Over the last years, the need to improve the railway infrastructure has appeared in order to face the growing traffic loads that have to be supported.

 

One of the objectives to obtain this improvement is to reduce the stress and pressure on the ballast layer. This is why a new type of sleepers was created by the end of 1990s, the frame sleepers. They consist of two sleepers placed longitudinally under the rails and joined to one another by two sleepers across them, thus adopting a rectangle or double H form.

 

With this layout, a larger support area for the sleepers is gained, the loads are therefore better spread and the pressure level on the ballast and the platform is lower. Moreover, the configuration of the frame sleepers provides the track with a higher stiffness compared to tracks with standard sleepers. Nowadays, some sections in Austrian, Swiss and Italian rail lines are equipped with frame sleepers so as to carry out technical and economic investigation.