Cold-formed Channel Sections Research Articles

New Buckling Curve for a Compressed Member with Cold-Formed Channel Cross-Section

The verification of a column made from a lipped cold-formed channel section, subjected to pure axial compression relative to the gross cross-section, often results in a combined verification of bending and compression due to the appearance of a shift of the centroid of its effective cross-section. Following Eurocode 3 rules, this requires the determination of two distinct effective cross-sections and various interaction factors. This paper, based on an analytic approach, offers a modification to the actual buckling curve, based on Ayrton–Perry formulation, to include the second-order effects raised by the eventual shift of the effective centroid due to local buckling of the compressed web plate. This eliminates the need to use an interaction formula. The modified buckling curve is verified based on a GMNIA analysis performed on a numerical parametric model, which was previously validated by laboratory tests. In addition, the results are compared with strength results provided by appropriate Eurocode 3 formulas and AISI Direct Strength Method for global-local interaction and with classic experimental results.

Experimental and numerical investigations on cold-formed titanium-clad bimetallic steel angle and channel section stub columns

Titanium-clad bimetallic steel (TCBS) exhibits outstanding corrosion resistance, and can be advantageously applied in corrosive environments. This study investigated an innovative application of TCBS in cold-formed stub columns. During the cold-forming process, TCBS demonstrated no discernible separation at the bonding interface of the Q235 substrate layer and TA1 cladding layer, indicating the maintenance of synergistic deformation between the cladding and substrate layers. The compressive behavior and ultimate resistance of cold-formed TCBS angle and channel section stub columns were investigated using both experimental and numerical methods. These tests included material tensile flat and corner coupon tests, initial local geometric imperfection measurements, and stub column tests. The stub column test comprised four cold-formed TCBS angle section stub columns and three cold-formed TCBS channel section stub columns covering the non-slender and slender cross-sections. The experimental results were utilized to validate the finite-element (FE) model, which was then used in a parametric study to obtain further numerical data at different cross-sections. A comparative analysis of the ultimate resistance from the tests and numerical analyses with the predicted results from design approaches in EN 1993-1-1, AISI S100, and the direct strength method (DSM) was revealed. The evaluation findings generally showed that the EN 1993-1-1 design method forecasts for cold-formed TCBS channel section stub columns were dangerous. The non-slender cross-section classification coefficient, which was inapplicable to cold-formed TCBS channel steel stub columns, was the primary cause of the above unsafe prediction. As for the design approaches in AISI S100 and DSM for cold-formed TCBS angle and channel section stub columns, as well as those in EN 1993-1-1 for cold-formed TCBS angle section stub columns, they were judged safe but conservative. The above prediction error was mainly caused by ignoring the enhancement in strength properties of the TCBS after the cold-forming process. The considerations mentioned above led to the proposal and demonstration of modifying recommendations that offered safe, accurate, and consistent design approaches to ultimate resistance for the cold-formed TCBS angle and channel section stub columns.

Assessment of residual resistant capacity of cold-formed Q1100 ultra-high strength steel channel section stub column with corrosion

Experiment and numerical analysis were conducted in this study to reveal the residual resistant capacity of the cold-formed Q1100 ultra-high strength steel (UHSS) channel section stub column with grooving corrosion. Based on the results of tensile coupon test, the strength properties of the Q1100 UHSS were barely changed by the cold-forming process. A clear reduction in the ductile properties was observed, after the cold-forming process. The load-end shortening curve of the cold-formed Q1100 UHSS channel section stub columns with different grooving corrosions were obtained through the axial compressive experiment. The initial resistant stiffness was reduced by the grooving corrosion significantly, because of the reduction in the cross-section area. Decrease in the corrosion angle and increment in the corrosion length enhanced the adverse effects of grooving corrosion on the resistant capacity. Local buckling was observed in the flange and web. The flanges near the corrosion weakening area were more prone to local buckling, because of the stress transfer from web to flange. A numerical modelling method was proposed to simulate the resistant performance of the cold-formed Q1100 UHSS channel section stub columns with different grooving corrosions, which was validated by the comparison in load-end shortening curve, ultimate resistance and failure mode. Effects of corrosion angle, corrosion length, and corrosion location on the resistant capacity and failure mode were investigated through the parametric study. Compared with corrosion location, the corrosion angle and corrosion length exhibited more significant effects on the resistant capacity of the cold-formed Q1100 UHSS channel section stub columns.

A numerical study on a novel demountable cold-formed steel composite beam with profiled steel sheeting

Cold-formed steel composite beams are known for their unique advantages, like being lightweight and ease of installation. The use of profiled steel sheeting in cold-formed composite beams reduces construction time and costs by acting as a permanent formwork in the composite beams. The current study presents a 3D finite element model of cold-formed steel composite beam specimens comprising a cold-formed double-lipped channel section, profiled steel sheeting, concrete slab, and bolted shear connector. Employing bolted shear connectors, structural components can be deconstructed and replaced after their service life expires or if they are damaged. The characteristics of the materials obtained from an experimental program were assigned to the finite element model. Geometric characteristics, material nonlinearities, and loading procedures were attentively simulated, and a dynamic explicit procedure was employed for the numerical analyses. A comparison of the results obtained from the finite element models and the available experimental results validated the precision of the models. Then, numerical studies were conducted to investigate the effects of various parameters, including compressive strength of concrete, thickness of concrete slab, height and grade of cold-formed steel section, thickness of profiled steel sheeting, number and diameter of shear connectors, on the behavior of the composite beam. The results showed that the height and grade of the cold-formed steel section and compressive strength and thickness of the concrete slab have a significant effect on increasing the capacity of the composite beam.

Improvement of CSM for high-strength S690 and S960 unlipped channel columns, beams and beam-columns

Existing design methods that are mainly based on cross-section classification usually predict conservative resistances for high strength steel (HSS) singly symmetric unlipped channel section members. This paper conducted numerical studies on the resistance of cold-formed S690 and S960 HSS channel section members under different loading types. Numerical simulations were firstly carried out to establish suitable finite element (FE) models, and then applied to parametric studies. The obtained numerical results were adopted to assess and modify the continuous strength method (CSM) for the design of cold-formed HSS unlipped channel section members under axial compression or bending loads. An improved beam-column design method of unlipped channel sections was proposed through providing a new linear design curve incorporating the modified CSM formulae, then to evaluate the newly method and the M - N interaction curves specified in existing standards, finally the reliabilities of proposed method were confirmed.

Design of sheathed built-up nested CFS channel studs in load-bearing LSF walls

Cold-formed steel built-up nested channel (NC) sections have been increasingly used to replace the commonly used lipped channel sections as the load-bearing studs of light gauge steel framed (LSF) walls with higher compression capacity. However, the related knowledge is limited and no research study has investigated such NC stud walls yet. In this study, an investigation was undertaken on the compression behaviour and capacity of LSF walls made of slender NC studs sheathed with gypsum plasterboards on both sides. Compression tests of sheathed NC studs were conducted first, which were then used in developing and validating suitable finite element models. The results obtained from tests and finite element models showed that plasterboards and stud-to-board screw connections had significant influence on the failure mode and compression capacity of sheathed NC studs, while the end fastener groups recommended in the current cold-formed steel design standards and the stud-to-stud screw connections had only marginal effects. Finally, a simple and conservative design method was proposed based on the Direct Strength Method equations in the current design standards. This paper presents the details of this research study, including the results, discussions and main findings.

Fire performance of lightweight concrete-filled LSF wall panels

Light Gauge Steel Frame (LSF) wall panels with cold-formed thin-walled steel-Lipped Channel Sections (LCS) and plasterboard linings are increasingly used in the construction industry due to their lightweight and constructability characteristics. However, due to the high thermal conductivity of the LCS, rapid heat transfer is observed in LSF walls, causing negative impacts to the fire performance of the LSF wall elements. Cavity insulation is one of the practical solutions used in the industry to improve the fire performance of LSF walls. Insulation materials such as rockwool, glass fibre, cellulose fibre, ceramic fibre are commonly used as cavity insulation materials in LSF walls. A novel approach in LSF walls is the introduction of lightweight concrete filling as a cavity filler. The effect of lightweight concrete filling on the fire performance of LSF walls was analysed with the numerical investigation in this study. Fire performance of conventional LSF walls with 12.5 mm and 15 mm single and double plasterboard with Autoclaved Aerated Concrete (AAC) with 600 kg/m3 density, Foam Concrete (FC) with 650 kg/m3 density and FC with 1000 kg/m3 density lightweight concrete fillings were compared with LSF walls without cavity insulation and rockwool insulation under standard and hydrocarbon fire conditions. It was observed promising improvement in insulation and load-bearing fire ratings in LSF walls with lightweight concrete filling. Among lightweight concrete materials considered, FC with 1000 kg/m3 density has exhibited the best fire performance. LSF walls performance could be enhanced with lightweight concrete fillings depending on the application with improved fire performance.

Elastic Buckling Loads of Cold-Formed Steel Channel Sections with Perforations

Cold-formed perforated steel sections have been commonly applied to meet the demands for technical installations, leading to the reduction of capacities of these such sections. The capacities of these sectional types have been considered in the American Specification AISI S100-16 using the Direct Strength Method (DSM). This method known as the innovative method for the design of cold-formed steel sections allows predicting the sectional capacities of perforated sections based on elastic bucking loads. Elastic buckling analyses are compulsory for the application of the DSM in the design. The determination of elastic buckling loads of perforated sections is cumbersome with the usage of current buckling analysis software programs. The paper, therefore, presents a simple method for the determination of elastic buckling loads of cold-formed perforated channel sections, especially the paper is aimed to introduce a module software program used for elastic buckling analyses of these such channel sections based on this simple method. This program is convenient for buckling analysis, and it becomes a key program for the application of DSM in the design of cold-formed perforated steel channel sections. This software program is subsequently utilized to investigate the effects of web hole dimensions on the elastic buckling loads of cold-formed steel channel sections with perforations under compression or bending. The investigated results provide fundamental understandings of the buckling behaviors of perforated channel sections due to the effects of the web holes.

Lateral Load Carrying Capacity of Concrete-filled Cold-formed Steel Shear Wall

A new type of innovative composite shear wall (concrete-filled cold-formed steel shear wall or CFCSW) is proposed, composed of cold-formed channel sections arc-welded together by 20 mm length of welds and filled with concrete. The main study of the CFCSW focuses on the overall behavior, ultimate load capacity, stiffness and ductility. Three specimens of CFCSW with an aspect ratio of 1.0 are tested under lateral monotonic load. Three-dimensional finite element models are developed and benchmarked with the experimental results. The validated models are used to carry out parametric studies to determine the influence of the parameters on the performance of the CFCSW. The parameters are the height, steel plate thickness, weld spacing and concrete thickness of the CFCSW. The experimental and finite element modeling results indicate that increasing the weld spacing from 105 mm to 211 mm improves the stiffness, ductility and load carrying capacity, and similarly, providing holes inside the wall increases the stiffness, ductility and peak strength of the CFCSW. The ultimate capacity of the CFCSW is most influenced by changing the height of the wall and least influenced by varying the concrete thickness of the wall.

Effects of connections on the behaviour of cold-formed unlipped channel section bearers

Cold-formed steel (CFS) unlipped channel sections are commonly used as bearers in floor systems while rectangular hollow sections (RHS) are used as joists. The transverse loads from the joists do not pass through the shear centre of channel bearers due to different joist to bearer and bearer to column connections. Hence, the channel bearers are subjected to torsion in addition to concentrated loads and bending. This study investigated the effects of two joist to bearer (bolted/welded) connections, two bearer to column (cap plate/angle cleat) connections and fly braces on the structural behaviour of channel bearers. Eight full-scale tests were performed using simplified floor arrangements, made of two unlipped channel bearers with eight and six RHS joists located at 450 mm spacing. Suitable finite element models of tested channel bearers including their connections were developed and validated in terms of ultimate failure moment, failure mode and deflections. A parametric study was then performed using the validated finite element models. The effects of bolted/welded joist to bearer connections and cap plate/angle cleat bearer to column connections on the behaviour of channel bearers were determined and discussed based on the experimental and numerical results. Suitable recommendations were then made to the design methods based on the observed failure modes, and the most suitable combination of connections for the CFS floor systems investigated in this study.

Partial Strength Beam-to-column Connection of Cold-formed Single Channel Section: Numerical and Experimental Study

A full understanding of complex structural behaviour can be developed perfectly by using the combination of experimental and numerical approach. Although the basic method to determine the moment-rotation responses of the beam-to-column CFS joints has recently established from the full-scale testing, practising the finite element modelling (FEM) nowadays could explore in-depth on the number of variables and potential failure modes. In this paper, three-dimensional (3-D) model to simulate the actual behaviour of the beam-to-column CFS joints has been proposed by using multi-purpose finite element package ABAQUS version 6.14 in order to validate analysis data against the experimental works. The approach of nonlinear material characteristics, contact and sliding between different components and adopting C3D8R solid elements are proposed in this model. A total of three (3) beam-to-column CFS connections consisting of three different types of beam depths were tested in isolation in order to observe the structural behaviour based on its strength and stiffness. Comparisons between experimental and FE analysis results in term of ultimate moment capacity have shown a good correlation with strength ratios ranging from 1.12 to 1.17. Therefore, it is possible to develop a realistic model for future parametric studies such as type and configurations of the connections.

Behaviour and strength of unlipped channel sections under combined bending and torsion

Cold-formed steel unlipped channel sections are commonly used as bearers in floor systems. The loads from the joists are commonly transferred through the flanges or webs of the channel section bearers and not through their shear centre. Therefore, channel section bearers are subjected to combined bending and torsion, resulting in reduced bending capacity. This research study has thus investigated the behaviour of thick unlipped channel sections under combined bending and torsion using validated finite element models of beams with an eccentric concentrated load at mid-span. The member moment capacities of unlipped channel sections were obtained from idealized finite element models under uniform bending and with equivalent web and flange distributed forces for bending and torsion. First yield torques and combined bending and torsion capacities of unlipped channel sections were obtained from finite element models validated using available experimental results. A numerical parametric study was also performed for currently available unlipped channel sections using validated finite element models and member moment capacities, combined bending and torsion capacities and first yield torques of unlipped channel sections were obtained. Two-separate bending-torsion interaction equations were proposed for positive and negative eccentric loading cases.

Impact of Geometrical Imperfections on Estimation of Buckling and Limit Loads in a Silo Segment Using the Vibration Correlation Technique.

The paper examines effectiveness of the vibration correlation technique which allows determining the buckling or limit loads by means of measured natural frequencies of structures. A steel silo segment with a corrugated wall, stiffened with cold-formed channel section columns was analysed. The investigations included numerical analyses of: linear buckling, dynamic eigenvalue and geometrically static non-linear problems. Both perfect and imperfect geometries were considered. Initial geometrical imperfections included first and second buckling and vibration mode shapes with three amplitudes. The vibration correlation technique proved to be useful in estimating limit or buckling loads. It was very efficient in the case of small and medium imperfection magnitudes. The significant deviations between the predicted and calculated buckling and limit loads occurred when large imperfections were considered.

Axial capacity of back-to-back built-up cold-formed stainless steel unlipped channels-Numerical investigation and parametric study

In cold-formed steel structures, such as trusses, wall frames and portal frames, the use of back-to-back built-up cold-formed stainless steel unlipped channels as compression members are becoming popular. The advantages of using stainless steel as structural members are corrosion resistance and durability, compared with carbon steel. Current guidance by the American Iron and Steel Institute (AISI) and the Australian and New Zealand (AS/NZS) standards for built-up carbon steel sections describes a modified slenderness approach, to consider the spacing of the intermediate fasteners. The AISI and AS/NZS do not include the design of stainless-steel built-up channels and very few experimental tests or finite element (FE) analyses have been reported in the literature for such back-to-back cold-formed stainless steel unlipped channel section columns. This paper presents a numerical investigation on the behavior of back-to-back built-up cold-formed stainless steel unlipped channel section columns. Three different grades of stainless steel i.e., duplex EN1.4462, ferritic EN1.4003 and austenitic EN1.4404, were considered. The effects of screw spacing on the axial strength of such built-up unlipped channels were investigated. As expected, most of the short and intermediate columns failed by either local-global or local-distortional buckling interactions, whereas the long columns failed by global buckling. All three grades of stainless-steel stub columns failed by local buckling. A comprehensive parametric study was then carried out covering a wide range of slenderness and different cross-sectional geometries to assess the performance of the current design guidelines of carbon steel built-up sections in accordance with the AISI and AS/NZS. In total, 647 FE models were analyzed. From the results of the parametric study, it was found that the AISI and AS/NZS are conservative by around 14 to 20% for all three grades of stainless steel built-up unlipped channel section columns failed through global buckling. However, the AISI and AS/NZS carbon steel design rules can be un-conservative by around 8 to 13%, when they are used to calculate the axial capacity of those stainless steel built-up unlipped channels which are failed in local buckling.

NUMERICAL INVESTIGATION OF THE EFFICIENT USE OF STIFFENERS IN COLD-FORMED CHANNELS SUBJECTED TO BENDING

This paper presents a numerical study to identify the geometrical dimension ratios of the section that make introducing stiffeners to the cold-formed channel sections, subjected to bending, most effective. A V-shape stiffener was introduced to the web and/or the lipped flanges of such sections. A series of nonlinear finite element models has been carried out to investigate the flexural behaviour of the stiffened beam sections. The study shows that introducing stiffener to the web of channel is more effective than if it is used in the compression flange, in terms of increasing the flexural strength and delaying of local and distortional buckling failure modes. However, such effectiveness is not absolute, but it is highly dependent on the geometric properties of the section such as; flange breadth to web height ratio (bf/hw) and web height to its thickness ratio (hw/t). Indeed, considering this finding would help in economic design of such sections and optimal use of material. Keywords: Cold-formed section; Stiffeners; Finite element analyses; bending.

Experimental investigation of post-fire mechanical properties of Q235 cold-formed steel

Abstract Cold-formed steels are commonly used in construction applications. However, there is a lack of understanding on its post-fire mechanical properties. This paper presents an experimental investigation on post-fire mechanical properties of cold-formed steels. The test specimens were cut from flat portion and corners of cold-formed channel sections, which were exposed to temperatures ranging from ambient temperature to 800 °C, and then cooled with water and air. The specimens are of grade Q235, with section thicknesses of 1 mm and 2 mm. The stress-strain curves and mechanical properties of the specimens were obtained from tensile coupon tests. Test results of post-fire mechanical properties are presented. Moreover, evolution of microstructure and fracture morphology of specimens with different cooling methods were examined. Finally, predictive equations are proposed for evaluating the post-fire mechanical properties of Q235 cold-formed steel channel sections.

Experimental investigation of high strength cold-formed channel sections in shear with rectangular and slotted web openings

Cold-formed steel channels with web openings in shear have been thoroughly investigated mainly with circular and square holes. However, web cut-outs are likely to be enlarged along the span length of members due to a limited web depth to provide more access for the building services in practice. The design of cold-formed sections with elongated web holes in shear was investigated and retained in the AISI S100–16 and the AS/NZS 4600:2018 using the empirical approach. This paper presents an experimental investigation of perforated channel sections with rectangular and slotted web openings in shear using a dual actuator test rig to minimise the effects of bending moments and obtain the predominantly shear capacity with an aspect ratio up to 2.0. The commercially available plain C-lipped channel sections with a depth of 200 mm and a thickness of 1.5 mm were chosen with varying sizes of central cut-outs. A new strategy for determination of the shear yield loads (Vy) together with the Vierendeel mechanism approach is presented in this study to propose a modified design for perforated channels with web openings having aspect ratios of holes up to 3.0 for the Direct Strength Method (DSM) of design of channel members in shear with elongated web openings. In addition, as required in the DSM method, the shear elastic buckling loads (Vcr) are extracted from the linear elastic buckling analyses using finite element method in this paper.

Cold Formed Steel Channel Sections with Flange Stiffeners

In recent years the utilization of cold formed steel has been redoubled. This is because high strength to weight ratio of the cold formed steel. The thicknesses cold formed steel members usually range from 0.3 mm to 6.35 mm. The most used cold formed sections are C and Z sections. These sections can be used as secondary beams (purlins) for roof covering, side girts, decks, and panels. Scope of this present study is to investigate the effect on load carrying capacity of cold formed channel sections provided with flange stiffeners. In this project, eighteen numbers of channel sections were analysed by keeping the height to thickness ratio (h/t) as constant and by varying flange width to thickness ratio (b/t) using Ansys 14.0. The h/t ratio and b/t ratio considered are 50 and 25, 35, 45 respectively. The thickness and span of all specimens were kept as 2 mm and 1500 mm respectively. Simply supported boundary condition and two points loading was adopted for both the numerical and experimental analysis. Three numbers of channel sections were fabricated and tested experimentally to check the consistency of results with numerical analysis. The ultimate load and deformed shape of three specimens were obtained from experimental results are compared with the analytical results acquired from Ansys 14.0.

Numerical modelling of web crippling failures in cold-formed steel unlipped channel sections

This paper presents a finite element analysis based study of web crippling failures in cold-formed steel unlipped channel sections with their flanges fastened to supports under one-flange load cases (EOF and IOF). Currently no design equations are available in the current cold-formed steel specifications to determine the web crippling capacities of unlipped channel sections with restrained flanges under one flange load cases. Hence the web crippling behaviour of unlipped channel sections was first investigated experimentally using 28 tests and suitable coefficients were proposed for the current web crippling design equation. However, the applicability of the proposed coefficients was limited to the tested channel sections. In this study advanced finite element models were developed in ABAQUS/CAE and validated in terms of ultimate failure loads, load versus deflection curves and failure modes. The developed models were analysed using nonlinear static and quasi-static analysis based on implicit and explicit integration schemes. This study addressed the effects of mesh size, element type, mechanical property model and inertia of support and loading plates. Also, the effects of two enhancement techniques of explicit analysis such as mass scaling and artificial loading rates with different thicknesses were investigated and the results are presented. A detailed parametric study was then conducted using the validated finite element models. New and improved design equations were proposed to determine the web crippling capacities of unipped channel sections using the results from both finite element analysis based parametric study and experiments.

Numerical investigation into the buckling behaviour of face-to-face built-up cold-formed stainless steel channel sections under axial compression

Stainless steel is becoming popular as structural members because of its increased corrosion resistance and durability, compared with carbon steel. In cold-formed steel structures, such as trusses, wall frames and portal frames, the use of face-to-face built-up cold-formed stainless steel channel sections as compression members are becoming increasingly popular. In such an arrangement, intermediate fasteners at discrete points along the length prevent the individual channel sections from buckling independently. Current guidance by the American Iron and Steel Institute (AISI) and the Australian and New Zealand (AS/NZS) standards for built-up sections describes a modified slenderness approach, to take into account the spacing of the screws. Not even a single experimental test or finite element analysis, however, have been reported in the literature for such face-to-face built-up stainless steel channel sections, to understand the effect of screw spacing. The issue is addressed numerically herein. This paper presents a finite element investigation on the behaviour of face-to-face cold-formed stainless steel built-up channel sections, subjected to axial compression. Three different grades of stainless steel i.e. duplex EN1.4462, ferritic EN1.4003 and austenitic EN1.4404 have been considered. The effect of screw spacing on axial strength of face-to-face built-up stainless steel channel sections was investigated. A comprehensive parametric study was carried out, covering a wide range of slenderness and different cross sectional geometries to assess the performance of the current design guidelines by AISI and AS/NZS. In total, 160 finite element models were analyzed. From the results of the parametric study, it was found that the AISI & AS/NZS are conservative by around 15% for all stainless steel face-to-face built-up columns failed through global buckling. However, the AISI & AS/NZS are un-conservative by around 5% for face-to-face built-up stainless steel columns failed through local buckling.