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Built-up back-to-back cold-formed steel (CFS) channel members (BBC members) are utilized as CFS compression members with enhanced load-bearing capacity in building structures. In this study, finite-element (FE) models of BBC compression members with pinned warping-fixed and pinned warping-free ends were established and verified using test results available in the literature. Using the developed FE models, detailed parametric studies were conducted to assess the behavior and capacity of slender BBC compression members with pinned warping-free ends, varying cross sections, and screw arrangements. The results were first compared with those of their individual (channel) members and BBC members with pinned warping-fixed ends. They were then used to evaluate the direct strength method (DSM) design rules in the CFS design standards used in North America and Australia/New Zealand. Finally, new reliable design rules based on the DSM equations and some analytical equations in the literature were proposed for the BBC compression members with pinned warping-free ends, together with suitable recommendations. This paper includes the main details of this study with a summary of its important findings and proposals. [ABSTRACT FROM AUTHOR]

This paper studies the structural performance of cold-formed steel (CFS) face-to-face (FTF) built-up channel sections subjected to axial compression at high temperatures. The material properties of G250 and G450 CFS channel sections at room and high temperatures were acquired from the literature, and the range of temperatures was from 20 to 700 °C. The influences of the section thickness, member length, screw number, and high temperature on the structural performance of such channel sections were examined via a comprehensive parametric analysis involving 576 validated finite element models. As the temperature increased from 20 to 700 °C, the mean axial capacity of the CFS-FTF built-up unlipped and lipped channel sections decreased by 88.9% and 90.2%, respectively. Based on the results of the parametric study, new design equations for the axial capacity of CFS-FTF built-up channel sections at high temperatures were proposed. The mean ratio of the EWM strengths calculated using the American standard (AISI 2016) and Australian/New Zealand standard (AS/NZS 2018) to the FE strengths was 0.77, while the mean ratio of the proposed design strengths to the FE strengths was 1.01. Finally, a reliability analysis was conducted, and it was found that the proposed equations could come close in predicting the axial capacity of CFS-FTF built-up channel sections at high temperatures. [ABSTRACT FROM AUTHOR]

Recently, there has been an increasing number of studies on the distortional buckling analyses of cold-formed steel (CFS) channels with web edge-stiffened holes. However, the literature about the analytical solutions is scarce, and the current design rules, e.g., the American Iron and Steel Institute (AISI 2016) and the Australian/New Zealand standards (AS/NZ 4600: 2018), provide little design advice for CFS channels with edge-stiffened holes. This paper presents an analytical method for estimating the bearing capacity for the distortional buckling of CFS channel beams with edge-stiffened rectangular web holes. To validate the proposed method, comprehensive finite element (FE) analyses were performed. The proposed design equations accurately forecast the distortional buckling moment capacities of the CFS channels with edge-stiffened holes. Specifically, the average error of the critical moment predictions for the distortional buckling of perforated CFS channel beams obtained by the proposed analytical method and the finite element method (FEM) is only 6.59%, where the maximum error reaches 17.76%. Moreover, a parameter study on the effect of the edge-stiffener length on the bearing capacity was carried out as well, and the results show that the edge stiffener indeed significantly enhanced the critical moment when it is below a threshold length, but the enhancement becomes unobvious once surpassing the threshold length. [ABSTRACT FROM AUTHOR]

Cold-formed steel structures have been progressively used in structural buildings in the forms of the typical channel and Zed sections. The channel sections under weak-axis bending can be found in various situations, especially under biaxial bending. The flexural capacities about the weak-axis, therefore, have specific impacts on the flexural capacities of the channels. The unsymmetrical feature of this channel section about the weak-axis results in a variety of behaviors and strengths of cold-formed steel channel beams with the change of moment directions. SupaCee - a new form of the channel section - made by adding stiffeners in the web of the channel section to increase the stability of the sectional web is also considered in the investigation. This paper, therefore, is aimed to investigate the behaviors and sectional capacities of the channel and SupaCee sections under the weak-axis bending. The considered sections are taken as the availably commercial sections in the market. The sectional capacities are determined using an innovative method namely the Direct Strength Method as regulated in the Australian/New Zealand Standard AS/NZS 4600:2018. The bending behaviours of the investigated sections are observed and analysed; the obtained strength results are the basis for the evaluation of sectional capacities of the channel and SupaCee sections under variations of moment directions. It was found that capacities of the channel and SupaCee sections under the weak-axis bending can be governed by local or distortional buckling depending on the moment directions, whereas the capacities of distortional failures are higher than those of local failures. Also, the innovative strengths of SupaCee sections under the weak-axis bending are not demonstrated in comparison with these such strengths of channel sections. [ABSTRACT FROM AUTHOR]

Full-scale shake table investigations are strongly required to understand the actual performance of storage racks and to improve the rack design guidelines. This paper presents the results of full-scale shake table tests on New Zealand standard storage rack frames with two-bay and two-level to determine the dynamic characteristics of a standard rack structure and to measure the damping of the system. The experimental program was conducted in three phases. First, the identification parameters including the natural frequency and damping of the system were determined through a series of preliminary tests. Then, shake table tests were performed to capture the inelastic response of rack frames under low to medium intensities of El-Centro ground motion. Finally, the shake-table tests were repeated with scaling down the time domain and broader ranges of ground motion intensities to consider the performance of taller rack systems. In addition, a comprehensive discussion on the damping of the system is also provided based on the test results. The performance of the rack frame is described through an extensive set of measurements, including rack displacement, pallet sliding, the acceleration of a concrete block and rack frame and the damping of the system in the down-aisle direction. The results indicate that the standard rack frames are able to endure large inelastic deformations without loss of stability. [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]

• The web crippling behaviour of cold-formed steel channel section having elongated edge-stiffened web holes under interior-two-flange loading condition was studied numerically. • The results of a total of 1,227 new finite element analysis were reported. • Design formulae for the web crippling strength reduction factor were suggested. • A direct strength method (DSM) equation was also presented to evaluate web crippling strength. In the past decade, cold-formed steel (CFS) channel sections having circular edge-stiffened web holes have been developed in New Zealand. Such edge-stiffened holes increase the strength of the CFS channel sections, compared to an equivalent section having unstiffened holes, while still allowing full service integration. In the case of web crippling, previous research has found that use of edge-stiffened holes almost results in the same strength of an equivalent channel-section having a plain web. Such circular edge-stiffened web holes can now be extended to elongated edge-stiffened web holes. However, for such elongated holes, no experimental tests have been reported in the literature. In this paper, a numerical investigation was carried out, and non-linear finite element (FE) analyses were used to investigate the web crippling behaviour of CFS channel sections having edge-stiffened web holes under the interior-two-flange (ITF) loading condition. The cases of both flange fastened and flange unfastened were considered. The FE models were validated against test results of sections having circular edge-stiffened web holes; good agreement in terms of the load–displacement curves and deformed shapes was shown. Using the validated FE models, a parametric study was carried out on CFS channel sections having elongated un-stiffened and edge-stiffened web holes, comprising 1,227 finite element analyses (FEA) results. Compared to sections having a plain web, for the case of an elongated opening, without any edge-stiffener, having an aspect ratio of two and three, the average reduction in web crippling strength was 39% and 49%, respectively. However, for an edge-stiffened hole, the reduction in the web crippling strength was reduced to only 2% and 16%, respectively. Finally, the design equations in the form of the web crippling reduction factor (R p) and the equations based on the direct strength method (DSM) for CFS sections with elongated web holes were proposed. [ABSTRACT FROM AUTHOR]

• Structural performance of cold-formed steel built-up section members under synchronous non-uniform bending and compression was investigated. • Thirty-five beam-column tests under unequal end moments were conducted to examine the effect of moment gradients. • Failure modes involving local, distortional and flexural buckling were found in the experiments. • Comparisons of experimental loading capacities with nominal strengths were performed to evaluate existing design rules. • Reliability analysis was performed to examine the appropriateness of current design codes. The experimental study presented in this paper aimed to examine the performance of cold-formed steel built-up section beam-columns experiencing non-uniform bending. The test program was performed on built-up open and closed sections that were manufactured from steel grades G500 and G550 zinc-coated sheets. The test specimens were assembled by connecting two identical channels with discrete connectors along the longitudinal direction. Two member lengths and two plate thicknesses were considered for the test specimens to investigate the stability of the newly designed thin-walled section beam-columns. In total, thirty-five beam-column tests were carried out under pinned supports. The test results including loading capacity, failure mode and axial load-lateral deflection response were obtained and are fully reported in this paper. Moreover, the comparison of experimental loading capacities with nominal strengths was conducted to evaluate the applicability of the interaction curves specified in the North American Specification AISI S100, the Australian/New Zealand Standard AS/NZS 4600, the European Code EN 1993–1-1 and the American Specification ANSI/AISC 360 with nominal bending and compression resistances calculated by direct strength method for the thin-walled section beam-column members under moment gradients. Overall, these design methods were conservative for strength predictions of the built-up open section beam-column members under unequal end moments. For the built-up closed section members experiencing synchronous non-uniform bending and compression, the aforementioned design methods generally offered slightly conservative strength predictions, except for the interactive formula in the European Code with bending and compression resistances determined by direct strength method. [ABSTRACT FROM AUTHOR]

Cold-formed C-channel sections have been used in portal frame sheds for a wide range of domestic, agricultural and light industrial applications for many years in Australia and New Zealand. However, in many cases the knee joint designs have been copied from hot-rolled portal frame designs, regardless of the clearly different nature of the sections being connected. Testing has demonstrated that many of the joint designs widely used in practice do not achieve the moment capacity of the sections and fail prematurely. Various alternative joint designs have been proposed and constructed, but many of these also fail to meet required capacities under test. This paper reviews the issues relevant to design and construction of such knee joints and considers the positives and negatives of the principal categories of joints currently used in the cold-formed shed industry. It summarises the findings from a large number of tests conducted over a number of years on many of these joints. It concludes with some cautionary notes regarding what is required for design and construction if these commonly used structures are to function as intended from a structural viewpoint. [ABSTRACT FROM AUTHOR]

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]

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]

This paper investigates the interior-one-flange web crippling strength of cold-formed steel channels at elevated temperatures. The stress-strain curves of G250 and G450 grade cold-formed steel (CFS) channels at ambient and elevated temperatures were taken from the literature and the temperatures were varied from 20 to 700 °C. A detailed parametric analysis comprising 3474 validated finite element models was undertaken to investigate the effects of web holes and bearing length on the web crippling behavior of these channels at elevated temperatures. From the parametric study results, it was found that the web crippling strength reduction factor is sensitive to the changes of the hole size, hole location, and the bearing length, with the parameters of hole size and hole location having the largest effect on the web crippling reduction factor. However, the web crippling strength reduction factor remains stable when the temperature is changed from 20 to 700 °C. Based on the parametric analysis results, the web crippling strength reduction factors for both ambient and elevated temperatures are proposed, which outperformed the equations available in the literature and in the design guidelines of American standard (AISI S100-16) and Australian/New Zealand standard (AS/NZS 4600:2018) for ambient temperatures. Then, a reliability analysis was conducted, the results of which showed that the proposed design equations could closely predict the reduced web crippling strength of CFS channel sections under interior-one-flange loading conditions at elevated temperatures. [ABSTRACT FROM AUTHOR]

• The structural behaviour of cold-formed steel T -stub connections with HRC and screws was studied experimentally and numerically. • The results of a total of 15 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. Cold-formed steel (CFS) T -Stub connections are widely used in single-story buildings, and their use is increasing in multi-story and long-span buildings. Recently, an innovative CFS T -Stub connection was developed using self-drilling screws and the Howick Rivet Connector (HRC), and such a newly-developed connection demonstrated excellent structural performance in the building industry. In this paper, a comprehensive experimental and numerical investigation was conducted to investigate the failure mechanism and structural behaviour of CFS T -Stub connections with a combination of HRC and screws under tension force, considering the effects of screw numbers. Firstly, a total of 15 new experimental tests were conducted on the CFS T -Stub connections with various numbers of screws. From the experiments, it was observed that the HRC was subjected to shear failures, while screws failed primarily due to tilting and bearing failures in all investigated specimens. Then, a non-linear elasto-plastic finite element (FE) model was developed and validated against the experimental results in terms of connection strength and failure modes. Finally, the design strengths obtained from the American Iron and Steel Institute (AISI 2016) & Australia/New Zealand standards (AS/NZS 2018) and Ahmadi et al. (2016) were compared with the test and FEA results, showing that the ultimate design strength of CFS T -Stub connections was overestimated by 16% and 14%, respectively. However, for T -Stub connections with HRC alone and with HRC and one screw, these design guidelines were unconservative by 5%. [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]

• A total of 41 cold-formed steel built-up I-sections were tested under ETF, ITF, EOF and IOF loading conditions. • Finite element models were developed to replicate the experiments. • Parametric study of 258 specimens was performed. • The existing codified web crippling design provisions were assessed. • Design rules were proposed based on the unified equation and direct strength method. This paper reports the experiments, numerical modelling and design of cold-formed steel built-up I-sections subjected to localised loadings. The built-up I-sections were made up of two equal-sized plain channels fastened back-to-back in the web. The web crippling tests were undertaken on 41 built-up I-section members under Interior-Two-Flange (ITF), End-Two-Flange (ETF), Interior-One-Flange (IOF) and End-One-Flange (EOF) loading conditions. The effects of the arrangement of screws along the web height were investigated. After the experiments, finite element (FE) analyses considering the initial local imperfections of the web of the specimens were performed and the validity of the FE models was assessed using the test results. A parametric investigation including 258 numerical simulations was conducted to expand the database and evaluate the influences of the screw arrangements in the web height. The test and numerical results indicated that the failure modes of the specimens with different screw arrangements were generally similar in each loading condition, and the screws located close to the flange-web junctions of the sections could generally provide maximum web crippling resistances of the built-up I-sections. The design recommendations on the arrangements of screws along the web height were proposed. The experimentally and numerically generated web crippling resistances were utilized to assess the current North American specification (AISI S100), Australian and New Zealand standard (AS/NZS 4600) and European code (EN1993-1-3). The results show that the existing codified design formulas lead to either conservative or highly unsafe results. Therefore, two sets of design formulas were derived on the basis of unified equation and direct strength method. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the buckling behavior of cold-formed steel built-up closed section members subjected to combined minor axis bending and compression. The channels were fabricated from zinc-coated steel sheets of grades G500 and G550 to compose built-up closed sections. A total of 30 beam-column specimens with nominal member lengths of 300, 900, and 1,500 mm as well as nominal plate thicknesses of 0.75 and 1.2 mm were eccentrically loaded under pin-ended boundary condition. The initial loading eccentricity was varied for the specimens in each test series to obtain the data evenly distributed in the axial load-moment interaction diagram. Experimental results including failure modes, loading capacities, and full-history responses of the test specimens were obtained. In addition, the experimental loading capacities were compared with nominal strengths to evaluate the suitability of the provisions as stipulated in the North American specification, Australian/New Zealand standard, European code, and American specification for the built-up section beam-columns. It is shown that the aforementioned design codes are overall unreliable and unconservative for strength predictions of the cold-formed steel built-up closed section members under combined minor axis bending and compression. [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]

• Numerical models for CFS built-up columns with spacers were developed. • Detailed nonlinear response of CFS built-up columns was investigated. • Predictions as per current Australian/European CFS standards were inconsistent. • Improved design equations were proposed for better/reliable strength predictions. This paper deals with the numerical investigation aimed to study the axial capacity and the nonlinear deformation response of pin ended cold-formed steel (CFS) built-up columns under monotonic axial loading, applied concentrically. The built-up sections were constructed by adequately spaced channel sections in a back-to-back configuration, connected through webs by means of connecting elements (CFS channels) called spacers. Self-driving screws were used as fasteners to assemble together the lipped channels and spacers. Finite element (FE) models were established and verified against the previously published built-up columns with similar configuration. An extensive parametric study was conducted by varying the key parameters like plate slenderness of the lipped channels, unbraced chord slenderness, and global slenderness in order to investigate their variation on the ultimate compression resistance of these built-up columns. The effective width method was used to determine the design strengths for these built-up columns using the AS/NZ Specifications and European Specification on cold-formed steel structures, which were later compared with the results obtained from the numerical parametric study. This study indicated that the provisions that are given in the current AS/NZS and European Specification in predicting the strengths of the built-up column with spacers had shortcomings. Therefore, new design equations for the reliable design strength predictions of the CFS built-up column composed of lipped channels with spacers were proposed. The incorporation of spacers curtailed the local buckling half-wave length, which improved the buckling resistance, predominantly in the columns failing by local buckling. [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]

The current design rules of double shear bolted connections in the North American and Australian/New Zealand specifications for cold-formed steel structures are mainly based on the design rules of single shear bolted connections. The design rules may not be applicable for elevated temperature conditions because the design rules of single shear bolted connections were based on tests conducted at ambient temperature. A total of 153 double shear bolted connection specimens were tested, where 102 specimens were tested using a steady-state test method and 51 specimen tests were conducted using a transient-state test method. Three thicknesses of thin sheet steel were used in the investigation. The connection strengths obtained from the tests were compared with the nominal strengths calculated from the North American, Australian/New Zealand, and European specifications for cold-formed steel structures. The current modification factor in the bearing strengths calculation for double shear bolted connections was evaluated at an ambient temperature. The reduced tensile strengths of the thin sheet steels obtained from tensile coupon tests at elevated temperatures were used to calculate the nominal strengths of the connections. It is shown that the strengths of the double shear bolted connections predicted by the three specifications are generally conservative at elevated temperatures. Five failure modes were observed in the tests: bearing, tear-out, net section tension, bolt shear, and material. [ABSTRACT FROM AUTHOR]