Day 187/365 of Steel – Robert Stephenson

Robert Stephenson (16 October 1803 – 12 October 1859) was an English civil engineer and designer of locomotives, tunnels and bridges. The only son of George Stephenson, the “Father of Railways” ,he built on the achievements of his father. Robert has been called the greatest engineer of the 19th century. His list of achievements is far too long for this post, I prefer to reflect on one of his inventions: tubular bridges.

Conwy Suspension Bridge and Railway Bridge
Fig 1: Conwy Suspension Bridge and Railway Bridge
Photo: © Jeff Buck

A tubular bridge is a bridge built as a rigid box girder section within which the traffic is carried. Famous examples include the original Britannia Bridge and the Conwy railway bridge, designed and tested by William Fairbairn and built by Robert Stephenson between 1846 and 1850.

Conwy Railway Bridge
Fig 2: Conwy Railway Bridge
Photo: © Jeff Buck

To support a train, the big tubes would need reinforcement by rows of small tubes, along the top and bottom. This makes the bridge at Conwy the ancestor of countless “box girder” bridges worldwide. The tubes were constructed on the shore, floated into position on pontoons and jacked up to the correct height.

Conway Tubular Bridge
Fig 3: Conway Tubular Bridge
Photo: Joost J. Bakker 

The Conwy railway bridge is a wrought iron tubular bridge. Being the first tubular bridge to be built, the design needed much testing on prototypes to confirm that it would be capable of carrying heavy locomotives, the testing being performed by Fairbairn.

Conwy Suspension Bridge from the castle
Fig 4: Conwy Suspension Bridge from the castle
Photo: Bencherlite

The successful result enabled the much larger Britannia bridge to be built. The current Conwy bridge has been reinforced by extra columns under the bridge into the river, but is otherwise virtually unchanged since it was built.

Conway Bridge. Floating of second tube, September, 1848
Fig 5: Conway Bridge. Floating of second tube, September, 1848
source: National Library of Wales

Since the destruction by fire of Britannia Bridge in 1970, Conwy railway bridge remains the only surviving example of this means of construction undertaken by Stephenson. I will dedicate a separate post on the Brittania Bridge later on.

About the Author:

Bruno Dursin – Managing Director at Believe in Steel. Bruno has more than 30 years of experience in promoting steel & steel solutions. His clients benefit from his extensive network within the building industry.

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