Integrating advanced three-dimensional modelling methodologies for predicting thermo-mechanical behaviour of steel and composite structures subjected to natural fires

Coupling methodologies were developed linking computational fluid dynamics (CFD) and finite element (FE = solid phase) computer programs for assessing the performance of structures in fire. A hierarchy of modelling strategies was examined, divided broadly into those methods where information is only passed from the CFD program to the FE program, referred to as 'one-way coupling', and more elaborate treatments where the structural response is coupled back to the CFD, 'two-way coupling'. Different coupling methodologies were systematically examined using four different CFD solid phase pairs (Jasmine/SAFIR, VESTA/DIANA, FDS/ANSYS and Jasmine/STELA). A common exchange file format was established to facilitate coupling. The program pairs were applied for three test cases: a hypothetical benchmark scenario with localised fires and various steel components, an experimental scenario involving a loaded beam-column assembly in a flashed-over fire, and an open car-park structure with transient car fires under varying wind conditions. A practical design example was also used for methodology comparisons. The merits of the different methodologies were identified and detailed recommendations provided. An efficient exploitation method is to conduct mainly one-way coupling calculations, performing a full two-way coupling for the final design stage. Under many circumstances, it is permissible to omit the structural members entirely from the CFD. Another useful 'hybrid' approach is to include the main structural elements in the CFD simulation in a simplified manner, thus allowing large elements to influence the fluid flow. It was established that these techniques can provide useful practical tools for structural fire design, permitting holistic assessment of fire and structural response.