Cold-formed Steel Sections Research Articles

Behaviour of Composite Column of Cold-Formed Steel Section with Web-Stiffener Integrated with Ferrocement Jacket

Cold-formed steel (CFS) is known as slender or class 4 section due to high ratio of web-to-thickness ratio. The compressive strength of this type of section is usually very low as it tends to fail due to distortion and warping before reaching the actual compressive strength. The aim of this study is to determine the ultimate capacity of build-up lipped CFS assembled with ferrocement jacket where web-stiffener is provided as the proposed composite column (CFFCC) is under axial compression load. Nine specimens of composite columns were prepared and tested. The main parameters varied in the CFFCC columns are column height, cold-formed steel thickness and influence of ferrocement jacket and web-stiffener. There are three different heights of the CFFCC composite column namely 2000mm, 3000mm and 4000mm used in this study. All CFFCC columns were tested under axial load where a thick steel plate is used to evenly distribute the applied load. The results show the effect of providing both the ferrocement jacket to increase the confinement effect and the web stiffener to provide sufficient lateral support to the column web. A significant increase in both the strength and the ductility of the specimens under axial loading has been recorded. The strength capacity of CFFCC has been improved by about 178% greater than that of bare steel column. Also it is found that, axial load capacity of CFS-ferrocement jacket composite columns (CFFCC) were increased with the increase in thickness of CFS. The use of web-stiffener has improved the axial load capacity of the column but not that significant.

Behaviour of Composite Column of Cold-Formed Steel Section without Web Stiffener Integrated with Ferrocement Jacket

Cold-formed steel (CFS) is known to be a thin section. Thus it is considered a weak slender steel section which limits the compression capacity of the column. The aim of this study was to determine the ultimate capacity of built-up lipped CFS (assembled with ferrocement jacket) as composite column (CFFCC) under axial compression load. Nine specimens of composite columns were prepared and tested. The main parameters that varied in the CFFCC columns were column height, cold-formed steel thickness, and influence of ferrocement jacket. There were are three different heights of the CFFCC composite column namely 2000mm, 3000mm and 4000mm used in this study. All CFFCC columns were tested under axial load by a thick steel plate. The results indicated that ferrocement jacket provided sufficient lateral support to the column web and significantly increased both the strength and ductility of the specimens under axial loading. The strength capacity of CFFCC improved significantly, about 149% greater than that of bare steel column section. It was also found that the axial load capacity of CFS-ferrocement jacket composite columns (CFFCC) had increased significantly (in the range of 20% to 40%) as thickness of CFS increased.

Flexural behaviour of axially and rotationally restrained cold-formed steel beams subjected to fire

This paper presents the results of a wide-ranging experimental research carried on the flexural behaviour of cold-formed steel beams subjected to fire. The main purpose of this work was to evaluate the influence of different cross-sections, especially of compound cold-formed steel sections, the axial restraint to the thermal elongation of the beam and the rotational stiffness of the beam supports. The results showed above all that the critical temperature of a cold-formed steel beam might be strongly affected by the stiffness of the surrounding structure depending on the relation between its stiffness and the stiffness of the beam.

Nonlinear behaviour of built-up cold-formed steel section battened columns

This paper discusses nonlinear behaviour and design of built-up cold-formed steel section battened columns. The built-up columns were pin-ended and consisted of two cold-formed steel channels placed back-to-back and were connected using batten plates. Nonlinear 3-D finite element models were developed to simulate the structural performance of the axially loaded columns. The nonlinear material properties of flat and corner portions of the channels, initial geometric imperfections, actual geometries and boundary conditions were carefully considered in the models. The finite element models were verified against tests, recently conducted and reported by the authors, on the same form of construction. The column strengths, failure modes, deformed shapes at failure, load-lateral displacement and load-axial strain relationships were predicted from the finite element analyses and compared well against the test results. In addition, the validated finite element models were used to perform an extensive parametric study investigating different parameters affecting the behaviour of the columns comprising different slenderness, column lengths, cross-section geometries, steel strengths, spacing between channels and different batten plates spacing. Furthermore, the column strengths predicted in the parametric study were compared with design strengths calculated using the North American Specification, Australian/New Zealand Standard and European Code for cold-formed steel columns.

Experimental investigation of built-up cold-formed steel section battened columns

This paper presents an experimental investigation on behaviour and design of built-up cold-formed steel section battened columns. The built-up columns were pin-ended and consisted of two cold-formed steel channels placed back-to-back at varied spacing of intersection. The two channels were connected using batten plates, with varying longitudinal spacing. The cold-formed steel channel sections were manufactured by brake-pressing flat strips having a plate thickness of 2mm. The built-up cold-formed steel section battened columns had different slenderness and geometries but had the same nominal length of 2200mm. The column strengths, load–axial shortening, load–lateral displacement and load–axial strain relationships were measured in the tests. In addition, the failure modes and deformed shapes at failure were observed in the tests and reported in this paper. Overall, the built-up column tests provided valuable experimental data regarding the column behaviour that compensated the lack of information on this form of construction as well as used to develop nonlinear 3-D finite element models. The column strengths measured experimentally were compared against design strengths calculated using the North American Specification, Australian/New Zealand Standard and European Code for cold-formed steel columns. Generally, it is shown that the specifications were unconservative for the built-up cold-formed steel section battened columns failing mainly by local buckling, while the specifications were conservative for the built-up columns failing mainly by elastic flexural buckling.

Statistical evaluation of a new resistance model for cold-formed stainless steel cross-sections subjected to web crippling

This paper presents a statistical evaluation according to Annex D of EN 1990 (2002) of a new resistance function for web crippling design of cold-formed stainless steel cross-sections. This resistance function was derived by Bock et al. (2013) through the use of carefully validated numerical models with the aim to propose a design expression for stainless steel sections, which are currently designed following the provisions for cold-formed carbon steel sections given in EN 1993-1-3 (2006). Although it was shown that the proposed design equation is appropriate for application to various stainless steels, the statistical uncertainties in material properties that the different types of stainless steels exhibit require an assessment of various partial safety factors. The statistical assessment showed that the proposed resistance function by Bock et al. (2013) requires adjustment to satisfy the safety level set out in EN 1993-1-4 (2006); A recalibration is performed herein. The web crippling design provisions given in EN 1993-1-3 (2006) and SEI/ASCE 8-02 (2002) American standard for application to stainless steel are also statistically evaluated herein. Comparison with test and numerical data showed that the predictions of the recalibrated resistance function are better suited and consistent than existing design provisions.

Experimental Testing of Innovative Cold-Formed "GEB" Section / Badania Eksperymentalne Innowacyjnego Kształtownika Giętego Na Zimno Typu „Geb“

Abstract One of the major advantages of light gauge steel structures made of cold-formed steel sections is their low weight so the production of typical single-storey steel structures of this kind of profiles is still rising. The well known profiles, e.o. Z-sections, C-sections and the so called hat-sections studied and described in the literature, are used mainly as purlins or truss components. A new profile GEB was patented for the use for primary load-bearing member in fabricated steel frames. According to the code [1] every novel cross section should be tested to assign the deformation shape and bearing capacity. The paper deals with the numerical and experimental research of bearing capacity of cold formed GEB profiles. The deformation shape and limit load was obtained from bending tests. The GEB cross section bearing capacity was also determined according to codes [1, 2].

Comparison on Section Properties and Flexural Behaviour for Cold-Formed Steel Built-Up Section

This paper performs analytical and experimental investigation on the section properties of locally produced cold-formed steel sections. Effective width method given by BS EN1993-1-3 is used to calculate the section properties for two slender cold-formed steel channel sections, namely KS200C20 and KS250C20. Local buckling and distortional buckling are taken into account in the calculation. Effective width method has significantly reduced the full sectional area and thus gives a relative lower value for the sectional resistance of cold-formed steel channel sections. The analytical results is compared to manufacturer’s data and differences of not more than 3.37% is recorded. Experimental study on the flexural behaviour on the two types of cold-formed steel channel sections is carried out. The results show that BS EN1993-1-3 has good agreement with experimental results for flexural resistance that included local and distortional buckling consideration. It is concluded that effective width method by BS EN1993-1-3 is suitable to calculate the section properties of of locally produced cold-formed steel channel sections.

Buckling analysis of thin-walled cold-formed steel structural members using complex finite strip method

In this paper, a generalised complex finite strip method is proposed for buckling analysis of thin-walled cold-formed steel structures. The main advantage of this method over the ordinary finite strip method is that it can handle the shear effects due to the use of complex functions. In addition, distortional buckling as well as all other buckling modes of cold-formed steel sections like local and global modes can be investigated by the suggested complex finite strip method. A combination of general loading including bending, compression, shear and transverse compression forces is considered in the analytical model. For validation purposes, the results are compared with those obtained by the Generalized Beam Theory analysis. In order to illustrate the capabilities of complex finite strip method in modelling the buckling behavior of cold-formed steel structures, a number of case studies with different applications are presented. The studies are on both stiffened and unstiffened cold-formed steel members.

Structural Behaviour of Cold-formed Cut-curved Channel Steel Section Under Compression

Cold-formed steel (CFS) with variety of shape, thickness and steel grade is becoming a popular choice of structure in civil engineering work and building, especially for roof truss system, pallet racking, wall panel and etc. Curved steel element is important in the analysis that be suited by the architectural drawing and structural demand. CFS with a curved section for unique roof truss design is studied. The CFS is curved by using the method of cut-curving in which the CFS section is cut at a certain length and then curved into desired profile. The experiment for determining the mechanical behaviour of the section is by using the compression strength of the column. The height of column is fixed at 600mm but the method for strengthening the cut-curving is varied. There are four types of cut-curving with a variation of strengthening method. The method for strengthening the cut-curved section is by using welding, plate and self-drilling screw. From the compression strength experiment, the cut-curved with full weld and plate is recorded, 21.26% less than the normal straight column.

Flexural behaviour of cold formed steel beams with Diagonal stiffener

The adaptability of the different shapes and sizes of section that are available leads to the potential use of Cold Formed Steel as a complete building material. To improve the elastic buckling stress of the whole thin-walled I section including flanges and lips in pure shear, intermediate stiffeners are added. In this paper, the results of the experiments conducted on cold- formed steel beam encased with diagonal stiffened webs with a view to study their flexural strength are presented. A total of 6 specimens were tested. 2 specimens each of cold- formed steel I section, cold-formed steel I section with diagonal stiffeners and cold-formed steel I section with diagonal stiffeners in filled with concrete was used. All the specimens were tested for flexural strength under two point loading by using reaction type vertical loading frame. Ultimate load carrying capacity and ultimate deflection of each type of beam is calculated and compared. From the experimental investigations carried out to study the flexural behaviour of encased cold-formed steel beams with and without stiffeners, it was found that Cold-formed steel section with stiffeners in filled with concrete has resulted in increased resistance to lateral-torsion buckling.

Experimental and numerical studies of fire exposed lipped channel columns subject to distortional buckling

Cold-formed steel sections are commonly used in low-rise commercial and residential buildings. During fire events, cold-formed steel structural elements in these buildings are exposed to elevated temperatures. Hence after such events there is a need to determine the residual strength of these structural elements. However, only limited information is available in relation to the residual strength of fire exposed cold-formed steel members. This research is aimed at investigating the residual distortional buckling capacities of fire exposed cold-formed steel lipped channel sections. A series of compression tests of fire exposed, short lipped channel columns made of varying steel grades and thicknesses was undertaken in this research. Test columns were exposed to different elevated temperatures up to 800°C. They were then allowed to cool down at ambient temperature before they were tested to failure. Suitable finite element models of tested columns were also developed and validated using test results. The residual compression capacities of tested columns were predicted using the ambient temperature cold-formed steel design rules (AS/NZS 4600, AISI S100 and Direct Strength Method). Post-fire mechanical properties obtained from a previous study were used in this study. Comparison of results showed that ambient temperature design rules for compression members can be used to predict the residual compression capacities of fire exposed short or laterally restrained cold-formed steel columns provided the maximum temperature experienced by the columns can be estimated after a fire event. Such residual capacity assessments will allow structural and fire engineers to make an accurate prediction of the safety of buildings after fire events. This paper presents the details of these experimental and numerical studies and the results.

Assessment of Connection Arrangement of Built-Up Cold-Formed Steel Section under Axial Compression

Cold-formed steel (CFS) with several of the advantages is selected in construction activity as structural and non-structural element. CFS with variety of shape, dimension and grade is chosen to replace traditional material that largely used before. In the study, CFS is utilised as a compression member to support beams element in the building. The column made with CFS is important to sustain the load and build the stable equilibrium circumstances. The column stability is the big issue that must be discussed and determined to prevent the buckling load, unmanageable deflection and lastly building collapse. So that, the study of structural properties and column capacity under compression load of the column is being investigated. Compression test of built up CFS channel that is attached at open side facing by using bolting through the web of the channel. A tensile coupon specimen of channel is taken at the flange and web of CFS channel to find the actual material properties the results that the CFS behave similar to a carbon steel with yield stress 500 MPa. Five arrangement of bolt that are margin of its mid height, compressed using a servo machine to get the axial capacity of the column. Under constant length of 900 mm and constant material, the end distance of bolt to the tip of the column are greatly affecting the column capacity by strengthening its bearing capacity. Hence, it is recommended that, the end distance of bolt must be placed at 20 mm to improve the bearing strength of the column, and the spacing of columns can be restudy for better results.

Experimental study of web crippling behaviour of hollow flange channel beams under two flange load cases

This paper presents the details of an experimental study of a cold-formed steel hollow flange channel beam known as LiteSteel beam (LSB) subject to web crippling under End Two Flange (ETF) and Interior Two Flange (ITF) load cases. The LSB sections with two rectangular hollow flanges are made using a simultaneous cold-forming and electric resistance welding process. Due to the geometry of the LSB, and its unique residual stress characteristics and initial geometric imperfections, much of the existing research for common cold-formed steel sections is not directly applicable to LSB. Experimental and numerical studies have been carried out to evaluate the behaviour and design of LSBs subject to pure bending, predominant shear and combined actions. To date, however, no investigation has been conducted on the web crippling behaviour and strength of LSB sections. Hence an experimental study was conducted to investigate the web crippling behaviour and capacities of LSBs. Twenty-eight web crippling tests were conducted under ETF and ITF load cases, and the ultimate web crippling capacities were compared with the predictions from the design equations in AS/NZS 4600 and AISI S100. This comparison showed that AS/NZS 4600 and AISI S100 web crippling design equations are unconservative for LSB sections under ETF and ITF load cases. Hence new equations were proposed to determine the web crippling capacities of LSBs based on experimental results. Suitable design rules were also developed under the direct strength method (DSM) format.

The Influence of Cross-Section Shape Changing on Work of Cold Formed Beam

The Necessity of taking into account the ability of cold-formed steel thin-walled profiles to gradually change its cross section shape proportionally to the load acting on it is considered. Free torsion constants Jt value for cold-formed profiles is justified. Underestimation of beam torsion due to ignoring of the cross-section contour deformation is assessed. The thin-walled Z and C-shaped cold formed steel sections recently are becoming more and more popular in the constructions of low-rise buildings. A characteristic feature of cold-formed thin-walled profiles in these structures is the need to consider not only the longitudinal and bending deformations, but also the deformations of torsion. Presently there are two approaches to analysis of structures of thin-walled cold-formed steel sections. One of them is based on the thin-walled beam theory designed by V.Z. Vlasov, another one is based on the super-critical load-carrying capacity theory. In the first approach the contour of the cross-section is non-deformable, in the second caseanalysis is carried out on the basis of a reduced cross-section, caused by local buckling of the compressed cross-section elements. Both approaches do not take into account the ability of cold-formed steel thin-walled profiles to change itscross section shape proportionally to the load acting on it. In this connection it is necessary to conduct theoretical and experimental studies of the cross-section deformation effect on behavior of cold-formed steel profiles.First of all,it is important to find out the range of section-length characteristics for cold-formed profiles in which the fact of not taking into account of contour deformation of the cross-section leads tothe significant, from an engineering point of view, error in the calculations. Also it is needed to estimatehowload types and connections applied on cross section influence on cross-section form changing.

Design of cold-formed steel channels with stiffened webs subjected to bending

The objectives of this study are to investigate the structural behaviour and evaluate the appropriateness of the current direct strength method on the design of cold-formed steel stiffened cross-sections subjected to bending. The stiffeners were employed to the web of plain channel and lipped channel sections to improve the flexural strength of cold-formed steel sections that are prone to local buckling and distortional buckling. An experimental investigation of simply supported beams with different stiffened channel sections has been conducted. The moment capacities and observed failure modes at ultimate loads were reported. A nonlinear finite element model was developed and verified against the test results in terms of strengths, failure modes and moment–curvature curves. The calibrated model was then adopted for an extensive parametric study to investigate the moment capacities and buckling modes of cold-formed steel beams with various geometries of stiffened sections. The strengths and failure modes of specimens obtained from experimental and numerical results were compared with design strengths predicted using the direct strength method specified in the North American Specification for cold-formed steel structures. The comparison shows that the design strengths predicted by the current direct strength method (DSM) are conservative for both local buckling and distortional buckling in this study. Hence, the DSM is modified to cover the new stiffened channel sections investigated in this study. A reliability analysis was also performed to assess the current and modified DSM.

Tests of cold‐formed steel portal frames with slender sections

AbstractCold‐formed steel sections are widely used in many applications such as structural frames, scaffolding systems, purlins and storage racks. In particular, cold‐formed steel portal frames can be an alternative to conventional hot‐rolled steel portal frames for industrial, rural and residential low rise buildings. The advantages of using cold‐formed steels include a higher strength‐to‐weight ratio and reduced material, erection and transportation costs.Over the past two decades a number of researchers [1] to [3] have undertaken tests on cold‐formed steel portal frames. The tests mainly focused on the behaviour of joints, and employed relatively stocky sections. Hence, they provided little insight into the effects of cross‐sectional instability on the overall stability of the frame.In this paper, three portal frame tests are described, the main purpose of which was to study the effect of cross‐sectional instability on the two‐dimensional sway failure of cold‐formed steel. The tests demonstrated significant local and distortional buckling before reaching the ultimate load. Finite element models were calibrated against the tests. The calibrated models therefore can be used for a parametric study to investigate the significance of the additional second‐order effects caused by local/distortional bucking. The paper details the tests and the numerical simulations.

Computational modelling of flange crushing in cold-formed steel sections

The computational modelling of the flange crushing phenomenon in cold-formed steel profiles is described in this paper, with particular emphasis to the development of shell finite element (SFE) models and performance of quasi-static analyses with an explicit integration scheme. Web crippling failure is widely recognised as the most relevant collapse mode of cold-formed steel members subjected to transverse concentrated loads. However, it has been experimentally and numerically observed that a somewhat different collapse mode may occur, due to the heavy stress concentrations stemming from the adoption of narrow bearing plates. This phenomenon, termed flange crushing, should not be confused with web crippling. Usually, the web crippling phenomenon is numerically investigated by means of non-linear static SFE models with an implicit integration scheme. In this study, SFE models are developed in ABAQUS code to study the flange crushing failure of a plain channel beam subjected to Internal Two Flange (ITF) loading conditions. These models are described in detail, as well as additional modelling concerns regarding quasi-static analyses and the explicit integration method. Different parameters are discussed in this article and the numerical results obtained are commented throughout. Such parameters include the (i) SFE type and mesh, (ii) load rate, mass scaling, adoption of smoothed displacement amplitude curves and control of inertial effects, (iii) contact and friction definitions, (iv) effects of forming cold-work and manufacturing process and (v) geometrical imperfections. Finally, the load–displacement response obtained with the quasi-static model and an equivalent non-linear static analysis are compared with the experimental test curves. It is concluded that very good results are achieved with the quasi-static approach, not only in terms of the ultimate load prediction, but also regarding the post-collapse load–deflection curve and the failure mechanism.

Post-buckling behaviour and DSM design of web-stiffened lipped channel columns with distortional and local mode interaction

This paper examines the design and load-carrying capacity of fixed-ended web-stiffened lipped channel columns eroded by mode interaction behaviour combined with distortional and local deformations. Initially, the paper presents the results of an experimental investigation of compressive tests on web-stiffened lipped channel columns fabricated from cold-formed mild steel with a thickness of 1.50mm, which is aimed at determining their failure load-carrying capacity; the experimental investigation also aims to provide experimental evidence of the occurrence of such coupling phenomena concerning distortional and local modes, namely, local-distortional interaction and distortional-local interactive failures. Then, the paper examines the ultimate strength data of experimental columns, both reported in this paper and collected from the literature, and concludes that the current direct strength method (DSM) provides very unsafe predictions concerning such a detrimental interaction nature. Next, two DSM-based design approaches, namely, the nominal strength against local-distortional (NLD) and distortional-local (NDL) procedures, are presented and evaluated on the basis of all available experimental ultimate strength data. Finally, proposals and design considerations based on the DSM-shape for the thin-walled cold-formed steel sections, which fail in mixed modes of distortional and local buckling, are presented.

Two-Stage Stress-Strain Models for Light-Gauge Steels

An accurate stress-strain relationship is needed for use in the advanced numerical modelling of cold-formed light-gauge steel members covering a wide range of strains. Existing stress-strain models for carbon steels are either capable of accurate predictions over a limited strain range or defined using many material parameters for a full range of strains. The values of some material parameters are not always available in existing design codes. This paper presents two stress-strain models for light-gauge carbon steels, which are capable of accurate predictions over the full range of tensile strains up to the strain at the ultimate stress. Both stress-strain models are solely defined using either three basic Ramberg-Osgood parameters ( E0, σ0.2, and n) or even two basic parameters ( E0, and σ0.2), and are based on a careful interpretation of existing experimental data of virgin materials and materials from flat portions of cold-formed steel sections. The accuracy of these two proposed models is demonstrated by comparing their predictions with experimental stress-strain curves.