VICTORIA SUSPENSION/CANTILEVER BRIDGE 1836 Bath HEW811 ST741 650 N51o 23' 0.9" W2o 22' 23.5"
This was the first bridge built by James Dredge (1794-1863), a brewer in Bath who became a successful self-taught engineer. He developed and patented a very distinctive type of bridge which combined the principles of suspension and cantilever. Each half of the bridge works as a right angle triangle, the hypotenuse of which is formed by the wrought iron rods extending along the deck at oblique angles up to the top of the pylons. The bottom tips of these two triangles meet at the center of the bridge. If you cut a Dredge bridge in two at the center, both halves would still stand, whereas if you did that with a conventional suspension bridge, it would collapse.
The chain of rods that loop from the top of each tower down to touch the outer edges of the deck at the center are simply positioning the rods which are actually supporting the bridge rather than having the chain itself provide its support as in a conventional suspension bridge. "Each chain (in a Dredge bridge) increased from a single wrought iron rod at the center of the bridge (deck) to the requisite number over the … (towers) by progressively adding an extra rod at each link position. This resulted in a significant reduction in the quantity of iron and in the self-weight of the suspension system. … Connected to each joint in the main chains was a pair of inclined bars which gave support to the deck. These 'oblique' rods … were all set at different angles to the horizontal. … This introduced compression into the deck: a fact which Dredge argued in his favour, since the conventional suspension bridge decks of his era were greatly affected by wind-induced oscillatory motion". (Don McQuillan "Dredge Suspension Bridges in Northern Ireland", THE STRUCTUAL ENGINEER Vol. 70., NO7 April 1992)
Of the fifty or so bridges that Dredge subsequently built in the British Isles, only seven others survive today: the Doldowlod Bridge in Wales, the Stowell Park Bridge in Wiltshire, two in Scotland at Aberchalder and at Inverness and three in Northern Ireland. This first one was built as a toll bridge across the Avon River to connect Upper Bristol Road with Twerton. It was built in six months and survived a severe storm during its construction. It has a length of 150 feet and a width of 18 feet six inches with a total iron content of 21 tons.
To find this bridge, look for a very inconspicuous street called Victoria Bridge Road on the south side of Upper Bristol Road (the A4). You will catch a glimpse of the bridge between buildings as you pass.
