Magdaléna Sobotková I . Design and Construction
FORTH ROAD BRIDGE
Magdaléna Sobotková I . Design and Construction
1 . INTRODUCTION
The bridge across the Firth of Forth is a vital link in Scotland ´ s strategic road network with more than 24 million vehicles every year .
When opened on 4 September 1964 , the Forth Road Bridge was the longest span suspension bridge outside the USA and the fourth longest in the world .
The main span is 1006m with equal side spans of 408m . It carries a two lane dual carriageway , without hard shoulders or strips . There is a separate cantilevered footway / cycle track on either side .
The main span has a steel orthotropic deck and the side spans have a heavier concrete deck . The deck has steel stiffening truss , wire rope hangers and vertically split cast steel cable bands .
The main cables are the primary load-carrying members , each carries almost 14 000t of load . They were aerially spun .
Each cable comprises 11 618 galvanized high-tensile steel wires 4.98mm in diameter , giving a compacted cable size of 590mm .
In 2001 the bridge was classed as a Category A listed structure .
2 . DESIGN 2.1 Background
A regular ferry service was instituted about the year 1130 and in 1164 it was granted a charter naming the crossing " Passagium Regina ".
Throughout the centuries , tunnel crossing and a chain bridge were under consideration . In 1890 a cantilever railway bridge was opened .
In the years following 1920 the idea of a road link was developed . Various locations were considered including the alignment via the Beamer Rock , where now the Queensferry Crossing is located . Investigations , studies and calculations were carried out and various schemes considered , including the addition of a second deck on the Forth Railway Bridge .
Shortly after the war , a scheme for a long span bridge over the River Severn was also considered , and due to its similarity with Forth Crossing some problems common for both bridges were considered together , particularly aerodynamic research including wind tunnel testing .
From 1947 necessary legal and financial issues were resolved and relevant contracts executed . The works of the preliminary contract commenced during the summer of 1958 .
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