Fire resistance and associated failure modes of axially restrained hollow core slabs

When a severe fire occurs in the central part of a large hollow core slab floor, the thermal expansion of the affected floor members will be highly restrained by the stiffness of the surrounding structure. The present paper presents the development of a numerical model to evaluate the structural performance of precast concrete hollow core slabs exposed to fire, taking into account the interaction with the surrounding structure and how it affects the fire resistance and failure mode. The performance of the model is validated against fire tests reported in the literature. Subsequently, the model is employed to evaluate the influence of various degrees of restraint on the fire resistance of three hollow core slab sections, with depths ranging from 200 mm to 500 mm. The results indicate that restrained thermal expansion can significantly enhance the fire resistance of concrete hollow core slabs with low span-to-depth ratios. Conversely, in hollow core slabs with a high span-to-depth ratio, the restraint provided by the surroundings can considerably impair the fire performance. Additionally, it is shown that the failure mode of hollow core slabs can change from ductile bending failure to a brittle shear failure mode in the presence of axially restraining boundary conditions.