Design Awards: 2003: Award

City of Manchester Stadium, Manchester

City of Manchester Stadium, Manchester

Architect

Arup Associates

Structural Engineer

Arup Associates and Arup

Steelwork Contractor

Watson Steel Structures Ltd

Main Contractor

Laing O’Rourke Ltd

Client

Manchester City Council

Manchester has a new iconic symbol for the city. It was completed in March 2002 as the centrepiece of the hugely successful XVII Commonwealth Games. The stadium was constructed on a derelict site and will act as a catalyst for the redevelopment of the surrounding area.

The Stadium structure utilises a mixture of structural systems. In-situ and precast concrete were used to construct the stadium bowl and structural steel supported from a cable-net of masts and steel cables to form the roof.

The City of Manchester Stadium is a remarkable structure due to several key features:

  • It is one of the most cost effective quality stadia of its size in Europe. Typical examples of multi-function components of the building are:
    • The stadium is circular to provide optimum views for spectators. It sweeps up from low sides on the North and South elevations that allow sun on to the grassed area, to high sides on the East and West giving protection from prevailing winds and low sun angles.
    • Roof Structural Liner Tray – these 150 deep aluminium panels act structurally to support the roof sheeting as well as creating a hidden zone for acoustic insulation, wiring and roof bracing. The trays also form a visually clean ceiling to the roof that would not usually be economically viable on aesthetic grounds alone.Concrete Ramp Towers – the eight concrete towers to the east and west of the stadium serve three distinct purposes. Firstly they support the spiral ramps that provide access and egress for spectators. Secondly the spaces within the concrete ramp drums are utilised for plant as well as toilet facilities. Finally they provide an elevated support for eight of the 12 roof masts.
  • The stadium is unique in Europe as a building of two distinct lives – initially a 41,000 seat athletics stadium and then to be permanently converted into a 48,000 seat football stadium (completion Summer 2003). The construction flexibility is central to the success of this transformation. The primary roof support structure that consists of a pre-stressed mast and cable-net system is independent of the roof-plane rafters and purlins. This allowed the roof to be added below the cable-net in whatever sequence was required.

The innovative mast and cable-net roof primary structure utilises a ‘grounded tension ring’ in order to create a prestress field against uplift wind loads. The structure comprises 12 cigar-shaped tubular steel masts up to 65 metres high. Eight of the masts sit on cone shaped tubular supports on top of the spiral concrete ramps at the East and West sides. The masts support 76 spiral strand forestay cables in fan-shaped groups of five or seven cables per mast. Each forestay supports an individual roof rafter. Just above the roof surface all forestay ends are connected by a system of four spiral strand cables that form the grounded tension ring (also referred to as the ‘catenary’). Prestress to the catenary and cable-net is provided by the four corner-ties anchored to the ground. The top of each column is tied back to the ground by pairs of backstays comprising groups of ‘Macalloy’ high tensile steel rods.

The erection scheme provided the greatest challenge for the team. The rafters, masts and pyramid supports were fabricated in transportable sections and then welded at site into complete elements. After carrying out risk assessments on the erection scheme it was decided to construct the rafters on temporary props generally supported on the concrete terrace. This allowed the construction of other elements to proceed at the same time without the constraints of sequence. If the masts and cables had been erected first, to provide support for rafters, any delay to the critical cable assembly would have a corresponding delay to the remaining work.

The catenary cables were assembled at ground level in the bowl of the stadium, on jigs which supported the nodes in the correct geometry. After clamping the four cables at the node points, the complete assembly was lifted on top of the rafters and supported on temporary works.

In conjunction with the above, masts were erected and made stable by the permanent backstays and temporary forestays connected to the temporary props supporting the rafters. At this stage the masts were positioned one degree forward of their pre-set geometry to facilitate fixing the permanent forestay cables.

The corner ties to the completed catenary were erected, connected to the catenary, and a pre-tension of 200KN applied. The permanent forestays from mast to catenary were fixed using a predetermined sequence that ensured the catenary displacements were within acceptable limits.

The final tensioning of the cable net could now commence – the basic sequence being to increase the corner tie tension to 1000KN simultaneously at each corner using temporary hollow jacks on the ends of the cables. This was followed by releasing the temporary forestays whilst at the same time adjusting the permanent backstays to maintain a minimum tension. When the majority of the load had transferred from the temporary forestays into the catenary the forestays were then released. Once all the forestays were released final tensioning commenced. Firstly all the backstays to the masts were jacked to length, all four pairs simultaneously, and the pins inserted into the anchorages. After all the backstays were complete the final tensioning of the corner ties commenced simultaneously increasing the tension to 2550kn. The final activity was to jack up the rafters from their supports install its linking member to the catenary node and remove the props.

In summary the structural solution for the stadium has produced a design that not only adds significantly to the overall stadium architecture but is one of the best value-for-money stadia of its size in Europe. It is a demonstration of overall building design, which can be attributed as much to the engineering and construction as to the architect.

Judges’ Comment

s:

The memorable “Mexican wave” roof is suspended from beautifully engineered tension masts, which themselves grow out of the distinctive circular ramp access routes. A catenary ring cable holds the roof down and this is incrementally readjusted to accommodate the fourth side of the stadium now being constructed.

Overall the impression is of an integrated and ingenious building where the design and construction of the steel work is central to the entire project.

New Hangars for TAG Farnborough Airport, Farnborough

New Hangers for TAG Farnborough Airport, Farnborough

Architect

REID Architecture

Structural Engineer

Buro Happold

Steelwork Contractor

Rowecord Engineering Ltd

Main Contractor

Bovis Lend Lease

Client

TAG Farnborough Airport Ltd

Part of the £45m redevelopment of TAG Farnborough Airport, which also includes a 35m high air traffic control tower and brand new terminal, the £9m three bay hangar is 290m long, 45m deep and 22m high at the apex and large enough to accommodate six Boeing 737s.

TAG Farnborough has a vision for the airport and seeks to differentiate themselves from other service providers in this field through the design and quality of the facilities it provides. The challenge set for the design and construction team of Reid Architecture, Buro Happold and Bovis Lend Lease was to accommodate the functional requirements with a design aesthetic that reflects the qualities of the TAG brand image and yet without a cost premium over the more conventional design and build ‘shoe box’ hangars.

The design team appreciated that they had to adopt a radical ‘back to first principles’ approach to meet this challenge and develop a design that was ultra efficient. As with most buildings, a very significant component of cost is the cladding – it was essential to reduce the area of the elevations as much as possible. The added benefit of reducing the volume of the building and minimising the clad elevations is improved aesthetics, reduced wind load on the structure and a reduced impact on the surroundings.

Various structural systems were explored with the arch proving to be the most efficient. The arch followed the natural profile of the plane geometry, ie maximum headroom where the tail fin is and reduced at the wing tips. From a structural point of view an arch is a very efficient structural system acting largely in pure compression minimising bending and deflection. Traditionally the arch reactions are resisted by either using thrust blocks, which would have been large and expensive, or by installing a tie between the arch ends. More usually in a tied arch of this type the tie is placed above the minimum level of the plane increasing the overall height of the building. To avoid raising the structure, the arch form was extended to ground level through the use of inclined “A” frames in the form of concrete filled tubes. In this way the tie could be placed underground in the form of prestressed reinforced concrete beam. By introducing roller doors in tail fin slots in the gable end of the hangar the elevation could be reduced further. Fit out of accommodation within the hangar envelope can then take place with offices and workshop accommodation located around the support legs, rather than in ‘bolt on’ accommodation at the back or sides of the hangar as is more normally the case.

A key concern in the design was the bending induced in the arch through asymmetric loading. Bending resistance was introduced by forming the arch from a trussed arch 3m deep formed from rectangular hollow section chords and square hollow section lacing. The trusses are spaced 9m and span 90m. Secondary trusses link the trusses together and reduce the buckling length of the chords. Each of the trusses is connected to “A” framed support via a pin. The “A” framed legs are made up of concrete filled circular hollow section legs and a headpiece fabricated from 80mm steel plate. Two wind trusses spanning 90m achieve lateral stability. To gain a detailed understanding of how the structure is behaving it was modelled as a three-dimensional non-linear model.

By working closely with the steelwork contractor an erection procedure was established which proved both simple, cost effective and reliable. Each 90m truss was split into three segments. A double bay was assembled on the ground comprising two truss segments linked with all connecting secondary trusses and purlins. These segments would then be lifted in place and jointed in the air. After an initial learning curve and some refinements this method proved very successful. The hangar steel was erected on programme.

The hangar construction commenced with ground works in October/November 2001. Steelwork erection started January/February 2002. The main hangar was completed in November/December 2002 with additional office space being added until April 2003. A total of 823t of structural steel (63 kg/m2) and approximately 100t of cold rolled steel was used in this hangar.

This project has been a good example of what can be achieved by close co-operation between the client, the design team and the specialist contractors and how creative design can achieve a result that completely satisfies the client’s aspirations at a cost of no more than conventional solutions and yet lifts the spirits and is a positive addition to our built environment.

Judges’ Comment

s:

A fundamentally simple concept that meets all the taxing demands of a fast-moving industry has generated a clear solution that is elegant in its design, rational in its engineering technology and economic in its means of implementation. This hangar now sets the standards to which others must aspire. TAG’s design and construction team has produced a winner!