Comparative experimental study of fire resistance of two-way restrained and unrestrained precast concrete composite slabs

This paper presents the results of tests to investigate fire performance of two-way restrained precast concrete (PC) composite slabs under the standard ISO 834 condition. The fire tests include three specimens with different load levels and boundary conditions - with or without restraints around the edges. Tensile membrane action was observed to a moderate extent in all specimens tested, including the reference test at ambient temperature. No debonding was observed at the interface between the bottom precast slab and the top cast-in-situ composite layer for the restrained PC composite slabs, but cracks formed at the interface in the un-restrained PC composite slab. These results demonstrate much increased fire resistance due to restraint effects (195 min vs. 130 min) if the same load (195 kN) is applied, but similar fire resistance if based on load ratio (131 min and 130 min at the same load ratio of 0.42). A number of existing theoretical methods developed for calculating tensile membrane action effects of two-way concrete slabs, as well as the conventional yield line theory, are employed to calculate the load carrying capacities. They indicate that for the type of slabs investigated in this paper, the improvement due to tensile membrane action is moderate.