Design Awards: 2012: Award

The Footbridge, MediaCityUK

footbridge_mediacity

Architect

Wilkinson Eyre Architects

Structural Engineer

Ramboll

Steel Contractor

Rowecord Engineering Ltd

Main Contractor

Balfour Beatty Regional Civil Engineering

Client

The Peel Group

 

The Footbridge at MediaCityUK spans the Manchester Ship Canal and is a signature element within the redevelopment of the region; former industrial docks located along the canal and now a new home for the BBC. Symbolising regeneration and allowing for future expansion the steel swing bridge was constructed from modular sections, while the deck was launched into position via an innovative sliding procedure. It links the MediaCityUK site with South Quay, adjacent to the Imperial War Museum North.

The bridge is a cable-stayed steel structure aligned roughly north to south that features a pair of asymmetric spans; on its northern side is the main span, approximately 65m long, which crosses the canal, while at the southern end is an approximately 18m long concrete-filled back span that serves as a counterweight. A fan-shaped array of masts supports the high-tensile, spiral-strand steel cables. Varying in height up to 30m, the masts converge at their base in a steel pedestal that is centred on the 9m diameter reinforced-concrete pier on which the bridge deck pivots. The pier is located in the canal and founded on bedrock, constructed in the dry via the use of a steel cofferdam system, the lower portion of which was left in place around the concrete shaft.

In order to meet the client’s desire for a ‘unique and memorable’ structure the asymmetrical profile of the bridge, along with the masts and cables, intentionally mimics the shape of the industrial cranes that once lined the docks. The existing public right of navigation continues – thus the bridge was designed as a movable structure, swinging to the west. Its closed clearance over the 10m wide navigation channel was set at 4.77m.

The design is far from being run-of-the- mill; this asymmetric cable-stayed structure’s main span pivots through 71 degrees to allow vessels to pass along the canal. Choosing a swing bridge design over a fixed crossing was one of the main design issues and the choice was made because of the public right of navigation. Although ships do not enter the Port of Manchester on such a regular basis as they once did, the bridge design had to accommodate any possible ship movements and usage could potentially increase as the redevelopment of the area progresses.

Structurally the bridge comprises two spans; the main pivoting span crossing the canal is 65m long, with a short back span of 18m. The latter was constructed as a hollow steel box and then filled with concrete to form the bridge’s counterweight for balancing the main span during opening.

The main span’s deck is fabricated as a shaped internally stiffened orthotropic steel box, with pedestrians walking on an epoxy aggregate applied coating. A fully welded structure, the deck box is sealed against the ingress of moisture making the internal areas maintenance free. Supporting the deck at 6m centres are steel cables, all anchored at their upper and lower ends using fork connectors onto steel outstand lugs aligned in the plane of the stays at the mast tip and deck connections.

The most economical method of constructing this bridge was to fabricate much of the structure off-site. To achieve this, the steelwork contractor fabricated the majority of the structure in modular sections, which were then brought to site to be welded together and assembled adjacent to the bridge’s final position.

With a width that fans out from 6m to 18m, the main span was fabricated in three sections, while the shorter back span was fabricated as one section. All steel sections had two coats of paint applied at the factory – a further two were applied once the welding had been completed.

Prior to the spans being assembled the steelwork contractor first had to install the steelwork for the pivot bearing. The pivot for the bridge comprises a large steel casting welded into the pivot zone of the steelwork deck and mounted on a slewing bearing, which in turn is supported on a fabricated steel structure. This arrangement provides vertical support, resists the overturning moment generated about the horizontal axes and also provides horizontal restraint during bridge rotation.

Both spans were then slid into position; the main span first and then the back span. Once these were in position temporary works were assembled to allow the masts and cables to be erected and installed. With temporary works supporting the spans, as well as beam and column steelworks supporting the masts, the cables were attached and correctly tensioned. Only when all of the cables were in position were the temporary works removed.

This was a unique project from start to finish; both in design and execution. Not only was the slide procedure and construction method slightly unusual, but the bridge’s design is also unique as the deck is curved in plan and elevation.

Judges’ Comment

This elegant cable-stayed swing bridge completes the pedestrian links at Salford Quays.

The tapering triangular box deck is curved on plan and elevation, and is supported by multiple masts at the bridge pivot points. The details of the structure and attachments are well-considered and executed.

This is analytically courageous and technically accomplished.

 

The Royal Shakespeare Theatre, Stratford-Upon-Avon

royal_shakespeare_theatre

Architect

Bennetts Associates Architects

Structural Engineer

Buro Happold

Steelwork Contractors

Billington Structures Ltd (Primary Steelwork) CMF Ltd (Auditorium Steelwork)

Main Contractor

Mace Group Ltd

Client

Royal Shakespeare Company

 

The Royal Shakespeare Theatre opened its doors in November 2010 following a £112.8M renovation. The theatre is one of the most iconic theatrical sites, and the Royal Shakespeare Company (RSC) wanted to create the best theatre in the world to perform and pay homage to Shakespeare plays.

The ‘Transformation’ project called for the retention of the existing theatre facade and foyer and the rebuilding of a larger theatre. This included the creation of a new 1,040+ seat thrust stage auditorium bringing the actors and audiences closer together based on courtyard theatres of the Middle Ages, with the distance of the furthest seat from the stage being reduced from 27m to 15m.

Several elements were involved in the overall transformation, including the refurbishment of the existing building and the demolition of the ‘picture frame’ auditorium which was originally built in the 1930s. Improvements to the Swan Theatre created an array of new public spaces, including a Riverside Cafe and Rooftop Restaurant, a 36m observation tower and improved backstage conditions. The new theatre was also made more accessible to people with disabilities.

The main part of the transformation involved structural steelwork extensions to three areas on the existing building, including the new auditorium and two new wings. This work required the seamless supply and installation of 580 tonnes of structural steelwork, as well as having to be sensitive to the needs of the area and fit comfortably alongside the remaining historic building.

The new auditorium sits in between the retained theatre fly tower and the 1930s Grade II listed Scott Foyer. The two main roof trusses span the length of the new auditorium at 24m long x 2.5m deep and weighing 36 tonnes. The trusses needed to be solid and were designed to support 25 tonnes of scenery which is to be suspended from them. They will also support a hanging technical gallery which will be used for lighting and sound equipment, plus two hung floors over the auditorium.

The complexity of the theatre brought with it many challenges during the erection phase. The biggest was making the improvements to the existing theatre building where the steel had to be erected in and around the building, with consideration given to the surrounding area and infrastructure. The most challenging element was working around temporary supports which were in place and could not be removed until the solid structure had been connected. Erection of the fabricated new fly tower behind the new stage area, took place on site within a very tight space. While erection of the columns was relatively straightforward, the internal trusses required splicing and lifting into the tower in small sections. This was a time- consuming task that required extra care during erection due to the Grade II listed building classification the theatre has.

The building’s architectural excellence involved the construction of a new ‘thrust stage’ main auditorium and remodelling of public and back-of-house spaces, whilst retaining the art deco interiors of the existing foyers. A public square and viewing tower were to be added as part of a master plan to enhance the visitor experience. The 32m high ‘lantern’ platform, giving visitors panoramic views across Stratford, has been positioned at the top of the theatre’s new tower.

Steel’s lightweight advantage suited the complexity of the project. The efficient design, fabrication and erection allowed the steelwork to connect back to the existing building’s retained facade. Overall around 36 tonnes of trusses were erected which were brought to site in three sections and assembled on site before being lifted into place with some complex lifts and manoeuvres.

The steel wing structure includes a 10m long Vierendeel truss which connects up the rooftop cafe’s canopy. This section weighed 10 tonnes and was brought to site in one piece prior to lifting into position.

Another complex part of the erection process was to erect new steelwork walkways to the retained fly tower. Access was very limited and the steel had to be lifted through a 2m x 2m opening in the tower’s roof.

Throughout the project there was a high degree of communication between the project team to value engineer and accurately produce prototype 3D models that not only drove the seamless installation of steelwork but helped achieve the most exacting of site programmes.

The models produced for all areas of the structure in erection sequence helped give project managers and all site operatives a better understanding of the complexities of the steel structure and its integration into and around the existing building.

Fire engineering on the building was achieved through a combination of shop applied corrosion primer protection, and intumescent coating to the exposed beams in the foyer.

Judges’ Comment

The complete remodelling of this iconic theatre and varied ancillary areas has been exceptionally challenging. The design team, main contractor and steelwork contractors have responded well to the evolving demands of the scheme. The steelwork has been key to dealing with the varied major areas, with interesting interactions of structural materials.

The breadth and popularity of the theatre’s activities illustrate the success of this complex project.

 

Peace Bridge, Derry-Londonderry

peace_bridge

Architect

Wilkinson Eyre Architects

Structural Engineer

Aecom

Steelwork Contractor

Rowecord Engineering Ltd

Main Contractor

Graham Construction

Client

ILEX Urban Regeneration Company

 

The Peace Bridge was conceived as a landmark structure across the River Foyle in Derry-Londonderry linking historically divided communities on the east and west banks.

The bridge is a self-anchored suspension bridge for the use of pedestrians and cyclists. The bridge deck is divided into two curved halves, each supported by the suspension system from a single inclined steel pylon. At the centre of the river, the structural systems overlap to form a ‘structural handshake’. The 312m long bridge has six spans in total, three of which are supported from the cables. The main river span is 96m, with a minimum clearance of 4.3m for navigation.

The bridge deck is an orthotropic steel triangular box section, fabricated from painted weathering steel, and stiffened both longitudinally and transversely. The transverse cantilever girders are fabricated I-sections connected to the underside of the sloping box web. A perforated aluminium decking system spans longitudinally between the cantilever girders. The convex edge of the deck is provided with a longitudinal stringer beam that connects the ends of the deck cantilevers and provides support to the parapet system.

The deck width varies fluidly from 3.5m at the ends of the crossing to 4.5m at pier locations in the river to allow space for fixed seating. The zone of aluminium decking meanders sinuously over the river varying in width according to location as it undergoes a transition from being supported by one deck box to the other with the transition in the main span. The porosity of the decking system between the box girders in the main span region is used to enhance the aerodynamic stability of the bridge.

The sweeping alignment of the deck and catenaries is supported over the water from two oppositely inclined pylons. Each has an overall height of c38m and rakes away from the bridge deck. The pylons are formed from tapering hexagonal fabricated steel box sections which transform into a triangular based pyramid at the tip.

The bridge deck is suspended from one edge by a filigree array of hanger rods comprising helically spun spiral strands. These are spaced along the concave edge of the deck at approximately 4.5m centres. The main catenary cables comprise locked coil strands. The cable geometry has been determined to support the deck system efficiently and ensure deck stability under wind and dynamic pedestrian loading.

The parapet is a bespoke stainless steel system with plate posts, tensioned wires and continuous welded top and hand rails. A feature at the pylons is the provision of bench seating with glazed back panels to provide a windbreak. Glazed panels are also provided in the span over the railway to provide the required level of protection over the line.

Particular care was taken in the selection of materials to minimise the whole-life cost; important due to the unique form of this bridge and its challenging environment. The internal surfaces of the deck boxes are unpainted weathering steel with sacrificial thickness to reduce the future maintenance costs, and minimise the risks associated with working in confined spaces. The main suspension cables are locked-coil strand with internal blocking compound and three outer layers of interlocking ‘z’ shaped galvanized wires which provide excellent protection against water ingress.

The bridge substructure generally consists of concrete pile caps on tubular steel piles. The pile caps were constructed using precast concrete shell sections to minimise wet working and reduce the environmental impact on the river.

Prior to fabrication, a comprehensive 3D computer model of the bridge pylons and deck was created which assisted the visualisation of the complex structure and simplified the checking process. Subsequently, the model was used to produce component, fabrication and assembly drawings.

The bridge deck sections were erected on temporary supports placed in the river using a large floating crane. The pylons were erected in a similar manner. The majority of work to install parapets, bridge lighting and aluminium deck systems was carried out in the Port assembly area minimising the extent of works required over water.

Following installation and welding of all deck units the suspension cable installation was undertaken in two stages. In the first stage the cables were anchored to the deck and pylon anchorages using a system of multiple winches and guides that hoisted the cable up from the deck. All of the hangers and clamps were attached to the cables as they were winched up to minimise working at height and over water. The hangers were all installed to their calculated final lengths.

In the second stage the suspension system was stressed by an innovative system of jacking the main catenary cables only. As a suspension bridge, the combination of unstressed lengths of suspension cables and hangers, deck weight and tower stiffness define the unique deck and cable profiles. The catenaries were stressed simultaneously using synchronised jacks to activate the whole suspension system in a single operation. The loads and geometry were comprehensively monitored and, as predicted, when the cable loads reached 98% of design values the deck was lifted off the temporary supports and was supported fully by the cable system.

From the overall arrangement of forms to the visual resolution of small details, the engineering and architecture of the bridge are seamlessly integrated. The structure is deliberately highly visible as it crosses the open water of the River Foyle and symbolic of its intended aim of uniting historically divided communities.

Judges’ Comment

This bridge is symbolic of recent political and physical developments.

S-shaped on plan, and sloping from the city walls to a development area to the East, the triangular box girder deck is supported from cables over two masts within the river. This robust construction is a fine example of careful detailing and complex fabrication.

This excellent bridge is much loved within the city and across Northern Ireland.

 

M53 Bidston Moss Viaduct Strengthening

m53_bidston

Structural Engineer

Amey

Steelwork Contractor

Cleveland Bridge UK Ltd

Main Contractor

Costain

Client

Highways Agency

The 730m multi-span box girder viaduct connects the M53 to the Kingsway Tunnel under the River Mersey and carries 63,000 vehicles daily on this strategic route to Liverpool. The viaduct was facing closure if not strengthened.

The complex project involved numerous innovative design solutions and 100km of new weld in extremely confined space conditions to strengthen and restore the viaduct to full network capacity, whilst maintaining live traffic at all peak times on the M53. The 100-week construction phase also included follow-on refurbishment activities including re-painting, drainage, lighting, cathodic protection and other highway works. To protect the road user, workforce and environment, 3.7km of box girder was housed within bespoke scaffold containment.

The main criterion for the design was to ensure strengthening work could be completed with minimal disruption to the road user. As such, most of the strengthening work was carried out inside the boxes and external faces of the box. A staged sequence was used minimising potential weakening of the structure due to drilling holes, cutting out large holes, applying heat to the structure and removing existing welds, which did not reduce the structural capacity of the structure significantly, allowing withstanding of the load effects from the interim loading.

The detailed structural surveys and analysis during the initial Phase A design period developed strengthening solutions bespoke to the project. With 604 unique boxes to be strengthened, the team developed specific solutions to suit requirements minimising the overuse of materials, maximising efficiency and steelwork techniques guaranteeing the 80-year design life.

It was recognised during the early stages that access through the structure was a serious health and safety concern due to the extreme confined spaces. A business case put forward demonstrated that by enlarging the 602 openings this would significantly reduce risk to the programme and budget, giving greater certainty to the scheme outturn. This resulted in a £6.016m target cost being approved in advance of the main works, saving a proposed £1.9m with a two week programme saving; the actual saving was £6.1m and 12 weeks’ early completion.

A full-time permit control and bespoke rescue team was maintained on site during all working periods who could respond and be at the scene of any incident within the extreme confined spaces in less than five minutes. Throughout the project, a full emergency and fire plan was maintained and several mock rescues and fire training events were held with the local fire department.

Working as an integrated team the number of solutions required was reduced to achieve the required strength. A number of value engineered solutions were completed – a good example of this was the strengthening of cross girder connections resulting in a saving of £700k.

Steel strengthening was utilised as it is compatible with the existing steel material. By strengthening the existing structure, this mitigated full replacement at a potential further cost of over £100m and reduced the embodied carbon by 85%, notwithstanding traffic disruption caused through taking a key strategic route into Liverpool offline. Steelwork allowed significant flexibility in design and construction, as well as reduced future maintenance costs when whole life cost is considered. Through the lightweight nature and unique installation methods utilised on the viaduct the project was able to limit the loading transmitting to the existing foundations.

The steelwork scope involved strengthening 3,900 linear metres of existing box corner welds both overhead and down hand, some 32,500 retrofit shear pin connectors enhanced the longitudinal shear transfer capacity of load from reinforced concrete slab to steel box. 140,000 holes required drilling in up to four plies worth of steel using close tolerance steel drilling which allowed the completion of holes at a diameter of 20mm within tolerance of 0.00mm + 0.15mm. To install over 565 tonnes of steel, 26,200m of finished weld was completed using highly specialised labour, varying between 1 and 14 runs, in excess of 100km.

Through utilising a bespoke containment system steelwork installation could progress seamlessly. The strictly controlled environment allowed first class application of corrosion protection paint utilising innovative equipment, currently the only project to be using such equipment.

A reduction of 99% of harmful fumes from painting operations delivered significant sustainable solutions.

With the entire site striving for continual improvement a true ‘Lean Culture’ was seen on the project which meant a drive to remove waste from processes and ensure smooth flow. Over 16 ‘Lean’improvements were delivered which represented a total saving of over £2.5m.

Through extensive engagement and flexibility of the steelwork installation significant savings were achieved. Of the original target cost of £25m through the installation of 387 tonnes of steel, a final 565 tonnes of steel was installed at a cost of £16.8m. This exceptional result was achieved through the extensive collaboration, integration and continual strive to optimise all solutions.

Judges’ Comment

The original bridge structure was executed by a shipbuilder in the 1970s, and this is the third exercise to strengthen it to current standards. The work of the designer and steelwork contractor has been outstanding in investigating, analysing and executing the strengthening throughout the 3km length.

Successfully and safely undertaking the extensive heavy welding inside the very confined boxes presented extraordinary challenges.

London 2012 Velodrome, Olympic Park, London

velodrome

Architect

Hopkins Architects

Structural Engineer

Expedition Engineering

Steelwork Contractor

Watson Steel Structures Ltd (Severfield-Rowen PLC)

Main Contractor

ISG Construction

Client

Olypmic Delivery Authority

 

The 6,000 seat London 2012 Velodrome will serve as an Olympic and Paralympic stadium for track cycling during the Games. In legacy use, it will take its place as the centrepiece of the VeloPark, a unique community cycling venue that will provide pleasure and employment to generations of Londoners and visitors from all over the world.

The Velodrome is a world-class venue that intelligently answers questions of function, beauty, sustainability, buildability and value. It has been delivered by a truly integrated design and construction team who have pursued an agenda of form following function. Inspired by the dynamism and geometry of the track and the engineering rigour of high performance bikes, the team’s design approach followed the desire for lean design throughout: putting the right material in the right places and removing unnecessary ‘fat’. Structural steelwork fits perfectly with this agenda, providing an ultra light, ultra strong roof solution.

The external appearance of the Velodrome is the result of ‘shrink wrapping’ a skin onto a steel skeleton of accommodation within. This both minimises the internal volume that needs to be heated and reduces the surface area (and cost) of the cladding. The roof form is generated by tightly wrapping a steel cable net down onto the seating bowl leading to the distinctive double curved roof form. Similarly, the outer wall is inclined reflecting how the facade is fixed directly to the back of the upper bowl. This ensemble appears to float over a glazed band splitting the upper and lower tiers – flooding the stadium with natural light and providing dramatic views, connecting events inside with the rest of the Velopark.

On track for a BREEAM ‘Excellent’ rating, the Velodrome boasts a number of impressive statistics: 29% recycled content in the building, natural ventilation, exceeding Part L (2006) by 30% and extensive use of natural daylighting to name but a few. The structural system is so efficient that the steel cable net roof is about 35% lighter than the roof of the next best comparable venue in the world.

From the outset, a steel cable net structure was the preferred choice for the 13,000m2 roof as it lends itself perfectly to the shape and span, providing a combination of strength and lightness.

A curved steel-framed ‘bowl’ supports the upper seating tiers and is topped by an undulating steel perimeter ring truss, which is used to restrain the roof cables.

 

 

Both utilise CHS and Catalogue column and beam sections extensively. Unusually for a cable roof, the perimeter ring truss is integral with the steel supporting bowl in order to take advantage of the strength and stiffness of the whole structure. The key advantage of this was that the ring truss became substantially smaller than a self- contained truss member would have been, enabling the re-use of a CHS reclaimed from the Petroleum Institute to form the truss chords. This integrated approach generated embodied carbon savings of approximately 3,500 tonnes.

The air-handling units were integrated into the voids formed between the skeletal structure of the steel bowl, while the seating terraces were affixed directly to the inside of the bowl and the building cladding was fixed directly to the outside. This detailed coordination was achieved using 3D modelling software to precisely communicate the positioning of the services, architecture and steelwork in the limited space.

Construction issues included design for temporary construction load cases where the main bowl forces are reversed compared to the completed state. To successfully resolve this, structural steel columns and hollow sections were the best choice of material, and included the use of Macalloy post tensioning bars for the primary piers.

Due to the design of the cable net the steelwork was erected to a very tight tolerance (± 5mm) 20m up in the air. This required extensive use of 3D surveying tools and a significant use of prefabrication. The design of the steel bowl was developed around prefabrication to improve speed, cut down on waste, and improve quality. The success of using prefabrication is shown in that the only curved elements of the structure became the chord members of the steel ring truss.

The steel upper bowl was fabricated and erected as a series of 2D factory prefabricated trusses using off the shelf

column sections and designed to be self stable on supporting piers following base bolt tightening. Permanent lateral bracing was used to tie the trusses together with no temporary steelwork required during the erection.

The desire to reduce working at height was a significant reason for opting for a cable net roof. The cables were laid out at ground level, clamped together and safety- netted. Only then were the cables jacked up into position: without any temporary works and completed in just three weeks.

The Velodrome’s overriding strength is as an example of the benefits of good collaboration. The early design input of specialists such as the steelwork contractor was critical to the success of this innovative integrated building design. Collaboration ensured the right material was used in the right place, and the use of structural steelwork played a vital role in enabling the initial desire for ultra-lean design to be realised as an iconic sporting venue.

Judges’ Comment

The capabilities and versatility of steelwork have been used well in this fine building. Using lean design, this exemplifies an integrated design/construction team mastering a complex brief to produce an exciting and sustainable result.

Truly an iconic world-class sporting venue which will endure in its legacy use in the VeloPark.

 

Olympic Stadium, London

olympic_stadium
© London 2012

Architect

Populous

Structural Engineer

Buro Happold

Steelwork Contractor

Watson Steel Structures Ltd (Severfield-Rowen PLC)

Main Contractor

Sir Robert McAlpine

Client

Olympic Delivery Authority

The brief was for a stadium of 80,000 capacity to host the London 2012 Olympic and Paralympic Games with the flexibility to transform into a smaller 25,000 capacity venue for the legacy. The requirement for a temporary 55,000 seat structure resulted in a lightweight demountable steelwork design consisting of trussed rakers on raking columns, which reduced the footprint and minimised the impact on the spectator circulation areas below the terracing.

To provide flexibility in both construction, dismantling and possible legacy uses the roof is structurally independent from the terrace structure. The roof consists of a 900m long ring truss supported on a series of inclined tubular columns. As the structure needs to be demountable, all site connections including those between the steel and precast concrete units are bolted.

The terrace superstructure consists of precast concrete units resting on large raking lattice girders, which are supported on concrete shear walls at the front and by raking steel columns along the span. The terrace girders were detailed as factory welded units and made as large as possible but within the easily transportable limits. The design was rationalised through the design development period to minimise the number of components and allow simple connections to be used.

The roof covering consists of a PVC fabric supported on a cable net with an inner tension cable ring and an outer steel compression truss. The outer ring truss is approximately 900m long and 12m deep and is supported at 32 positions by inclined raking tubular columns down to ground level. The ring truss was designed to be fully bolted with simple flange connections for ease of erection and dismantling, and the individual sections are faceted rather than curved which reduced the fabrication cost.

The inner cable tension ring consists of ten 60mm diameter cables connected by steel brackets at 6m centres which in turn support a continuous walkway. The ring truss is supported by 80mm diameter suspension cables from the top boom of the compression truss, and the whole system is tensioned by 70mm tie down cables connected to the bottom boom of the compression truss. Sitting on top of the inner cable ring are 14 large pyramidal lighting towers, each 30m high and weighing 34 tonnes, which are restrained to each other and back to the compression truss with a secondary cable system.

The terrace steel structure was erected on two fronts working from the south east corner using crawler cranes, followed closely by the installation of the precast terrace units using separate tower cranes. The precast units were installed by the steelwork contractor and, to minimise any site clashes, all the units were incorporated into the steelwork model during the detailing stage.

The ring truss was delivered to the central area as individual components and assembled in jigs into sections 30m long weighing approximately 100 tonnes each. The leading edge of the truss had to be supported by temporary works from the terrace structure until the ring truss was completed, at which point it became self stable.

The cable tension ring was assembled at low level on a temporary platform at terrace level. The suspension and tie down cables were fixed at high level to the compression truss and laid out across the terrace using temporary mats to prevent damage to either the precast units or the cables themselves. When the inner ring assembly was complete, temporary pulling cables were fixed to the ends of the suspension cables and attached to 32 separate strand jacks located on the top of the inner tension ring. The 32 strand jacks were then operated simultaneously which pulled the inner ring into tension and raised the ring truss of the temporary platform. The tie down cables were connected during the lifting process. Once the net was suspended at its final level, the permanent connections from the suspension cables to the inner ring were made and the pulling jacks and temporary cables removed.

Erection of the lighting towers was extremely challenging due to the weight and lifting radius, and the fact that they were not self-stable until the final high-level circumferential cable had been connected and pre-stressed. The 14 lighting towers were fully assembled and fitted out at ground level. The top ‘A’ frame assembly was lifted off the ground with a 600t capacity crawler crane. The pair of 18m long legs and a 40m long temporary strut were then lifted and fitted to the underside of the ‘A’ frame using a second crane. Each of the assemblies then weighed 43 tonnes and was lifted with a 600t crawler crane.

Following installation of all 14 towers on their temporary supports the upper high level circumferential stability cables and the rear stability cables were fixed and pre-stressed. Before the temporary struts could be removed, verification that the cables had been pre-stressed to the required load, and that the stability of the lighting towers had been transferred to the cable net system, was required.

The final erected geometry of the roof and lighting towers was verified by using a full 3D laser scan of the entire stadium structure. The cable net pre-stress forces were also independently checked using cable vibration measurements to calculate the natural frequencies and forces in the cables.

The Olympic Stadium was completed within budget and handed over three months early.

Judges’ Comment

The requirement for a severe reduction in capacity after the Olympics has resulted in a lean design, with expressed exo-skeletal steel superstructure. This has been stripped of the usual layers of periphery accommodation.

There is clear definition between different structural systems, with white-painted tubular roof, and black steelwork for the seating bowl.

The architecture provides clarity to the structure, and its subsequent disassembly.