Launching gantry

While superficially similar, launching gantry machines should not be confused with movable scaffolding systems, which also are used in segmental bridge construction.

However, ground access to the spans may be challenged by the presence of existing infrastructure or bodies of water, or the height to which the segments must be raised can exceed the reach of ground-based cranes.

[1]: 38 The most visible feature of a launching gantry are the twin parallel girders,[1]: 38  which can either be above (upper-beam) or below (lower-beam or underslung) the bridge deck.

[1]: 41  The launching gantry machine usually is sized to the construction project, with the length of the twin main girders approximately 2.3 times the distance between spans.

If the segments (or girders) are delivered instead at the bridge deck level, the launching gantry moves back to allow the forward trolley to pick up the front end of the next segment (or girder), while the back end of the segment (or girder) is supported by the transportation vehicle; as the forward trolley moves forward, the rear trolley takes over supporting the back end from the vehicle.

In either case, the launching gantry girders and hangers essentially serve as falsework prior to tensioning.