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• 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]

• 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]

• 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]

• 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]