Fire Design of Unprotected Composite Steel and Concrete Slabs / Neapsaugotuju Kompozitiniu Plieniniu-betoniniu Plokšciu Elgsenos Ugnyje Skaiciavimas

The paper presents fire design of composite steel-concrete slabs and a description of the use of the advantages of such a structure. Following the review of scientific literature on composite steel-concrete slabs, behaviour under fire temperature may confirm that this solution has no negative consequences for the construction of the building in fire. Profiled steel sheet is a very important building component, because it helps ensuring integrity and insulation properties. Such sheeting serves as a restraint preventing the spread of fire and hot gases, as well as protects the concrete from direct heat action not allowing its chipping off. Fire tests show that the construction of composite steel-concrete slabs without a protective coating under influence of fire is an important bracing frame provided by these conditions. In addition, it may be too conservative to establish the fire resistance coefficient for each element. Maybe it is not necessary to protect all load bearing steel elements in a building from fire, especially when they are in one setup with composite steel-concrete slabs. Fire protection methods make it possible for composite steel-concrete slabs to behave under a plastic bending moment allowing increased temperatures and distributing evenly in an element. The paper provides a brief description of methods for fire design. It analyzes the fire design method according to EN 1994-1-2:2005 regarding unprotected composite steel-concrete slabs exposed to fire from the bottom according to the standard temporary temperature curve. The paper provides an example of the calculation of composite steel-concrete slab according to described method without longitudinal reinforcement and the composite slab with longitudinal reinforcement. Results of calculations let to designate fire resistance of composite slab to heat isolation (I parameter) and the resistance value of the bending moment. Solutions for extra fire protection or increasing bending moment value depend on estimated results.