London Bridge

Colechurch’s London Bridge

Colechurch’s bridge took 30 years to build and stood for a further 625 years. It had 19 piers, built on foundations made of rubble, which were held in with several rows of closely-spaced pilings made of elm wood. Pilings are heavy posts put into a riverbed to support the foundations of a bridge.

Having so many piers created narrower channels in the river, making the water flow through faster. This was damaging to the bridge, as the strong current had a scouring action against the bridge’s foundations, which increased the rate of erosion.

The seventh span from the south end was a timber drawbridge, which opened up to let sailing ships through. A span is the distance between two supports for a bridge.

Many shops and houses were built along the rest of the bridge.

When Westminster Bridge was built, it posed a threat to the toll revenue of London Bridge. It was therefore decided to improve London Bridge by removing all the houses and one of the piers, to make the road over the bridge wider, as well as making space for river traffic.

As maintenance costs of the bridge continued to rise, in 1800, a select committee of the House of Commons recommended rebuilding the bridge.

Sir John Rennie’s London Bridge

John Rennie designed the new bridge, but died before it was built, so it was left to his sons, Sir John and George, to carry out his plans.

Work began on the bridge in 1824, and the first stone was laid on 15 June 1825. The bridge was officially opened on 1 August 1831 by King William IV.

It had much fewer arches than before, which allowed the Thames to flow through at a slower rate. The bridge was 67ft 6in wide and made out of granite. Its piers were supported by nearly 2,000 timber pilings.

Rennie’s bridge cost £1.4m (£154m in 2018).

Today’s London Bridge

Increased pedestrian and vehicular traffic in 1964 meant that a wider bridge was needed.

However, engineers Mott, Hay & Anderson found that a wider bridge would need stronger foundations. This led to a new, three-span, concrete bridge being created in its place, and this is the bridge we see today.

The width of today’s bridge is 107ft. It has a centre span measuring 340ft, and two 260ft side spans.

With only three spans, London Bridge also now has even fewer piers, which created improved, wider navigation channels for river traffic.

It has two piers in the tideway, compared to four in Rennie’s bridge. The headroom under the bridge was also increased by 2ft 3in.

Difference the bridge has made

As the first bridge, and first road bridge, in London, the historic significance of London Bridge is clear.

It provided the first-ever permanent crossing of the River Thames for early people, horse and wheeled traffic, and now for vehicles, too. Before the bridge, people had to rely on ferries to cross the river.

It was such a well-used bridge that it led to Southwark Bridge being built to try to relieve the congestion.

It connects major road routes north of the river to those to the south.

In engineering terms, it demonstrates the progress in materials used in bridge building – from the early timber to the now much stronger and longer-lasting concrete and steel.

How the work was done

The superstructure – the part of the bridge that sits on the foundations and carries the traffic - of the current bridge was designed as four, pre-cast box beams (like a hollow box).

There was a strict requirement for the bridge to remain open as much as possible during its rebuilding.

The traffic congestion and limited working space at the bridge meant that the precast box parts were brought up the river by barge from the casting yard in Surrey Commercial Dock.

A temporary gantry (a bridge-like overhead structure with a platform to support equipment such as a crane), built across the river on column supports, was used to put the precast box units in place.

The gantry was able to carry one box of the new bridge at a time and move it sideways into position. The box units were then connected with joints made of concrete.