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HQ right on cue

Twickenham - A timely return to form for the England Rugby team is being echoed by the construction of a new South Stand at England's home. Mark Hansford reports from Twickenham.

On the pitch, English rugby may owe its return to rude health to one man - the heroic Jonny Wilkinson - but at its spiritual home, Twickenham, it is a very different story. The fact that a full house of 82,000 was able to witness the great man's return in the opening two matches of the Six Nations, not to mention the four Wilkinson-free autumn internationals, owes much to the team efforts of Carillion, the contractor rebuilding the stadium's South Stand.

Completion of the new stand is the final piece of the Twickenham jigsaw. The North, East and West stands were rebuilt during the 1990s and the new 40m tall South Stand will make the whole arena a three-tiered bowl, the largest dedicated rugby stadium in the world.

But smashing down the 10,000 seat, 26 year old posttensioned concrete South Stand, with its cable stayed barrel vault roof, and replacing it with an £80M, 17,000 seat stand made of, precast concrete, insitu concrete and structural steel was never going to be easy.

Work is taking place while the stadium is in operation and contractor Carillion must enable it to operate at a minimum capacity of 65,000. And this minimum is being increased incrementally as the new stand develops in line with demands from client the Rugby Football Union (RFU).

The new structure also incorporates a four-star hotel, conference centre, health and fitness club and a 400 seat performing arts centre.

Carillion took over the job as part of the portfolio of projects it acquired when it bought Mowlem in early 2006. Mowlem won the fixed-price contract in early 2005 and arrived on site on 18 July 2005, eight days after Controlled Demolition had blown down the original stand. Time was of the essence, as the RFU wanted the 7,600 seat lower tier available for the opening Six Nations match with Wales on 4 February 2006. 'Unlike many other buildings, if this one was not complete it would be noticed - international rugby matches don't get rescheduled because the contractor wasn't ready. It had to be there, ' says Carillion project director David Goward.

Mowlem had rebuilt the other three stands in the 1990s with insitu concrete, but this stand, with its wrap-around 'commercial building' was a different prospect.

'The commercial building has made it different in a number of ways, ' says Goward, himself a veteran of Mowlem's previous Twickenham work.

'For a start we couldn't have tower cranes sat back - they had to come up through the building - and on the back of the other stands there are staircases. We have got spiral ramps (one on each corner).

They are not unusual, but they do take up a lot of space.' Each spiral is in a 25m diameter insitu C35 concrete drum. 'They work as shear cores for the predominantly steel-framed commercial building, ' says Goward.

The commercial building is designed to work independently of the stand itself, with a lift core between the two drums providing a third shear core.

The other three stands were little more than tin shacks before they were rebuilt. 'It was going to take longer to clear and we were going to have piling to do, the obvious way to save time was to use precast concrete for the lower tier, ' says Goward. This was designed, supplied and installed by ABC Structures (see box); the tier was ready for the Wales game. So far so good.

The next milestone was to have the second and third tiers - along with the roof - ready for the autumn internationals, starting on 10 November against Australia. 'That was a big target for us, ' says Goward.

The middle and upper tiers are steel framed with the same precast concrete terracing, the roof is a steel truss inlled with purlins and a translucent cladding. They are cantilevered off an insitu concrete Vierendeel sway frame.

Named after Belgian engineer Arthur Vierendeel, this truss has rigidupper and lower beams, connected by vertical beams. At Twickenham the vertical beams are a massive 1,500mm by 750mm at 7m centres. The joints are also rigid.

In this statically indeterminate truss, all members are subject to bending moments. By eliminating diagonal members, the creation of rectangular openings for windows and doors is simplied since this truss can reduce or eliminate the need for compensating shear walls.

Unfortunately onstruction did not go smoothly. 'There had been some problems, ' says Goward. 'The west drum was to be built on the site of an existing electricity substation that we were going to rebuild and incorporate into the drum's core.

'We built the new substation, but there was quite a long delay in getting disconnected and reconnected. That delay meant we couldn't start piling or anything, ' explains Goward.

The delayed construction of the concrete sway frame in turn delayed Cleveland Bridge, which was contracted to erect the steel frame and precast concrete terracing for the middle and upper tiers. 'We needed the three cranes being used to erect the concrete frame gone, so we could erect Cleveland's larger cranes, ' says Goward. 'This was going to delay them.' Carillion decided to ask the RFU if it could install two additional tower cranes so Cleveland Bridge could get started on the middle and upper tiers while the concreting work was nished off.

'Running with ve tower cranes was difcult, but we managed, ' he says, ruefully adding that the RFU was about to crank the pressure up further by springing a surprise rugby xture on the contractor.

'We had the date of 10 November originally, but then the client asked if he could arrange another match. We said 'when?'; he said '5 November'. We said 'okay', but then the RFU started to bill it as the grand opening of the stand, against New Zealand, with reworks!

'We didn't want to become the next Wembley, so we put in a huge effort, ' says Goward.

And the team made it, with the last section of precast concrete terracing going in on the Monday before the game. England were hammered, but Goward's team were still jubilant.

'We all got a lot of pleasure from meeting the deadline. The feeling is like the Oxford and Cambridge boat race. Both teams have rowed the course, but one team is elated and the other at. We were elated.' That said, Goward knows there is still no room for complacency, with a 41m cantilever roof still to go on and a hotel to complete.

The steelwork should be up and the cranes down by the end of April. The roof cladding will be installed by the end of May. 'We are pushing on with the roof and you will see a lot of difference by the time of the France game [on 11 March], ' says Goward.

If England triumph in Dublin this weekend, that will be a Grand Slam decider.

A vitalised Twickenham

Who's who

Client: Rugby Football Union Architect: Ward McHugh Associates Designer: Arup Contractor: Carillion Precast concrete subcontractor: ABC Structures Precast concrete supplier: Bison Concrete Products Steelwork subcontractor: Cleveland Bridge Demolition contractor: Controlled Demolition Precast power play While the three previous stands were constructed with an insitu concrete lower tier, the RFU's tight programme requirements ruled out its use on the South Stand.

The lower tier's concrete superstructure provides lateral restraint to the insitu concrete frame at the back of the terracing.

This in turn supports the steel cantilevered middle and upper tiers as well as the cantilevered steel roof structure.

In cross section, the 450mm wide, 500mm deep precast concrete raker beams for the lower tier span in two sections from the insitu columns at the rear of the terracing. These columns form part of the insitu concrete Vierendeel sway frame.

The 10t raker beams are supported at their mid points on circular precast concrete columns. Precast concrete beams span the rear two bays of precast columns supporting the prestressed hollowcore ooring spectator concourses at two levels.

The last 10 bays at each end of the South Stand curve round to meet the existing East and West Stands, with these structures supporting the ends of the last bay of terracing.

The 2,200 precast concrete units that were required for the construction of the lower tier were erected in eight weeks, with no units having to be returned to the factory from site.

A further 1,800 precast concrete units were supplied for the middle and upper tiers as well as 18,500m 2 of prestressed hollowcore and solid slab ooring, together with 220 stairights and associated landings for the commercial building.

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