Chapter 4: The Construction Process of Segmental Bridges
by diagonal bracing and transverse trusses at the upper front and rear.” Wheels allow longitudinal movement of the form traveler on rails on top of the superstructure. For stability of the traveler it can be held down by a counterweight at its rear end (Mathivat 1983). After advancing, the traveler is anchored down to the cast parts of the superstructure with tendons at its back, as Levintov (1995) writes. Thus, the overturning moment from the load at the traveler tip can be resisted. It is mentioned that for structural reasons the form traveler main beams are located above the webs of the concrete box girder, so that construction loads can be transferred into the main load-carrying system of the bridge directly. The longitudinal main beams of the form travelers need not necessarily be located above the webs. Form travelers are also used in configurations with the main beams in a lateral position, leaving the bridge deck free (Podolny and Muller 1982). Mathivat (1983) further distinguishes so-called self-supporting assemblies, where the stiffening effect of the form panels contributes to the stiffness of the whole form traveler.
Suspended from the traveler are not only the adaptable forms for exterior and interior of the concrete segment, but also working platforms on different levels that can be accessed from above.
220.127.116.11 Launching Girders
Apart from various types of cranes that can be used to place precast segments, launching girders are widely used for this purpose. Levintov (1995) mentions limited access under the cantilever and great height of bridge superstructures above ground as reasons why launching girders would be used. They are very feasible for bridges with several spans, as due to their length they can be advanced over gaps that are still to be bridged. During construction they are moved forward on rails whenever a major part of the bridge superstructure has been completed.
Launching girders, also called launching gantries, are large trusses that are placed longitudinally on the bridge superstructure. One or more movable crane devices for transportation of the precast