Abstract
Cold-formed steel (CFS) construction can lead to more efficient designs compared to hot-rolled steel members as a consequence of its high strength, light weight, ease of fabrication, and flexibility in their cross-section profiles. However, CFS members are vulnerable to local, distortional and overall buckling modes. This paper develops a numerical model to investigate the flexural strength and failure modes of CFS back-to-back channel beams and verifies the efficiency of an optimisation framework previously proposed. The model incorporates non-linear stress-strain behaviour and enhanced corner properties obtained from coupon tests, as well as initial geometric imperfections measured in physical specimens. To simulate the behaviour of a bolt bearing against a steel plate in the back-to-back section, a connector model is used that takes into account both slippage and bearing deformations. The developed Finite Element (FE) models are verified against six four-point bending tests on CFS back-to-back channel beams, where excellent agreement is found between the experimental results and the FE predictions. The validated FE models are then used to assess the adequacy of the effective width method in EC3 and the Direct Strength Method (DSM) in estimating the design capacity of conventional and optimum design CFS channel beam sections. The results indicate that both EC3 and DSM provide accurate predictions for the bending capacity of lipped channel beam sections. A comparison between FE predictions and tested results show that, the geometric imperfections can change the FE predictions of ultimate capacity by 7%, while the strain-hardening of CFS material at the round corners has negligible effects. It is also shown that EC3 uses a reduced cross-sectional property to calculate deflections, which can reasonably predict deflections with a slight overestimation (6%) at the serviceability load level.
Highlights
Cold-formed steel (CFS) members have traditionally been employed as load-carrying members in a wide range of applications, such as roof purlins and structural envelopes
The model takes into account the non-linear stress–strain behaviour of CFS material, the strain hardening effects at the round corners due to the cold-working process, and the experimentally measured initial geometric imperfections
The numerical model was validated against an experimental program on a total of 6 lipped channel back-to-back beams
Summary
Cold-formed steel (CFS) members have traditionally been employed as load-carrying members in a wide range of applications, such as roof purlins and structural envelopes. CFS members have become increasingly popular in low- to mid-rise multi-storey buildings [1] and CFS portal frames with short to intermediate spans [2,3], as shown in Fig. 1(a) and (b). CFS sections are increasingly being offered as an alternative to hot-rolled steel elements since they provide greater flexibility in terms of cross-sectional profiles and sizes, which can lead to more efficient design solutions with less redundant material. CFS components are made of thin plates, which have inherently low buckling resistance. This results in reduced strength for CFS elements, which limits their performance in multi-storey applications.
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