| Dorman
Long Technology |
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| Sutong Cable
Stayed Bridge. Lowering of 3050 tonne steel caisson to pier 4 |
The Sutong bridge across the Yangtze river near Shanghai has a main span
of 1088m, which will make it the longest cable stay bridge in the world
when completed in 2007. Construction of the 118m x 52.3m x 18m thick pile
cap to the main cable pylon P4 is currently underway by CHEC.2nd Navigation
Engineering Bureau, the main contractor for the north side foundations and
approach spans. The reinforced concrete pile cap is supported on 135 No.
2.85m diameter steel piles and has a 2m thick permanent steel caisson to
the sides which is designed to minimise damage to the pile cap during ship
impact. This steel caisson also acts as permanent formwork for casting of
the pile cap concrete. The bottom 7m of the caisson was assembled above
water level on temporary support brackets welded to the piles, and then
carefully lowered into the water using strand jacks. DLT were heavy lift
sub-contractors to CHEC for this lowering operation, which took place on
October 19th 2004. |
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| The lowering operation was carried
out using 16 No DL-S418 strand jacks, each jack having a safe working load
of 418 tonnes, powered from 4 No DL-L114/4/D hydraulic power packs. The
whole operation was controlled using the recently developed DL-P40 computer
control system, which uses a state of the art CAN network for ultra reliable
communication between jacks, power packs and the control computer. Accurate
control of load distribution between the jacks was essential for a safe
lift and to achieve this the client specified a maximum differential movement
between any two jacking points of 10mm. The 3050 tonne, 7m deep, caisson
was an unusually stiff load to handle as a relative movement of 10mm between
adjacent jacking points would cause a load redistribution of 35% of the
jack load, a situation which would quickly lead to a jack overload if not
automatically detected and corrected by the DL-P40 control system. Periodic
level surveys and strain gauge readings were taken around the box by the
client during the lowering operation to check that we were achieving this
requirement. The DL-P40 computer control system has intelligent nodes at
each jack that constantly monitor the jack stroke in relation to the max/min
jack stroke advised to it by the DL-P40 control unit, and can instruct the
power pack to adjust the oil flow to itself to maintain its position within
the required stroke range. In practice it was found that a stroke range
of just 5mm was required to maintain a stable load balance between the jacks. |
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DL-S410 strand jacks powered by DL-L114/4/D power packs.
Each of the diesel powered hydraulic power packs can operate up to 4 jacks |
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| Strand jacks were mounted on temporary cantilever frames,
evenly spaced around the perimeter of the caisson, and were connected to
temporary jacking brackets welded to the inside wall of the caisson |
