Purpose This paper aims to describe the theoretical background and main hypotheses at the basis of SAFIR®, a nonlinear finite element software for modeling structures in fire. The paper also explains how to use the software at its full extent. The discussed numerical modeling principles can be applied with other similar software. Design/methodology/approach Following a general overview of the organization of the software, the thermal analysis part is explained, with the basic equations and the different possibilities to apply thermal boundary conditions (compartment fire, localized fire, etc.). Next, the mechanical analysis part is detailed, including the time integration procedures and the different types of finite elements: beam, truss, shell, spring and solid. Finally, the material laws are described. The software capabilities and limitations are discussed throughout the paper. Findings By accommodating multiple types of finite elements and materials, by allowing the user to consider virtually any section type and to input the fire attack in multiple forms, the software SAFIR® is a comprehensive tool for investigating the behavior of structures in the fire situation. Meanwhile, being developed exclusively for its well-defined field of application, it remains relatively easy to use. Originality value The paper will improve the knowledge of readers (researchers, designers and authorities) about numerical modeling used in structural fire engineering in general and the capabilities of a particular software largely used in the fire engineering community.

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