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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]

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]

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]

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]