Opened on March 5, 1850, the Britannia Bridge was the second bridge across the Menai Straits, this time connecting the Isle of Anglesey to mainland Wales by rail – twenty four years earlier, Thomas Telford’s Menai Bridge had brought a road connection between the two, and now a rail link between the port of Holyhead, on the west of the island, and London was deemed necessary.
Robert Stephenson was chief engineer on the project and along with his engineering consultants, William Fairbairn and Eaton Hodgkinson, decided to build it to a tubular design supported by masonry piers, in order for it to be sufficiently stiff to support the heavy load of the trains passing across it. The two main spans of rectangular iron tubing were 460 feet (140 meters) long, and each weighed 1,500 long tons. Two additional spans of 230 feet (70 meters) completed what was essentially a 1,511 feet (461 meter) long girder. Until that time, the longest wrought iron span had been a mere 31 feet 6 inches (9.6 m). Hodgkinson believed that the tubes would also need the support of suspension chains, but Fairbairn calculated that they would prove unnecessary. Local limestone was used for the piers and the tubes were constructed on the banks and then floated on barges and lifted into position by hydraulic pumps.
Unfortunately, the bridge that we see today is not the same Britannia bridge that opened that day: in 1970, some local teenagers using an open flame to look for bats inside the tubes of the bridge, dropped the torch and set alight to the inside of the tubes. The fire was so ferocious and burned for so long, due to the height and construction of the bridge, which limited access for the fire brigades from both sides, that it worked its way along the entire length from the mainland to the Anglesey side before burning out, leaving the iron tubes structurally unsound. Thus the Britannia bridge was rebuilt, but with a slightly altered design and in two stages: around the restored stonework piers, steel arches were built under the long spans and the bridge reopened to rail traffic in January of 1972; above the rail deck, an upper level carrying a two lane road (the A55) was opened to cars in 1980. In the past decade, increased traffic has caused much discussion over the need for a either a third Menai crossing, or a conversion of the Britannia bridge.
To learn about other interesting civil engineering projects, visit the "People and Projects" section of the ASCE website.