The Fire Temperature Field Of PC Box Girder Bridge And Fire Performance Research

The PC bridge is developing rapidly in China and playing a more and more important role in the nation economy, meanwhile it suffers the more threat of disaster such as the fire. The materials properties and mechanical characteristics of bridge structural will change after firing, which would jeopardize the normal use of the bridge and may even cause collapses.So it is important to study on the fire performance of PC girder Bridges, this paper carries out the following research.(1) This paper introduces the research status of fire accidents on bridges. With summarizing the thermal parameters of concrete and tendons performance at high temperatures, it determines the parameters and indicators of the follow-up simulation.(2) This paper obtains the distributive rule of surrounding temperature field with the numerical simulation of the space temperature field of bridges in the situation of firing by FDS software and uses heat release rate(HRR) instead of the condition offire burning. Then it considers four factors influence on the surface temperature field of box girder, the factors include various of simulation space, thermal boundary condition, height from firing source to beam bottom and time on simulating. Pointed out that adiabatic surface temperature as thermal load loading to bridge surface for thermal coupling analysis is more accurate.(3) Based on the theory of thermal analysis, the survey gets the distribution of section temperature of box girder bridge after three hours' firing, with the method of transient heat transfered by ANSYS.Then it studies the changing rule of temperature field with fire time, the influence of protective layer thickness on the bearing temperature of prestressed reinforcement, the effect of different temperature fields' loading on the section temperature of box girder and the impact of coefficient of heat conduction putted forward by various scholar on temperature field. Getting a result that the protective layer thickness has a good effect on prestressed concrete resistance to fire,15 cm is best.(4) On the basis of the thermal analysis, the research analyses the high temperatures deformation of prestressed box girder bridge w ith the method of indirect coupling by the finite element software, ANSYS.The deformation of box girder section is not harmonious and the initial tensioning prestress has litter effect to the deflection.(5) At last, this paper uses FDS software to reappear the fire, then compares with the test results of bridge after the fire in combination thermodynamic analysis results.The research of bridge fire is feasibility in the assessment of the bridge after firing.