Variant--BGEM | gantry

Bridge Girder Erection Machine

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A major variant of gantry crane is the bridge girder launcher, also called bridge erection machine. This type of machine is used to place bridge girder on the bridge piers. The biggest distinction of bridge erection machine from typical gantry cranes is its moving mechanism. Instead of having movable supporting legs, these machines allow relative movement between its girder and its legs along the direction of the girder. As you can see in the above picture, bridge erection machine usually has three or four legs. And its working procedure can be divided into two major steps.

Working Procedures

Cover a new span

This step is to position the main beam of the bridge erection machine on top of a new span of the bridge for which the machine is going to place girder. This procedure requires the machine's girder to move forward.

One type of bridge erection machine has moving systems at the bottom of its legs so it can move the girder by moving the entire machine. This type of machine mostly involves those used in railway bridge construction, for the rails can be directly used as the moving tracks of the machine. And this type of machine usually only needs three legs.

Another type of bridge erection machine doesn't have moving systems installed on its legs. So when covering a new span it requires the beam of the machine moving forward relative to its legs. Such moving is usually driven by hydraulic jack built in the machine or by an external propulsion vehicle, and there are supporting roller systems between the legs and the beam of the machine to allow the relative movement.This type usually needs four legs to move forward alternatively.

Step1:

Step2:

Lift the bridge girder in position

Once the main beam of the machine has moved on top of the span, the front leg will be fixed on the pier and begin to withstand force. The next procedure will be lifting girder from a girder transporter and transport it along the main beam to the installation position. For most bridge erection machine, there are at least two hoisting trolleys, these trolleys can move along the beam direction as well as the perpendicular direction. So, no matter the component is an integral bridge girder or a piece of the girder, these hoists can fit them in required positions.

Main Types

Hydraulic Walking Bridge Girder Launcher

This type of bridge girder launcher has four supporting legs. The main mechanism for the machine's beam to move forward is the internal hydraulic power which can push the beam on the rollers of the legs. And because it has four legs, so as long as there are three legs holding the weight of the crane, another leg can be suspended and traveled forward.

Because cantilever length in this type of crane is not very long, so there is no need to carry the girder as a counterweights.

Bridge Girder Launcher with Guide Beams

This type of bridge girder launcher uses guide beams as a method to assist the moving forward of the main beam. So the typical three legs model can be viewed as a combination of a two-leg main beam and a two-leg guide beam. And the front leg of the main beam is movable along the top of the guide beam.

This type of machine requires movable legs of the crane, and it can usually travel on top of a rubber tire transporter.

Self-carrying Bridge Girder Launcher

The video shows the newest SLJ900 Integral bridge girder erection machine made in China. This type of machine installs rubber tires at the bottom so it doesn't need a girder transporter.

And another noteworthy advantage is that it can travel by itself to the construction site, unlike conventional bridge erection machine which needs to be dissembled for transportation and re-assembled on site. This also makes it easy to move among different working zones.

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