Idealized steady state interaction between railway vehicle and track

There are two types of distinct periodic dynamic waves in the history of th e wheel/rail contact force. The first is caused by the variation in overall track stiffness owing to the effect of tie spacing. The second is caused b y the travelling motion of the wheel and the oscillations of discrete suppo rts, In the present train speed range these dynamic forces are usually less than 5 per cent of the static load, except that the coupled wheel/track re sonant frequencies are excited at some speeds. The resonant forces due to d iscrete supports may be larger than 5 per cent of the static load in some c ases. The magnitude of the resonant force mainly depends on the unsprung ma ss, tie spacing, vehicle primary and track ballast damping, rail stiffness and the stiffness on each support.