One of the most recognisable structures on the Cam, Queens’ College bridge was originally built in 1749 by James Essex the Younger. Since then it has been rebuilt twice to the original design of William Etheridge, once in 1866 and again in 1905. In 1866 the bridge deck was changed from a stepped design to the current sloped deck. In 1905 a complete rebuild of the bridge was required due to weathering of the original oak structure.

William Etheridge’s design was based on work by James King on what has become known as tangent and radial trussing. Originally used to create the temporary formwork used in the construction of London Bridge, the arch describes an arc of a circle. The main members lie tangent to this circle and their arrangement is designed to ensure they are in compression only with very little bending moment. The connections between these main members transfer compressive stresses. The radial members are fixed normal to the circle of the arch and they support the top rail as well as making the bridge lattice into a more rigid structure. The bridge deck is then attached to the bottom of the radials near the intersection of two tangents.

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.

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.