Development of a Eurocode-based design method for local and distortional buckling for cold-formed C-sections encased in ultra-lightweight concrete under compression

An innovative direction in the field of light-gauge building systems has been presented in recent years when the cold formed steel (CFS) C-sections are encased in an ultra-lightweight material. The advantages of the two materials are integrated, resulting in a unique complex structure in which the encasing material provides heat insulation and fire protection. In addition, this material supports the CFS parts, which leads to an increase in their resistance to stability failures. This paper presents an innovative design procedure for encased CFS elements based on the specifications of Eurocode by applying the effective width method. The new design is based on analytical and numerical basis, incorporating the continuous bracing action of the encasing material by an elastic half-space-model, similar to sandwich beam theory. Close-form equations are derived to calculate the encased CFS's local and distortional critical stress. Furthermore, the applicability of the new design is demonstrated using a large set of experimental data of newly tested members and previously published ones. Results show that the trend of calculated and measured results matches well, making the proposed design method applicable in the investigated domain.