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Kessock Bridge Inspection and Maintenance Gantry Cat III

Eadon Consulting Ltd were employed to carry out an independent check of the new underdeck access inspection gantry for the Kessock Bridge. The gantry is used for access for inspection and minor maintenance purposes, running on rails under the bridge deck. Eadon were able to utilise their significant experience in the access gantry field to work with the designer to ensure the gantry delivered on client requirements, conformed to the relevant design codes and most of all is reliable and safe for end user.

Key facts

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Location

Kessock Bridge, Inverness

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Client

BEAR Scotland Ltd acting on behalf of Transport Scotland

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In Partnership with

C Spencers

The Kessock Bridge is a cable-stayed bridge which carries the A9 trunk road near Inverness. At just over a kilometre in length, the 240 metres main span of the bridge crosses the Beauly Firth connecting the village of North Kessock and the city of Inverness.

The resulting profile of the bridge is relatively complicated resulting in a gantry which must be able to correct for both roll and pitch as the gantry traverses the bridge. Further to this the spacing between the rails upon which the gantry runs varies along the length of the bridge requiring actuation of the bogie units to vary the transverse wheel centres.

The gantry itself comprises an upper ‘bridge’ structure which spans between the rails with a lower ‘cradle’ section. The cradle features two bespoke elevated working platforms to allow access to the bridge deck soffit and girder edge faces and can translate from side to side, ensuring the EWPs can access all the required features.

These tough requirements resulted in a gantry with multiple interlinked hydraulic and control systems and some challenging structural requirements.

The independent check provided by Eadon conformed with the requirements of BD 2/12 Technical Approval of Highway Structures and was a Category 3 check. Checking work included the production of hand calculations, STAAD Pro beam element FE models to assess the structure as a whole and fully detailed ANSYS FE Models to assess local details where necessary. Eadon’s wide ranging experience of structural, mechanical, electrical and hydraulic systems meant they were able to deal with all aspects of the complicated design and ensure the checking work was complete in time for the installation of the gantry on the bridge.