Fire behaviour of reinforced concrete slabs under combined biaxial in-plane and out-of-plane loads

To better understand the fire behaviour of in-plane restrained reinforced concrete slabs, this paper presents the results of five fire tests on two-way spanning concrete slabs under compressive biaxial in-plane and flexural out-of-plane loads. The data presented include furnace temperatures, temperature distributions, vertical and horizontal deflections, restraint forces, crack patterns, and characterisation of spalling of the five slabs during both heating and cooling phases. Comparison of the results indicates that the fire behaviour of the restrained slabs is dependent on the restraint type, restraint level and the aspect ratio, and thus increasing the in-plane forces may result in an increase or a decrease of the mid-span deflections of the concrete slabs. Fire behaviour of the restrained slabs are considerably different from those of the simply supported slabs, and thus the effect of uniaxial or biaxial in-plane restraints on the failure mode should be considered to develop reasonable failure criteria for these slabs. In addition, it is suggested that the corners of the in-plane restrained slabs should be reinforced by arranging the whole span top steels along two directions since the corners fracture easily with large diagonal cracks during the fire tests.