In fire cover work of steel structure, kind of covering material to be used, thickness of fire cover and safety of the work are problems to be settled. Logically, it can be said that it is necessary to know first for what time and at what temperature members are presumed to be heated and what degree of temperature increase is allowable from a viewpoint of the structural strength. Upon knowing these conditions, it can be concluded that such and such fire covering is necessary to satisfy these conditions. Such a logic is an engineering method for fire resistance design to be naturally taken. However, regretfully, such a method have not been authorized at present by the Building Code of Japan, and consequently buildings of dangerous design and of overdesign seem to coexist without a clear judging criterion. In order to insure safety in a rational manner excluding such as inconsistency, a rational fire resistance design method as mentioned above is required to be established. Basic thinking method for fire resistance design, as well as a calculation method for designed fire duration and a method for authorization of structural strength of steel members, were explained in detail in "Fire resistance design for steel structures" by Dr. Hikaru Saito, in the BRI Research Paper, No. 53, 1972.

In this paper, various calculation methods required in relation with fire cover in fire resistance design, namely, methods to calculate steel temperature during fire, fire endurance duration of members, required thickness of fire cover etc., will be introduced with examples comparing with results of fire tests.