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Suspended animation

Bridges are hot news at the moment, as architects span the disciplines. We look at the most talked-about recent examples

The 0resund Bridge is one of those fantastic projects that, for some reason, merited very little coverage in the UK press.Completed in July this year it is an audacious project which has scooped a number of prestigious awards and, more importantly, changed the face of a nation (or two).

Linking Sweden's third city, Malmo, with the Danish capital, Copenhagen, the bridge is part of the ambitious Trans-European Network to connect the transport systems of countries in central and eastern Europe and the Mediterranean.

The world's longest cable-stayed span, carrying road and rail traffic, is an impressive feat of engineering and political will, symbolising Europe's ambitious transportation plans.

The two-level structure is constructed with steel trusses using diagonals to connect the upper and lower decks. These naturally stiff trusses - deep enough to take a train - are uniform throughout the bridge but modified at the cable-stayed main spans to place every other diagonal in the same direction as the cables.The truss has a constant 20m bay length along the full length of the bridge and a single span of 490m over the international navigation channel.

Together with a 4km immersed tunnel at the western approaches and a 4km artificial island, the 0resund scheme runs a total length of 15,840m.

Handover on the £1.2 billion project was three months ahead of schedule and has proved a great success, changing economies as well as travel patterns.

Back in the UK, while bridge building has not changed in terms of investment levels over the years, it has shifted in emphasis.The relentless building programme of motorway bridges during the past half century - predominantly simple concrete structures - has moved towards small-scale or pedestrian footbridges.

The shift in focus in travel politics during the last decade has led to a greater priority for pedestrians and the marginalisation of the car. Enshrined in policy - from the European Pedestrian Charter to the government's White Paper on Integrated Transport and the Traffic Reduction Act - this has had an effect on the investment in UK transport infrastructure and political priorities.

There has also been a change from engineering to architectural solutions. Martin Knight of Wilkinson Eyre, which has designed more than 50 bridges worldwide, considers that bridges have now come into the architectural mainstream because, on their own, 'engineers were producing utter drivel'. Also, 'the iconography of the bridge has brought them into the public consciousness'. However, even though Lottery money has increased their profile, bridges still remain a niche market.

Matthew Wells, director of Techniker, believes that the architectural love affair with bridges springs from the excellence of particular highprofile individuals - specifically Calatrava, who has been an inspiration to most architects and engineers alike.

Recent interest, though, comes from a realisation that bridge design is 'a truly collaborative process between architects and engineers - Egan in practice'.

Engineering solutions, in association with architectural input, he says, 'adds value to, what is in effect, a relatively simple process'.

On the next two pages we examine some of the best examples of recent bridges in the UK.

Hungerford Bridge

Isambard Kingdom Brunel's bridge carrying trains into London's Charing Cross Station is one of the least attractive rail river crossings across the Thames. Puddled, outdated and cramped, it also serves as one of the main pedestrian crossings from the Embankment to the BA London Eye. To enhance the area, and to provide an access to many of London's millennial tourist attractions, Lifschutz Davidson has designed a new pedestrian crossing - hung from the sides of the existing structure.

The original proposal for the bridge had new piers driven into the bed of the Thames to support steel pylons. These pylons rise at an angle to 18.5m above the level of the existing bridge and support the cable stays holding the new footbridge. These are tied back to the mass of the original bridge supports. The piers' structural design requirements informed the submission of the concept design and was clearly an obvious factor in the scheme proposal.

The £30 million millennium project, managed by Westminster council, was due for completion in spring 2001. But as the piling of the foundations began, safety fears surfaced over possible Second World War bombs in the river bed which might be detonated by accidental impact or vibration of the pile-drivers. Fears were not eased by the fact that the the dredging of the river in a pre-start 'safety sweep' found nothing.

Detonation of a dormant device is also of concern to London Underground, putting the nearby Bakerloo Line at risk of cracks, and hence flood damage, to the line.

Project architect Charles Brothwick speaks for everyone who has had dealings with the public sector. 'Many discussions on this subject had taken place with London Underground, ' he says, but 'when dealing with public bodies it's difficult to put your finger on their exact requirements'.

A revised design has just been given planning approval, resiting the first pier support from an area likely to cause damage to the Tube network, onto the northern Victoria Embankment.

The bridge is now scheduled for completion in spring 2002.

To cover the increased cost, London mayor Ken Livingstone is giving an additional £16.7 million.The sum is seen as a cheaper option than protecting the Tube tunnels and maybe abandoning the line for the duration of the work.The additional funds are to cover all eventualities, including contract costs, fees, compensation and insurance. Livingstone says: 'Londoners will now expect Westminster council, the Cross River Partnership and other partners involved in this project to ensure project costs do not overrun further.'But the issue of liability won't disappear so easily.

Gateshead Millennium Bridge

Apparently, it is windy and rainy in Newcastle upon Tyne in autumn.While this might be obvious to most people in the frozen North, it seems to have passed by the organisers of the programmed installation of the Gateshead Millennium Bridge.

Scheduled for installation at the beginning of November, crisis talks within Gateshead council caused it to be put back due to anticipated high winds.With a weather window of only a few days, the tides were no longer adequate to satisfy the crane lifting criteria.

The Asian Hercules II crane which eventually carried the bridge to its setting is one of the biggest floating cranes in the world (crane hire is approximately £250,000 of the £18 million budget). It was moored in North Shields for more than two weeks waiting for a break in the weather.The 10,000 tonne barge, with 100m high lifting legs, supported the four fixing points, including a massive temporary lattice beam. A 35mm diameter tensioned steel chord temporarily held the shape in transit.

The NEC form of contract parcels off the liability for steelwork delivery to the steel fabricators and engineers (Watson Steel of Bolton) and crane operator (SMIT International), which both accepted that their subcontracts were weather-dependent.The main contract allows for charges to accrue only once the bridge was hoisted. It finally set down its cargo to 3mm tolerances on Monday 20 November.Because the bridge has no traditional tie bar, it is held in shape in-situ by the buttress walls at each shore.

It now has to undergo power connections and commissioning tests until June 2001.

The scheme, developed by Wilkinson Eyre and Gifford & Partners, met the functional requirements of the brief and created a beautifully stylish structure - the first opening bridge to be built across the Tyne for more than 100 years and the world's first rotating bridge. The designers allowed a clearance 'goalpost' of 35m wide by 25m high to allow safe passage of shipping when the bridge is open. As a fail-safe, the pierside supports have also been strengthened.

Captain Gary Wilson, the harbourmaster with control of activities on the waterways, insisted on concrete-filled steel collision barriers to prevent shipping from damaging the bridge.

Though this was not part of the brief and the Tyne is no longer a major shipping lane, what have become known as the 'Harbourmasters' Piles' remain.The ties linking each pile are rapidly collecting the detritus of Newcastle nights out and it seems that the bridge will be blighted by these paranoid risk-avoidance measures.

Plashet Bridge

Plashet Grove Girls'School in Newham, south London, had been campaigning for 28 years for a safe, secure and covered walkway linking its two sites, situated on either side of a busy main road.When funding was finally secured, the borough engineers' original scheme proposals were rejected by the planning authority, with the express advice that they get an architect on board to resolve the design deficiencies.

Architect Birds Portchmouth Russum and structural engineer Techniker proposed a new scheme to suit the £500,000 budget.Because of the different alignment of the two buildings, the bridge was designed with a curve (which also avoided a couple of mature trees). The concept, as described by project engineer Megan Maclaurin, was to create 'a journey between two buildings, with a meeting space in the centre'.

The bridge has been built in two sections.The perimeter is constructed with 915mm carriage beams (the largest standard size steelwork available), with the steel sheet deck spanning between the lower flanges and acting as torsional restraint to accommodate the curvature of the bridge.The upstanding carriage beams act as balustrades. Alternating galvanised steel hoops, bolted to the beams, form the roof structure which is covered with PTFE roof panels, clamped at the beam perimeter.

At the central meeting point, the carriage beam has been revised to provide seating.

The bridge is supported on sculptured steel piers fabricated from 32mm plate. Initial considerations for a cantilevered bridge were rejected because the spans would have made the bridge, as Maclaurin says, 'too lively', the new engineering euphemism for structural movement.The location of the piers was determined by the setback required at the roadside to minimise impact hazard. Bridge width was determined by the maximum size sections transportable by road from the fabricators in Doncaster.

A weekend road closure was sufficient to lift the three main sections.With the design team present throughout, a 300 tonne crane started the lift on Saturday evening, working through the night and completing the final section at 6pm on Sunday.

After the appointment of the new design team, the scheme took one year to complete, with the construction period accommodated in the six-week summer holiday.The bridge opened on 7 November.

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