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Built-up box sections are becoming increasingly popular for column members in cold-formed steel (CFS) construction; uses of such sections include CFS trusses, space frames, and portal frames. In this article, the built-up box sections are formed through two identical lipped channels connected at their flanges with self-drilling screws. In such an arrangement, independent buckling of the individual channels is prevented by the screws. This paper presents an experimental investigation on axial capacity of built-up CFS box sections. Tests were conducted for different values of slenderness from short to slender columns. In total, the results from 16 experimental tests are reported. Of these, 8 tests were conducted on built-up CFS box sections and the remaining 8 tests were conducted on single channel sections. Load-axial shortening relationship, and failure modes are discussed for built-up columns. Nonlinear finite element (FE) models were developed for built-up CFS box sections and single channels. FE models considered material nonlinearities, initial imperfections and modeling of intermediate fasteners. FE results showed good agreement against the test results. A parametric study was conducted which comprises 148 models to investigate the effect of fastener spacing on axial capacity of built-up CFS box sections. Both FE and test results were compared against the design strengths calculated in accordance with the American Iron and Steel Institute (AISI) and Australian and New Zealand Standards (AS/NZS). From the comparison, it was observed that the AISI & AS/NZS are conservative by around 17% while determining the axial capacity of such built-up CFS box columns. • Experimental tests were conducted on CFS built-up box sections under axial compression. • Results from an experimental regime and elasto-plastic finite element are reported. • Local and overall imperfections are considered in FE models • The validated FE model was used for a parametric study to investigate the effect of screw spacing. • The design strengths in accordance with the AISI & AS/NZS are conservative by around 17% for CFS built-up box columns [ABSTRACT FROM AUTHOR]

Cold-formed steel (CFS) is a popular form of construction in New Zealand and the developed world because it can be cost-effective, durable, sustainable, resilient to extreme environmental and seismic loads and easy to install. When used in domestic and medium-rise buildings, T-Stub connection between CFS channel sections is formed by using self-drilling screws which connect the flanges. In the literature, no prior investigation on the tension capacity of such connection has been reported. Therefore, this paper describes a novel test procedure for determining the tension capacity of such CFS T-Stub connection and the associated mechanism of failure. An experimental test program that comprises thirty experimental tests is reported in this paper. Three channel section thicknesses were examined: 0.55 mm, 0.75 mm, and 0.95 mm. All specimens failed as a result of tilting of the screws and bearing failure. Non-linear elasto-plastic finite element (FE) models were developed, and the predictions were validated against the experimental test results. It was adjudged that there was reasonable agreement in terms of connection strength and failure mode prediction. Finally, the design strengths derived from current design standards were compared with the experimental failure loads. It was found that the American Iron and Steel Institute (AISI 2016) and Australian and New Zealand Standard (AS/NZS 2018) are conservative by 6% and unconservative by 10% for the initial and final failure loads of T-Stub CFS connections, respectively. • A novel cold-formed steel T-stub connection was studied experimentally and numerically. • The results of a total of 30 new experimental tests were reported. • Finite element analysis was conducted and validated against the test results. • The prediction accuracy of current design standards was evaluated. [ABSTRACT FROM AUTHOR]

This paper presents an application of the Digital Image Correlation (DIC) based technique to investigate the block shear failure mode of bolted connections made of high strength cold-reduced G450 sheet steel. In conjunction with the conventional testing approach, the DIC provides detailed failure information on connection behaviour and its correlation with macroscopic material tests. A total number of 12 tests of 3 mm thickness specimens were tested at the University of Sydney. The experimental results provide a better understanding on how the failure of the bolted connections progress. The features of the new block shear equations recently adopted in the North American Specification for Design of Cold-Formed Steel Structural Members (AISI S100:2016) and the Australian/New Zealand Standards 4600:2018 Cold-Formed Steel Structures have been clarified. • A block shear failure experimental program of bolted connections using high strength G450 sheet steel is performed. • The Digital Image Correlation (DIC) is used to observe the failure of the bolted connections. • Test results are compared with the predictions in AISI S100:2016 and AS/NZS 4600:2018. • The average shear area used in the block shear equation in the latest AISI S100:2016 and AS/NZS 4600:2018 has been confirmed. [ABSTRACT FROM AUTHOR]

The use of cold-formed steel (CFS) channels with web holes are becoming increasingly popular. Such holes, however, result in sections becoming more susceptible to lower axial compressive resistance. Traditional holes are normally punched at the web and un-stiffened. Recently, a new generation of CFS channels with edge-stiffened holes has been developed by the CFS industry but no information is available in the literature to accurately predict the axial capacity of such sections. The current design guidelines in accordance with the American Iron and Steel Institute (AISI 2016) and Australia New Zealand standards (AS/NZ 4600:2018) do not provide any design rules for CFS channels with edge-stiffened holes. In this paper, a numerical model that accurately simulated results from the experimental testing of CFS channels with edge-stiffened holes under axial compression as published in a previous paper by the authors was employed to carry out a parametric study which involved 348 finite element (FE) models. Variables which were examined included column slenderness, stiffener length, fillet radius, hole size, hole location and hole spacing. A comparison of the numerical results with current design rules for CFS channels with un-stiffened holes revealed that the design equations were not accurate for such sections; design equations are therefore proposed in which an enhancement factor is applied to the original equations. The enhancement factor was obtained using bivariate linear regression analysis. The proposed design equations closely predict the enhanced axial capacity of CFS channels with edge-stiffened holes. • A new generation of CFS channels with edge-stiffened holes was studied through finite element analysis • The FE model was validated against the previously published data for CFS channels with edge-stiffened holes • A parametric study which involved 348 FE models was conducted. • Variables are slenderness, stiffener length, fillet radius, hole size, hole location and hole spacing. • The developed design equations could predict the capacity of CFS channels with edge-stiffened holes. [ABSTRACT FROM AUTHOR]

The present paper reports the numerical parametric study on the structural behaviour of battened cold-formed steel built-up box columns composed of four lipped angles. The validated numerical model with the experimental results reported by the author in the comparison paper was employed to carry out parametric studies to produce numerical data over a wider range of global column slenderness by varying the sectional compactness of the lipped angle section, batten spacing, and global column slenderness. The numerically derived results were employed to check the accuracy of the current design rules. The results of the assessment revealed the limitation of the current design rules in the prediction of the capacity of the CFS built-up battened box columns, which was mainly associated with the influence of unbraced chord slenderness and interconnector stiffness on the buckling behaviour. Therefore, improved design procedure was proposed in the framework of AS/NZS specifications (AS/NZ 4600:2018) and European standards (EN1993-1-3:2006) for the safe, less scattered and reliable design strength predictions of battened CFS built-up columns composed of four lipped angles. • The CFS built-up battened column composed of four lipped angles were investigated. • Lower unbraced chord slenderness can improve the axial strength by up-to 28%. • Also, it is more dominant in intermediate columns with lower sectional compactness. • AS/NZ-4600's upper limit for the relative unbraced chord slenderness is recommended. • Reliable design equations are proposed for CFS battened columns. [ABSTRACT FROM AUTHOR]

Cold-formed steel (CFS) Tab connections are popular due to their rapid fastening and ease of installation, and their applications have increased recently in Pacific countries, including Australia and New Zealand. This type of connection consists of a Tab plate formed from the web of the supporting beam and is screwed to the joist web, providing a dependable load path from the joist to the galvanized C-section supporting beam. However, no studies have been reported in the literature for the shear capacity of such connections. This paper presents a shear test program designed to determine the shear capacity of CFS Tab connections and to identify their failure mechanism. The experimental program included three different beam sizes, C-150, C-190 and C-240. Each test was repeated three times, resulting in nine tests in total. All the specimens failed in plate yielding and plate tearing, which occurred on the tension side of the plate (top region). Nonlinear finite element (FE) models were then developed and verified against the test results. The FE results showed good agreement with the test results in terms of connection stiffness, connection strength and failure modes. Finally, it was shown that the design equations given in the Australia/New Zealand standard (AS/NZS 4600) and American Iron and Steel Institute (AISI S100) for predicting the combined bending and shear capacity could predict the ultimate shear capacity of CFS Tab connections investigated in this study. • The results of monotonic shear tests of a novel CFS Tab connection are reported. • CFS Tab connections failed in plate yeailding and tearing. • A nonlinear FE model is developed. Results showed good agreement with the test results. • A design procedure is proposed for predicting the shear capacity of CFS Tab connections. [ABSTRACT FROM AUTHOR]

Cold-formed steel (CFS) back-to-back channels are becoming a popular choice for use in load-carrying members in building structures. These built-up channels often include web holes for installation of services. Traditional web holes are un-stiffened, which can restrict the size and spacing of holes. Recently, a new generation of CFS channels with edge-stiffened holes has been developed and used widely in New Zealand. No research has been reported in the literature to investigate the axial strength of back-to-back channels with edge-stiffened holes. Experiments are required on back-to-back channels with edge-stiffened holes so to understand the effects of composite actions between the back-to-back channels on the axial strength of such channels. This paper presents a total of 162 new results comprising 27 axial compression tests and 135 finite element analysis (FEA) results on the axial strength of back-to-back channels with edge-stiffened holes, un-stiffened holes and plain webs. Prior to compression tests, initial geometric imperfections were measured using a laser scanner. Tensile coupon tests were also conducted to determine the material properties of both the flat and corner portions of the channels. The test results show that for the case of back-to-back channels with edge-stiffened holes, the axial strength increased by 6.6% on average, compared to a back-to-back plain channel. For comparison, the same section with un-stiffened holes had a 12.4% reduction on average in axial strength, compared to a back-to-back plain channel. A nonlinear elasto-plastic finite element (FE) model was then developed, and the results showed good agreement with the test results. The validated FE model was used to conduct a parametric study involving 135 FE models to investigate the effects of column slenderness, diameter of hole, screw spacing, stiffener lengths and stiffener fillet radius on the axial strength of such channels. Finally, the tests and parametric study results were compared against the design strengths calculated in accordance with the American Iron and Steel Institute (AISI) (2016) and Australian and New Zealand Standards (AS/NZS) (2018) for back-to-back plain channels and against the design equations of Moen and Schafer (2011) for back-to-back channels with un-stiffened holes. It was found that the AISI (2016) and AS/NZS (2018) are only 3% conservative to the test results. The Moen and Schafer equations (2008, 2009, 2011) are conservative by 21% on average for back-to-back channels with un-stiffened holes. Deformed shapes at failure from experiments and FEA. Unlabelled Image • A new generation of back-to-back CFS channels with edge-stiffened holes is examined. • Results from an experimental regime and elasto-plastic finite element are reported. • A parametric study involving 135 FE models was conducted. • Variables included column slenderness, hole size, screw spacing, stiffener lengths and stiffener fillet radius. • Edge stiffened hole-channels can outperform plain channels in terms of axial strength. [ABSTRACT FROM AUTHOR]

This paper describes an experimental and numerical investigation to study the flexural capacity of back-to-back gapped built-up cold-formed steel (CFS) channel sections under four-point bending. The gap between the back-to-back channels was formed through intermediate link-channels which were screwed to the webs of the back-to-back channels. A total of 90 results comprising 18 laboratory tests and 72 finite element (FE) analysis results are reported on the flexural capacity of back-to-back gapped built-up CFS channel sections under four-point bending. Three different types of channels were considered to form the built-up channels: plain channels, channels with one web stiffener and channels with two web stiffeners. Two different beam spans as 1000 mm and 2000 mm were tested. Initial geometric imperfections were also measured prior to bending tests for all test specimens. A nonlinear FE model was then developed, the results of which showed good agreement against the laboratory test results. Using the validated FE model, an extensive parametric study was conducted to investigate the effects of web stiffeners and link-channel spacing on the flexural capacity of such gapped built-up beams. It is shown that design in accordance with the American Iron and Steel Institute, AISI (2016) and Australia/New-Zealand standards, AS/NZS (2018) can be conservative by as much as 27%. The flexural capacity of back-to-back gapped built-up sections with two web stiffeners was increased by 10% on average, when compared to the capacity of gapped built-up beams with plain channel sections. • Eighteen laboratory tests are reported on the flexural capacity of back-to-back gapped built-up CFS channel sections under four-point bending. • Three different types of channels: plain channels, channels with one web stiffener and channels with two web stiffeners were used to for the gapped built-up beams. • A nonlinear FE model was then developed, which included initial imperfections and modeling of link-channels and fasteners. • An extensive parametric study was conducted to investigate the effects of web stiffeners and link-channel spacing on the flexural capacity of such gapped built-up beams. • It is shown that design in accordance with the AISI & AS/NZS can be conservative by as much as 27%. [ABSTRACT FROM AUTHOR]

Cold-Formed Steel (CFS) members with slotted perforations in webs are used in civil construction to amplify the thermal and energy performance of structures. However, the slotted webs reduce the structural performance of the element, prominently their shear, bending and combined bending and shear strengths. Many research studies have been undertaken to examine the behaviour of CFS channel sections subject to bending. Yet, no research has been performed to investigate the distortional buckling behaviour of slotted perforated CFS flexural members. Finite Element (FE) models of CFS channels with staggered slotted perforations were developed herein to investigate their distortional buckling under bending stress. A parametric study was conducted in detail by developing 432 slotted perforated CFS FE models based on the validation process with available experimental results. In particular, this paper presents the FE analysis details of CFS flexural members with slotted perforations subject to distortional buckling and results. The reliability of the current Direct Strength Method (DSM) for CFS flexural members with web holes subject to distortional buckling in accordance with the North American Specification (AISI S100) (2016) and the Australian/New Zealand Standards (AS/NZ 4600) (2018) was investigated. Modified DSM formulae for slotted perforated CFS flexural members subject to distortional buckling were also proposed. • Distortional buckling behavior of CFS beams with staggered slotted perforations have been investigated. • Finite element models showed good agreement with available test data. • All influencing parameters were considered in the parametric studies. • Staggered slotted perforations reduced the distortional buckling flexural capacity up to 23%. • New direct strength method based design equations were proposed for distortional buckling. [ABSTRACT FROM AUTHOR]