Determination of the steel fire protection material thickness by an analytical process—a simple derivation

Structural fire safety is assured if the design value of the effect of the actions (thermal and mechanical) is lower than the design value of each structural element fire resistance or, in other words, structural safety is assured when the steel temperature in a fire situation only reaches values less than the structure critical temperature. The critical temperature is the temperature that causes structural collapse in a fire situation. The temperature in the structural element can be determined either experimentally or analytically. In the case of a structure covered with thermally protective material, such methods serve, in practice, to determine the thickness of the protective material. In this work, a previously unpublished expression for the calculation of the temperature in thermally protected steel structural elements in fire is derived. Comparisons with international recommendations and with experimental and numerical analysis results are made. In view of its simple form and derivation, the use of such expression is recommended for the revision of the Brazilian Standard “Steel structures fire design”.