Experimental and numerical study on the fire resistance behavior of steel truss girder structure in double deck suspension bridges

To investigate the fire resistance behavior of the double deck steel truss suspension bridge, two scaled models of double deck steel truss segment with a similarity ratio of 1:10 were designed and fabricated based on a large-span suspension bridge. The fire resistance tests of scale models with and without fire protection were conducted under load conditions, and the heat release rate of fire source was determined as 50 MW. The deformation characteristics and temperature distribution of the scale models under different fire protection schemes were studied, and the fire resistance behavior of the double deck steel truss was preliminarily revealed. The results showed that the bridge deck of experimental model without fire protection exhibited the local depression, and the transverse beams and web members appeared bending deformation and local bucking. In addition, the web member exhibited a significant temperature gradient across the section, with the maximum temperature on the fire side reaching 1007 ℃, while the temperature of the back side was only 336.5 ℃, making it more prone to local buckling. The temperature of main components of the model with fire protection was lower than that without fire protection. The maximum temperatures of the web member, diaphragms plate and bridge deck of the experimental model without fire protection were 1007 ℃, 654 ℃ and 712 ℃, respectively. However, the temperatures of each component under the protection of fireproof materials were reduced by 29.0 %, 52.3 % and 45.4 %, respectively. The steel truss girder model was characterized by the failure of components, resulting in irreversible deformations. The proposed fire protection scheme proved to be effective, achieving commendable fire resistance and thermal insulation performance. ● The fire tests were conducted for steel truss models with and without fire protection. ● The deformation characteristic and temperature distribution of steel truss models under fire protection were studied. ● The fire resistance behavior of double deck steel truss structure was preliminarily revealed.