Design Awards: 2010

A40 Perryn Road Footbridge

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Architect

Grimshaw

Structural Engineer

Hyder Consulting (UK) Ltd

Steelwork Contractor

S H Structures Ltd

Main Contractor

Carillion Civil Engineering

Client

Transport For London

Perryn Road Footbridge is a high quality steel bridge designed to fit a highly constrained site and to meet challenging accessibility requirements. The bridge layout and architecture required careful consideration to successfully create a crossing that is attractive, safe to use and serves the needs of the local community and the client.

Land availability was severely restricted and compounded by numerous buried services that ran under the footway. Construction of the footbridge had to be undertaken within the constraints of the main contract with regard to working areas, working times and lane closures. The footbridge design allowed construction to satisfy the many conflicting and preexisting constraints and was programmed to minimise disruption.

The architecture provides a clearly understandable link through the “spiralling ribbon” formed by the stairs, ramps and main span parapets. The choice of finishes, architectural lines and structural arrangements successfully integrate the different elements of the crossing. The bridge supports cantilever over the footways with unique asymmetrical spiral staircases winding around and cantilevering from the supports. The ramps are as compact as possible, yet have a maximum gradient of 1:12 and regular landings. Expanded steel mesh screens on the ramps allow good visibility for users and protect the privacy of nearby houses. Both stairs and ramps were provided to cater for all users, and the arrangement allows common entry points for all, and features a bespoke lighting scheme to maximise the security of users.

The bridge supports are major steel fabrications having numerous functions but nonetheless are elegant structural elements. The main span and supports are fully integral, with full moment connections between the truss and supports. To ensure the safety of the crossing the supports were required to withstand the onerous requirements of full collision loading. Dynamic analysis revealed that the supports were important factors in the bridge harmonics. To provide the necessary stiffness and mass, but retain a slender profile, the supports were fabricated in 40mm steel plate and then concrete filled. The only viable foundation locations were extremely restricted areas off the back of footpath. Whilst increasing the main span, these locations avoided costs and risks of delays associated with significant service diversions. To utilise the available foundation areas the bridge supports were required to cantilever off concrete plinths/pilecaps well away from the carriageway. Large mechanical connections, utilising machined shear plates, dowels and high tensile bars, connect the bridge supports to the foundations and transmit significant ultimate limit state loads into the foundations.

The bridge truss comprises curved upper and lower chords that are connected by variously sloping straight bracing members. All the chords and bracing are circular hollow sections, and the sizing and truss geometry was carefully developed such that no stiffening or overlapping of members is required at joint nodes. The chord members are curved to parabolas, the top chords being in vertical planes whilst the bottom chords are in inclined planes to give the bridge deck an elegant vertical profile. Further subtleties to the truss design are that the cross frames are skewed to match the bridge supports; there are elements of symmetry in the truss; and the bottom chord returns in an elegant loop supporting short back spans and the top of the stairs. The structural arrangement of this integral bridge allows a shallow span/depth ratio such that the truss does not rise above the parapets. The bridge deck and guardrails form a continuous ribbon with the link spans, cradled within but distinct from the open tubular steel structure.

The bridge was transported to site, painted and erected as one unit. the bridge supports were erected and concrete filled. During a single night-time road closure, the first permitted on the A40, the lightweight main span was lifted into position and made fully integral with the supports, which had been concrete filled, using bolted connections. Construction of the stairs, ramps and footway works then continued and the bridge was partially opened in June 2009. The footbridge was fully opened in October 2009.

Judges Comment

Steelwork is used imaginatively in this high quality scheme for a very constrained and challenging site in a residential area.

Crossing one of London’s busiest arteries, the skewed deck on cantilevered supports, with spiral staircases and compact stacked ramps, provides access for all types of users.

A well considered and executed urban design produces a robust yet elegant solution.

Energy Recovery Plant, Corus Port Talbot

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Architect

Lazarus & Associates Ltd

Structural Engineer

Siemens Vai

Steelwork Contractor

Rowecord Engineering Ltd

Main Contractor

Rowecord Engineering Ltd

Client

Corus Uk Ltd

The new Energy Recovery Plant will allow the harnessing of the off-gas, rich in carbon monoxide, generated by the ‘Basic Oxygen Steelmaking’ (BOS) process as a source of energy for on-site power plants. To facilitate this new process, a large gas holder along with 3km of associated pipe work and two 70m high stacks, was needed.

Central to the scheme was the new 75,000m3 gas holder which has been constructed roughly equidistant between the power plants and the BOS plant. Approximately 2,700 tonnes of steelwork went into this large structure which is 63m high to the apex of its rooftop vent, 54m in diameter and erected from steel plates.

To avoid excessive working at height, and to minimise the use of scaffolding, the entire gas holder was built from the roof down – one ring of steel at a time using hydraulic jacks to lift the whole structure up to allow the next ring to be welded to the one previously installed.

Early works on site involved ground preparation and piling, prior to concrete slab and steel floor plate being installed. This then allowed the main steel erection programme to begin, with the uppermost ring of plate steel installed first. Each steel plate is 2.4m high x 11.3m long and one circumference – with welded connections – took seven days to complete.

Next the roof framework was erected consisting of a series of 600mm deep rafters which fan out to the perimeter from a central point that was temporarily supported on a trestle. The roof structure also includes steel bracing while all connections for this part of the structure were bolted. Once the roof was clad the structure was raised by a series of hydraulic jacks placed around circumference. The jacking process took approximately five hours and raised the entire steel ring 2.4m, which allowed another complete circumference of steel plates to be installed – this was repeated until the gas holder reached its full height.

As each successive circumference of steel plates was inserted the structure’s weight increased and so the number of jacks had to be increased from 24 at the start to 120 units at end. Likewise, the steel plates’ thickness also increased – due to extra loadings – from 10mm for the upper rings to 16mm thick plates at the bottom.

The final steel ring included a 6m wide access opening, which served the dual purpose of allowing the cherry pickers, used inside the structure’s footprint, an exit route and allowed the gas holder’s internal steelwork to be inserted. Internal steelwork was brought to site ‘piece small’ and once inserted was bolted together. This steelwork included the 18m high piston which when assembled weighed 480 tonnes. As gas enters the holder the piston, which rests on a lattice framework at ground level, rises to 1.5m from the roof when full. As the piston rises an attached rubber membrane, fixed to both the piston and the wall of the holder, unfolds and acts as a seal preventing gas leaks.

This is a project with environmental, cost and energy efficiency credentials.

Judges Comment

In a tough industrial environment, this large scheme shows how steelwork contributes to enormous environmental benefits.

Waste gases (previously flared to atmosphere) are now treated and transported via nearly 5 kms of large pipeline on complex steel support structures, to a large welded steel gas-holder for re-use. The challenges of working in an operational steelworks were huge. The project saves energy and Corus reduces atmospheric emissions

Structural steelwork on a large scale is key to the astonishing pay-back time of less than 3 years! This is outstanding.

Cathedral Bridge, Derby

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Architect

Ramboll

Structural Engineer

Ramboll

Steelwork Contractor

Briton Fabricators Ltd

Main Contractor

Dean & Dyball

Client

Derby City Council

Cathedral Bridge is a new pedestrian link and a cycleway which has also been designed to form a meeting place where people can sit and take in views of the surrounding area.

The new swing bridge had to respond to site constraints associated with a lowbanked, fast-flowing river that can rise quickly by up to 1m. The bridge provided a flexible structure low enough to integrate well with the flood-plain environment, swift enough in its mechanics to respond to water fluctuation as needed; its sharp steel profile evokes associations with the tools – scissor, needle – used throughout the local history of textile manufacture.

The basic form is derived from tailors’ shears, in particular the action of the hinged blades as they open and close. The bridge deck evokes one of the blades with the pivot along its length and the force to open and close the blade applied at the opposite end.

It was the client’s wish to re-instate the 18th Century mill race once used by the famous Silk Mill. This was achieved by designing a single bridge that could span both the river and the mill race in one economic structure. The bridge’s kinked back-span links across the mill race while also contributing structural efficiencies to the design, since it counterbalances the main bridge deck which spans across the Derwent. The 20m high needle-like mast is connected to the hollow box steel section bridge deck by three pre-stressed steel cables: these provide support along the deck’s thicker outer edge, keeping the overall structural depth slender. Operation of the swing bridge mechanism is effortlessly controlled by one person standing at the tail end of the bridge on the western bank, using a specially designed consol.

Feasibility analysis took prominence in early design phases as this complex bridge had to be tuned to function under variable loading conditions both in its open and closed positions, as well as in its transitional mode. During transition the bridge rotates about a vertical axis on a central massive cast steel pivot bearing located under the mast. The tail end bearing is supported along a concealed track concentric to the pivot point, and a roller mechanism concealed beneath the elbow of the bridge deck provides continual vertical support. The nose end of the bridge is entirely unsupported during transition. Projected deflection values were calculated to within a hair’s breadth, pre-cambering the structure for efficiency of construction. Robustness was built into the design to account for unexpected behaviour during the building programme, but the first swing of the bridge came in absolutely level.

Keeping the structure as lean as possible reduced the use of materials, all of which were sourced and fabricated within 15 miles of site. Ecological sensitivity was taken into account. The design is futureproofed to accommodate potential rises in water levels. Analysing the structure to achieve the slimmest possible steel deck depth meant it was possible to calculate a generous tolerance for floodwater rise.

Judges Comment

The skewed swing bridge provides a novel and successful solution to linking parts of the city which previously only had road bridges, hostile to cyclists and pedestrians.

The box girder deck is cable-stayed and slender, and the inclined mast is of Y-shape cross section. The fabrication, particularly of the mast, is of very high quality.

Steelwork shows its capabilities yet again.

The Rose Bowl, Leeds Metropolitan University

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Architect

Sheppard Robson

Structural Engineer

Arup

Steelwork Contractor

Fisher Engineering Ltd (Severfield-Rowen Plc)

Main Contractor

Bam Construction Ltd

Client

Leeds Metropolitan University

The Rose Bowl provides Leeds Metropolitan University with a landmark, easily identifiable building.

Central to the project is the Rose Bowl lecture theatre ‘pod’ which sits ‘half in and half out’ of the atrium and contains one 250-seat theatre, two 140-seat and four 60- seat theatres. As well as having an unusual oval bowl-like shape, tapering outward as it gets higher; the structure is clad in distinctive triangulated reflective glass panels fixed to a bespoke aluminium backing frame system. A series of bridges crosses a semi-public atrium linking the ‘pod’ to the outer U-shaped four-storey main floorplates, which house the offices and ancillary teaching spaces.

The building is built over a two to three storey basement car park which extends significantly beyond the footprint of the building. The sloping site introduces a full storey height difference across the building with access at ground floor into the central atrium beneath the ‘pod’, and at first floor directly into the building and on into the main lecture theatre. From ground level up the structure is steel framed to provide maximum flexibility to the floor plate. Cellular beams were used to allow the coordination of mechanical and electrical services into the void. Clear spans of 15 metres are found throughout the building with perimeter columns set back into the space to create a clean façade. The whole of the steel frame rises off the concrete basement columns and transfer structure located within the ground floor slab.

The outer four-storey faculty block and two-storey plant enclosure were erected in phases to facilitate access to working faces. The faculty building steelwork was initially erected up to third floor level and then used as a working platform for the operation of MEWPs to allow the safe erection of the remaining steelwork to the upper levels.

The pod structure itself consists of a series of Y-shaped feature columns connected to a circumferential truss, or diagrid, extending around the envelope of the pod. Temporary stability during pod erection was ensured by tying the circumferential trusses back to the four internal main columns, which were in turn temporarily tied together to form a central braced core.

The ring of Y-columns at the base required a 100 tonne mobile crane, as each of these columns, brought to site as complete pieces, weighed around 5.5t. The first column to be installed was held in position using the crane, and then the adjacent columns were installed using a second crane and tied together with a beam to provide stability. Once the first two columns were installed and stabilised, the entire ring of columns was completed by tying them into adjacent members and the central braced core.

Once the central core and ring of Y columns were in place, the steel diagrid and floors were erected using the temporary core to control the position of the diagrid and provide stability. On completion of the diagrid shell to third floor level, the concrete deck was poured and the pod became self stable. The remaining diagrid and floors were then installed and the temporary bracing removed.

Fabrication of the Y-shape columns and diagrid members required extremely high levels of accuracy to achieve the necessary tolerances. The Y-shaped columns are complex sections fabricated from individual plates of varying thicknesses of between 20 and 55mm. Each “Y” consists of three tapered branches of triangular section which increase from approximately 350mm in depth at their tips to about 450mm at the central node.

All of the individual plates were blasted before fabrication with the completed assemblies blasted again prior to painting. All steelwork then received intumescent fire protection, including the Y columns to ensure that the optimum level of fire resistance was achieved.

Judges Comment

This university development has three teaching blocks, but the interest is in the splendid ovalshaped structure in the centre.

Tapering outwards as it rises, the Rose Bowl’s frame is supported by Y-shaped two-storey triangular columns, which have been designed and fabricated with crisp corners. The overlying storeys are carried by a vertical diagrid, with elegant bolted connections.

The careful detailing and fine fabrication are commendable.

Legacy Roof, London Aquatics Centre

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Architect

Zaha Hadid Architects

Structural Engineer

Arup

Steelwork Contractor

Rowecord Engineering Ltd

Main Contractor

Balfour Beatty Group Ltd

Client

Olympic Delivery Authority

The London Aquatics Centre will mark the gateway to the 2012 Olympic Park. The stunning waveform shape of its complex steel roof sweeps dramatically upwards in a smooth curve from the south end and then down again over the northern cantilever, while the western and eastern tips curve upwards at the edges.

The 11,000m2 structure spans a column free area 160m long and up to 90m wide. It is supported on bearings on two concrete cores 54m apart near its northern end and on a concrete wall at its southern end. The roof contains about 3,200 tonnes of structural steel, of which 2,000 tonnes are fabricated plate girders with the structural connections totalling around 600 tonnes.

The roof structure comprises a series of long span trusses spanning lengthways over the main pool hall from a transverse truss mounted on the southern retaining wall bearings to another transverse truss spanning between the northern concrete cores. The main trusses lie in a fan arrangement to create the plan shape of the roof. The centre fan trusses cantilever northwards beyond the north transverse truss to form an overhanging canopy over the main public entrance plaza of up to 30m.

The centre fan trusses carry load in truss action, spanning between the north and south transverse trusses which carry the load down to the supporting bearings on the concrete structure below. Due to the roof geometry, arches are formed in the wing areas to the west and east of the central area. Under uniform loading the two opposite inclined arches in the wing areas balance each other, forming a compression hoop around the roof perimeter. A tension force arises from the change in geometry of the compression hoop in plan at the kinks which occur at the wing tips, and this is resisted by a tension tie across the centre and a resulting tension force occurs in the central fan trusses.

Due to the arched shape of the northern transfer truss, lateral thrusts are developed. In the final condition these are resisted by tensions in the plaza level slab. However, as this slab could not be cast until some time after completion of roof erection, it was necessary to install a temporary tie comprising eight high tensile steel bars between the north cores. This was pre-stressed before the roof was lifted off the temporary trestles.

Lateral stability is provided by a system of horizontal and diagonal cross braces in the roof surface between the top chords of the fan trusses. All of the trusses are formed from fabricated H-sections. The plate thicknesses of the sections vary along the length of the trusses to ensure efficient use of material, with plate thicknesses varying between 8mm and 120mm. At site the members were bolted together to produce erectable truss lengths of around 30-40m. The trusses were lifted onto preerected lines of temporary trestles and joined together with bolted splices.

In the permanent condition the roof is designed to be fixed on plan at its northern bearings and free to slide longitudinally at the southern end. However, due to site constraints, it was necessary to construct the roof from south to north, starting with erection of the southern transverse truss which weighed just over 70 tonnes. It was necessary to initially restrain the roof in a longitudinal direction with temporary works at the southern end and then, later in the programme, a controlled transfer of restraint to the northern bearings was carried out whilst simultaneously releasing the southern end.

When 50% of the roof had been erected one of the intermediate lines of trestles had to be removed to allow excavation to start for the deep dive pool. This was achieved by jacking the roof up at the trestle positions to relieve the load from them. The remaining two main lines of trestles were left in position until the main roof structure was complete. On completion of the main erection, the roof was lifted using strand jacks mounted on temporary towers at the south end and allowing it to rotate about the northern bearings. Once the roof was clear the strand jacks were locked off while the trestle heads were dismantled before the roof was lowered to its final position.

All of the bolted connections in the primary structure were designed to be nonslip using tension control bolts. In situations where bolt access was limited by geometric constraints, tension control studs were used. The structure contains about 70,000 bolts.

Due to the highly corrosive environment, rather than leaving faying surfaces unpainted they were coated with zinc silicate paint, slip tests having first been carried out to establish that a suitable slip factor could be achieved. The zinc silicate was used as a primer generally and exposed surfaces were over coated with MIO. In the final condition the steelwork is all concealed by upper and lower surface cladding and so no decorative coat needed to be applied.

A network of 600 linear metres of steel walkways installed throughout the roof space will provide access for regular inspection and maintenance of the structure as well as lighting equipment and other plant.

Temporary stands to the west and east of the structure will provide seating for 14,700 of the full complement of 17,500 spectators for the Olympic mode. These will be removed and recycled on completion of the Olympic and Paralympic Games. The final perimeter façade will then be installed for the legacy mode to provide outstanding community facilities for East London’s future.

Judges Commment

An heroic engineering achievement which has overcome severe programme and constructional problems. A necessarily complex structure delivers the form and shape at the heart of what will become the emblematic and beautiful icon of the London 2012 Olympics.

This is a high profile success for structural steelwork.

The Infinity Footbridge, Stockton-On-Tees

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Structural Engineer

Expedition Engineering

Steelwork Contractor

Cleveland Bridge UK Ltd

Main Contractor

Balfour Beatty Civil Engineering

Client

Stockton-On-Tees Borough Council

The Infinity Footbridge, a unique linkage for pedestrians and cyclists, is formed of two graceful steel arches that flow into one another, spanning 60m from the south bank to the central pier and a further 120m to the north bank of the river, with the 2:1 ratio reflected in the rise of the arches. Such is the length of the north span that it makes the Infinity Footbridge one of the longest footbridges in the UK.

The arches are fabricated from weathering steel to form trapezoidal hollow box sections which vary from 1500mm to 400mm deep and 2500mm to 200mm wide. The arches’ box sections bifurcate on plan over the central pier and are supported by four steel arms. The arms in turn land on two 3-tonne solid machined pieces of high grade steel, forming the central nodes. These neatly resolve forces from the arches, horizontal cables and supporting legs beneath, which then sit on concrete piers below the water line. The deck is made from pre-cast concrete units suspended from the arch by hanger cables and post-tensioned along their length by a pair of longitudinal cables running either side of the deck. These cables also act as ties for the arch which resolve the horizontal thrust within the structure. The deck is finished with a stainless steel handrail which incorporates the bridge’s dynamic lighting system.

Through the design process the bridge was reduced to a minimum number of key structural elements. Each element was considered in order to increase its efficiency and robustness, whilst reducing the need for future maintenance and thus the whole life cost of the bridge. Working with 3-dimensional digital models was central to the design of the Infinity Footbridge. The shape of the arches was perfected using form-finding 3D analysis techniques. The structural analysis model was linked through to the geometrical model, allowing simultaneous updates to both structural and visual models.

As the project moved into the construction phase several contractual barriers were overcome to allow construction information to be delivered in a single digital 3D model. This extensive embrace of the digital 3D model led to project-wide efficiencies and removed the risk of interpretation errors. By avoiding cumbersome 2D paper representations of complex geometry in favour of precise digital 3D models, the project exemplifies the leading edge of coordinated steelwork design and fabrication.

The form-found arches were joined over the central support to provide continuous beam action allowing uneven patch loading to be carried without greatly increasing the depth of each arch.

A rowing course in the Tees meant that any support in the river would need to be off centre. This constraint was transformed into an opportunity by using the shorter stiff span on the south to allow the northern arch to span 120m and come down to a section of just 300x700mm.

This geometry introduced curvatures in the box section plates that exceeded limits in the standard codes which resulted in the 1971 Merrison Report (the father of BS 5400) which covers these limits having to be dug out and dusted off! Through a close working relationship with the Category III checker a methodology was agreed on which ensured the bridge could maintain its graceful form and efficient geometry and meet plate slenderness requirements.

The arches were formed from hollow sections, yet it is not practical to inspect the condition of the steel inside the arch. Weathering steel was therefore used to ensure that the internal surfaces would have adequate corrosion protection. Similarly, the corrosion risk from de-icing salts on the deck was taken into account. As an Icon for North Shore and the whole of Stockton-on-Tees, the Infinity Footbridge is expected to outlive its creators. To combat the significant threat of chlorine attack, the deck has been constructed using stainless steel reinforcement.

The phenomenon of pedestrian induced vibrations on footbridges is well known, hence extensive analytical analysis was undertaken to identify the structure’s natural frequencies and expected behaviour under a variety of cases. This led to the inclusion of seven tuned mass dampers which were discreetly hung within the soffit of the deck units. Following extensive onsite testing of the final structure the analytical model proved highly accurate and the dampers, once released, were seen to perform as predicted.

Lifting the larger steel arch provided a special challenge. Sections of the arch were fabricated in nearby Darlington and then carefully welded together on the river bank. In a single lift using the UK’s largest mobile crane, the large north arch was lifted into place. For the many users of the river there was very little disruption – although there was an impressive display of heavy engineering!

Delivery of the Infinity Footbridge provides both a key driver for regeneration and a well loved local landmark.

Judges Comment

An inspirational project which fulfils the client’s brief for a landmark to open up a development area.

The elegant structure clearly describes the forces on it, and its simplicity belies the technical complexities which were handled by good teamwork. Attention to detail is evident throughout.

This is steelwork at its most dramatic.

Audi West London

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Architect

Wilikinson Eyre Architects

Structural Engineer

Expedition Engineering

Steelwork Contractor

Rowen Structures Ltd (Severfield-Rowen Plc)

Main Contractor

ISG Interiorexterior

Client

Volkswagen Group UK Ltd

The high visibility of the site alongside the elevated section of the M4 in west London presented the client with an opportunity to display his product in an innovative and striking manner. An important aspect of the brief to deliver a landmark project was to consider the product marketing.

The structure is a seven-storey, 30,000m2 celebration of automotive engineering and technical expertise. The five-storey superstructure contains three floors of showroom and sales areas, with offices, marketing and conference facilities over the top two floors. Below ground, a two-storey basement contains futuristic workshops and diagnostic facilities.

Steel is the client’s structural material of choice from bespoke steel boxes submerged below the basement slab to trapezoidal tapering raking columns at the southern façade. The use of a steel frame in the superstructure has allowed a highly flexible floor plan for future renovations to the showroom and office spaces, while the use of a steel intensive perimeter sheet-piled basement has provided significant cost, aesthetic and construction programme benefits below ground.

The building architecture was deliberately pared down by the architect to allow the main features, the cars themselves, to stand out. The structural frame and simple floor arrangements maximise light and airiness. From the full glazing of the main façade to the translucent Kalwall cladding of the rear display areas, natural light is brought deep onto the floors.

Steel was the clear choice for a versatile and flexible floor plan. Long span steel plate girders have been used to allow large (19m span) column free floor plates while squeezing the floor sandwich to a meagre metre from ceiling to finished floor level. To enable the tight floor construction, early coordination of the services with the structure was essential.

Considering the thickness of the floor construction required, composite steel floor decking was the natural choice. The benefits of simple fire protection, speed and safety of construction as well as providing a very lightweight floor were obvious from the outset.

The exposed internal roof structure is a key feature providing a backdrop of engineered architecture to the cavernous rear display space. The single curve of the roof is formed of curved rolled sections simply and elegantly braced and connected. The economic design extends to the lightweight steel roof deck, chosen to provide the roof structure, architectural finish and acoustic attenuation. The speed of erection of the roof deck enabled the quick closing of the building envelope following the steelwork erection.

While the primary roof structure is based on a single axis of curvature, the southern M4 facing edge of the building introduces a curve on plan producing doubly curved eaves. This geometrically challenging edge, fabricated from steel, was included in the primary steelwork package to ensure a crisp, engineered finish.

The design team developed 3D model information that was used directly by the steelwork contractor to bend and fabricate the roof edge. Key details, such as the roof edge cantilevers, were developed by the team in 3D ahead of the appointment of a contractor and included in the tender drawings with the aim to transfer as much useful knowledge as possible.

In the two-storey basement, the use of steel sheet piling for the perimeter walls provided the best balance of resistance to imposed loadings, speed of construction – 3500m2 of sheet piling was installed in less than two months – final appearance and cost. One of the greatest successes of the perimeter sheet piling is the highly aesthetic finish gained without the need for a secondary facing.

On entering the building the space immediately opens up with a double height façade articulated by primary steel columns. The tapered trapezoidal columns are fabricated from 20mm plate and lead the eye through the space. They give context for the hanging mezzanine, with the angle of the steel tension rods echoing the geometry of the leaning façade.

The design of the vehicle restraint system made use of steel plasticity theory to develop a catenary restraint and allow a visually lightweight high tensile steel rod to be used in place of an elastically designed structural section.

In the workshops, but hidden from view, are 26 submerged steel boxes. Each box comprises over half a tonne of fabricated stiffened steel plate designed to contain and protect the hydraulic mechanisms of the workshop car jacks. The jacks are state-ofthe- art car supports that can elevate the cars 2m above the workshop floor and then retract below the basement slab at night. The boxes protect against hydrostatic and clay heave forces and continue the waterproofing line of the basement. The plate thickness allows for sacrificial corrosion over the lifetime of the building.

Early consideration of the buildability of the main frame allowed the steel erection to take place with minimum temporary bracing or supports. The building frame was conceived as a central spine comprising two stability cores and the building atrium. From this spine the north volume, braced via floor slabs and roof trusses, spans to slender perimeter box columns. To the south, the floor beams provide a tie restraint to the inclined tapering façade columns.

The construction methodology is expressed in the exposed roof structure, where central primary roof beams taper to a simple pin at the connection to the northern and southern structures either side.

Throughout the project steel has consistently emerged as the optimum material choice. In particular its ability to provide an economic solution while expressing engineered design has worked to great effect. The highly visible steel structure with carefully considered detailing, provides a stunning backdrop to the automotive design on display

Judges’ Comment

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Comprehensively well designed and economical in form, the structure and its details reflect a technical ethos. The building showcases the values that Audi project to its public, with great panache.

This is an appropriately stylish and racy building, showing structural steelwork to great effect.