Shear resistance of prestressed hollow core floors exposed to fire

Prestressed hollow core units are now the most widely used type of precast flooring. This success is largely due to the highly efficient design and production methods, flexibility in use, surface finish and structural efficiency. Fire tests conducted during recent years in some laboratories resulted in premature shear failure. Similar types of failure were not stated in other laboratories and never at real fires. The reason lies in the faulty test set-up, neglecting completely the influence of connections and surrounding structure on the fire resistance of hollow core slabs. This paper provides a detailed analysis of the effect of fire on prestressed hollow core floors, explains the phenomenon of induced thermal stresses in the webs of the units and the principle of the interlocking effect to realise sufficient shear capacity at fire. Four full-scale fire tests were carried out at the Technical Universities of Liège and Gent in Belgium, to investigate the influence of parameters governing the shear capacity of hollow core slabs exposed to severe fire. The omission of shear reinforcement is completely compensated by correctly designed connections, which also constitute the basis for the stability of the floor at ambient temperature.