Research On Temperature Temporal And Spatial Distribution Of Concrete Box Girder Based On Thermodynamics And Structural Health Monitoring

Bridges in service may suffer from a variety of coupled effects, included operational conditions, environmental effects, performance deterioration and even natural disasters. Especially, thermal load is a crucial part of environment effects. Stochastic factors, such as solar radiation, ambient temperature and wind combine to uncertain and nonuniform temperature distribution of concrete box girder, which maybe give rise to serious stress, displacement, even worse cracks and performance deterioration due to temperature. Besides, vibration based damage detection methods maybe fail to detect damage for the reason that environmental conditions, especially temperature effects will mask slight and modern degree damage. It’s necessary to distinguish single factor effect from coupled structural response before structural health monitoring really applied to damage detection and condition assessment. So we should investigate temperature distribution of bridge sections. Traditional numerical heat transfer based on finite element method can’t reveal the stochastic influence of uncertain factors which include solar radiation, ambient temperature and wind. The result can’t consist with in-situ filed monitoring temperature very well. So it is more worthwhile focusing on the research of setting up real thermal load model based on field monitoring temperature data. The research in my paper involves the following parts:Firstly, the model of solar radiation is found. According to space geometrical relationship, the function relation between solar altitude angle, azimuth angle and latitude, declination, solar hour angle is obtained. Considering the azimuth angle and inclined angle of different surfaces, incident angle of the solar ray is obtained. Then boundary heat flux can be attained in the way above. Besides, the shelter effect of cantilever flange give rise to the time-varying shadow on the surface of web.Then, the thermal analysis of three-dimensional concrete box girder is conducted by finite element modelling. Numerical simulation results of temperature spatial and temporal distribution are copmputed at the combined effects of ambient temperature, solar radiation and heat convection. Besides, the influence of time-varying shadow which lead to nonuniform heating is also involved in the heat transfer analysis.Finally, on the basis of certain thermodynamics model, we propose a temperature spatial-temporal distribution reconstruction method based on kalman filtering. This method considers the influence of measurement noise and uncertain boundary heat flux. It can utilize limited temperature sensors to get optimal estimation of unkonwn solar radiation parameters and temperature at any location of inner solid body. A numerical case is employed to verify feasibility and validity of the proposed method. Then the accuracy and robustness of different measurement noise level and initial temperature value are validated.