In order to model the structural behavior under fire, three separate analyses need to be conducted: a) fire propagation and growth (fire modeling), b) transient heat transfer in structural members due to fire, and c) structural analysis to account for both thermal and mechanical load. Advanced methods for fire modeling are based on computational fluid dynamics (CFD) approach. Typical heat transfer analysis is conducted using finite element analysis (FEA) approach employing solid 3-D or 2-D shell elements. Structural analysis is often conducted using a FEA approach, but employing beam and shell elements, especially for large structures. While both thermal and structural analyses are conducted using finite elements, fire modeling is often carried out using finite difference method (FDM), where the computational domain is discretized using rectangular grids. The computational domain is made up of right parallelepipedic volumes called meshes. Fire modeling is also conducted with the finite element method in some cases. Typical outputs of a fire model are heat flux and gas temperature field, which are inputs to the heat transfer model as thermal boundary conditions. Subsequently, the transient temperatures computed by the heat transfer analysis in the entire computational domain comprising structural members are inputs to the structural analysis model. However, this transfer of data is rather complicated because of the difference in the level and type of discretization used in each of these analyses. As mentioned earlier, fire modeling using CFD approach uses FDM, while both heat transfer and structural analyses use FEA approach. Since the type of discretization is different, a mapping tool is therefore required to transfer temperatures and heat flux from fire model to a heat transfer model. This is because the coordinates of nodes or grid points in both models may vary....
Citation: Technical Note (NIST TN) - 1828
NIST Pub Series: Technical Note (NIST TN)
Pub Type: NIST Pubs