Wheel/rail impacts at a railway turnout crossing

The vertical dynamics of a common Swedish railway turnout under the load of moving vehicles is investigated. The turnout is described by a linear finite element model with modal damping. The model of the turnout (a section of it) has a length of 36 sleeper spans surrounding the crossing. Rails and sleepers are modelled with uniform Rayleigh-Timoshenko beam elements. The rails are connected via railpads (linear springs) to the sleepers, which rest on an elastic foundation. The vehicles which model the dynamic behaviour of trains are discrete systems of masses, springs and dampers. They pass the turnout on the through rails at a constant speed and only vertical dynamics (including roll and pitch motions) is studied. The wheel/rail contact is modelled by use of a non-linear Hertzian spring. The train/track interaction problem is solved numerically by using an extended state space vector approach in conjunction with modal superposition for the turnout. The analyses show that the rail discontinuity at the crossing leads to an increase in the wheel/rail contact force. Both smooth and irregular transitions of the wheels from the wing rail to the crossing 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. The impact at the crossing will then be small, giving a maximum wheel/rail contact force which is only 30-50 per cent larger than the static contact force. For uneven transitions, the severity of the impact loading at the crossing depends strongly on the train speed. The increase in the 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.