Large-scale experiment on the behaviour of concrete flat slabs subjected to standard fire

The use of concrete flat slabs in multi-storey buildings is increasing, and the current fire design guidelines for flat slabs are based on research carried out a few decades ago. Since then, material properties of concrete and construction techniques have changed, which require new experiments to be carried out to assess the fire performance of concrete flat slabs. In this work, the fire resistance of flat slabs was investigated at a large scale (3.78 m × 4.75 m) under structural loading and exposed to ISO 834 fire conditions. The boundary conditions were partially fixed, compared to previous tests where they were free to expand. These modified boundary conditions simulate closer to the actual conditions and capture the effects of membrane action on punching shear behaviour. No spalling occurred during the 3-h duration of the test. The test was also extended to investigate the behaviour during the cooling phase, as it is critical with restrained support conditions. Results show that the duration of fire resistance is significantly higher than that of similar tests with no lateral restraint. Heat propagation and deformation recovery during the cooling phase were also measured. Improved fire resistance duration suggests that the punching shear resistance is enhanced by restrained support conditions.