Fire tests of short-span LSF floor systems made of lipped channel joists

Light gauge steel framed (LSF) floor systems are increasingly used in low- and mid-rise buildings due to their superiorities in terms of load-bearing capacity, non-combustibility, durability, sustainability, and ease of fabrication and erection. Their behaviour is detrimentally affected by fire, resulting in the reduction of their bending capacity and stiffness. Previous research studies on LSF floor systems are limited, with most studies not focussing on the Australian floor systems. This research study evaluates the behaviour of short-span load-bearing LSF floor systems through one ambient temperature test and six fire tests. Test results revealed that cavity insulation has minimal impact on the fire resistance levels (FRL) of LSF floors protected by two or three layers of fire-rated gypsum plasterboards. Increasing the plasterboard thickness or adding an extra layer significantly enhanced the FRL. Plasterboard joints in the ceiling were identified as potential vulnerabilities, while enhancing their performance would lead to higher FRL for the floor system. Importantly, the cold flange temperature was shown to be the critical parameter governing the failure of channel joists in LSF floors. This study has shown that the structural and thermal behaviour of the tested short-span load-bearing floors was consistent to that observed in the previous full-scale LSF floor tests reported in the literature. Hence such short-span load-bearing floor tests can be used to determine the FRLs at significantly reduced cost and time. Finally, some design recommendations are provided, offering valuable insights for fire design engineers.