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launch backward

The Shenzhen Western Corridor Project

is a ‘segmental box girder bridge’ which connects the New Territories in Hong Kong and Mainland China as a link in the ‘Deep Bay Highway ’. This highway bridge, actually is two bridges, one in each direction, is built on columns with spans of 70-75 metres and up to 38m heigh. The superstructure of the bridges are constructd with ‘precast box girder segments’ which are mainly erected by a Deal ‘Launching Gantry ’, one of the world's largest launchers, using the ‘balanced-cantilever ’ method. End-spans are built in complied ‘segmental-span’ erection (9-10 segments) hanging on special stress-bars in the twin triangular Steel Truss of the ‘Launching Gantry ’.
With two main winches ( capacity 138 tons each) the launcher is able to lift two segments at the same time into place, where high-strength epoxy is spread on both matching faces and with temporary ‘high-tensile-bars’ stressed to the ‘pier-segment or last erected pair of segments’.
After this proses the launcher slides to the other bridge deck to lift and place the next pair of segments. During this time we carry out permanent ‘post-tensioning’ of cantilever tendons in the last erected pair of segments. And so on until 22 segments, 11 on each site of the ‘pier-segment’ are placed to build a 75m balanced-cantilever T-span.
The ‘Launching Gantry ’ with a length of 184.6 metres and 6.7 metres heigh, supported by two lower cross beams, 6.3 metres high with a length of 40 metres. They are equipped with eight 400 ton hydraulic jacks for levelling, and the gantry is able to slide from the south-bound deck to the north-bound deck by a ‘chain-drive’ and launch itself forward, or if necessary backward. In the ‘self launching process’, the gantry moves from one pier-segment to the next. These precast pier segments, which had been lifted and placed on the columns beforehand, rest temporarily on eight 200 ton hydraulic jacks and are ‘nailed’ with high tensile wire strands to the pier-column. The ‘Launching Girder ’ is equipped which two additional support legs, one at each end. The front pendular leg is fixed, and the rear support leg is movable, driven by a ‘capstan system’ like the cross beams and the winches.
When supported on these legs, the launcher is able to move the front or rear cross beams hanging on rollers in the two ‘twin triangular trusses’, which comprise the main parts of the ‘launcher ’.
All activity related to the ‘Launching Gantry ’ is carried out above the water. All assembling, delivery of the segments and material has to be organized using barges, barge-crane and not forgetting the tide. Also the weather plays a big role here because ‘Hong Kong’ is a typhoon region, and we will need to secure the ‘launcher ’, depending on the work activity on any particular day.

Created on ... February 26, 2005
copyright © Uwe Baier