It is well-known that tensile membrane action in concrete floor slabs can enhance the fire resistance of a composite steel frame building. Vertical supports provided by protected beams along the edge of slab panels play an important role in the development of the tensile membrane action. The present study investigates the effect of fire insulation delamination on protected beams, as might occur in an earthquake, on the fire resistance of composite floors subject to fire following an earthquake. The results show that fire insulation delamination considerably reduces the development of tensile membrane action. Based on the results obtained, two methods of improvement are presented to enhance the development of tensile membrane action concurrent with fire insulation delamination. It is found that increasing slab thickness and improving fire protection rating can enhance the fire resistance of the whole building even with fire insulation delamination.