Page B2.2 . 14 February 2001                     
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    Gateshead Millennium Bridge

    (continued)

    The regeneration program includes a new art gallery, a concert hall, and the spectacular £22 million Gateshead Millennium Bridge. Linking the new developments on both sides of the river, it will be the first opening bridge to be built across the River Tyne for more than 100 years.

    The regeneration program is part of a joint bid by Newcastle and Gateshead to become the European Capital of Culture in 2008.

    Seven Bridges Suite

    The new structure is the latest addition to the Tyne's famous bridge collection that covers a half-mile stretch of the river. In the 1960s, when there were only five, the world-famous group, The Nice, named a symphony—The Five Bridges Suite—after them.

    One of these, the Tyne Bridge, which opened in 1928, was based on the same design as the Sydney Harbor Bridge. It was the first in the world to span a river with no supports in the water.

    Another, the Swing Bridge, designed by Sir William Armstrong, was the largest opening bridge of its kind when it was completed in 1876.

    A third, the High Level, was designed by local pioneering engineer Robert Stephenson. This was the first bridge to use the revolutionary twin deck design with trains on top and a road underneath.

    Design Innovations

    So it seems fitting that the Tyne should once again see the construction of a revolutionary bridge. The elegant parabolic shape of the Gateshead Millennium Bridge echoes the familiar outline of its mentor, the Tyne Bridge. Its opening mechanism is a world first, and yet it is based on a simple principle. The bridge has just one major moving part—itself. The whole structure pivots upward to form a gateway arch. This revolutionary idea is reminiscent of Santiago Calatrava's audacious giant sail design for the Milwaukee Art Museum. When closed, small river craft can sail beneath the bridge.

    But for larger vessels, the cable-stayed, double-arched structure pivots at an angle of 40 degrees to give an 82-foot (25-meter) high navigational clearance. This was a requirement specified by the enthusiastic client, Gateshead Council, which also provided the project management.

    The 'cable-stayed opening' footbridge has two lanes to help avoid conflicts between walkers and cyclists. Pedestrians use the inner walkway and cyclists the outer deck. A stainless steel fence separates the two, with built-in perforated steel benches on the pedestrian side, providing views upriver.

    While the footway is solid steel, the cycle path is perforated aluminum, with gaps to give a view of the water below. There are breaks in the central barrier to allow cyclists to stop and walk up a step onto the footway to take in the views.

    The lighting units built into the decks of the bridge can produce millions of different colors, allowing it to stage dramatic light shows and stunning reflections in the water.

    The designers' attention to detail is further demonstrated in how the bridge cleans itself. Every time the bridge opens, any litter dropped on the deck will automatically roll into special traps.

    A Marvel of Construction Engineering

    The award winning bridge, designed by consulting engineers Gifford and Partners with architects Wilkinson Eyre, was built by Gateshead-based construction company, Harbour & General, in the AMEC yard in Wallsend, some six miles (9.6 kilometers) downriver from Newcastle and Gateshead.

    Kvaerner Markham Engineering, based in Sheffield, designed the electro-hydraulic actuation and control systems on the bridge as well as the support hinge assemblies, which withstand the large axial and radial thrusts that are produced during opening and closing.

    At each end of the bridge, the deck and arch converge on the support hinge assemblies. These assemblies consist of a cylindrical shaft supported at either end by a support bearing.

    To open the bridge, a bank of hydraulic rams push against a steel paddle attached to the cylindrical shaft, which pushes the whole structure through the required opening angle.

    Phil Snowsill, Kvaerner Markham's senior design engineer on the project explains that high loads were applied to these quite compact components. To add to the design complexity, the components themselves had to be visually attractive as well as functional.

    The Kingston-Upon-Thames firm, FEA provided consultation and LUSAS analytical software, which helped optimize the distribution loads providing the applicable minimum weight.

    At the fully open position, the suspension cables lie horizontal, holding the pair of arches together. Huge 15-ton (14,000 kilogram) castings on either side withstand the outward and radial thrust loads.

    A full 3D staged analysis was carried out to model the construction sequence, including the journey up the River Tyne, as well as the opening and closing operation with its inevitable loads.

    The essential part of the design process was the calculation of the initial forces of the opening operation, which helped determine the required profile for the bridge deck.

    As Shapour Mehrkar-Asl, of Gifford and Partners explained, "The forces and displacements produced from the LUSAS analyses were used to decide upon the final design and the staged construction method."

    That Big Crane

    The unique 940-ton (850,000-kilogram) steel bridge was floated six miles up the River Tyne and lifted into place by a crane taller than London's Big Ben.

    The Asian Hercules II is the second-largest floating sheerleg crane in the world. It has a deck the size of a soccer field, and its main lifting legs project over 350 feet (107 meters) into the air.

    The self-propelled 10,560-ton (9.6 million-kilogram) barge is over 250 feet (76 meters) long, over 100 feet (30 meters) wide and has enough power to lift a weight equal to over 4,000 cars. Amazingly it only needs a crew of twelve to operate it. Each of its eight mooring wires is over 2600 feet (800 meters) long.

    The crane was built in Singapore in 1996 where it worked until it left for Europe in early 2000. On its way through the Mediterranean, it lifted a heavy deck of over 1,200 tons (1,088,600 kilograms) weight into position on an offshore Egyptian oil field and then installed two bridges in Spain. Next, it headed to Newfoundland, Canada, where it worked for nearly a month on the Terra Nova oil field.

    The Assembly Task

    The floating of the bridge upriver to the Gateshead Quays was a spectacle and, in itself, an amazing feat of engineering. Imagine a giant crane, taller than Big Ben and almost as wide as the river itself, carrying a bridge the width of the river.

    The operation needed a perfect combination of water levels, currents, wind speed, and weather conditions, and it took three days.

    On day one, the crane lifted the bridge at the AMEC yard in Wallsend where it had been constructed. With the chains and lifting bars, it weighed more than 1,210 tons (1,100,000 kilograms). Because the bridge is longer than some parts of the river are wide, it had to be turned around 90 degrees so it was pointing upriver.

    On day two, the bridge was floated upriver to the Gateshead Quays. The crane is the largest vessel ever to float this far up the Tyne. It had just eight feet (2.5 meters) clearance either side of the riverbanks. Once it arrived, the bridge was carefully lowered into place to within a tenth of an inch (one millimeter) tolerance.

    On day three, the Asian Hercules II removed the main support strut weighing 165 tons (150,000 kilograms) and withdrew from the site. The crane's job was done.

    In February, 2001, hydraulic rams and electric motors that open the bridge will be installed. March will see its first test opening. In May, the computer-controlled lighting system will be installed, and in August, 2001, the bridge will finally open to traffic.

    To see the bridge slide smoothly into place was to watch history in the making. In the years to come, the Gateshead Millennium Bridge will become as famous a landmark as the Tyne Bridge.

    Don Barker is a freelance writer and photographer in London, UK, who has lived and worked in Europe, Australia, Thailand, Sri Lanka, Hong Kong, and Singapore.

     

    Continue...

    ArchWeek Photo

    Model to illustrate in-service stresses in the cast steel pedestal.
    Image: FEA Ltd.

    ArchWeek Photo

    Asian Hercules II 'resting' in Wallsend six miles down river from Newcastle/Gateshead.
    Photo: Don Barker

    ArchWeek Photo

    Profile of the pedestrian and cyclist portions of the bridge.
    Image: Gateshead Council

    ArchWeek Photo

    Asian Hercules II 'resting' in Wallsend six miles down river from Newcastle/Gateshead.
    Photo: Don Barker

    ArchWeek Photo

    The cast steel pedestal in place.
    Photo: Don Barker

    ArchWeek Photo

    The top of the parabolic arc.
    Photo: Don Barker

    ArchWeek Photo

    Looking towards Newcastle with the Baltic Mills on the left and the regenerated quayside on the right.
    Photo: Don Barker

    ArchWeek Photo

    The Gateshead Millennium Bridge with its predecessor, the Tyne Bridge, in the background.
    Photo: Don Barker

     

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