Read the text and improve your knowledge of foreign experiences in bridge building

Numerous bridges and one barrier span the River Thames in London. The London Bridge is the oldest in Great Britain and dates back to the time when the Romans invaded Britain and built the first bridge at the place of the wooden Celtic structure by AD 60. The Danes destroyed it in 805 but its replacement also crashed in 1091. Londoners rebuilt the bridge, but it burned down in 1136.

By 1209, a self-taught builder who proposed an arch bridge out of stone (fig. 9.1a) rebuilt the Old London Bridge once again. It was the first European masonry bridge. Its total length was of about 300 m with the spans of 20 m high above the water. The bridge consisted of 19 pointed arches, built on piers; a 20^th opening was a wooden drawbridge. The stone pier foundations were inside cofferdams with timber piles driven into the riverbed. The cutwaters, surrounded by loose stone fillings, protected the bridge piers. As a result, the bridge looked as if it were a dam because the reduced waterway was a quarter of its original width. It caused essential water level differences, and boat sailing was very dangerous and became one of the thrills of Londoners.

The Old London Bridge resulted into an overcrowded village with its chapel and passageways between the multistory houses, built above the shops lining both sides of the road between the fortified gates at either end of the bridge. The heads of traitors were stuck on the gate spikes until the 17^th century. From time to time, the bridge suffered from fires, though buildings and the bridge itself were made of stone. In 1282, five arches of the Old London Bridge collapsed under the pressure of winter ice.

a - the Old London Bridge
b – the Rennie’s London Bridge	c – the London Bridge today

Figure 9.1 History of the London Bridge

By 1762, Londoners removed the houses to widen the carriageway. Two central arches became one large arch, but it turned into a serious erosion problem for the riverbed. To protect the remaining piers they had constantly to pour gravel. In 1831a new granite structure with five semi elliptical stone arches was built several yards upstream by Sir John Rennie, but in 1971 its stone facing was dismantled and shipped stone-by-stone to the USA where Rennie’s bridge was re-erected in Arizona (fig. 9.1b). Prestressed concrete beams by Harold Knox King replaced Rennie’s stone arches in 1972. The modern London Bridge reaches 104 m in overall span length (fig. 9.1c).