ABSTRACT
The vertical dynamics of a common Swedish railway turnout under the load of a moving vehicle is investigated. A special interest is devoted to the wheel/rail load impact occurring at the turnout crossing (the frog), where the wheels move over from the wing rail to the nose. The severity of the load impact depends on several factors: (a) the change of track stiffness at the crossing, (b) the change of mass distribution (the mass of the nose has an un-even distribution and is larger than the mass of the rail), (c) the irregularity perceived by the wheel when moving from the wing rail to the nose (or vice versa), and, (d) if the crossing is not well maintained there might be a difference in height between the wing rail and the nose.
Both smooth and irregular transitions of the wheels from the wing rail to the nose have been examined for varying speeds of the vehicle. Under perfect conditions, the wheels will change quite smoothly from rolling on the wing rail to rolling on the nose. At low speed the load impact will then depend only on the change of track stiffness, and the calculated maximum wheel/rail contact force at the crossing is only 30 to 50 per cent larger than the static contact force. For uneven transitions, however, the severity of the impact loading at the crossing depends strongly on the train speed. The increase of contact force, as compared with the static force, is of the order of 100 per cent at 70 km/h and 200 per cent at 150 km/h.
