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Mathematical Bridge, Cambridge
River Cam, Queens' College, Cambridge, UK
associated engineer
William Etheridge
date  July 1749 - September 1750, rebuilt 1866, 1904-5
era  Georgian  |  category  Bridge  |  reference  TL445581
ICE reference number  HEW 469
A much admired footbridge across the River Cam, connecting the old and new parts of Queens' College in Cambridge. Constructed of timbers bolted together, it appears to be an arched bridge but is composed of straight segments. It was rebuilt most-recently in 1905 and remains in use.
Queens' College was founded 1448 by Margaret of Anjou, wife of King Henry VI. The first bridge on this spot was built in the 16th century, and gave direct access from President's Lodge (built c.1460) on the east side of the Cam to the fields west of the river. The timber bridge was rebuilt in 1699-1700.
The original of the present bridge was built in 1749-50, coinciding with the construction of a brick wall along the east river bank. William Etheridge (1709-1776) designed it he was foreman carpenter on Old Westminster Bridge and also designed Old Walton Bridge in Surrey, both completed in 1750. His design for the bridge at Queens' College is a single-span scaled-down version of the three-span Old Walton Bridge.
The Queens' bridge spans 12.2m between masonry pier-style abutments and has a timber deck. The arch is formed by setting long straight timbers at radial tangents to the soffit, ensuring that each member is in compression. The timbers continue into the parapets, where they are jointed to form a truss.
The Queen's College Magnum Journale records that on 6th October 1748, Etheridge was paid 21 for the design and a model of the bridge. The model remains in the college's possession.
The contractor was James Essex (1722-84), who was paid 160 for building the bridge. Other bills amounted to 151 12s 9d (151) for a mason, 114 16s 8d (115) for a bricklayer and 8 13s (8.65) for labour. When the bridge was completed, the workmen were given a celebratory supper costing 17s 9d (89p).
The oak superstructure of Etheridge's bridge has had to be refurbished twice, owing to decay. The first repairs took place in 1866 and cost 348 7s (348). The work included replacing the original stepped deck with a sloping timber decking.
In 1904-5, the entire timber structure was rebuilt in teak. Bolted connections replaced the original iron screws and oak pins.
The name Mathematical Bridge derives from its so-called 'geometrical construction'. A similar structure carrying Garret Hostel Lane over the river was dubbed a 'mathematical bridge', though it only existed 1769-1814. The name was also applied to the Queens' bridge, and it stuck.
The Mathematical Bridge is a rare survivor of 18th century tangent and radial trussing techniques. It became a Grade II listed structure in April 1950, despite only being a replica.
Contractor: James Essex
Contractor (1904-5): William Sindall
Research: ECPK
bibliography
http://list.english-heritage.org.uk
www.queens.cam.ac.uk
reference sources   CEH E&CBDCE1
Location

Mathematical Bridge, Cambridge