Fire performance of functionally-graded-material sheathed load bearing thin-walled structural framing

Abstract

This paper presents the fire rating performance of load-bearing thin-walled system sheathed with Functionally Graded Material (FGM) board under standard ISO834 fire through numerical simulation. FGMs are one of the new classes of advanced composite materials that possess continuous variation of material properties within a given direction. The composition of the FGM sheathing is defined by the volume fractions of the constituents’ materials (metal/ceramic) based on the power-law (P-FGM) material function. The general rule of mixtures is then used to predict the thermo-mechanical properties of the FGM sheathing. Fire rating analyses for the Cold-Formed Steel (CFS) wall system were conducted under steady-state conditions where the elastic buckling load from bifurcation analysis under fire conditions was first obtained. Then using the RIKS ON algorithm, collapse analysis was performed in a time frame until failure deformation occurred. The effect of non-uniform temperature on mechanical and thermal properties of the wall stud was included at each time frame in both elastic and collapse analysis. From the FE analysis using ABAQUS, it was observed that the use of FGM as a sheathing material for fire protection increases the failure time for all load ratios compared with the traditional gypsum board. The increase in failure time has a significant implication for improving the safety of occupants during fire scenarios. The study also shows that the novel composite material (FGM board), if properly designed, can lead to an alternative fire protection material in the thin-walled system.