Reinforced Concrete (RC) flat plates are commonly used in residential, commercial, and industrial concrete structures. As new fire design codes move towards performance-based design, fire rating of RC elements shall consider the restraint effect and the overall behavior of the structure. In this study, the behavior of a multi-story flat plate structure during fire exposure is investigated using numerical simulations conducted with ABAQUS software. A threedimensional finite element model is then carried out on the RC flat slab structure exposed to standard ISO-834 fire at different location arrangements. The model investigates mid-span deflection, shear demand on the columns, bending moment and the membrane action of the floor slab. The latter plays a main role to increase the capability and ductility of the slab at longer fire exposure to compensate the reduction in the flexural capacity. Also, shear demand in columns becomes bigger in cases of more than one surrounding slab exposed to fire at the same time