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Supplied: Bearing Replacement
and Diagonal Bracing Tensioning

Royal Albert Bridge

The royal Albert bridge near Plymouth carries the Great Western railway over the river Tamar into the Cornwall peninsula. It remains the only rail link with the South West Designed by Isambard Kingdom Brunel, the bridge was opened in 1859 and as an important part of the UKs industrial heritage it is protected by a Grade 1 listing. This means that changes cannot be made without permission of the regulatory authorities. Brunels Bowstring Suspension Bridge design has a
distinctive double arch arrangement for the two center spans which resulted from complex engineering problems, not least of which was the Admiralty requirement of 100ft clearance above high water level to allow the tall masted ships of the British Navy to pass below. Bedrock foundations for the centre pier are 80ft below the mean sea level so that the overall height from bed to deck is a phenomenal 180ft!
As part of a maintenance contract it was required to replace some of the bearings on the western approach viaduct and to re-tension some of the wrought iron cross braces on the main spans. Bearing specialist Ekspan was appointed to carry out the work.

Job Brief

Background Information

Project Team

Clients: Railtrack
Client Consulting Engineer: Hyder Consulting
Main Contractor: Dean & Dyball
Sub Contractor: Ekspan Ltd
Start Date: January 2000
Completion Date: May 2000

 

After research and review by the project team and due to the complex characteristics of the structure, it was agreed to replace the old timber bearings with new oak bearings to Brunels original design. The introduction of modern bearings and new articulation would have been inappropriate. Brunels system worked well and had endured! As the main rail link into Cornwall, access for work was restricted to weekly five hour periods each Saturday night, during which time, work had to be completed ready for rail traffic to meet rail schedules. Ekspan designed new jacking points and this feature was later discovered in the original Brunel design. By the same engineering logic we had re invented a system that had been discarded in the repair work of 1927. The speed of bearing replacement then enabled our engineers to use the three-hour possession periods during weekdays and greatly accelerate the programme. Brunels attention to detail was evident once again. He understood and provided both permanent and temporary works in his original design.

 

To re-tension the cross bracings and provide new data, Ekspan designed a hydraulic tensioning system which allowed
the diagonals to be restrained and cut. Uniquely, the existing tension was then measured and the cross bracings retensioned
to the new specification. The live load information gathered during works added new facets to our understanding of the dynamics of the structure.


  

Looking back towards Saltash under Brunels Royal Albert Bridge

 

Ekspan's Solution

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