Balanced Cantilever

(Info From BBR Holdings)

With the cantilevering method, the superstructure of bridges is usually built from one or more piers by means of formwork carriers. Normally the structure advances from a short stub on top of a pier symmetrically in segments of about 3 m to 5 m length to the mid span or to an abutment, respectively (load balancing method).

The prestressing tendons are arranged according to the moment diagram of a cantilever, with a high concentration above the pier. Towards the mid span or the abutment the number of tendons gradually decreases.

The use of the cantilevering construction method, for medium and long span concrete bridges, is recommended especially where a scaffolding is difficult or impossible to erect as e.g., over deep valleys, wide rivers, traffic yards or in case of expensive foundation conditions for scaffolds.

Incremental Launching

(Info From BBR Holdings )

The incremental launching method is particularly suited for the construction of continuous post-tensioned multi-span bridges. It consists of casting 15 m to 30 m long sections of the bridge superstructure in a stationary formwork behind an abutment to push a completed section forward with jacks along the bridge axis.

The sections are cast contiguously, one after another and are then stressed together. The superstructure, growing section by section is launched over temporary sliding bearings on the piers until the bridge is completed. In order to keep the bending moment low in the superstructure during the extrusion phases, a launching nose made of steel is attached to the front of the bridge deck. The launching nose is dismantled after the superstructure has reached the opposite abutment.

However, the spans should not exceed 60m approx. and the bridge sections must be constant. Furthermore the superstructure of the bridge has to be continuous over the whole length and straight or have a constant curvature in plan and elevation.