Segmental Launching Gantry is generally used in the erection of Highway Bridge and MRT Bridge, using precast segmental pre-stress concrete box beam (PC beam) assembly. The main feature is the high efficiency of self-travelling construction. It’s composed of the main beam, leg and winch trolley. The main girder is used for bearing load, the leg is to transverse moving, longitudinal moving, leveling, support, cross span, cross scale and other functions, while the winch trolley is used for lifting the precast girder.
Use girder transport trolley or beam transport ship to feed girder (two beam feeding type as under-bridge and rear feeding), Segmental Launching Gantry in turn lifts each segment girder and suspend on the main beam and then accurate contraposition, gumming and pushing into the whole girder, Segmental Launching Gantry unloads and places on the bridge pier, and connect the adjacent bridges by wet seam, this completes the single span, and then the Segmental Launching Gantry self-crosses to the next erecting.
According to the assembly mode of the present section beam design (mainly to see the wet joint position),it can be divided into:
1) Full symmetry assembly:
From the pier sides to the bridge center, the wet joint is in the middle of the span. Side span uses temporary support erection without using the segmental launching gantry.Generally it is equipped with 1-2 hoisting crane. Full symmetry assembly is more special and it is generally used for large span bridge.
2) Symmetrical cantilevers + half span cantilever:
The design of the bridge is that 4-5 piers as a section of continuous beam, then disconnect the expansion joint. Therefore, the segmental launching gantry should not only have symmetrical cantilever function, but also need to have the ability of half span assembly in each section of the continuous beam pendulous. This machine needs to prepare 1-2 cranes, and it is more widely used in the box girder bridge with large span.
3) Segmental Launching Gantry of full span cantilever assembling:
The wet joint and expansion joint are on the piers. Erect the full span in the middle of the two adjacent piers. It is used for medium span bridge, only equipped with 1 set of hoisting crane. The specific way is divided into high cantilever and low cantilever.
According to the travelling system and erection methods, it can be divided into the upper bearing and the lower bearing type:
- Upper type:
Segmental Launching Gantry travels on the upper deck (or at the top of pier) , segmental beam erects suspending under the main girder. It has shifting over amplitude function. Scope of application: ①Totally symmetric cantilever ②Symmetrical cantilever + Half span cantilever ③Full span cantilever ④Water or obstacles under the bridge
- Lower type:
Segmental Launching Gantry walks on the pier cap under the bridge deck, segment beam erects on the main girder. It does not have the traversing over amplitude function. Scope of application: ①Full span lower cantilever project ②Lower pier ③Heavy segmental beam
Type Selection Requirements
Type selection design needs to provide the bridge design drawings and other technical requirements of Client, including bottom bridge structure, upper girder design and site working environment, the main technique parameters needed to be clear:
- Maximum segment beam lifting weight
- Maximum suspension weight
- Bridge span
- Segmental block section size and lifting point position
- Pier section size, height and bending bearing capacity
- Deck longitudinal slope and transverse slope
- Minimum curve
- Type of beam feeding