Axial strength of back to back cold formed steel short channel sections with unstiffened and stiffened web holes.

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

Cold-formed stainless steel is becoming popular as a structural member with its increased corrosion resistance and durability when compared with carbon steel. Examples of cold-formed steel structures include trusses, wall frames and portal frames. In cases where increased axial capacity is required, it is becoming increasingly popular to use back-to-back gapped built-up channels, instead of just back-to-back sections. In such an arrangement, however, the beneficial effect of the gap between the back-to-back cold-formed steel channels is ignored by the current design guidelines (American Iron and Steel Institute and the Australian and New Zealand Standard and Eurocode (EN 1993-1-3)) for both cold-formed carbon as well as cold-formed stainless steel. We have considered this issue both experimentally and numerically through finite element analysis for cold-formed carbon steel; from the results of this work, design recommendations were proposed. These results, however, are not applicable to cold-formed stainless steel. This issue is addressed numerically herein. Using the finite element model previously developed for cold-formed carbon steel, an extensive parametric study, comprising 589 models is described. Three different grades of stainless steel, that is, ferritic EN1.4003, austenitic EN1.4404 and duplex EN1.4462 have been considered. The effect of the gap between the two back-to-back channels, slenderness, link-channel spacing and different cross-sectional geometries are investigated. The finite element results were then used to verify the accuracy of current design guidelines by the American Iron and Steel Institute and the Australian and New Zealand Standard and Eurocode (EN 1993-1-3). It was found that the American Iron and Steel Institute and the Australian and New Zealand Standard and Eurocode (EN 1993-1-3) can be over conservative by as much as 68% when calculating the axial capacity of such built-up gapped stainless steel columns. Therefore, a design recommendation is proposed to modify the non-dimensional slenderness so to consider the gap. This leads to the American Iron and Steel Institute and the Australian and New Zealand Standard and Eurocode (EN 1993-1-3) being within 7% conservative to the finite element results.

Effect of thickness on the behaviour of axially loaded back-to-back cold-formed steel built-up channel sections - Experimental and numerical investigation

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.

Experimental and numerical investigation into the behaviour of face-to-face built-up cold-formed steel channel sections under compression

Web crippling capacity of fastened cold-formed steel channels with edge-stiffened web holes, un-stiffened web holes and plain webs under two-flange loading

Behaviour of laced built-up cold-formed steel columns: Experimental investigation and numerical validation

Back-to-back built-up cold-formed steel un-lipped channel sections are used in cold-formed steel structures; such as trusses, wall frames and portal frames. In such built-up columns, intermediate fasteners resist the buckling of individual channelsections. No experimental tests or finite element analyses have been reported in the literature for back-to-back built-up coldformed steel un-lipped channel sections and specially investigated the effect of screw spacing on axial strength of such columns. The issue is addressed in this paper. The results of 95 finite element analyses are presented covering stub to slender columns. The finite element model is validated against the experimental tests recently conducted by authors for back-to-back built-up cold-formed steel lipped channel sections. The verified finite element model is then used for the purposes of a parametric study to investigate the effect of screw spacing on axial strength of back-to-back built-up cold-formed steel un-lipped channel sections. Results are compared against the built-up lipped channel sections and it is shown that the axial strength of un-lipped built-up sections are 31% lesser on average than the built-up lipped channel sections. It was also found that the American Iron and Steel Institute (AISI) and the Australian and New Zealand Standards were over-conservative by around 15% for built-up columns failed through overall buckling, however AISI and AS/NZS were un-conservative by around 8% for built-up columns mainly failed by local buckling.

Cold-formed steel (CFS) channel infilled with concrete could increase its ability and stiffness by avoiding failure due to local buckling. Besides, the built-up bolted CFS channel column could serve as permanent formwork, decreased waste material and yet increase economical construction. This study aims to investigate the strength of built-up CFS channel columns infilled with concrete. Two CFS channel sections are situated face to face, connected and strengthen by using M10 bolts and nuts. Then, the 900 mm built-up column is filled with normal concrete of grade C30. Six samples with different end and central bolt spacing were tested. Material properties of CFS and concrete, and the mechanical properties of bolts are also investigated. From the result, the column with concrete on shortest end bolt spacing gave highest ultimate load and reported 68 – 78 % different when compared to similar column without concrete infilled. The failure mode of the column is global buckling and supports yielding, and the concrete is failed due to cracking and breaking. Equation of the relationship between bolt spacing either at the end or central and ultimate load is established.

Numerical investigation and design of cold-formed steel built-up open section columns with longitudinal stiffeners

Concrete-filled built-up cold-formed steel (CFS) columns offer enhanced load-carrying capacity, improved strength-to-weight ratios, and delayed buckling through providing internal resistance and stiffness due to the concrete infill. Integrating sustainable alternatives like self-compacting geopolymer concrete (SCGC) with low carbon emissions is increasingly favoured for addressing environmental concerns in construction. This review aims to explore the current knowledge regarding CFS built-up composite columns and the performance of SCGC within them. While research on geopolymer concrete-filled steel tubes (GPCFSTs) under various loads has demonstrated high strength and ductility, investigations into built-up sections remain limited. The literature suggests that geopolymer concrete’s superior compressive strength, fire resistance, and minimal shrinkage render it highly compatible with steel tubular columns, providing robust load-bearing capacity and gradual post-ultimate strength, attributed to the confinement effect of the outer steel tubes, thereby preventing brittle failure. Additionally, in built-up sections, connector penetration depth and spacing, particularly at the ends, enhances structural performance through composite action in CFS structures. Consequently, understanding the importance of using a sustainable and superior infill like SCGC, the cross-sectional efficiency of CFS sections, and optimal shear connections in built-up CFS columns is crucial. Moreover, there is a potential for developing environmentally sustainable built-up CFS composite columns using SCGC cured at ambient temperatures as infill.

Axial capacity of CFS built-up columns comprising of lipped channels with spacers: Nonlinear response and design

Web crippling behaviour of cold-formed steel channels with elongated un-stiffened and edge-stiffened web holes under end-two-flange loading condition

Moment capacity of cold-formed channel beams with edge-stiffened web holes, un-stiffened web holes and plain webs

Elastic shear buckling of cold-formed steel channels with edge stiffened web holes