Natural fire safety concept : the development and validation of a CFD-based engineering methodology for evaluating thermal actions on steel and composite structures

A CFD-based engineering methodology has been developed for determining the thermal behaviour of structural elements in steel/composite-framed buildings subjected to natural fires. An embedded mesh solver was developed and implemented into the SOFIE CFD code to accurately determine heat conduction within composite solid components. The solver was made accessible via a graphical user interface, JOSEFINE, enabling efficient specification of structural elements such as I-beams and columns, with and without protection. A systematic and progressive validation of the CFD-based methodology was undertaken to ensure confidence in, and the robustness of, the procedure. Key controlling parameters were determined from an analysis of the results. Further insight into the model performance was provided by comparative simulations undertaken with the Ozone and MRFC zone models. The heat transfer parameters pertaining to the simple models defined in the structural Eurocodes (EC1, EC3) were reviewed. Recommendations are presented on equivalent parameters derived from the CFD simulations. Critical analysis of the simple methodologies has shown that, in some situations, the theoretical ambiguities of the basic governing heat transfer equation may lead to significant errors in the calculated heat flux. Further recommendations have been developed as "best practice" guidance for the advanced methodologies covering general fire science issues, as well as those specific to structures in natural fire, such as smoke, high-temperature material properties, moisture/intumescence effects, distributed burning, and CFD-specific issues including the general procedures for running simulations, for selecting physical and numerical models and performing appropriate sensitivity studies and making adequate reference to relevant validation.