Investigation of plasterboard fall-off in lightweight floor systems under fire conditions

In lightweight floor systems, fire rated gypsum plasterboards, used as ceiling, play a vital role in providing the required fire resistance level (FRL). The fall-off behaviour of plasterboards in fire and the resulting heat penetration significantly impact the FRL. Plasterboard fall-off temperature and time are key parameters in the fire design of lightweight floor systems. This study has investigated the fire behaviour of gypsum plasterboards in floor-ceiling systems, using the results from 56 full-scale standard fire tests. It revealed that in cavity insulated floor assemblies, while plasterboard fall-off occurred rapidly, the insulation delayed the floor failure after fall-off, unlike in non-insulated floor assemblies where floor failure typically followed shortly after the base layer fall-off. Additionally, minimum failure temperatures were determined for plasterboards used in Australia for each layer in floor assemblies. New suitable equations were then proposed for predicting the plasterboard fall-off times, which can be employed to estimate the FRL by considering ceiling conditions and post-fall-off failure times. This study has provided a good understanding of the fire behaviour of gypsum plasterboards and essential data for estimating the FRL of lightweight floor systems. • The fire behaviour of gypsum plasterboards was investigated using 56 full-scale floor fire tests. • Gypsum plasterboard fall-off was identified as a key factor governing the failure of lightweight floor systems in fire. • Determined the average failure times for both insulated and non-insulated floor configurations post-plasterboard fall-off. • Determined the minimum failure temperatures for plasterboards used in Australia for each layer in floor assemblies. • Proposed suitable equations to predict the plasterboard fall-off times and FRLs of LSF floor systems.