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Severn Bridge gantries

30/08/2022

Eadon was pleased to see the successful installation of two high level gantries on the Severn Bridge in Bristol in July.

The Severn Bridge, which carries the M48 between England and Wales, is over 50 years old and is one of a small number of cable suspension bridges in the UK. The platforms will enable engineers to inspect the suspension cables as part of an ongoing maintenance and inspection program.

Back in 2006, significant levels of corrosion were found on the bridge’s suspension cables. To address the problem, a dehumidification system was installed along with an acoustic monitoring system to track further deterioration.

Similar problems with corrosion were found on the Forth Road Bridge in Scotland, and the Humber Bridge near Kingston upon Hull.

Every 5-10 years an inspection of the main cable is carried out on each bridge, involving removal and replacement of wires making up the main cable so that they can be sent away for testing. Since 2016, Eadon has designed the gantries to allow for this process to happen on the Severn, Forth Road and Humber Bridges. The gantries are designed in accordance with the Eurocodes and BS EN 1808:2015.

For the Severn Bridge gantries project, Eadon Consulting supplied detailed design drawings to Amey who were responsible for fabricating them. Having designed the gantries with sustainability in mind, we incorporated extension pieces into our gantry design which offers flexibility to reuse the same main sections of the platform that were used in the 2019 inspection of Humber Bridge main cable.

As this was such a critical piece of temporary equipment, we provided an Approval in Principle (AIP),

Severn Bridge gantry

Severn Bridge gantry

Design Certificate, Construction Compliance Certificate and arranged the completion of a Category 3 (CATIII) in accordance with CG300 Technical Approval of Highway Structures. Alongside the design of the gantries including detailed drawings, calculations and certificates, we also put together a Designers Risk Assessment, pre-installation Test Schedule, Lifting Schedule and Operation & Maintenance (O&M) Manual.

Eadon engineers attended site to witness testing of the gantries as well as carrying out pre and post installation inspections of the gantries on the main cable.

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