When spinning was complete the cable was hexagonal in shape — it was then compacted into the round shape we see today and wrapped laterally with 9 gauge galvanised wire.
The cable was further protected by painting using red lead paste between the cable and wrapping wire and the whole cable was then painted. This technique for spinning parallel wire suspension cables was first developed by John Roebling on the Brooklyn Bridge in the 19th century, and has subsequently been used on the Golden Gate, the Severn and many other famous suspension bridges worldwide.
The main cables are anchored at each end to take the 13, tonnes of total load in each cable. The concrete is strengthened by steel post-tensioning strands grouted into conduits. The tunnel lengths vary between 56 and 79 metres. The deck of the bridge is suspended from the main cables by steel hanger ropes. These measure 57 mm in diameter on the side spans and 48 mm in diameter on the main span.
The shortest hanger is 2. Each new hanger comprises a pair of ropes, each with its own single socket. This updated socket design is an improvement on the original, as it allows for just one rope of the pair to be replaced as required.
The suspended deck is made up of a steel stiffening truss with three longitudinal air gaps at roadway level to improve aerodynamic stability. The main span between the two main towers measures metres long. The two side spans between the main towers and side towers are metres long.
On the main span the deck is an orthotropic stiffened steel plate. However, on the side spans the deck is of composite construction — a mm thick reinforced concrete slab on steel beams. On all suspended spans the surfacing is limited to a thickness of 38 mm. The main expansion joints are embedded in the roadway underneath the main towers. Articulated trains slide over curved girders, allowing the suspended deck to expand and contract as required by temperature, wind loading and weight of traffic.
They are the oldest and the largest of their kind in Europe. The joints had been due for replacement in , but the project has been deferred until after the opening of the Replacement Forth Crossing, in order to minimise costs and disruption to traffic.
Failsafe devices have been fitted to ensure the safety of bridge users in the meantime. The approach viaducts are significant structures in their own right. Reinforced concrete piers support a continuous deck structure consisting of twin steel box beams with transverse beams and outriggers.
The deck is comprised of a reinforced concrete composite slab and 38 mm surfacing. The South Viaduct is metres long, and is supported by ten concrete piers and the side tower. It is divided into two separate structures with an expansion joint at the third pier from the side tower. The deck of the new bridge will have two lanes in each direction as well as hard shoulders to ensure that breakdowns do not cause congestion.
Designers claim this will also allow buses to be moved from the Forth Road Bridge in high winds or other dangerous weather conditions. As the new bridge will be a designated motorway, it means learner drivers and motorbikes under 50cc will not be allowed on it.
Mr Glover told the BBC that travelling across the new bridge would be much smoother than the current one, because it only has two joints on the whole deck. John Swinney, the finance secretary at the time, said the lower cost was a result of "successful management" and the "delivery of key milestones". Mr Swinney also announced the new bridge, which has been completely publicly funded, would be toll-free like all other road bridges in Scotland. Nicola Sturgeon, who was then deputy first minister, said the project would be completed by the end of The bridge's technical director Mike Glover said the weather in the Firth of Forth had been "particularly unkind", especially at the point when they were m in the air attaching cables.
More than 15, people have been involved in the project since the inception of plans for a new bridge in The structure is m above high tide ft , equivalent to about 48 double decker buses stacked on top of each other. The steel required for the bridge deck weighs a total of 35, tonnes - equivalent to almost Boeing s. The combined steel required for North and South viaducts weighs 7, tonnes - enough to make another 23 Kelpies. The bridge has windshielding to almost entirely eliminate the need for closures during the frequent periods of high winds in the Forth estuary.
Cables can be replaced with more ease than on the Forth Road Bridge - it can be done as part of normal maintenance works without closing the bridge. The foundations of the bridge are large caisson - circular steel structures - sunk into the mud of the estuary to bedrock level.
The south caisson is the height of the Statue of Liberty. It is 35m in diameter and when it was constructed it was 50m in height. At the southern tower they poured 16, cubic metres of concrete over a period of 15 days continuously from barges on the river. Image source, Pathe. Image source, PA. Related Topics. The bracing between the towers in the shape of a St Andrews Cross adds to its stylish appearance.
It is also the largest to feature the cross hatching cables, adding extra strength, stability, and giving a distinctive elegance. Whilst we currently have no upcoming events why not learn a little more about the history of the Three Bridges, from the true beginnings in !
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