Figures 17 + 18 : NAV during launch
5 . CABLE STAYED DECK 5.1 Deck segments
The cable stayed deck comprises a single composite box girder approximately 40m wide and 4.9m deep comprising a steel open topped box „ tub “ with a reinforced and post-tensioned concrete slab with extending side cantilevers . Cables descend in two planes approximately 5m apart from each tower to stay anchor webs either side of the bridge ´ s centre line , with crossing stays employed mid span to stabilise the central tower .
The segments are 29.8m wide and 16.2m long , weighing up to 320t . The cable stayed deck totals almost 31,000 tonnes . The segments were fabricated in China and delivered directly to the port at Rosyth . Each segment was trial assembled with its adjacent segment in correct alignment to achieve correct fit-up at the welded joint and match drill the bolted stiffener connections .
Each of the steel sections is made up of five key components ; bottom plate , inclined web assemblies , stay anchorage webs , side cross frames and centre cross frames .
A 250mm thick reinforced and prestressed composite slab is connected by conventional shear studs to the steel superstructure . The slab thickens to up to 600mm at the towers . The slab is transversely posttensioned to limit cracking in service . The fixed point of the bridge is at the Central Tower where the composite deck is effectively clamped to the tower by means of longitudinal and transverse post-tensioning through monolithic construction at the so-called Central Tower ‘ power joint ’. At the flanking towers , lateral support only is provided by means of a series of free sliding ( non-guided ) spherical lateral bearings , along the horizontal principal axis .
Figure 19 : Typical cable stayed bridge deck cross section
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