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Mace checks in early at Heathrow

SITE REPORT

The first phase of Heathrow's giant new air traffic control tower has been delivered six weeks ahead of schedule, despite a tight construction programme on a fully operational airfield. Damian Arnold went airside to discover the secrets of Mace's success

JACKING an 87m-high tower into the air with cables is a major construction challenge in any circumstances, but doing it in the middle of operating runways at the world's busiest international airport is a daunting undertaking.

So the Mace-led project team at Heath row can give themselves a pat on the back. The first completed phase of the airport's giant air traffic control tower has been handed over to National Air Traffic Services six weeks ahead of schedule. The rest of the tower is due to be handed over next month.

Additional challenges on the £50 million project included having to roll the 1,000 -tonne prefabr icated glass cabin of the control tower two miles from where it was built next to Terminal 4 to its home near the apex of the airport's Star of David grid. The 32m-high glass cab and the triangular steel stalk that supports it like a giant Toblerone then had to be jacked up into the air wh ile nearby aircraf t came and went on the Gulf taxiway ? one of the busiest at the airport.

'There were a number of technical challenges that would be difficult enough in their own right, without such difficult site conditions, ' observes Peter Czwartos, production leader at Mace. 'But to do it in such a conf ined space in a live airport environment was a major logistical challenge. Everything had to be planned 100 per cent. There was no scope to improvise.' The schedule was beaten thanks to four vital time-busting strategies. The first and key decision was to prefabricate the tower's viewing cabin off-site. This was carried out simultaneously with the building of the substructure throughout 2004. BAA estimates that this parallel processing shaved roughly a year off the schedule.

The second strategy was to prefabricate the cabin's 50 -tonne roof on the ground at the same t ime as the main structure was being constructed next to it.

'Building the roof at ground level enabled us to do it faster and more safely than at height and it let us construct the roof at the same time as the cab, ' says Mr Czwartos.

The payoff was an eight-week time saving ? provided the team got the roof lift right.

'We needed a good weather opportunity to be su re that when we star ted it we could finish it. All the tresses had to be bolted on at the correct torque to every mullion, which took seven hours. If you abandoned it, too much weight would be exerted on one or two connections and the structure would buckle.' The third time-saving measure, which shaved a week from the programme, was to take an alternative approach to access. The scaffold tower used for assembling the cab elements on site would conventionally be erected right next to the cab.

But on this project it was erected further away and connected with a link bridge. This created enough space for the cab and two sections of the supporting mast to be raised onto the 200-tonne lifting yoke and three trailers before the scaffold had to be struck.

The fourth strategy was to construct the tower's three-storey base building before its permanent supporting cables were installed. It would have been easier to build it after the cables, but as a result the team was able to work on the base building during the day and on the cables at night. This kept the critical path open in case fitting the cables overran ? which in the event they did ? and saved an estimated six weeks.

'It meant that putting up the permanent cables was no longer critical and it took the heat out of the situation, ' recalls Mr Czwartos.

A curved piece of steel was fitted onto the corners of the base building for each of the six locked strand steel cables to rest on while they were tensioned up.

The technique also doubles as a method statement should client BAA need to change the cables in future.

The overall success of the tight programme hinged on negotiating the two-mile journey of the cab from Terminal 4 along the southern runway to the site. This required the most risk analysis. Had the structure got stuck on the runway chaos would have ensued.

Risk analysis was carried out independently by engineering consultant Keith Allardyce, who deconstructed the move to tease out every eventuality.

'He kept asking questions like could the cab get stuck during its journey to the site? When was the last time the trailers' power packs failed?

What would happen if the driver of one of the trailers had a heart attack half way through the move? What do we do if a certain piece of equipment fails?' says Mr Czwartos.

Every turning point along the winding route through the airport was mapped out with GPS co-ordinates so that base control could tell the driver exactly when to turn the trailers.

A three-strong team from the Health & Safety Executive was given free rein to analyse the moving plans and the solution to lift the tower. This involved three lifting towers with temporary strand jacks to raise the structure hydraulically and suspend it while sections of the steel supporting mast were slotted underneath. A control system was needed that maintained the correct tension in the guy cables during lifting and kept the structure plumb.

The complex engineering required a multi-disciplinary team of people but getting them on and off an 'airside' site could be very time-consuming, because of comprehensive security checks.

The problem of delivering materials to the site was eased by the use of T5's landside consolidation centre, a temporary storing area from which a dedicated team of drivers specially qualified to drive airside would ferry them to and from the site. But for those workers needed airside, there was no getting away from waiting around in the cold to be let in.

'It can be very time consuming getting people through security checks, especially if they get stuck behind a coach-load of people about to be deported, ' says Mr Czwartos.

'They could be waiting up to 45 minutes to get on site. Our logistics strategy was based on doing as much as possible landside.'

BAA's mammoth T5 project is now nearly three-quarters complete and the airport operator says that it remains on schedule to open on March 30, 2008.

The Air Traffic Control Tower is now being fitted out in time for the official handover of the tower to National Air Traffic Services in March. NATS has already begun to fit out the cab section.

So far 275,000 sq m of pavement-quality concrete has been laid out of a total of 650,000 sq m over the course of the project.

Work is now starting on installing the glazed link bridges that will span the interchange plaza, connecting the departures level of the main terminal building with the multi-storey car park.

This year, track in the Heathrow Express tunnels will be completed, as will the pedestrian walkways and mechanical equipment such as ventilation fans and bracketry for the overhead line equipment.

Electrical power stations will be running for the first time, which will allow the ventilation system to be commissioned.

The rail systems team hit a new record last Wednesday for the UK's furthest concrete pump. The team's concrete pumpline, in the Heathrow Express extension tunnel, stretched 1.9 km.

Throughout 2006 the power rails will be installed in the Piccadilly Line Extension along with remaining rail systems such as signals and lighting.

Work on the PicEx junction will be completed and handed back to London Underground allowing the loop line to Terminal 4 to start again in September.

On the main terminal, specialist contractor Schmidlin has completed the glass facade, excluding access gaps for plant and materials. Over 5,500 glass panels, covering 30,000 sq m, have now been installed.

Fit out and services installation will continue in both the main terminal and the satellite building. Commissioning for the satellite building will begin in September.

Towering ambition

ONE OF the knock-on effects of the mammoth Terminal 5 project was that, once it is completed in 2008 on the west side of the airport, Heathrow would require a taller, more centrally located control tower.

The existing control tower near to Terminals 1, 2 and 3 is just under 40 m high and on the east side of the airport.

The newly built 87m-high steel structure will offer a panoramic view of the whole airfield, enabling controllers to see the tailfin of every aircraft.

Planning permission for the structure was granted on condition that it would be very slender, since it would be visible from the surrounding countryside as far away as Windsor Castle. The resulting design from architects Richard Rogers Partnership and engineer Arup was for a slender, triangular, structural tube mast.

Under enabling works, which started in 2003, an aircraft stand on the site was decommissioned and its fuel mains removed. At the beginning of 2004 work started on the concrete substructure including concrete anchor blocks 4m deep.

At the same time construction started on the prefabricated superstructure on the site of a baggage storage area near to Terminal 4.

The prefabricated cabin and steel mast sections were transported to the site from Terminal 4 at the end of October 2004 in a two-hour night-time move.

The structure was jacked up in early 2005 and the temporary strand jacks were replaced with massive steel cables that stabilise the structure.

At the same time the three-storey base building was constructed.

At the time of writing the bridge linking the tower with Terminal 3 is just about to complete and bespoke Japanese-designed dampers is being installed in the tower to prevent it from swaying in strong winds.

NATs is due to be handed the rest of the tower in March 2006 and the building is due to be fully operational by November 2006.

The T5 Agreement KARL Devlin, BAA project manager, says the contract was deliberately vague to encourage teamwork among the contractors and avoid recriminations if something went wrong.

'There is an acceptance that the contractors will have to manage change, ' he says of the contract known as the T5 Agreement.

'For the suppliers involved it's a low risk, but in return for that we are expect ing people to perform, ' he adds of a job which used just one full-time quantity surveyor.

Peter Czwartos, Mace production leader, says the agreement worked well when it was found that the four bolted connections pulling the six steel cables were shedding load into the concrete base and stretching the bolts. The bolts were re-tensioned without recriminations and the job continued apace.

Project details

Contractor: Mace Architect: Richard Rogers

Structural engineer: Arup

Temporary works designer: Dorma Long

Trailers for moving cab: Fagioli

Glass supplier: Schmidlin