The types and characteristics of launching gantry in China

1, The types
a, According to different construction methods, it consists of the field-casting and field segmental assembly.
b, It divides into the movable supporting system and movable standing system in light of carrying the mould plate or not. For the movable supporting system, we cast the concrete girder on site. However the movable standing system is to assemble the pre-cast segmental concrete girder on the machine.
c, It consists of the upstroke movable supporting system and downstroke movable supporting system according to the piers position.
Nowadays the upstroke movable supporting system is the most popular one.

2, The upstroke movable supporting system
Compared with the downstroke movable supporting system, the advantages and disadvantages of the upstroke one are as following:
Advantages: The main body structure is above the piers. Thesupporting structure is installed the pier top or the erected girder. Therefore there is no need to prepare the temporary bracket next to the pier and save the space under the bridge. So it’s specially applicable for the overpass bridge, city viaduct and some complicated construction projects. Also it’s convenient to construct the first and last girders.
Disadvantages: It is a large-sized machine. Before casting thegirder, we must guarantee that the next former girder has been solid enough to bear the heavy loading on it. It’s not convenience in the whole construction period because of some auxiliary facilities such as poles and booms. While unfolding the base mould, we must in the method of flip-down which requires the enough space under the bridge. Therefore its applicable scope has been limited.

3, The downstroke Movable supporting system
Its advantages and disadvantages are as following:
Advantages: The machine won’t be restricted by the girder width. It adopts the direct supporting method which makes it convenient to adjust the linear of the base model. Because its frontal area is smaller than the upstroke one, so the wind-resistance will be better in the construction period. Especially in the bad weather and circumstances, its safety is very high.
Disadvantages: Because it needs to install the large size bracket under the bridge, the enough space must be provided. The unfolding method is horizontal direction, to guarantee its stability we need the counterweight facility. While unfolding, the occupied space of the both sides needs to be large enough. The first and last girder will be more difficult to erect in the whole construction period because of the existed front and rear guide beam.
4, The movable standing system
Compared with field casting the whole span concrete girder, this type of machine has the following characteristics.
Advantages: Every segment has the consistent appearance, applies to prefabricated industrialization, high quality, prefabricated and assembled in parallel operation and short construction period.
Disadvantages: The constructor needs to prepare the enough land to pre-cast and store the girders. The transportation will be affected by many factors such as delivery vehicle, assembly machine and transportation channel ( tunnel), also the technology aspects like linear controlling.