Abstract: In order to study the impact of high temperature on the key part of the bottom of the upper deck when a vehicle fire occurs in the lower deck of a double-deck suspension bridge, a typical double-deck suspension bridge fire numerical simulation model is established based on the FDS, and the highest temperature point on the temperature observation line at the bottom of the upper deck is taken as the research object to analyze the effect of the different vehicle fire powers and the inward ambient wind speeds of the common sea surface wind level on the temperature and offset distance of the highest temperature point on the temperature observation line in the case of a large vehicle fire. The quantitative analysis method is used to establish mathematical models. The results show that: when the heat release rate varies between 30 and 200 MW, and the inward ambient wind speed varies between 0.1 and 6.7 m/s, the temperature of the highest temperature point on the temperature observation line at the bottom of the upper bridge deck is directly proportional to the heat release rate, and inversely proportional to the wind speed, and the offset distance of the highest temperature point is inversely proportional to the heat release rate; the amount of change of the dimensionless highest temperature is directly proportional to 0.8 power of the dimensionless fire heat release rate and is negatively correlated to the dimensionless inward wind speed; the dimensionless maximum temperature point offset distance has a complex logarithmic relationship with the dimensionless fire source power with an overall trend of negative correlation, and a nonlinear increasing logarithmic relationship with the dimensionless wind speed with a positive trend. Therefore, the effects of fire source power and inward wind speed on the maximum temperature point in vehicle fires on double-deck suspension bridges are competitive, and this mathematical model can be used for bridge fire protection design and accurate prediction of the maximum temperature point at the fire scene.

Key words: double-deck suspension bridge, vehicle fire, engineering thermology, fire dynamic simulation, dimensional analysis