Chapter 5: Bridge construction

Concrete bridges are either cast-in-place or they are assembled from prefabricated elements. Composite structures, which combine steel, precast and cast-in-place structural members, are also used.

Cast-in-place structures are concreted on stationary or movable scaffolding, and incrementally launched or cast progressively, segment by segment. Structures can also be cast outside the obstacles and consequently rotated or lifted into the design position.

Only relatively short bridges (up to about 100 m) are concreted all at one time on a stationary scaffolding located along the entire length of the structure. These structures are usually prestressed by continuous tendons that are tensioned from both ends. In the case of longer bridges, the structures are usually cast incrementally, span by span, with short cantilevers protruding into the next span. The joints between the sections are usually chosen at sections where the dead-load bending moments are zero. In the case of a constant cross-section, the section width is approximately 1/5 of the span length. The bridge decks are prestressed by continuous cables tensioned and coupled at the joint. Because of the possibility of cracks (see Chapter 10), only one half of the cables can be coupled at the joints.