The load-carrying capacity of a structure in case of fire depends on its ability to withstand mechanical and thermally induced stresses despite the degradation in material strength and stiffness. In practice, advanced calculation methods are increasingly used in addition to simplified method at structural member level. Up to now, the analysis has usually been carried out under the assumption of a nominal fire curve with continuously increasing temperatures. However, the traditional methods are of limited applicability for architecturally and technically demanding building structures.

Advanced calculation methods have the potential to predict the fire behaviour realistically. They are suitable for a performance-based design on the basis of natural fire curves. Appropriate material properties are essential. At present, however, no material data applicable to all steel grades can be formulated for the cooling phase of natural fire scenarios.

The research project intends to develop models for the material behaviour under natural fire curves. On the basis of the results of experimental investigations, stress-strain relationships for the cooling phase will be developed. In addition, their effects on the structural behaviour will be investigated by means of case studies.