The influence of the lateral contact point trajectory and the rotation of the monoblock on the impact loads in railway turnouts

A new wheel–rail interaction model for the prediction of turnout impact forces is presented. Although the model is based on the classical "moving irregularity" approach, it is novel in the sense that it accounts for the lateral shift of the wheel–rail contact position during load transfer between the crossing nose and wing rail. This lateral shift increases the mobility of the track due to the rotational response of the monoblock under off-centred excitation. It is shown that the resulting stepwise variation of the wheel and track mobilities upon impact can profoundly influence the impact force time history. It is furthermore shown that these effects are particularly emphasized during the trailing move when the wheel impacts on the off-centred wing rail and much less during the facing move when the impact is absorbed by the crossing nose which is located in the plane of symmetry of the monoblock cross-section. Apart from the stepwise shift upon load transfer the lateral wheel–rail contact point position varies continuously along the longitudinal coordinate of the turnout. Simulations show that these continuous variations have a negligible influence on the impact force time histories and that a simplified model with constant shift gives satisfactory results. A comparison of the calculated crossing nose and wing rail accelerations shows encouraging agreement with field measurements. It is concluded that omission of the rotation leads to an overestimate of the track vibrations. Especially for the trailing move, this overestimate becomes substantial for frequencies above 100 Hz.