Estimation of the Vibration Serviceability Deflection Limit of a High-speed Railway Bridge Considering the Bridge-Train Interaction and Travel Speed

The static and dynamic displacements of high-speed railway bridges, which are determined by the load conditions, travel speed, and span, may cause passenger discomfort when they are excessive. In the Korea Railway Bridge Design Specifications, the allowable deflection is based on the train travel speed. It is, however, not sufficient for considering the vibration serviceability. The Eurocodes has also been quoted in the design guidelines of the Korean Honam High-speed Railway (KRNA, 2007). For the determination of the vibration serviceability of a passenger train, the Eurocodes proposes a deflection limit based on the vibration serviceability obtained from the ratio of the deflection to the span and considers the bridge-train interaction. However, the maximum speed and maximum span in the Eurocodes are 350 km/h and 120 m, respectively. Moreover, it does not provide a detailed process for determining the deflection limit based on vibration serviceability. It is therefore difficult to use the deflection limit as the design limit in increasing the span and travel speed. Hence, to ensure passenger comfort and enable changes in railway techniques, it is necessary to develop a vibration serviceability-based deflection limit that flexibly responds to changes in the railway environment regarding bridge span and travel speed. This study was conducted to determine the deflection limits of Korean railway bridges based on their vibration serviceability and considering the bridge-train interaction and increase in travel speed. In this paper, the bridge-train transfer function is developed using a simplified bridge-train model comprising a single mass-spring system. It is then verified by dynamic analysis of the bridge-train interaction. A parametric study and bridge-train dynamic interaction analysis are used to determine the correlation between the vertical acceleration of a car body and the bridge displacement with increasing travel speed. In addition, the vertical acceleration of the car body is shown to increase with increasing travel speed, and an amplification coefficient of the vertical acceleration of the car body is suggested. Further, a vibration serviceability deflection limit for high-speed railway bridges is developed in this paper using the transfer function and the amplification coefficient. Here, the deflection and vibration of the bridge are assumed to be respectively sinusoidal and harmonic. The suggested vibration serviceability deflection limit is also compared with those in the Eurocodes and the Shinkansen.