Vertical Load-Carrying Natural Frequency of Railway Continuous Steel Truss Bridges

In this paper, the vertical load-carrying natural frequency of 3 x 64 m through stud welding railway steel truss bridge is calculated using the vehicle-bridge system model, and the rule with time and some influence factors to the continuous bridge vertical load-carrying natural frequencies are analyzed, when 20 high-speed passenger vehicles with the same parameters are travelling on the bridge. The results show that when the vehicles are distributing on the whole bridge, the bridge vertical load-carrying natural frequency is periodically varied, and the periodic time is T=L_v/v. Also, the bridge vertical load-carrying natural frequency is related to the unsprung mass and the stiffness of the unsprung of each wheel-set of the vehicle, the vehicle's length, and the mass of the vehicle. But it is independent of the speed of the train. When the length of the train is shorter than the length of the bridge, the periodic changing stage of the vertical load-carrying natural frequency would never occur, and then the vehicle-bridge system would not incur vertical resonance.