Performance of Jointed S&C Bearers

Long bearers are used at switches and crossings (S&C) to maintain the gauge and prevent relative lateral movement between the rails for all possible routes a train may take. Traditionally, these bearers are formed of continuous timber or pre-tensioned steel reinforced concrete beam, up to 6 m or more in length. However, restrictions on the availability and cost of access time for track works have led to the development of new jointed bearers. These allow modules of S&C to be pre-constructed and loaded onto road/rail vehicles for joining on site, reducing the track access time required and saving money. Jointed bearers have elements that are not much longer than plain line ties (<3.0 m). However, joining the bearer elements presents challenges. Two types of solution are currently available: (1) flexible joints—which allow some relative rotation and vertical movement between the connected ends of the bearer parts; (2) rigid joints, which may give a bending stiffness close to that of a continuous beam. The type of joint has implications for crossing performance, and the existence of alternative designs suggests that a universal solution has not been identified. This paper presents results from a laboratory study carried out to evaluate the effect of joint type on performance. In testing, repeated loading representative of >1 million cycles of a 20 tonne (20,000 kg) axle load was applied to the railseats of bearers supported on a ballast bed. Settlements and resilient movements at locations along the bearers were measured and analysed. The results show that the type or absence of a joint significantly affects the settlement and resilient deflections along the bearer length.