Abstract：Dynamic characteristics of reinforced concrete slab in fire are changed over time, and the change law is useful for damage identification of concrete slabs after fire. In this paper, the vibration characteristics of reinforced concrete slabs in fire were investigated based on fire damage identification theory and classical thin plate vibration theory. The reinforced concrete slab was divided along the thickness direction and was assumed as the transversely isotropic plate. Moreover, in process of heating, the position of the neutral axis caused the changes of stress distribution in the plate. Therefore, the changes of dynamic response during the process were considered. The basic differential equation of vibration of the building was built, and the dynamic characteristics were obtained through the equation. Then, the one-dimensional heat conduction was entered into the stiffness. The floor stiffness across fire evolution was obtained through the thickness direction integral. Finally, the damage limit and stiffness hinge was obtained. The damage identification method of reinforced concrete after fire was presented by using frequency as fingerprint parameter.

Keyword：fire;reinforced concrete slab;transversely isotropic;neutral axis;differential equation of vibration;vibration identification;