Contractor McAlpine-Monberg Thorsen joint venture is due to start pile-driving operations in the river bed this week.
Architect Foster and Partners, engineer Ove Arup & Partners and sculptor Sir Anthony Caro have revised the design of the south end of the £15.9m footbridge. Now, pedestrians alighting at Bankside will exit the 370 m long, 4 m wide bridge through what its designers call the "eye of the needle".
The new design for the south end replaces a 30 m diameter, ramped, circular sculpture by Sir Anthony that featured in the 1996 competition-winning second-stage design.
Why the design changed
In the latest design, cables staying the bridge at the south end have been raised from the deck in two wings, and raked back to land on the bank underneath the deck.
The design change was initiated by Ove Arup to increase the height of the bridge deck at the south end after conducting a ship impact study in June 1998.
The surface material for the deck of the bridge has also been changed from teak to aluminium, because of difficulty in finding a renewable source of the right quality and quantity of teak.
The cost of the bridge has risen to £15.9m from £10m since the Corporation of London gave planning permission for the north end last June.
Malcolm Reading, project director for client the Millennium Bridge Trust, says the additional cost relates to the trust's planning obligation to the Corporation of London to provide lift access at the north end of the bridge.
It also enabled funding for archaeological works on the site and the installation of double glazing at the City of London School so its pupils were not disturbed by noise during construction.
The increased cost also covers new street furniture and stainless steel sculptural markers by Sir Anthony at the north end – one of which features the logo of one of the funders, HSBC – and relandscaping of the bridge approach at the south end.
The footbridge is being funded with £7.1m from the Millennium Commission, £3.5m from the Corporation of London, £1.8m from the Cross River Partnership and £3m from HSBC. Lord Sainsbury of Turville, Hugh and Catherine Stevenson and Southwark council have also contributed funds. English Partnerships has funded the removal of a defunct jetty from outside the Tate Gallery at Bankside.
Foster and Ove Arup, with consultant Lerch Bates, have custom designed an open, glass elevating platform called an "inclinator" to provide 24-hour disabled access to the bridge deck at the north end, where it lands at the top of a flight of steps.
The sides of the aluminium bridge will be lit at night by 8 m long polycarbonate light pipes containing cold cathodes designed by Claude Engle. Mirrors at one end of the translucent glass tubes reflect the light to create a continuous light source.
The cables that support the Millennium Bridge are held by clamps 4 m outside the bridge deck, rather than from above, as in a traditional suspension bridge. This design has the effect of reducing the vibrations caused by the wind.
Chris Wise, director of engineer Ove Arup, said pedestrians crossing the bridge will be able to feel the tension in the cables. "It will be more like floating than walking," he said.
A double row of wind deflectors on chest-level stainless steel handrails reduces wind speed, sheltering pedestrians on the deck. Wise said the wind deflectors resembled the aerofoil at the back of an Formula 1 racing car. Wise and project engineer Roger Ridsdill Smith wind-tested this technology during six visits to a wind tunnel in Toronto, Canada.
Digital cameras have been set up at both ends of the bridge that will transmit images of the bridge construction to a web site run by the Financial Times, organisers of the 1996 design competition, at www.FT.com. The bridge is due to be opened by the Queen on 19 April 2000.