Chapter 4: The Construction Process of Segmental Bridges
Balanced Cantilever Construction
Temporary Tower with Vertical Prestressing
Figure 4-1: Balanced Cantilever Construction
Balanced cantilevering can be carried out with cast-in-place or precast segments. For cast-in- place balanced cantilevering a set of two form travelers is required, one for each arm of the cantilever. For multi-span bridges the form travelers can be dismantled after finishing cantilevering from one pier and can be set up for new use on the next cantilever.
In case of a bridge with variable box girder depth the pier table segment will be the most massive segment of the superstructure. This segment needs to be constructed prior to cantilevering to provide a working platform from which the two form travelers can start. It also includes diaphragms that facilitate the flow of forces from the cantilever arms into the piers. Because of size, geometry, and construction separate from the rest of the superstructure the pier table segment will take a considerable amount of time to construct. It can be put into place either with large precast segments or as cast-in-place with formwork mounted on the pier shaft.
An interesting pier design specifically feasible for cantilevering is mentioned by Fletcher (1984), who points out that a pier consisting of transverse twin walls is advantageous as it provides stability for cantilevering but allows horizontal movement of the superstructure from thermal elongation through flexing of the wall panels.