Hungerford Bridge

The Hungerford Bridge crosses the River Thames in London, and lies between Waterloo Bridge and Westminster Bridge. It is a steel truss railway bridge — sometimes known as the Charing Cross Bridge — flanked by two cable-stayed pedestrian bridges that share the railway bridge's foundation piers, and which are properly named the Golden Jubilee Bridges.

The south end of the bridge is near Waterloo Station, County Hall, the Royal Festival Hall, and the London Eye. The north end is near Embankment Station, Charing Cross Station, Embankment Pier and the Victoria Embankment. The bridges have step and lift access.

History
Hungerford Bridge was designed by Isambard Kingdom Brunel and opened in 1845 as a suspension footbridge. In 1859 it was bought by the railway company, to extend the South Eastern Railway into the newly opened Charing Cross railway station. The railway company replaced the suspension bridge with a structure designed by Sir John Hawkshaw, comprising nine spans made of wrought iron lattice girders, which opened in 1864. The chains from the old bridge were re-used in Bristol's Clifton Suspension Bridge. The original brick pile buttresses of Brunel's footbridge are still in use, though the one on the Charing Cross side is now much closer to the river bank than it was originally, due to the building of the Victoria Embankment, completed in 1870. The buttress on the South Bank side still has the entrances and steps from the original steamer pier Brunel built on to the footbridge.

Walkways were added on each side, with the upstream one later being removed when the railway was widened. In 1951 another walkway was temporarily added when an Army Bailey bridge was constructed for the Festival of Britain. In 1980 a temporary walkway was erected on the upstream side whilst the downstream railway bridge and walkway were refurbished. It is only one of three bridges in London to combine pedestrian and rail use; the others being the Fulham Railway Bridge and Barnes Railway Bridge.

The footbridge gained a reputation for being narrow, dilapidated and dangerous. In the mid-1990s a decision was made to replace the footbridge with new structures on either side of the existing railway bridge, and a competition was held in 1996 for a new design. The concept design was won by architects Lifschutz Davidson and engineers WSP Group. Detailed design of the two bridges was carried out by consulting engineers Gifford (company). The two new 4-metre wide footbridges were completed in 2002. They were named the Golden Jubilee Bridges, in honour of the fiftieth anniversary of Queen Elizabeth II's accession, although in practice they are still referred to as the "Hungerford Footbridges".

Further justification for new footbridge structures both upstream and downstream of the railway bridge was that the railway bridge's brittle wrought iron support pillars were vulnerable to impact from riverboats. Especially following the Marchioness disaster it was felt these should be clad in concrete at water level but the bridge's owners, Railtrack, could not afford the work. The Golden Jubilee Bridges achieved this protection at no cost to Railtrack.

The new footbridges
The new footbridges posed an engineering challenge. Their construction was complicated by the need to keep the railway bridge operating without interruptions. There was also the problem of the Bakerloo Line tunnels passing only a few feet under the river bed as well as the potential danger of unexploded bombs in the Thames mud. Despite extensive surveys of the riverbed, London Underground was unwilling to accept these risks and preliminary works were stopped in 2000. The design was modified so that the support structure on the north side, which would have been within 15 metres of the tube lines, was moved out of the river bed and onto Victoria Embankment. Excavation near the tube lines was carried out when the tube was closed and foundations were hand-dug for additional security. It is estimated that the footbridges took one million hours of labour to create.

The 300 m-long decks were raised using an innovative method called incremental launching, in which each 50 m-long section was pulled across the river using a 250 m-long steel truss weighing 300 tonnes. This process was repeated five times until each deck spanned the river, supported by six temporary piers made of steel and concrete. The seven 25-tonne pylons were then raised over the subsequent two weeks. Once the pylons had been installed, the decks were jacked up to enable their connection with the cable stays suspended from the pylons. The concrete deck was then lowered into its final position and the temporary piers and supports were dismantled.

The design of the bridges is complex. Each of the two decks is supported by inclined outward-leaning pylons. The decks are suspended from fans of slender steel rods called deck stays — there are 180 on each deck, made up of over 4 km of cable — and are held in position by other rods called back stays. Because the pylons lean, the back stays are under tension. The deck is secured in place by steel collars fitted around (although not supported by) the pillars of the railway bridge; the collars are themselves attached to the bridge's foundations by tie-down rods. The entire structure is thus held in place by exploiting the tensions between the pylons and the various stay rods and struts.

The new bridges won the Specialist category in the Royal Fine Art Commission Building of the Year Award in 2003. It gained a Structural Achievement Award commendation in the 2004 Institution of Structural Engineers awards, and has won awards from the Civic Trust and for its lighting design.