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Civil Engineering heritage: Scotland - Lowlands and Borders
Date 2007
Event ID 606533
Category Descriptive Accounts
Type Publication Account
Permalink http://canmore.org.uk/event/606533
An old stone bridge over the Tay at Perth was swept away by a flood in 1210. It was rebuilt and either it or its
successor often damaged and repaired, being entirely rebuilt from 1599–1617. It is said to have had eight arches and to have been destroyed in 1621 when six arches collapsed in a flood, a disaster ascribed to the town’s ‘iniquity’. After this the river was crossed by ferries until Smeaton successfully achieved the present bridge from 1766–71.
The bridge has seven masonry arches over the river and two land arches to provide extra flood capacity. The spans increase towards the central arch which is 75 ft wide. The original road was 22 ft wide, but was widened in 1869, none too elegantly, to provide the present cantilevered footways by means of cast-iron brackets and parapets. The masonry of the arches and abutments is pink Perth sandstone. Over the piers the spandrel faces are decorated architecturally by rings of stone infilled with black whinstone suggestive of transverse cavities.
In fact, the internal structure of the bridge is hollow to reduce weight, but by means of longitudinal spandrel
walls mounted on the arches supporting the roadway – a technique subsequently adopted by most bridge engineers for large masonry spans. The cavities are bridged over internally by pointed arches, with iron ties placed laterally above them to counter any outward thrust, an early application of this technique.
The piers were founded, some within coffer dams, on timber piles with starlings (a protective timber surround
with masonry infill extending up from the foundation to just above low-water level). These measures were based on careful site investigation and trials by John Gwyn the resident engineer, who also determined the as-builtposition of the bridge and superintended most of its building by direct labour. The cost exceeded £20 000.
This 893 ft long bridge, then Scotland’s and Smeaton’s largest, now carries about five million vehicles per annum without weight restriction. On the north face of the west abutment is a record of the Tay flood levels from 1814 to the present day.
Traffic conditions were improved with the opening downstream in 1960 of Queen’s Bridge, the first long
span prestressed concrete structure in Scotland.
R Paxton and J Shipway
Reproduced from 'Civil Engineering heritage: Scotland - Lowlands and Borders' with kind permission of Thomas Telford Publishers.
