Application of the direct strength method to functionally-'raded-material-sheathed cold-formed steel beam channel members under nonuniform elevated temperature

摘要

The objective of this paper is to examine the application of the Direct Strength Method (DSM) to determine the strength of cold-formed steel (CFS) beam channel members under non-uniform elevated temperature using Functionally Graded Material (FGM) as a thermal barrier. Functionally graded materials are advanced materials characterized by non-homogenous material system with gradual gradation of material property within a given dimension. The composition of the FGM sheathing is defined by using the volume fractions of the constituent materials distributed across the thickness direction. When a cold-formed steel member is subjected to fire (or a thermal gradient) on one side of the panel, material properties change - but this change happens around the cross-section and along the length creating a member which is potentially non-uniform and unsymmetrical in its response even if the apparent geometry is uniform and symmetric. The heat transfer analysis is completed using ABAQUS to obtain the time-dependent temperature distribution on the CFS cross-sections. The influence of sheathing material on the response of the members is compared with the strength of same sections with gypsum board as a thermal barrier. DSM strength formulations are examined following stability analyses performed to characterize how local, distortional, and global buckling of the members evolve under elevated temperature, in which mechanical properties are considered temperature dependent.