Numerical and Experimental Studies on the Dynamic Coefficient of a U-shaped Girder for Urban Rail Transit
The mechanical behaviors of U-shaped girders in urban rail transit differ in the spanning and transverse directions,and a dynamic coefficient of 1.40 in the current design code will result in material waste.Considering the bidirectional stressing characteristics,the U-shaped girder of the Nanjing Subway Line S6 Urban Rail Transit was selected as a case study,and a train-bridge coupling dynamic model was established.The effectiveness of the model was verified by comparing the test and calculated results.The dynamic coefficients of the different responses were analyzed by changing the train speed and formation.The results indicate that the girder bottom only bears longitudinal tensile stress but carries both transverse tensile and compressive stresses in the same section.The maximum dynamic coefficients of the deflection,longitudinal stress,and lateral stress were 1.231,1.216,and 1.362,respectively,in the full-and fixed-load cases of the 6-car formation.When determining the dynamic coefficients of a single-track U-shaped girder,the influence of the train formation should be considered,and the values should be distinguished according to the stressing directions.We recommend a value of 1.30 when calculating the deflection and longitudinal stress and 1.40 when calculating the lateral stress.This paper proposes reasonable values for the dynamic coefficients of U-shaped girders and provides a reference for structural optimization.
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