Building of the bridge
It is difficult for us to comprehend the scale and complexity of the construction of a new railway like the Great Western or Cornish Railway today. Among Brunel’s gifts was to understand that, if passengers were to fully appreciate the romance of the railway, its engineering had to be invisible. The trains should float over the landscape with such apparent ease that their passengers did not notice if they were climbing hills or fording water. To achieve this, Brunel and his team designed numerous viaducts, tunnels, embankments and sea defences. Arguably his greatest challenge – and achievement – was on the Cornish Railway where he designed the Royal Albert railway bridge to cross the River Tamar at its narrowest point of 1,100 feet at Saltash allowing sufficient height for sailing ships to pass underneath.
Brunel’s solution was a two-span bowstring suspension bridge with a single rail track. Each of two main spans was a wrought iron tubular arch with a profile in the form of a parabola. Sets of suspension chains hung on each side of the tube in a catenary curve with the tube’s rise equalling the dip of the chains. To create enough room for sailing ships to pass beneath the bridge, Brunel proposed a central pier and two spans each of 465 feet.
There were two principal difficulties. First, the creation of the pier in the middle of the river, which Brunel solved by designing a Great Cylinder to be floated into position and to act as a coffer dam. The second was the raising of the main spans. These were built on the Devon foreshore and floated into position. The Cornwall pier was erected first and jacked up three feet at a time to enable the brickwork on the landward pier and ironwork on the central pier to be erected beneath.
Brunel’s solution was a two-span bowstring suspension bridge with a single rail track. Each of two main spans was a wrought iron tubular arch with a profile in the form of a parabola. Sets of suspension chains hung on each side of the tube in a catenary curve with the tube’s rise equalling the dip of the chains. To create enough room for sailing ships to pass beneath the bridge, Brunel proposed a central pier and two spans each of 465 feet.
There were two principal difficulties. First, the creation of the pier in the middle of the river, which Brunel solved by designing a Great Cylinder to be floated into position and to act as a coffer dam. The second was the raising of the main spans. These were built on the Devon foreshore and floated into position. The Cornwall pier was erected first and jacked up three feet at a time to enable the brickwork on the landward pier and ironwork on the central pier to be erected beneath.