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Civil Engineering heritage: Scotland - Highlands and Islands

Date 2007

Event ID 930361

Category Descriptive Accounts

Type Publication Account


Allt-na-Slanach Viaduct, Moy

(Institute Civil Engineers Historic Engineering Works no. HEW 0601/02)

This is a timber trestle viaduct erected to carry the single line from Inverness to Perth over the Allt-na-Slanach burn. It was completed in 1897 and provision was made for a double line of track. The designer was Murdoch Paterson and the contractor, John Ross & Son.

Timber was chosen to limit the weight of the structure on the marshy ground. The viaduct has five spans of 23 ft, the centre one spanning the burn. The structural form is simply-supported timber beams supported on four vertical posts across the width of the bridge. The spans of the beams

are reduced to about 11 ft by angled supporting struts to the posts at each end which are themselves braced by similar struts and longitudinal members at a lower level. This arrangement together with transverse raking struts at the sides provides essential stiffness.

In 2001 fungal decay was found in the timber and in the following year a £2.6 million programme of work was undertaken to protect the timber and strengthen the bridge. Specially designed concrete members were introduced to form a new structure on separate foundations such that no railway loading is now carried by the original structure, although it still supports the side gangways. It is the last timber viaduct existing on a main line Scottish railway, a rare and substantial survivor of a once fairly common bridge type.

R Paxton and J Shipway, 2007.

Reproduced from 'Civil Engineering heritage: Scotland - Highlands and Islands' with kind permission from Thomas Telford Publishers.

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