The classification of launching gantry

Launching Gantry

It is a bridge construction machinery which moves along the pre-laying rails to erect the concrete girders. Because of its high efficiency, its design principle has been considered fully in the designing process of the China Railway Bridge Girder. It owns the large body and has exceeded the railway transportation limit, so it must be dismantled while delivering. After arriving at the construction site, we will assemble and install before it’s been put into practice.

The launching gantry crane belongs to the special hoisting machinery. Its purpose is that hoist and erect the pre-cast box girder or T girder on the piers. Its basic working procedure is: hoist the girder from the beam transporter firstly, then the machine to place the girder on the pier through longitudinal and horizontal traveling.
The general launching gantry in China includes three types. They are widely used for erect the reinforced concrete beams and pre-cast concrete beam.
1, The single girder launching gantry
The single girder launching gantry is one of the bridge construction machinery. Its boom is a box-girder which overhangs forward. The front part equips with a collapsible column consisted of the left and right poles. The machine can move to the position with empty load on its own, then make the front column straight and place on the piers. When the girder travels along the boom, the purpose of the boom likes a supporting structure. Firstly lift the girder with the special gantry crane to the beam transporter. Then align the carrier with the rear part of the launching gantry. Hoist the concrete girder with the two trolleys installed on the boom and moving them along the boom. Place the girder on the pier. To meet the demand of the curved bridge, the machine can swing moderately in the horizontal plane. The method of placing the girder is the same as the double cantilever launching gantry. The advantage of this machine is no counterweight, no other facilities to push the girder, higher levels of mechanization, improved safety performance.
2, Double cantilever launching gantry
The double cantilever launching gantry is one of the bridge construction machinery. This type of machine was used in Soviet in the earlier stage. Introduced into our country in 1948, its lifting capacity contain 45t and 80t whose front and rear arms are steel plate. In 1950s, adjust the front and rear arms to architecture and the lifting capacity has approached 130t. This machine can not move on its own and needs to be pushed by the locomotive. The front arm is used to lift the girder, and the rear arm to hoist the counterweight, both of them couldn’t move in the horizontal plane. During the erecting period, the girder can be lifted only the beam has been carried to front arm by the specific 80t beam transporter. In order to make the machine working convenient, the bifurcated cable must be laid in the bridge ends. When the machine has hoisted the girder, the axle load will increase. However, the new road base is a little loose. Therefore we must take some reinforcement measures to the construction road, such as press the road base with a heavy vehicle, add the sleeper and so on.
3, Double girder launching gantry
The boom of this kind of bridge girder launcher is consisted of two box girders. The whole machine body is the box girder. There are two folding columns in the front and rear parts of the machine. Also two trolleys are equipped above the two box girders and horizontal and longitudinal moving forward and back along the pre-laid rails. The concrete girder will be carried to the rear part of the machine through the beam transporter, hoist it with the two trolleys and move forward along the rail to the proper position. Then place the girder on the pier. Both of the ends of the machine can accomplish the lifting and erecting, there is no need to turn round while erecting the opposite direction. To meet the needs of curved bridge, the machine can swing in the horizontal plane. Also there is no need to prepare the bifurcated cable and specific beam carrier for the construction while feeding the girder. To guarantee the machine can work continuously, the rail must be laid ahead of time. Generally speaking, the last two kinds of launching gantry can lift the rail on their own, in this way the construction efficiency will not be influenced and delayed. According to the actual demands, sometimes we will make the temporary bridge girder launcher. For example: in the project of the South coast of Yangzi River in Jiujiang, we made a specific 300t launching gantry temporarily to erect the 40m pre-cast concrete beam. To accomplish the project construction timely, some constructors equip with the steel scaffold pole pieces, removable beam or military beam to compose the simple bridge girder launcher.