What I'd like to present you today is our research on the local buckling behavior of steel sections subject to fire. I'll begin by talking about some aspects of steel and fire and then about stress-based design models usually used for local buckling, especially in fire. And, finally, before drawing conclusions, I will present you a strain-based calculation model developed in Professor Fontana's laboratory. The local buckling behavior is important for the design of steel structures. At ambient

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... mperatures we usually have to consider local buckling only for thin-walled structures, but at elevated temperatures we may consider local buckling even for compact sections. And additionally the failure modes at ambient temperature and at elevated temperature in fire may be different, as we can see for the double T profiles -they are compact sections allowed for plastic design -at this slide, where flexural buckling is occurring at ambient temperature and local buckling at elevated temperatures. This slide shows similar cross sections. The main reason for local buckling of compact sections is that local buckling primarily depends on strains, and is therefore more articulated if large strains are required, as it is the case for the non-linear material behavior of steel at elevated temperatures, and thermal strains and stresses. For elevated temperature in fire, the strength and stiffness of steel decreases and, additionally, the typical linear-elastic, ideal-plastic stress-strain relationship becomes distinctly non-linear.