LAUSR

Abstract Light gauge Steel Frame (LSF) floor-ceiling systems made of thin-walled cold-formed steel structural members deliver innovative, lightweight and cost effective solutions for many floor assemblies. However, the mechanical properties of cold-formed steel structural members deteriorate in fire. Hence fire rated gypsum plasterboard ceilings are required to protect them and avoid premature failures of floor assemblies. However, the behaviour of LSF floor-ceiling systems in fire is not well understood. Hence a series of small-scale standard fire tests was undertaken to investigate the fire resistance of cold-formed LSF floor-ceiling systems of varying configurations. Configurations included structural plywood as the subfloor, gypsum plasterboard ceilings, thin steel sheathing, different joist sections such as lipped channel beam and rivet fastened rectangular hollow flange channel beam and rockwool cavity insulation. The effects of these parameters on the fire resistance of LSF floor-ceiling assemblies are discussed in this paper. Fire resistance improvements of 21–32% were observed when steel sheathing was used in varying configurations. This shows the potential of using thin steel sheathing below the gypsum plasterboard that enhanced the insulation failure times by resisting gypsum plasterboard fall-off. However, cavity insulation led to reduced fire resistance times while plywood subfloors exhibited rapid decomposition and burning when the temperature exceeded 234°C. This paper presents the details of the small-scale standard fire tests of LSF floor-ceiling systems of varying configurations and the results in terms of time-temperature curves and fire resistance times.