PUNCHING SHEAR OF RESTRAINED REINFORCED CONCRETE SLABS UNDER FIRE CONDITIONS

The punching shear resistance of reinforced concrete slabs involves material property degradation and the effects of restrained thermal expansion in both the slabs and columns, in addition to the complexities of shear mechanisms in concrete. This paper examines how the restraint of thermal expansion in the slab affects its punching shear capacity in fire. It presents a series of tests on fifteen slabs under a combination of applied load and fire, using a purpose-built restraint frame that allowed the boundary restraint actions to be controlled and monitored. The test results demonstrate that unrestrained slabs can fail very soon after the start of heating, whereas the equivalent restrained slabs survive up to two hours of heating. One of the restrained slabs failed in cooling, possibly due to tensile actions that developed due to the restraint conditions.