Capacity of cold-formed steel channels with edge-stiffened web holes in bending, shear and web crippling

Abstract

Thin-walled structural channel members as floor joists and bearers are commonly manufactured with cut-outs to allow access for building services such as plumbing, electrical, and heating systems in the walls and ceilings. The presence of web holes in the members will cause changes in the stress distribution and consequently, there will be changes in the buckling characteristics and ultimate strength. Traditional web holes are normally punched or bored and are un-stiffened, which can restrict the size and spacing of web holes. To overcome these restrictions, a new generation of cold-formed steel (CFS) channel beams with edge-stiffened web holes developed by the CFS industry has been widely used. Such CFS channel beams, when used as floor joists and bearers, are often subjected to concentrated loads; hence experiencing shear failure, bending failure, and web crippling failure. However, in the literature, limited work is available on the behaviour of such CFS channel beams in bending, shear, and web crippling. Furthermore, the current design guidelines, such as the American Iron and Steel Institute (AISI, 2016) and the Australian and New Zealand Standards (AS/NZS, 2018), do not provide any design guidelines for determining the capacity of such CFS channel beams with edge-stiffened web holes. The aim of this research is to investigate the effects of edge-stiffened web holes on the capacity of such CFS channel beams in bending, shear, and web crippling. In total, 82 laboratory tests were performed, covering web crippling tests, bending tests, and shear tests. For comparison, specimens with un-stiffened web holes and plain webs were also tested. The material properties of test specimens were determined from tensile coupon tests. The results obtained from laboratory tests show that the CFS channel beams with edge-stiffened web holes performed better than those with un-stiffened web holes in terms of ultimate capacity for all three loading cases. Nonlinear finite-element (FE) models were also established and validated against the experimental results, which showed good agreement both in terms of ultimate capacity and deformed shapes. The validated FE models were then used to perform a parametric study involving 1335 FE models to investigate the effects of different parameters on the capacity of such channel beams. To evaluate the performance and accuracy of current design guidelines of CFS channel beams with un-stiffened web holes, the test and FE results were compared against the design capacities predicted by the current design guidelines such as AISI (2016) and AS/NZS (2018). The comparison results show that design capacities predicted by AISI (2016) and AS/NZS (2018) are conservative and unsafe for calculating the capacity of CFS channel beams with edge-stiffened web holes for all three loading cases. Based on the experimental and numerical results, suitable design equations in the form of capacity reduction factors were developed using bivariate linear regression analysis for calculating the shear capacity of CFS channel beams with edge-stiffened web holes. A reliability analysis was carried out to evaluate the accuracy and reliability of the proposed design equations, indicating that the proposed design equations can closely predict the shear capacity reduction factors of CFS channel beams with edge-stiffened web holes.