Numerical study and proposal of new design equations for steel decking concrete slabs subjected to fire

This paper presents a numerical study on structurally continuous steel decking concrete slabs subjected to fire. This is an important subject for improving the fire design methods of this type of elements. Slabs with tension, compression and/or both steel reinforcement types have been tested. The results of twelve full-scale slab fire resistance tests carried out by the authors have been used in the calibration of the numerical models. Despite the compression rebars being more thermally protected, the use of tension rebars proved to be a good design solution, because just from the initial 5 min of fire, a detachment of the steel deck was registered. In this sense, slabs without tension rebars performed like a non-reinforced concrete slab. The detachment of the steel decking suggests that this type of slabs should not be fire designed as a composite element. There is no interaction between the steel decking and the concrete just from the beginning of the fire exposure. Nevertheless, when the steel decking detaches and stops contributing to the mechanical resistance of the slab, it continues to work as a thermal barrier. Another important conclusion is that the simple calculation method of EN 1994-1-2 needs an update for taking into account these phenomena. A new methodology for the mechanical and thermal design of these slabs in case of fire is proposed.