After the first strand had been spun of each cable , the remaining thirty-six strands were spun in nine groups of four - the work being carried out alternately on east and west cables .
When completed , the group of 37 strands in each cable hung in hexagonal shape . All the wires were squeezed throughout their lengths into a compact and approximately circular formation by four purpose-built compacting machines which had hexagonal frames hinged at the tops .
192 cable bands which consisted of two semi-cylindrical steel castings , machined inside to fit the cable , were clamped together at top and bottom , each band by four to eight high tensile steel bolts or screwed rods with washers and nuts on each end .
The last major operation on the cables was wrapping them round from end to end between the cable bands with galvanized wires under tension . This was done by means of two large wrapping machines which weighed four tons each and were packed off the top of the cable .
" Each machine consisted essentially of two tandem drums on which the wrapping wire was wound , and from which it was pulled off and wrapped round the cable by means of a power-driven revolving flyer . The drums , which encircled the cable , were split at the bottom and hinged at the top to enable them to travel past the cable bands . The machines could be moved up or down the cable by means of their own hauling winches and were capable of wrapping while travelling up or down hill ." ( 4.76 , p . 471 , 1965 FRB ).
The suspenders were each made up of steel wire ropes , which were looped over grooves at the top of the cable bands , and terminated in common sockets at the lower ends . The longest suspenders weighed four tons and were over 300 ft ( 91.4m ) long .
4.7.3 The Suspended Structure
The steelwork of the suspended structure was erected in two phases .
In the first pass four 15-ton derricks , mounted on temporary crane girders in the deck , erected each panel of steelwork in front of them , working out from either side of the span .
The first 90 ft ( 27.4m ) length of deck was cantilevered out from each side of each tower and the derricks assembled on them before the end of cable spinning . When each panel of steelwork had been assembled and connected to the suspenders , the temporary crane tracks were extended , and the derrick moved out to the end of the panel in order to erect the next one .
The work continued in this way until 18 panels had been erected on either side of each tower . Then work on the two fronts in the main span had to be halted until the remaining four panels had been built in each side span and connected to their bearings at the side towers .
There was little difference in the levels of steelwork each side so it was decided to move both cranes forward and to erect the last top chord on the east side with the south derrick and on the west side with the north derrick and by this the bridge gap was closed at mid-span .
Figure 9 : Cable wrapping machine
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