Fire Resistance of Concrete Slabs in Punching Shear

Twelve specimens of reinforced concrete slab-column connections were tested to investigate fire resistance of punching shear. Half of the specimens were tested at room temperature to determine punching shear strength. Half were tested for fire resistance. The parameters of the specimens included steel reinforcement ratio, concrete compressive strength, and fire loading type. Fire resistance tests were carried out under constant maximum service loads at elevated temperatures according to ASTM E119 time-temperature curve. Temperature distribution, time-deflection relationship, and fire resistance were measured to determine the mechanical behavior of the slab-column connections subjected to fire loading on either the tension side or the compression side of the slabs. Experimental results showed that slabs heated on the compression side did not fail for up to 8 h, whereas those heated on the tension side failed at around 4 h. Specimens using normal-strength concrete have better fire resistance than those using high-strength concrete. The normal-strength concrete specimen also showed no spalling, whereas the high-strength-concrete specimen spalled under fire loading on the compression side. (C) 2013 American Society of Civil Engineers.