Punching shear tests on flat concrete slabs at high temperatures

This paper investigates the effect of fire on the punching shear resistance of flat concrete slabs supported by columns. A real scale test program was executed consisting of 6 slabs with a connected column stub at one side. The slabs have dimensions of 3.2 m x 3.5 m, while the columns are 0.65 m in length. All slabs have the same concrete composition, but differ in the amount of shear reinforcement. Two slabs are tested at ambient temperature and 4 slabs are submitted to an ISO 834 fire test under a full service load according to EN 1992-1-1. During the fire, the deflextions and temperature development were measured. Explosive spalling of the column and slab bottom appeared typically around 30 minutes of fire, resulting in column corner spalling and total loss of the bottom concrete cover of the slab. In case the slabs did not fail after 120 min of fire exposure according to the ISO 834 curve, the load was increased up to failure. After the fire, spalling depths of up to 90 mm were noticed. The moisture content was obtained from reference cubes