Chapter 4: The Construction Process of Segmental Bridges
220.127.116.11 Progressive Placement Method
The progressive placement method, in comparison with the balanced cantilevering method, is a one-directional process as shown in Figure 4-2. All cantilever segments are subsequently placed at the tip of a cantilever that is built across all spans. Both cast-in-place and precast segmental construction can be used. Often stay cables from the tip of a temporary tower on the superstructure support the cantilever. With growing cantilever superstructure this support mechanism has to be advanced. Another method of support is use of temporary towers, which are mentioned in Section 18.104.22.168. According to Mathivat (1983) this method is competitive for spans between 30 to 50 m in length, whereas incremental launching and balanced cantilevering are also used for much longer spans.
Progressive Placement Method
Figure 4-2: Progressive Placement Method
Progressive placement has several advantages, as Mathivat (1983) points out. First of all, the placement process does not have to switch sides as it occurs in the balanced cantilevering method. Thus process control is simplified. In addition to this, good access to the placement location is given on the already completed part of the bridge superstructure. With the progressive placement method horizontal curves can easily be accommodated.
From a structural point of view the progressive placement method is advantageous in substructure design. Only vertical forces from the dead load of the superstructure under