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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]

• 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]

• 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]

• 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]

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]