A new ductility index for railway prestressed concrete sleepers with holes and web openings considering fragility and failure criteria

Prestressed concrete sleepers (or railroad ties) are designed in order to transfer wheel loads from the rails to the ground of railway tracks and to secure rail gauge. Their design generally takes into account static and dynamic loading conditions. Some sleepers have been retrofitted on site to install accessory equipment such as signaling, fiber optic, equipment cables, etc. Without protection, the equipment will be damaged either by ballast corners or by tamping machine. Thus, concrete sleepers are often pre-drilled in order to create holes and web openings to cater cables internally so that they would not experience detrimental or harsh environments. Also, the retrofits on concrete sleepers for automatic train control device and similar signaling equipment often require holes and web openings. In contrast, the effects of holes and web openings on structural capacity of concrete crossties have not been thoroughly investigated. This paper thus highlights experimental methods to investigate the effect of holes and web openings on the fragility and failure of railway concrete sleepers. The insight into the fragility and failure modes has resulted in a proposal to develop a new ductility index that can better inform the structural capacity and health monitoring for retrofiting prestressed concrete crossties with holes and web opening, which is also suitable in practice.