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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 a thorough experimental and numerical investigation into the structural behaviour of a novel cold-formed steel (CFS) telescopic stud system under axial compression. A total of 40 specimens were tested, considering variations in screw configurations, steel grades, and section thicknesses. The test results revealed that tilting and bearing led to failure in all screw connections. In comparison to the single-screw connection with a gap at the middle of the web, the telescopic studs with 2 screws in the web, 2 screws in the flanges, and 4 screws in both the web and flanges showed approximately 35–37% higher strengths. A nonlinear explicit dynamic finite element model was then developed and validated against the test results in terms of its connection strengths and failure modes. The experimental results were compared with the design strengths determined by the current design standards (AISI S100 (2016), AS/NZS 4600 (2018), Eurocode 3 (2006), BS5950–5 (1998) and GB50018 (2002).). The comparison results revealed that the AISI S100 (2016) and AS/NZS 4600 (2018) are conservative, underestimating the connection strengths of telescopic studs with different screw layouts by 1–13%. • The connection strengths of telescopic studs under compression were studied experimentally and numerically. • The results of a total of 40 new experiments 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 experimental program investigating the local and/or distortional (sectional) buckling of built-up cold-formed steel sections subjected to pure compression. The experiments were designed to study the influence of key parameters, including buckling mode, cross-section geometry and fastener spacing, on the ultimate sectional capacity of built-up columns. Three singly- or doubly-symmetric built-up sections were considered with two sets of component lipped channel sections, one buckling predominantly in the distortional mode and one buckling in the local mode. The component sections were connected using self-drilling screws at three different spacings. Material properties, geometric imperfections and residual stresses of the specimens were measured prior to testing. A total of 36 specimens with a length of 1 m were tested under concentric compression between fixed ends, which was achieved through a special end plate connection. The specimens failed in either distortional or the interaction of local and distortional buckling modes. Compared to the sum of the capacity of component sections, the ultimate capacity in built-up columns with distortional buckling mode increased significantly with the reduction of screw spacing, whereas the increase was minor for specimens that failed through local-distortional interaction. The ultimate strength of the specimens was predicted using the current Direct Strength Method, where either conservative or overly unconservative predictions were obtained depending on the considered composite action level in the elastic buckling analysis. • Experimental study of built-up sections with more than two component sections. • Fastener-constrained distortional and local buckling failure modes. • Influence on strength of cross-section geometry and fasteners spacing. • Comparison of experimental strengths to predictions by the Direct Strength Method. [ABSTRACT FROM AUTHOR]

Built-up back-to-back cold-formed steel channel (BC) members are increasingly used as studs for increasing the compression capacity of light gauge steel framed (LSF) walls, even though the knowledge of their behaviour is limited. In this study, the behaviour and capacities of LSF walls made of slender BC members sheathed with gypsum plasterboards on both sides were investigated using a series of compression tests and detailed finite element studies based on validated models. The numerical and experimental results showed that (1) screw connections of BC members had marginal effects on the compression capacities of the investigated sheathed BC members with non-staggered stud-to-board screw arrangement, and the capacities were mostly equal to twice the capacities of their individual members, (2) the restraints provided by the plasterboards and stud-to-board screw connections effectively prevented sheathed BC members from in-plane flexural buckling and considerably improved their compression capacities, and (3) the Direct Strength Method in the current design standards in combination with the guidelines and recommendations proposed in this study conservatively predicted the compression capacities of these members. Details of this research study, its results and findings are presented in this paper. [Display omitted] • Investigated the behaviour of built-up back-to-back channel (BC) studs sheathed with gypsum plasterboards. • Plasterboards and stud-to-board screws restrained sheathed studs from in-plane flexural buckling and improved the capacity. • The capacity of sheathed BC studs with non-staggered stud-to-board screws was about twice the individual member capacity. • The effect of stud-to-stud screw arrangement was marginal. • Conservative DSM-based design guidelines and recommendations are proposed. [ABSTRACT FROM AUTHOR]

Screwed connections are commonly used in fabricating built-up cold-formed steel (CFS) members. However, the knowledge and understanding of their behaviour and design are limited. This research study investigated the shear behaviour and capacity of the screwed connections used in built-up CFS members. It included a series of shear tests of screwed connections between two single channel members as used in built-up back-to-back CFS members, failing by tilting and bearing. Tests were conducted at both ambient and elevated temperatures. Using the results from these tests and available literature, this study has shown that the design equations for the tilting and bearing capacity of screwed connections in the current CFS design standards are reliable for the screwed connections in built-up CFS members at ambient temperature. It has then shown that the same design equations can be used to predict the tilting and bearing capacity of these screwed connections at elevated temperatures if they are used in combination with the proposed reduction factor equations for elevated temperature capacities. Details of this research study, its results and findings are presented in this paper. [Display omitted] • The shear behaviour of screwed connection in built-up CFS members was investigated. • Curling of connected parts was minor because of the effect of edge flange elements. • The accuracy of current design equations in predicting their capacities at ambient temperature was investigated. • Equations were proposed for predicting the reduction of their capacity with increasing temperatures. • Improved design guidelines were proposed for their capacities at elevated temperatures. [ABSTRACT FROM AUTHOR]

In order to investigate the shear performance and determine the shear strength of cold-formed steel (CFS) clip angles with multiple lines of screws, a series of CFS clip angles were tested under in-plane transverse shear loading. The tested pieces involved CFS clip angles with various thicknesses, aspect ratios, and screw arrangements. The test program, experimental observations, and test data results are presented in this paper. Based on the results from the experiments and finite element elastic buckling analysis, two design methods were developed for determining the nominal shear strength of load bearing clip angles without consideration of the deformation. Shear design method for CFS clip angles with consideration of deformation was also proposed. In addition, the ASD safety factors, LSD and LRFD resistance factors were produced to support the proposed design methods. [Display omitted] [ABSTRACT FROM AUTHOR]

This paper presents a study on the behavior of screw connections in sheathed cold-formed steel (CFS) walls. A finite element (FE) model with solid elements was developed to investigate different failure modes. Suitable solution techniques, element types, mesh sizes, screw modeling, and geometric and material non-linearity were considered in model development. Since the behavior of the sheathing boards is similar to that of other quasi-brittle materials, the Concrete Damage Plasticity (CDP) model was used to model the material behavior using both classical plasticity and continuum damage mechanics. Uniaxial experimental tests were performed on fiber-cement board samples to define material parameters used in the CDP model. The load displacement behavior, ultimate strength, and failure modes obtained from the developed FE model were validated against available experimental results on walls sheathed with cement or gypsum boards. The validated FE model was then used to perform parametric study to investigate the effect of different design parameters on the connection behavior. These parameters are: board type and thickness, CFS profile thickness, screw diameter, screw length, and edge distance. The results of the parametric study were used to develop a design equation for the screw connection strength using nonlinear regression analysis. • Finite element model with Concrete Damage Plasticity of screw connection. • Material properties of fiber-cement boards from tests. • Parametric study of the behavior of sheathed screw connections. • Design equation to evaluate the ultimate strength of sheathed screw connection. [ABSTRACT FROM AUTHOR]