In 2002, Manchester will host the Commonwealth Games, and the east of the city will undergo radical changes to prepare for it. From the ambitious expansion of its airport to the troubled regeneration of the area around the new Sportcity, 黑洞社区 takes a look at the city's most exciting and controversial projects. Here, 黑洞社区 reports on the construction of the state-of-the-art athletics stadium.
A small tractor tugs a hoe across the parched surface of a dusty island of earth. Hunched over the vehicle's wheel, the driver's attention is fixed directly ahead as he steers along a criss-cross route, sowing the seeds that will soon transform the brown earth into a lush carpet of grass. In less than a year this will form the arena for the stunning City of Manchester Stadium the venue for the Commonwealth Games when they return to England for the first time in 68 years.

Around the perimeter of the scored earth, a team of men are busy laying a thick black oval of tarmac 鈥� the first of many such layers that will form the games' running track. Soaring high above the track on the newly completed concrete stands, another team can be heard clattering sheets of aluminium into position to clad the cantilevered horseshoe roof. Elegant two-tiered stands surround the track on three sides, and to the north preparations are under way for the installation of the temporary stand that will complete the circle.

Sowing the grass and laying the running track before the winter rains set in have been a top priority for Laing, the stadium's principal contractor and construction manager. "It was critical to get the roof finished on time so that we could get the cranes out of the stadium to allow the grass to be seeded and to lay the running track," says Graham Lumberg, Laing's project director. The eight-lane running track's construction is critical 鈥� it needs accreditation from the International Amateur Athletics Federation before the games can go ahead.

Curiously, given the amount of care and attention fostered on the grass and running track, the 拢115m stadium will only be used for athletics for a total of 10 days. In that time it will host the games' opening and closing ceremonies along with the athletics programme. On the night the games finish, Laing will return to the site to begin the 10-month conversion from a 38,000-seat athletics venue into a 48,000-capacity home for Manchester City. "We're really building a football stadium that will be temporarily used for athletics along the way," Lumberg explains.

The stadium's metamorphosis from an athletics to a football venue will involve the contractor removing the running track (which is recyclable) and the central swath of grass. Laing will then excavate the stadium's bowl a further 6 m to create the football pitch and add a third tier of seating. The 10,000-seat north stand, built for the athletics, will be removed to allow a permanent stand to be constructed to complete the oval of seating for the football stadium (see "How the athletics stadium will be transformed into a football ground"). However,for the time being, the construction team's efforts are focused on getting the stadium ready for the games' March 2002 handover. "It is a demanding construction programme for a unique building," says Lumberg.

Laing started on site at the end of December 1999, after usurping Amec, the original preferred contractor, six months after the project was put up for tender a second time. "We were gutted in May when we didn't win the job," confesses Lumberg. So, when the opportunity to retender arose, Laing was quick to pull together the same team, which included the design manager and the project engineer from the Cardiff stadium scheme. "They bring to the job the expertise we gained in Cardiff which we've mixed with our local knowledge of the market and contractors," says Lumberg. The team was handed a 70% complete design by Arup Associates, the stadium's architect.

The guaranteed maximum price form of contract, which was responsible for the contractor's loss of a reported 拢30m on the Cardiff scheme, has been left behind. This time, Laing's role as construction manager/principal contractor carries far less risk.

Piling was already under way for the stadium when Laing's site accommodation started to arrive. With a tight construction programme of 26 months, the first task was to push on with erection of the stands' cast concrete structure, floor slabs and raker beams that will support the precast concrete terracing. At the same time, eight satellite drums were constructed outside the perimeter of the main stands, each housing a spiral ramp to allow spectators access to the seating. Reaching skywards from the roof of these drums, steel masts now support a fan of steel cables to carry the roof structure.

Two concreting teams were used to construct the stands, one on each end of the horseshoe to speed construction. The teams worked from the northern tip of the east and west stands to meet in the middle of the southern stand. Lumberg says that this was a "big challenge" in the winter weather. Installation teams followed the concreting crew southward to fit the precast concrete seating sections.

In turn, the steelwork erectors, who were desperate to complete the installation of the roof steelwork to free the site of cranes and allow work on the track to start, chased the installation teams. Meanwhile, beneath the stands, another team putting up blockwork partitioning also began the chase south. With such a tight construction programme, most contractors were on site seven days a week. This strategy was not without risk. "If there was one cock-up, the whole programme would have collapsed like a pack of dominoes," says Lumberg.

The teams employed six tower cranes; three on each side of the stadium. One of each trio of cranes was used to construct the access drums, and the other two were used in the construction of the stands. These were supplemented by crawler cranes on the single terrace south stand. The cranes were essential to lift into place the 3800 precast concrete seating units and, later, to construct the stadium's structurally innovative roof.

Peter Budd, a director at Arup's Manchester office, describes the roof as "the trick to the stadium's elegance". It is a tension structure designed to give spectators an uninterrupted view of the action, as its cantilevered construction means that the terraces can be free of columns and other supports. The roof is cantilevered over the seating from the concrete columns supporting the back wall of the stadium. Steel forestay cables connected close to the canopy's outer lip transfer the weight of the cantilevered canopy to the top of one of 12 40 m high raked-steel masts where backstay cables then transfer this load to the ground outside the stadium's perimeter.

To tie the roof down in high winds, a second series of cables has been fitted to act in the opposite direction to the forestay cables. This second system comprises four cables that circle above the overhanging lip of the stadium's roof, forming a giant oval that mirrors the oval running track below. This is tied to the ground in each of the stadium's four corners to create a rigid roof structure (see "Raising the roof").

With the structure complete, all that now remains is to finish installing the roof's cladding. The cranes have long since disappeared from inside the stadium and work can finally begin on installation of the track. The project is due for handover on 10 March to allow final preparation for games to take place. Lumberg is confident that this part of the project will be delivered on time and to budget.

Following the games, Lumberg and his team will be back on site to complete the stadium's transformation into a football venue. Handover for this phase is set for July 2003. "Will the stadium be completed on time? It'll have to be," says Lumberg.

How the athletics stadium will be converted into a football ground

Immediately after the stadium has hosted the 2002 Commonwealth Games, it will be converted into a football ground for Manchester City. Laing has just 10 months to carry out this transformation. The main problem in reconciling the two different activities is that the oval athletics track requires an area of approximately 175 脳 92 m2, but the football pitch only requires 115 脳 75 m2. This means that if the stadium were to be used as a football stadium without conversion work, fans would be too far from the pitch to enjoy the action. Arup Associates, the stadium鈥檚 architect, has proposed a novel solution to the problems of accommodating the differing requirements of the two events. Only three of the football stadium鈥檚 four stands will be constructed for the Commonwealth Games. The stands will line the west, south and east sides of the track; the stands to the east and west will have two tiers of seating and the stand to the south will have just a single tier. On the north side of the stadium, a bespoke temporary stand to hold 10,000 spectators will be built using steel tubes and fittings. To accommodate the running track, this stand will have to be sited 30 m further out of the stadium than its permanent replacement. Originally, the architects proposed using temporary stands for the north and south stands. However, this idea was dropped because Laing was concerned that the 10-month period for the stadium鈥檚 conversion would not allow sufficient time to construct both. 黑洞社区 two temporary stands was also a more expensive option than constructing one. The really clever bit of the design is the stadium鈥檚 adaptability once the games have ended. As soon as the closing ceremony is over, Laing will return to the stadium to remove the temporary stand. Then, in a 44-week spell, the running track will be removed, along with the grass outfield, and the stadium鈥檚 bowl will be lowered by 6 m. In the process, 95,000 m3 of earth will be removed 鈥� all through the vacant north side of the stand. Removing the earth will expose the players鈥� entrance and allow access from the changing rooms that have already been constructed in the basement of the west stand. Once the excavation is complete, an additional tier of seats will be constructed on the newly-created earth slopes, adding another 10,000 seats, and a new pitch will be grown in the lowered centre of the newly-formed bowl. To speed the transformation, Laing has managed to carry out some of the fit-out necessary for the football stadium during the fit-out for the games, including areas like the hospitality suites and corporate boxes. Finally, a north stand will be constructed to mirror the existing south stand and the roof will be joined up to complete the oval. The precast concrete seating units for the stand have already been constructed and are being weathered in a yard in Cheshire so that when they are installed they will blend seamlessly with the other stands. 鈥淭here is definitely a critical path through the project,鈥� says Lumberg. 鈥淲e have to build the north stand, fit the roof steelwork, then grow the pitch,鈥� he says. The stadium will be owned by Manchester council and leased to Manchester City Football Club.

Raising the roof

1 Before the 50 m long steel rafters that project from the stadium鈥檚 walls could be craned into position, they were bolted into pairs using the purlins. 鈥淚t was quicker and easier to perform this operation on the floor,鈥� explains Neil Kitchener, Laing鈥檚 project engineer. 2 A framework of temporary steel was erected around the perimeter of the running track. 3 Once that was complete, the pairs of rafters were lifted into position so that the rear section could be attached to the concrete supporting columns forming the outer wall of the stadium; the front of the rafters rested on the temporary steelwork frame. Once in place, the remaining purlins were connected to join the rafter pairs together. 4 With the rafters in position, the 12 supporting masts were erected, one on top of each of the eight access drums, and two mounted on the ground at each end of the stadium. The masts were held in position at the front using temporary forestay cables, connected from the top of the mast to the temporary steelwork, and at the back using the permanent backstay cables, which at this stage were not tightened fully. 5 Next, the oval of four cables, called a caterary, was installed in a ring above the rafters and the permanent forestays were connected to the masts. Because the four cables had to be installed as a complete loop, it even had to cross the area of the stadium where the temporary stand is to be installed. 6 It was then a simple matter of tensioning the backstay cables to support the weight of the roof and to stress the caterary cables to resist uplift on the roof by tensioning tie-down cables in each of the stadium鈥檚 four corners. 7 With all the cables tensioned and the roof structure held rigid, the temporary works could be removed. Finally, the aluminium cladding is added.

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Credits

client Manchester City Council Special Projects Office principle contractor and construction manager Laing architect Arup Associates structural and M&E engineer Arup cost consultant Davis Langdon & Everest structural auditor Modus enabling works Alfred McAlpine steelwork Watson Steel precast concrete CV Buchan concrete frame Heyrod/Laing partnership M&E engineer Haden Young Architectural auditor HOK/Lobb, AFL