on ultimate strength. • The ultimate strength-based modeling of the CFDST columns was carried out. • The axial loading condition was considered in the modeling. • Reliable and accurate numerical models were developed. • Optimum properties for the CFDST column with the CHS were achieved.

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.

Design of sleeve connections with cross-bolted on circular hollow sections under axial tension

This present paper evaluates the behavior and resistance capacity of cross-bolted sleeve connections with circular hollow sections (CHS) under axial tension. This connection allows harmony in the continuity of the tubes. The cross-bolted sleeve connection with CHS comprises outer tubes connected by an inner tube and cross bolts at 90°. Therefore, an experimental, numerical, and parametric study was conducted to identify the connection's possible failure modes. The experimental tests were developed with cross bolts at 90°, which enable the identification of fracture through the effective net area, bearing failure, and bolt bending. Finite element (FE) numerical models were developed and validated by Ansys software to provide a parametric study. Thus, such a parametric study was carried out using the verified FE models. The failure modes were evaluated considering the effects of geometric properties concerning their type and location; a relative slenderness limit for the design of connections was proposed, directing the occurrence of a failure in the outer tube. Normative prescriptions do not foresee the design of the sleeve. Therefore, new formulation methods for estimating the strength were proposed, allowing the design of these connections.

Structural testing and numerical modelling of T-joints between cold-formed S690 circular hollow sections under brace in-plane bending

This paper presents a comprehensive investigation into the structural behaviour of T-joints between high strength S690 cold-formed circular hollow sections (CFCHS) under brace in-plane bending, and deformation characteristics of these T-joints under both monotonic and cyclic actions are examined experimentally and simulated numerically. These T-joints between S690 CFCHS were found to deform with a high level of resistances and ductility under both monotonic and cyclic actions.Through an integrated numerical modelling approach developed by the authors, advanced three-dimensional finite element models of CFCHS with solid elements were established. With a proper definition of weld collars at the brace/chord junctions of the T-joints between S690 CFCHS with different diameters and thicknesses, these models were readily adopted to perform a heat transfer analysis, a thermomechanical analysis and a structural analysis sequentially with compatible element types and meshes. Hence, the effects of the welding-induced residual stresses at the welded brace/chord junctions onto the structural behaviour of these T-joints were readily assessed. Consequently, these advanced models are demonstrated to be able to predict rationally deformation characteristics of these T-joints between S690 CFCHS under monotonic and cyclic actions of brace in-plane bending with a high degree of structural accuracy.

Bearing Capacity Test and Calculation Theory on CHS X-Joints Stiffened with Joint-Plates

In this study, three circular hollow sections (CHS) tubular X-joints strengthened with different external stiffeners or not were investigated by experimental and nonlinear finite element anlaysis (FEA) to study the bearing capacities, failure modes, and the strengthening effect of joint-plates. The test results showed that the bearing capacity of the X-joints could be improved by using the stiffened joint-plate, and the joint failure process was delayed, and the cambered surface of chord was straightened by tensile braces. Compared with the tested results, the nonlinear FEA could simulate the failure modes and its bearing capacity behavior of steel tubular X-joints well. To estimate the contribution of joint-plates on bearing capacity, four kinds of parameters were selected, and the corresponding FEA of stiffened X-joint were performed. Then, the influencing law on bearing capacity of different parameters was investigated. According to the superposition method of bearing capacities, the annular calculation model and the multi-parameter calculation theory of stiffened circular steel tubular X-joints were proposed, in which the coefficients were determined through regression analysis. Lastly, the comparisons on tested, simulated, and theoretical bearing capacities of stiffened X-joints were carried out, and there had good agreement between them.

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.

Fatigue behaviour of non-welded wrapped composite joints for steel hollow sections in axial load experiments

Design and execution of fatigue load dominated circular hollow section (CHS) multi-membered structures, such as offshore jacket and floating structures for wind turbines, truss bridges, etc., is hinged on fatigue performance of critical welded joints. An innovative jointing technology of wrapped composite joint connects steel hollow sections by direct bonding through a fibre reinforced polymer composite wrap, which completely avoids welding and therefore has superior fatigue performance than welded joints. In this study first results on fatigue performance of the wrapped composite joints is presented. Tensile cyclic loading tests on wrapped composite X-joint specimens were carried out to characterise their fatigue performance under different constant amplitude load ranges and compare it to equivalent welded joints. In addition, the influence of surface roughness of steel tubes and re-testing (load history) on fatigue performance of wrapped composite joints, as well as the influence of fatigue loading on residual static resistance was investigated in experiments. Preliminary S-N curves of wrapped composite joints are established. The tests results showed that X45 wrapped composite joints exhibited steadier stiffness degradation and 10–100 times longer fatigue life than their welded equivalents. Through 3D DIC surface strain measurements and post-failure microscopic insights to cut specimens, different failure modes including de-bonding at glass fibre composite-to-steel interface, delamination/fracture of the composite layers and fracture of steel brace are distinguished. The relationship between joint stiffness degradation rates, crack propagation rates and nominal stress ranges in the brace are established, based on which a preliminary fatigue life prediction of wrapped composite joints can be made. The re-tested specimens exhibited superior fatigue performance than virgin ones, while specimens with poor steel surface roughness showed worse fatigue performance. After fatigue loading with 40% of stiffness degradation, the specimens were found to still have the potential to sustain its original static resistance.