The launching girder for the elevated section of the Dubai Metro Project has arrived in Dubai.

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20 Dec 2006

Over 13 meters wide, 15 meters high and about 109 meters long, the launching girder will be used to lift and position viaduct segments to form the elevated section of the project. This method is commonly used in erecting segmental bridges and railways. The launching girder will be certified by an independent third party safety company, and will be subjected to safety and quality tests including a full load test and manufacture tests for the erection component.

The girder will be positioned over the span to be constructed, supported by a tower connected to the end of the deck and the next pier. The Launching Girder is expected to be first used in early January, 2006. Complete assembly of the girder will be established approximately 60 days before installation on the span.

Adnan Al Hammadi, Director of Construction said, "Erection by overhead launching girder is probably the most common system utilized in this type of construction, as it involves the use of launching girder situated above the bridge deck to build the segments one by one.

"The girder is usually equipped with at least one primary winch which is used to pick up the precast segments and carry them into their approximate erection position. It is generally accepted that all of the segments should be suspended within the girder to allow it to take up its fully loaded shape before beginning the process of aligning and joining the span together. The daily average of erection will be 18 metres to 25 metres", he added.

The system for lifting, hanging and adjusting the spans is critical in terms of both the safety and the erection progress, and careful thought goes into this process. Alignment and connection of the spans usually starts from one end with each successive segment being joined to the span length.

Once the full span has been completed, post-tensioning is applied in stages and the weight of the span is transferred either to heavier suspension points at the ends of the launching girder or to jacks on the final support structure. After this load transfer has been affected, the individual segment hangers can be released and the span can be lowered into its final position. The launching girder can then be moved forward to the next span and repeat the process.

The benefits of this method as the foremost and fastest way of viaduct constructions can be summarized as follows: the equipment is relatively self-sufficient, it is flexible in terms of segment delivery, as they can be delivered from the front, below, or behind for example, finally, it is capable of dealing with a wide range of variable span geometries both in terms of segment size, span alignment and curvature.