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Civil Engineering heritage: Scotland - Highlands and Islands
Date 2007
Event ID 962613
Category Descriptive Accounts
Type Publication Account
Permalink http://canmore.org.uk/event/962613
Conon Bridge (Railway)
(Institute Civil Engineers Historic Engineering Works no. HEW 2543)
A substantial single-track skew viaduct on the former Highland Railway at Conon Bridge, built in 1862. The structure, which is still operational, is of five segmental arches, each of 73 ft span on a skew of 458 to the river. Each arch is composed of four ribs 334 ft wide, 4 ft deep at the springing and 3 ft deep at the crown. Unlike a common skew arch these ribs spring from haunches perpendicular to their spans and not their pier lines.
The keystones at the centre of each arch are bonded to the adjacent arch, as are the arch-rings at the haunches. Iron cramps were also inserted occasionally in the arch-ring joints to connect the ribs. The height of the deck is 45 ft from the bed of the river, which is rock, and made an excellent foundation. When the centring supporting the archstones until the keystone was placed was removed, it is recorded that there was no settlement of the ribs.
The designer and builder of the bridge was Joseph Mitchell, engineer to the Highland Railway. He at first favoured an iron-girder bridge at this site, but chose a masonry arch bridge on the grounds of durability.
R Paxton and J Shipway, 2007.
Reproduced from 'Civil Engineering heritage: Scotland - Highlands and Islands' with kind permission from Thomas Telford Publishers.
