b ) Augmentation above
This would require the same work as with the replacement cable situated above the existing cable . The main difference was that in this case not all load would be transferred into the new cable . The size of it could therefore be smaller ; its exact size would depend on assessment of the long-term capacity of the existing cable - .
c ) Augmentation to side
This would involve construction of a new cable to the side of the existing cable with a percentage of loads in the existing cable being transferred over to the new cable . The cable would be formed from PPWSs , consisting of 37 strands each of 127 wires , with the cable having a compacted diameter of 380mm . Such a cable would carry approx . 30 % of the existing main cable loading . The new hangers would be inclined and connected to the existing connection bracket at the top chord of the stiffening trusses .
Anchorage considerations were similar to those described for the replacement option , with new anchorages being provided .
The main towers would carry the off-centre load and the localised moments that any cantilevered support would induce in the tower legs at the connection points .
It would be possible to erect a new leg from pier head level to support the new cable directly . The new leg
would be approx . 2.8m x 1.2m in plan with a crosssectional area of 0.38m 2 and its support could be provided by its connection to the existing towers located at the intersection of the tower cross bracing and the legs of the main towers .
Footways would be widened . The new saddles on the side towers would be positioned to angle the cables down to their anchorage points .
7 . MAIN CABLE ANCHORAGES INVESTIGATION
Following the 2004 / 5 inspection of the main cables , when corrosion was found in their wires , the investigation work of the main cable anchorages was carried out in 2011 – 2013 mainly with the aim to determinate their remaining service life .
The main cable anchorages are formed of concrete filled tunnels within rock . The concrete cast within the tunnels creates four large , individual , concrete plugs to which the main suspension cables are attached . The tunnels were pre-tensioned by galvanised steel strands within grouted ducts . In the design no access to inspect , maintain or monitor the system of pre-tensioning was provided .
The main cable , comprising 11618 wires in 37 bundles , is split into 37 separate strands at the splay saddle located within the anchorage chamber .
Figure 3 : Augmentation to Side
1 / 2017
Figure 4 : Replacement Above