Behaviour of LSF truss floor-ceiling systems under standard fire conditions

An experimental study was conducted to establish the FRLs of commonly used LSF truss floor systems in Australia. The initial phase of this research investigated the behaviour of LSF truss floors using short-span fire tests. In this study, four full-scale tests of LSF truss floors were conducted at ambient temperature and under standard fire conditions. Fire tests provided valuable test data in terms of temperature-time curves of sheathing and truss members, deflection-time curves and failure times for LSF truss floor systems for a load ratio of 0.4. Two 16 mm thick plasterboard ceiling configurations, one with two layers and another with three layers were used, both incorporating cavity insulation. The tested floor assembly with two plasterboard layers achieved FRLs of 90/90/90 min, whereas an additional layer increased them to 120/120/120 min. Comparisons with short-span fire tests revealed that the resultant FRLs matched those from the current and previously conducted full-scale fire tests, implying that short-span tests can also be used as a cost-effective and time-efficient strategy for verifying the fire resistance of new or existing LSF truss floor systems. The predictions of truss capacity in fire using AS/NZS 4600 provisions agreed well with fire test results. This study provides essential design recommendations for 10 truss floor-ceiling configurations, enabling the fire safety design of LSF truss floor systems.