Cover Story: Wembley Stadium
Designed to give the appearance of solidity without incurring the penalty
of high wind loads, the arch has a lattice form consisting of 41 steel rings
(diaphragms) connected by spiraling tubular chords. The arch tapers at
its ends and is supported on concrete bases founded on piles 35m deep.
Inclined to the vertical, the arch is held in position by a series of forestay and
backstay cables tied to the main stadium structure.
Wembley Stadium (usually shortened to just Wembley) is located in the
Borough of Brent in North West London, England. Primarily a football venue,
Wembley is owned by The Football Association (The FA) via its subsidiary
Wembley National Stadium Limited, and hosts England’s home international
football matches and the main English domestic cup finals. The Stadium is
also used for music concerts and other sporting events. Wembley will host
the 2011 UEFA Champions League Final.
Immediately following its opening, it was often referred to as the “new
Wembley Stadium” to distinguish it from the original stadium.
One of the most expensive stadia ever built, Wembley’s 90,000 capacity, makes it
the second largest stadium in Europe, and is the largest in the world with every seat
under cover.
The previous Wembley Stadium (originally known as the British Empire
Exhibition Stadium or Empire Stadium) was one of the world’s most famous
football stadia, being England’s national stadium for football, and because
of the geographical origins of the game was often referred to as “The
Home of Football”. It hosted the European Cup (now the UEFA ChampionsLeague) final a record five times, and is one of seventeen stadia to have
held a FIFA World Cup final. In 2003, the original structure was demolished
and construction began on the new stadium, originally intended to open in
2006. This was later delayed until early 2007. The final completion date of
the stadium was 9 March 2007, when the keys to the stadium were handed
over to the FA.
Building
Wembley was designed by architects HOK Sport and Foster and Partners with
engineers Mott MacDonald, built by Multiplex and funded by Sport England,
WNSL (Wembley National Stadium Limited), the Football Association, the
Department for Culture Media and Sport and the London Development
Agency. It is the most expensive stadium ever built at a cost of £798 million
(roughly US$1.57 billion) and has the largest roof-covered seating capacity
in the world. The leading edge of the north roof is in turn suspended from the
arch by the forestay cables. Cables from the arch are arranged in a diagonal
pattern to help spread loads to control in-plane bending while also providing
out-of-plane restraint to resist buckling.
Design
The all-seater stadium is based around a bowl design with a capacity of 90,000, protected from the elements by a sliding roof that does not completely enclose it. It can also be adapted as an athletic stadium by erecting a temporary platform over the lowest tier of seating.
The stadium’s signature
feature is a circular section lattice arch of 7 meters (23 ft) internal diameter
with a 315 meters (1,033 ft) span, erected some 22° off true, and rising to
140 meters (459 ft) tall. It supports all the weight of the north roof and 60%
of the weight of the retractable roof on the southern side. The archway is the
world’s longest unsupported roof structure. Instead of the 39 steps climbed,
in the original stadium, to enter the Royal Box and collect a trophy, there are
now 107.
A “platform system” has been designed to convert the stadium for athletics
use, but its use would decrease the stadium’s capacity to approximately
60,000. No athletics events have taken place at the stadium, and none are
scheduled. The stadium is linked to Wembley Park Station on the London
Underground via Olympic Way, and Wembley Central via the White Horse
Bridge. It also has a rail link—provided by the Wembley Stadium railway
station—to London Marylebone and Birmingham.
The initial plan for the reconstruction of Wembley was for demolition to begin
before Christmas 2000, and for the new stadium to be completed some time
during 2003, but this work was delayed by a succession of financial and legal
difficulties. It was scheduled to open on 13 May 2006, with the first game
being that year’s FA Cup Final. However, worries were expressed as to
whether the stadium would actually be completed on time.
The new stadium was completed and handed over to the FA on 9 March 2007, with the total cost of the project (including local transport infrastructure redevelopment and the cost of financing) estimated to be £1 billion (roughly US$1.97 billion). According to Josephine Cutts the press Officer at Foster and Partners the stadium is a recognizable feature on London’s skyline, the 316m wide.
Success
Our work on the new Wembley Stadium was recognized in two prestigious
industry awards announced in October 2007. At the Institution of Civil
Engineers (ICE) annual dinner held on 11 October, Wembley was awarded
ICE London’s 2007 Merit Award. Innovation, engineering quality and
contribution towards sustainability are the hallmarks of winning entries. At the
Builder and Engineer Awards – a celebration of the best in British engineering
and construction – Wembley was awarded Sports and Leisure Project of the
Year.
Unique features
The roof structure was designed in close collaboration with architects Foster and Partners and HOK Sport for Wembley National Stadium Limited. Its unique features - retractable roof panels and the arch - were developed in response to the particular requirements of the stadium, one of which was the need for a high quality grass pitch in order to achieve UEFA 5 star stadium status. By using retractable roof panels, which retract to the south, it allows as much daylight and ventilation to reach pitch level as possible.
The end
solution is an architecturally strong design which is structurally efficient. And
the arch is by no means a cosmetic feature – it supports the north roof and a
sizeable area of the south roof.
In October 2005, Sports Minister Richard Caborn announced: “They say the Cup Final will be there, barring six feet of snow or something like that”. However in December 2005, the builders admitted that there was a “material risk” that the stadium might not be ready in time for the Cup Final and in February 2006, these worries were confirmed by the FA moving the game to Cardiff’s Millennium Stadium. The delays started as far back as 2003.
In December 2003, the constructors of the arch, subcontractors Cleveland Bridge, warned Multiplex about rising costs and a delay on the steel job of almost a year due to design changes which Multiplex rejected.
Cleveland Bridge were removed from the project and replaced by Dutch firm Hollandia with all the attendant problems of starting over. On 30 March 2006, the developers announced that Wembley Stadium would not be ready until 2007. All competitions and concerts planned were to be moved to suitable locations. On 19 June 2006 it was announced that the turf had been laid.
On 19 October 2006 it was
announced that the venue was now set to open in early 2007 after the dispute
between The Football Association and Multiplex had finally been settled.
WNSL, a subsidiary of The Football Association, is expected to pay around
£36m to multiplex, as well as the amount of the original fixed-price contract.
This meant that the Wembley Stadium was ready for the 2007 FA Cup Final
on 19 May 2007. The keys to the new Wembley stadium were finally handed
over to the owners on 9 March 2007 ready to be open and used for upcoming
FA Cup football matches, concerts and other events.
Facts on the stadium
The stadium contains 2,618 toilets, more than any other venue in the world. It also has a circumference of 1 kilometers (0.6 mi). At its peak, there were more than 3,500 construction workers on site. 4,000 separate piles form the foundations of the new stadium, the deepest of which is 35 m (115 ft).
There are 56 kilometers (35 miles) of heavy-duty power cables in the stadium. 90,000 m³ (120,000 cu yds) of concrete and 23,000 tonnes (25,000 shorttons) of steel were used in the construction of the new stadium.
The total length of the escalators is 400 meters (¼ mi). The Wembley Arch has a diameter greater than that of a cross-channel Eurostar train. The new pitch is 13 ft (4.0 meters) lower than the previous pitch.
The pitch size is 115 yards
(105 meters) long by 75 yards (69 meters) wide, slightly narrower than the
old Wembley. The new 6,350 ton roof covers an area of over 45,000 square
meters (11 acres), 4 acres (16,000 m2) of which are movable and rise to 52
meters (170 ft) above the pitch.
The Arch
Adding to its dramatic presence, Wembley Stadium illuminates the northwest London sky on match days. The vision adopted for the arch was a tube of light that would hover over the stadium at night creating an iconic statement.
To achieve the desired effect, 258 metal halide floodlights have been mounted within the arch to illuminate the internal faces of the lattice and the structural rings that hold it all together. Because the arch is lit from within, the outer faces remain dark and increase the dramatic effect by adding depth and contrast and giving the appearance that the light is trapped within the lattice structure. One of the most significant milestones in the construction of Wembley Stadium was the final positioning of the arch, completed at the end of 2005. Since the arch was lifted in June 2004 it had been temporarily supported on five restraining cables.
Structural engineers from the Mott Stadium Consortium worked closely with main contractor Multiplex and thesteelwork sub contractor to transfer the load – over 1300 tonnes – to the permanent cable net and eyebrow catenary cable. This complex procedure involved first rotating the arch forwards to allow the catenary cable to be connected to the perimeter prismatic truss. The arch was then rotated back to a position where the load was shared between the cable net and the temporary restraining lines. At this point four backstay cables were fixed and post tensioned to help stabilise the arch while the geometry and load distribution in the cable were checked. Finally, the arch was rotated until fullload transfer was achieved and the remaining backstays fitted to restore the arch to its final position of 112 degrees to vertical. Laying back the arch was a prerequisite to de-propping of the roof structure, which has been supported on temporary roof towers. De-propped, the roof was the last key milestone in Wembley’s development. The roof now suspended from the arch and cable net reveals the truly spectacular column free structure covering 90,000 seats.” added Josephine Cutts.
