A rough assessment of railway bridges for high speed trains

Resonance vibrations have been observed on railway bridges subjected to high speed trains. An elementary theoretical model of a bridge was investigated using the integral transformation method which provides an estimation of the amplitudes of the free vibration In addition, the analysis gives the critical speeds at which the resonance vibration may occur. They are caused by two reasons: repeated action of axle loads and high speed itself. While the first cause of critical speeds has been reached on today's high speed lines the second one not yet. The maximum amplitudes of resonance vibration appear at the moment when the last axle leaves the bridge and, therefore, their values were calculated for the deflection, bending moment and acceleration of the bridge deck. Simple expressions similar to dynamic impact factor were given to these values which enable to assess the railway bridges for high speed trains. Comparison of the theory with the experiments is satisfactory.