Richard, who initially studied Chemical Engineering, but now with his own company, had a full house to hear his talk about the bridges built on the site of the present London Bridge, of which there have been at least 4, and which had fascinated him both for their Engineering and social history.
The Romans built the first ones in timber, as part of their roads infrastructure, choosing a spot that was fordable at low tide and traversable at high tide by ferry. The North bank was more solid and led to higher ground – todays Cornhill, where a settlement sprung up – and Londinium was founded. Today, the bridge connects The City of London with Southwark.
King John built the next significant timber bridge, 26 feet wide, 800 feet long, opened in 1209, which lasted over 600 years. The Engineer was a clergyman Peter de Colechurch and it remained the only bridge over the Thames until 1729 when Putney Bridge was built.
19 spans, with buildings crammed on it until 1760. Waterwheels, piers which were so close that the water rushed through with a difference in level of 5 feet, it took an hour to cross the Bridge because of the density of people and traffic which was eventually instructed to ‘keep left’. Severed heads, including those of Oliver Cromwell, Thomas More and William Wallace, were also displayed up to the 1700s.
Construction and maintenance of the Bridge was financed by tolls, and in 1282 the Bridge House Estates was formed to administer the fund, to continue with the maintenance. This Trust still exists and has assets of over £500m, owning property in London, bought with excess tolls in the past. The trust has contributed to the construction of Tower Bridge, Blackfriars Bridge, Southwark Bridge, Millenium Bridge and maintains them all at no cost to Londoners, as well as giving excess to charity.
In 1831 the next Bridge, in stone, designed by John Rennie, replaced the ailing timber one, when a history of fires, settlement, ice, and overcrowding led to its demise.
The much bigger new one lasted until 1973, when the stone shell was sold to McCullough Oil Co., taken to Arizona, and reconstructed to look like the old bridge.
The present structure, built at no cost to London, funded by the Bridge House Estates, is a series of prestressed postensioned concrete box girders with stone cladding and built around the old one without interrupting traffic. That’s Civil Engineers for you!
Lots of facts and figures, expertly presented, had us absorbed for a most entertaining and interesting morning.