The bridge is located at Queens' College in Cambridge and spans
the River Cam about 12 meters between stone abutments. For me this is a really beautiful structure, so simple and yet fascinating. Its unique mathematical
design forms an arch from straight members, what has become known as tangent
and radial trussing.
 |
| The photo with tangential members highlighted (Image by Cmglee) |
Simply put, the arch is formed by setting the long straight
timbers at tangent to the circle describing the underside arch
of the bridge. Other
timbers are positioned radially to hold the tangents together and make the
whole structure self-supporting and rigid. The connections between tangent and radial members are
bolted together to form a truss. The bridge deck is then attached to the bottom
of the radials. The highlighted timbers
(tangents) on the upper photo nicely demonstrate the arch formation.
 |
| Image by Bill Reid |
About the bridge name
Its official name is simply the Wooden Bridge, but is also known as the Queens'
bridge. Its builder James Essex the Younger designed twenty
years later a similar structure (to replace Garret Hostel Bridge), which
he called a mathematical bridge. After it
broke down the name has clung to the bridge at Queens' College.
The construction timeline
The Mathematical Bridge was built in 1749. According
some other written sources, the bridge was completed in 1750. The builder was James
Essex the Younger and designer was William Etheridge, an English civil engineer
and master carpenter who was previously working on several wooden bridges of
mathematical design (e.g. Old London Bridge or Westminster Bridge and Walton
Bridge). In 1748 Etheridge produced the design and model for the Queens’ bridge.
The bridge was rebuilt first time to the same design in
1866. Some modifications have also been undertaken. The
original stepped bridge deck was replaced with the current sloped timber deck.
In 1905 the bridge was completely
rebuilt. The entire timber structure of
oak has been replaced with teak and bolted connections replaced the original
iron screws and oak pins.
So, the bridge is
literally a replica.
 |
| The original Etheridge's model of a bridge in 1:16 scale |
The Queens' College
still possesses an original Etheridge’s model of 1748.
An inspiration for the bridge design
William Etheridge's design for the Mathematical Bridge was based on work by James King, master carpenter and a man with considerable
self-taught mechanical knowledge. King used this system of tangent and radial trussing
in his 1737 design for a wooden Westminster Bridge, which was not completed.
This is the earliest known example of this type of bridge structure.
The construction of a wooden bridge was abandoned, and
a few years later the construction of the stone Westminster Bridge has begun.
 |
| Arch construction support timbers - The Westminster Bridge centring |
James King used the same system of tangent and radial
trussing for the timber supporting structure (centring) during the construction of stone arches. This design
permitted shipping to pass under the arches while they were being erected. After
King’s death in 1744, Etheridge took over the work at Westminster Bridge
construction, as well as the whole of King’s system of trussing.
Other bridges of the same design
The Old Walton
Bridge across the River Thames was also
designed by William Etheridge and was
completed in 1750. At that time, the bridge was described as the most beautiful wooden arch bridge
in the world. The Walton Bridge’s main
span was 40 meters, with two side arches of 13 meters. Unfortunately, it lasted
only until 1783 when was
dismantled due to the stone replacement.
The
bridge was an inspiration for the Italian painter
Canaletto. The beautiful white wooden structure has been immortalized in Canaletto's two paintings.
 |
| A detail of the painting by Canaletto - A View of Walton Bridge (1754) |
As
mentioned above, there was a bridge of similar design on the River Cam, which
broke down in 1812. It was frequently called the 'Mathematical Bridge'. The
bridge at Queens' College owes its popular name to this bridge.
In
1924. was built a smaller
version of the Queens’ bridge, at Iffley Lock in Oxford. The Iffley
Mathematical Bridge was a
tribute to the bridge over the Cam River.
 |
| Mathematical Bridge at Iffley Lock, Oxford (Image by Matt Fascione) |
Despite the fact that
present Mathematical Bridge is a replica of 18th century original, it became
a Grade
II listed building for its special architectural and historic
interest.
 |
| The President's Lodge and the Mathematical Bridge, Queens' College Cambridge |
Sources:
3. Dulwich Picture Gallery, London
4. Ruddock Ted (1979), Arch Bridges and their Builders 1735-1835
No comments:
Post a Comment