The effect of convex bearers on track geometry irregularities in turnouts

While concrete bearers are generally assumed to be completely straight, the situation contradicts the said assumption. The prestressed structure tends to bend bearers in a horizontal direction, which can significantly affect the turnout geometry. In this research, the convexity of bearers has been evaluated with individual tachometer measurements and continuous geometry trolley. Measurement results revealed that the convexity of a bearer is mostly 2-4 millimetres, but it can change permanently during loading. One problem appears in the crossing area, where high dynamic loads can cause the convex bearers to straighten and lead to local level irregularities. Another major problem is at the heel of turnout, where long bearers change to two separate short bearers. Because short bearers settle differently than long bearers, cant and twist irregularities develop in that transition area. Convex bearers should not be forced to straighten during the tamping process. In these situations, an adjustment plate between the rail and bearer is often needed. With convex bearers, it is impossible to reach a completely horizontal track geometry, both in straight and diverging routes at the same time without adjustment plates. The convexity-induced cant can be left intentionally in the diverging route, where it is acceptable due to lower speeds and a lower maintenance limit.