Combined effect representative value determination method of sectional temperature differences for bridge box girder and ballastless track slab

Significant asynchrony exists between the extreme sectional temperature differences (STDs) of the high-speed railway (HSR) box girder and the ballastless track slab. Structural flexural deformation analysis based solely on univariate extreme temperature gradient may lead to distortion and redundancy. To address this issue, a method based on the maximum entropy principle is proposed for the unbiased estimation of the combined representative STDs for the box girder and track slab. Firstly, a model transforming spatial temperature measurements from multiple points into a one-dimensional equivalent linear STD for the structure is established. Secondly, an unbiased fitting method is proposed for the estimation of extreme STD based on the maximum entropy principle. Using measured data samples, the optimal marginal distributions for the univariate values are fitted. Thirdly, based on long-term measured temperature of the box girder and track slab system, a method for determining the combination coefficients of extreme STDs over multiyear return periods is proposed. The study reveals that due to the differences in structure size and shielding effect, the magnitude and seasonal pattern of the STD of box girder are significantly different from those of track slab. The joint exceedance probability model of the STDs of box girder and track slab, fitted using the maximum entropy principle, can quantitatively characterize the time lag effect of their temperature fields over multi-year return periods. Compared to the traditional extreme value analysis models, the proposed method based on maximum entropy principle can provide a more unbiased probability distribution function without making any distribution assumptions in advance. The proposed method can be used to determine the combined STD effects of HSR box girder and track slab, improving the accuracy of temperature effect analysis and providing support for more economical and safer service of HSR.