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Perth Bridge
River Tay, Perth, Perth and Kinross, Scotland, UK
Perth Bridge
associated engineer
John Smeaton
Allan Duncan Stewart
date  1766 - October 1771, 1869
era  Georgian  |  category  Bridge  |  reference  NO120238
ICE reference number  HEW 318
photo  © Carron K and licensed for reuse under this Creative Commons Licence
The present Perth Bridge carries West Bridge Street across the River Tay, and is at least the third structure on the spot. A masonry bridge of seven arches, it was Smeaton's second major bridge and its design incorporates the lessons he learned in building Coldstream Bridge. It is still used by road traffic.
In 1210, a flood swept away an old stone bridge over the River Tay at Perth, though it’s not clear if the bridge was the first one here. It was rebuilt and the structure, or its successor(s), suffered cycles of damage and repair. During 1599-1617, the bridge was entirely reconstructed by master mason John Mylne (d.1621). It is said to have had 11 arches but was 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.
Over 140 years later, Thomas Hay (1710-87, 9th Earl of Kinnoull) campaigned for a new bridge over the river. In 1765, an Act of Parliament was passed for its construction and John Smeaton (1724-1792), already famous for Eddystone Lighthouse (completed 1759), was appointed to carry out the design. His bridge, the present one, remains in daily use. At 272.2m long, it was then Scotland's longest.
Perth bridge has seven arches over the river plus two land arches that provide additional flood capacity. The easternmost arch is semicircular and the other eight are segmental. The spans increase towards the middle of the bridge, with central arches of 22.9m.
Construction began in 1766, commencing with a bridge pier near the east bank. All piers were under construction by 1768, and the arches were completed in 1771. Dressed pink Perth sandstone has been used for the the piers, arches and abutments is dressed pink Perth sandstone.
The piers, some of which were constructed within cofferdams, are founded on timber piles with starlings (a protective timber surround with masonry infill extending from the foundation to just above low water level).
Above the piers, the faces of the spandrels carry an architectural detail typical of Smeaton’s bridges — masonry circles, each with four keystones and moulded rims, with black rubble whinstone centres. Their appearance is suggestive of through voids, possibly infilled later.
To reduce its overall mass, and incidentally save money on materials, the bridge’s internal structure is hollow, with the roadway supported by parallel longitudinal spandrel walls mounted on the arches. The internal cavities are spanned by pointed arches, with lateral iron ties placed above them to counter any outward thrust.
Perth Bridge is the first to have been built using this structural technique and, says a commentator, if the hollow spandrels were "not the most daring of [Smeaton's] innovations in bridge construction, they were certainly the most successful". The technique was adopted subsequently for designing bridges with large masonry spans.
The construction methods were based upon careful site investigation and trials by Smeaton's trusted resident engineer John Gwyn (c.1733-89). Gwyn also determined the bridge's as-built position and superintended most of its construction by direct labour.
The cost was £26,631, half raised by government funds from forfeited Jacobite estates and half coming from private investors. Initially, a halfpenny toll was charged to cross the bridge, collected from a toll house (NO122239, completed 1772) at Bridgend. Tolls were levied until 1883.
In winter 1773-4, the bridge’s stability was tested by sheet ice followed in February 1774 by a rapid thaw. Ice became wedged under the arches, creating a natural dam. Perth was flooded but the bridge held firm. It has survived subsequent floods and the north face of its west abutment carries a record of the River Tay’s flood levels from 1814 onwards.
Originally the bridge’s roadway was 6.7m wide. In 1859, a horse-drawn tramway was laid over the deck. In 1869, the deck was widened by engineer Allan Duncan Stewart (1831-94) to provide extra capacity. The original stone parapets were removed and cantilevered footways constructed on either side, carried on cast iron brackets. Cast iron lamp standards and parapets were added at the same time. In 1905, the tramway was electrified, continuing in operation until 1929.
Traffic congestion over the bridge was alleviated in 1902, when Victoria Bridge (NO121234) opened to the south of Smeaton’s structure. Victoria Bridge was replaced in 1960 by Queen's Bridge, built on the same line. The Victorian steel truss was jacked up and used as a temporary support for the modern three-span bridge, which was the first long span prestressed concrete structure in Scotland, with a maximum span of 47.9m.
In May 1965, Smeaton’s 18th century Perth Bridge was Category A listed. It still carries around five million vehicles per year without vehicle weight restriction.
Resident engineer: John Gwyn
Contractor: direct labour
Lamp standards and parapets (1869): James Laidlaw, Glasgow
Research: ECPK
reference sources   CEH SLBBDCE1

Perth Bridge