Large-scale test as the basis of investigating the fire-resistance of underground RC substructures

Fire disasters occurring in underground structures generally result in severe damage. In order to investigate the fire performance of typical underground structures, a large-scale fire test on a three-span frame structure was carried out. The tested model was loaded both by vertical and horizontal earth pressures. The applied temperature history, representing the time-dependent fire load, was determined by simulations of fire scenarios in the underground structure with the help of the software FDS. The paper contains test results of the temperature of the air in the furnace, the concrete and the steel bars in the structural model, and the state of deformation of the model. Apparent phenomena, such as cracking and spalling, were observed throughout the whole testing process. The results show that a very dangerous situation of the underground structure exposed to fire may occur during the cooling process. Curling of the top slab was observed during the heating process. More attention in fire-resistance design must be paid to the columns. The fire test results are useful for validation of numerical models and for further fire-resistance research of underground structures.