Analysis of Local Characteristics of Track Dynamic Irregularity at the Girder End Regions in Kilometer-Level Span Bridge

The girder end region is one of the weak points affecting operational stability and safety on kilometer-level railway bridges, featuring continuous track irregularities spanning over tens of meters, and often suffering from substandard ballast quality. Addressing the two issues, taking a kilometer-level span suspension bridge as a case, the local characteristics of dynamic track irregularities were analyzed at the girder end regions of long-span bridges. First, the distribution of track dynamic irregularities was analyzed based on the results from special tests conducted under extreme environmental temperatures. Then, the complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) method was introduced to dissect the intrinsic properties within the original signals, and the local characteristics of track dynamic irregularities with spatial wavelengths concentrated within 20m have been well revealed. Based on the principle of maximum entropy, these local fluctuation characteristics can be assessed through the standard deviation of track geometry deviations calculated in 10m unit sections. Ultimately, through fractal analysis, a negative correlation was identified between the fractal dimension and the stiffness of the ballast bed, and it was found that the ballast state on the approach bridge side is notably deteriorated, while that on the main bridge side remains in a great state. The findings can help assess the service condition of girder end structures based on dynamic detection results, providing a reference for the operation and maintenance of kilometer-level span railway bridges.