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Split second timing for Gatwick bridge lift

BRITAIN'S LONGEST airport link bridge was lifted into place across a major taxiway at Gatwick airport this week, four hours ahead of schedule.

Work to lift the 167m long prefabricated curving central span took place on Monday evening, after being moved into position between plane movements on Sunday night.

The span was fitted with steel Y-frame legs which will support its soffit 22m above the ground, high enough to allow a 747-400 jumbo jet to pass beneath it.

Two additional sections were due to be lifted in at either end this week to complete a total 197m link to a new aircraft facility, Pier Six, for 12 additional aircraft stands on the airport's North Terminal.

'We ended up four hours ahead of schedule, ' said Steve Taylor, project manager for lifting contractor Fagioli PSC.

The firm carried out the three hour strand jacking lift, using eight 450t jacks on four corner towers, and also moved the whole assembly 1.5km across the busy London airport's taxiways the previous night.

The bridge, along with its two lifting towers, weighed 2,650t and required a 120 axle assembly of computer-synchronised self-propelled modular transporters (SPMTs) to move it from the assembly site. The two legs followed on Monday evening using the same SPMTs.

Client British Airport Authority's project manager John Setra told NCE that the move had required split second timing to fit in with ongoing aircraft movements as the bridge crossed taxiway crosspoints.

'One more week and we would have hit the school half term holidays and the operation might have been impossible, ' he said.

Taxiway closure time for the lifting and final fit-out operations is also very limited.

'And to have built this bridge in place would have meant closing the key taxiway for seven months, ' he added.

Using a landside site on the perimeter of the airport allowed structural steel contractor Watson Steel and Swiss envelope fitter Schmidlin to complete their work in relative ease, with easy non-secure access to bring in the fabricated steel components.

The whole bridge was preassembled at the landside site, including all its M&E fit-out from travelators to glazing and all the cladding, said Stephanos Samaras, project leader for Arup. Arup and architect Wilkinson Eyre Architects won a design competition for the £100M airlink in 1999.

Structure of the long slim bridge is unique, 'based on the human spine', he explained.

A central triangular crosssection - 'strictly speaking trapezoidal' - steel box supports steel ribs for the concrete floor structure. Above that runs an inverted triangular shape truss of pyramidical tubular steel elements.

'That has a variable depth for maximum strength where required, ' said Samaras.

It creates a low curving form following the bending moment but allowing the bridge to keep to stringent height limits required to avoid interfering with airport radar systems.

The glazed sides of the bridge taper inwards at 11infinity, both to prevent reflection glare on aircraft and to keep them cleaner and reduce maintenance.

Because of the variable height between the intersection and the floor, the bridge has a 'waisted' form at walking level.

The central spine also separates the estimated 50,000 arriving and departing passengers who will walk across it each year.

The main span together with the Y shaped legs forms a portal frame structure once the whole is in position, added Samara.

The construction method was originally devised by Cleveland Bridge, which was working as part of the project team in 2001.

'But the 9/11 events caused a rethink as passengers levels dropped heavily, ' explained Setra.

The project was restarted last year following a partial recovery in passenger levels but Cleveland was busy with other work.

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