| doi:10.3850/978-981-08-6218-3_SS-Fr021 |
 Final Paper PDF
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FULL SCALE FIRE TESTS OF A NEW LIGHT GAUGE STEEL FLOOR-CEILING SYSTEM
B. Baleshana, M. Mahendranb
Faculty of Built Environment and Engineering, Queensland University of Technology, Brisbane, Queensland.
ab.baleshan@student.qut.edu.au
bm.mahendran@qut.edu.au
EXTENDED ABSTRACT
Cold-formed steel members can be assembled in various combinations to provide costefficient and safe light gauge floor systems for buildings. Such Light gauge Steel Framing (LSF) systems are widely accepted in industrial and commercial building construction. An example application is in floor-ceiling systems. Light gauge steel floor-ceiling systems are made of thin-walled lipped channel joists with plasterboards and/or floor boards connected to their flanges on both sides. LSF floor-ceiling systems must be designed to serve as fire compartment boundaries and provide adequate fire resistance. However, since they are made of thin cold-formed steel sections, they can heat up quickly under fire conditions, resulting in rapid reduction to their strength and stiffness. Plasterboards provide protection to steel joists during building fires by delaying the temperature rise in the cavity. The fire resistance rating of a floor is its ability to remain stable under exposure to fire. Currently fire rating of LSF floor systems is provided simply by adding more plasterboard sheets to the steel joists. Innovative fire protection systems are therefore essential without simply adding on more plasterboard sheets, which is inefficient. Hence a new composite LSF wall and floor system has been proposed recently at the Queensland University of Technology to provide higher fire rating under fire conditions. A new composite panel system was developed in which insulation was used externally between plasterboards instead of the conventional cavity insulation located within the stud space.
This research investigated the structural and fire performance of LSF floor systems with the new composite ceiling unit under standard fire conditions. Full scale tests of the new LSF floor systems based on the composite panel system for the ceiling unit were conducted under standard fire conditions. Conventional floor systems with and without cavity insulation were also tested. The insulation used in these tests was rock fibre. This paper presents the details of the experimental study into the thermal and structural performance of three LSF floor assemblies.
The LSF test floor specimens were built using four joists, two tracks, two layers of plasterboard and one layer of plywood. The floor area was more than 5 m2 (2.4m x 2.1m) with a span of 2400 mm and the floor specimen was simply supported along its two short sides. The LSF floor specimens were first loaded to pre-determined values, and then exposed to standard fire conditions on the ceiling side. A propane fired gas furnace was used in this research to undertake the full scale fire tests according to the standard cellulosic temperature-time fire curve given in AS 1530.4. The gas furnace only allowed test floor specimens to be set in a vertical position. Hence the transverse loads on the floor specimens were applied in a horizontal direction.
Fire tests showed that torsional buckling and flexural buckling about the minor axis of joists were fully prevented by the lateral support offered by the dual layers of plasterboard. The central joists in all the specimens experienced local failures at the support. Local web buckling waves were observed along the length of joists. This experimental study provided the fire performance results for the LSF floor systems using both conventional (with and without cavity insulation) and external insulation. Most importantly the results showed the superior performance of LSF floor system using external insulation over cavity insulation. Detailed results of time-temperature profiles and structural behavioural characteristics of joists in LSF floor systems obtained from this study can be used in their numerical analyses.
Temperature measurements showed that structurally similar LSF floor panels will fail when their joists reach a critical maximum temperature and the fire resistance can be increased only by delaying the maximum temperature in the joists. This is confirmed by the increase in fire resistance time in one of the tests, which was achieved by the delay in temperature rise in joists by the use of external insulation. This study has shown that the use of cavity insulation led to poor thermal and structural performance of LSF floors. In contrast, the thermal and structural performance of externally insulated LSF floor system was superior than traditional LSF floors with or without cavity insulation. Details of fire tests and the results are presented and discussed in this paper.