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Continued...
A fifth platform is to be used at the top of one tower, where
galvanised steel protection sleeves will be removed, the cable inspected and the
protective covers replaced with new seals and gaskets. All the platforms are
winched into position from the bridge deck, using pulleys mounted on the main
suspension cable.
Once the sampling and inspection procedure is completed at each
position, the cable has to be returned to its original shape. This is achieved
with the use of a special compacting machine capable of applying a maximum
hydraulic load of 95 tonnes at 700bar. The equipment consists of four identical
segments linked by hydraulic cylinders which are powered by an electric motor.
Once in position around the cable, it is controlled by an operator through a
hand-held pendant, with gauges monitoring hydraulic pressure and providing
readings to the operator.
Spencer also required a mechanised technique that would ensure the
wrapping wire would be applied consistently at the correct tension and also
ensure that each turn of the wire would lie tightly against the previous one.
The machine designed by Bennetts consists of two ring assemblies,
one rotating inside the other. Two spools are mounted on the outer ring, which
is driven by an electric motor to deploy the wire around the cable, while four
compactors press each turn of the wire against the previous one. Wire tension is
shown on a control panel and can be adjusted by the operator reducing or
increasing the torque of the motor.
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