Union Chain Bridge

Ex-British Navy Captain Samuel Brown recognized the value of malleable cast iron for use in suspension bridges, and his Union Chain Bridge is the oldest of its type known to be still standing.

The Union Chain Bridge is the oldest known suspension-type bridge able to transport vehicles and known to be standing today. Completed in 1820, it has a 437 foot span between pylon tops and crosses the River Tweed, connecting England with Scotland 5 miles upstream from Berwick-upon-Tweed. It was designed and constructed by Captain Samuel Brown, an industrialist and former officer in the British Royal Navy with ironwork made by the firm he co-founded — Brown, Lenox & Co. in Newbridge, South Wales. Its original purpose was the transportation of lime and agricultural products by horse-drawn wagon. 

Samuel Brown’s main business was the forging of wrought iron anchor chains in his London factory situated at what is now the Isle of Dogs on the River Thames. In 1813 the famous Thomas Telford and ‘Sam’ Brown had independently designed a proposed suspension bridge with a span of 1,000 feet over the River Mersey near Liverpool, designs which were considered too ambitious for the time. In 1819 Telford went on to design and build the Menai Straits Bridge and Sam Brown the Union Chain Bridge. John Rennie, one of the most highly respected civil engineers of the time advised on Brown’s design except for the ironwork. 

Brown was quick to realize the value of malleable cast iron, originally developed by Henry Cort in 1783–1784. Recent improvements had allowed the material to be wrought and rolled into shapes with high tensile properties. In 1817, Brown obtained a patent for suspension bridge design employing the bar-link principle. He made the links for the Union Chain Bridge of round section with eyes forged into each end and connected to adjacent links by means of pins and shackles and to the suspension rods by means of a cast iron saddle over the link joints. There are twelve chains, each made up of links 15 feet long and 2 inches in diameter. They are arranged in pairs placed one above the other, three on each side of the bridge. The joints in each pair are staggered 5 feet from the adjacent pair so that the suspender rods are spaced at 5 feet. The deck system is made of timber.

Union Chain Bridge has had several major restoration efforts since built, the latest in 2021–2022 which involved complete dismantlement, refurbishment and partial replacement of the deck and suspension system components and repointing of the masonry pylons. The earlier chain ground anchors have been superseded.

Resources

Samuel Brown and Union Chain Bridge, by Gordon Miller and Stephen K. Jones, 2017