Abstract: To reveal the radiation distribution characteristics of cable fires inside steel box girders, FDS was used to simulate and study the radiation influence range under different fire source powers and diaphragm spacing. The flame radiation and smoke radiation characteristics received by targets in the fire chamber of steel box girders were analyzed, and the radiation prediction formula was constructed to obtain the critical safety distance. The results show that with the increase of the ignition source power and the decrease of the diaphragm spacing, the radiation influence range increases significantly, and the temperature error of the modified McCaffrey flue gas layer can be less than 5% considering the heat transfer characteristics of the multi-chamber steel box girder and the steel structure. The radiation distribution prediction model considering flame radiation and flue gas radiation can effectively predict the radiation distribution in the area of the steel box girder in the area greater than 0.6m from the center of the fire source. Using 10 kW/m2 as the critical ignition heat flux to define the critical safety distance of box girder cable, the minimum safety distance of cable laying in steel box girder is 0.8m.

Key words: steel box girder, chamber fire, radiation, numerical simulation