Abstract: Based on the mesh transposition method,a method of modeling collapsing solid in grid and coupling with the flow field was proposed.The FDS was enhanced with this method to make iteasible to model and simulate the collapsing solid.The improved FDS software was used to simulate the same fire scene of no structure collapse and structure collapse. For the scene with solid- collapsing, the temperature and CO2 is completely the same with none solid- collapsing scene before collapse,while it is consistent with the flashover phenomenon caused by the collapse in the actual fire after the collapse. It proved that the modeling method could simulatesolid-falling and its influence on fire well.

Key words: building fire, mesh transposition, solid collapse;fluidsolidcoupling, software enhancement