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Humber Bridge
Kingston upon Hull, , Humberside, UK
Humber Bridge
associated engineer
Freeman Fox & Partners
date  March 1973 - 24th June 1981
era  Modern  |  category  Bridge  |  reference  TA022250
ICE reference number  HEW 204
photo  PHEW
A dramatic suspension road bridge across the Humber Estuary, from Hessle to Barton. When built it had the longest span in the world at 1.41km, and it still has the longest suspended central span in Britain. Around 6.5 million motorists now use the bridge each year.
Sir Ralph Freeman (1911-98) planned a multi-span road bridge on this spot in 1927, and in 1935 he suggested a suspension bridge. In 1955, Freeman Fox & Partners' senior partner Sir Gilbert Roberts (1899-1978) proposed a suspension bridge with a 1.4km central span. The idea met with approval and the Humber Bridge Act was passed in 1959.
The Humber Bridge Board was set up but lacked the funds to begin construction. It was not until 1971 that the government decided to lend the board 75 percent of the cost. Freeman Fox & Partners designed the bridge, with partner Bernard Wex (1922-90) in charge. The south approach road was constructed in July 1972 and work began on the bridge substructure in March 1973.
The bridge's spans are suspended from hollow reinforced concrete towers 155.5m high. This was the first major suspension bridge to use concrete in this way. The north span is 280m long and the south span 530m long. The central span has a clearance of 30m above high water.
The north (Hessle) tower and shore anchorage are founded in firm chalk. The reinforced concrete tower foundation is 44m long, 16m wide and 11.5m deep, sunk 8m into the chalk. The south anchorage is a block of mass concrete weighing 190,000 tonnes. To reduce the heat of hydration in the concrete, up to 60 percent of the Portland cement was replaced with ground granulated blast furnace slag.
The south (Barton) anchorage and tower are founded in fissured clay. The concrete anchorage is larger than that on the north side, weighing 300,000 tonnes and dug 35m into the clay. It sits on a cellular raft designed to limit clay heave and was constructed within a network of reinforced concrete diaphragm walls. The south tower is 500m from the shore and is supported on two 24m diameter hollow reinforced concrete caissons, sunk 8m into the clay.
Both towers were constructed using slipforming, and they were completed by July 1976. Cable spinning took place between September 1977 and July 1979.
The steel cables are 700mm in diameter and weigh 5,500 tonnes each. Each consists of 37 strands and each strand is made up of 404 lengths of 5mm high tensile galvanised steel wire. The cable on the shorter northern span contains 800 additional wires, in four extra strands. Each cable is designed to withstand a load of 19,400 tonnes.
Once the cables were in place, the deck could be hung from them, and this was done by working from the centre of the bridge towards the towers. The deck was erected between October 1979 and July 1980.
The road deck is constructed of welded steel box sections, topped by an asphalt wearing course. It carries a dual two-lane carriageway and two combined footpath/cycle tracks. The deck structure is 28.5m wide and 4.5m deep. It is suspended from the main cables by 242 inclined steel hangers.
Wind loading is always a factor in the design of large bridges. The Humber Bridge is designed for wind speeds of 47m per second (169kph or 105mph) on the deck and up to 67m per second (241kph or 150mph) at the top of the towers. Wind tunnel testing at the National Maritime Institute, Teddington, determined the structure's aerodynamics.
The first traffic crossed the bridge on 24th June 1981, with the official opening by Queen Elizabeth II on 17th July. Tolls have been levied in both directions from day one.
All the 36mm diameter steel bolts that secure the deck hanger clamps around the cables were replaced in 1995-8 as part of routine bridge maintenance. There are 2,904 bolts in all.
In recent years, the Humber Bridge’s suspension cables have suffered significant corrosion — a problem that also afflicts the Severn Bridge in Wales and the Forth Road Bridge in Scotland. The red lead paste and galvanised iron wrapping used during construction has not been sufficient to keep water out of the cables.
After inspections in 2009, widespread cable corrosion was discovered where water collects at the low points of the catenary, though there were few broken wires. Water had found a way into the voids between wires (which can be up to 20 percent of the cross-sectional area of the cables), something not anticipated at design stage.
A cable dehumidification programme began in December 2009 and was completed in January 2011 at a cost of £14m. Pressurised dry air (relative humidity 10 percent) was blown through the cables, absorbing moisture as it passed. To prevent water becoming trapped, work started at the top of each cable and progressed downwards. The work reduced the relative humidity of the air inside the cables from 90 percent to 40 percent.
At the same time, the cables were monitored acoustically in a £1m project. The tiny sounds of occasional wires snapping were recorded, helping to indicate the extent of corrosion.
Architect: R.E.M. Slater
Administration building design: Parker & Rosner
Landscape design: Prof Arnold E. Weddle
Contractor (towers and substructure): John Howard & Co
Steelwork: British Bridge Builders Ltd
Bolt replacement (1995-8): High Rise Services
Dehumidification engineering (2009-11): AECOM
Dehumidification contractor (2009-11): C. Spencer
Acoustic monitoring (2009-11): Physical Acoustics
Research: ECPK
"Engineering the Humber Bridge" by the Humber Bridge Board, 1981
reference sources   CEH E&C

Humber Bridge