Design Awards: 2011: Award

Exposure, Lelystad

exposure_01

Architect

Antony Gormley Studio

Structural Engineer

Haskoning Nederland BV

Steelwork Contractor

Had-Fab Ltd

Main Contractor

Had-Fab Ltd

Client

Municipality of Lelystad

Exposure is based on Antony Gormley’s own body and stands 25.6m high. The initial shape was created when the artist was covered in plaster of Paris and removed from the shell when the plaster had set. This shell was surveyed by Cambridge University who produced an electronic 3D wire model. This model was then used by the engineers for the project to refine member locations to Gormley’s instructions. The design was then imported directly onto the steelwork contractor’s detailing package. The process of the transfer from design software to the detailing package was breaking new grounds as it had never been done before with such a complex project.

With such a detailed and precisely engineered project a web viewer tool was used to provide the engineer with 3D details of the nodes so that he could confirm that the construction met his design requirements. The detailing process took approximately 12 months to complete.

The web viewer tool was also essential in the fabrication process to gain the true angles of members as well as rotational and other important dimensional checks. It is safe to say that this project would not have been possible just 10 years ago, however with the advancement of modern CAD technology and direct links with CNC fabrication machinery the project was executed using detailed CAD information by interrogating the model using the laptop on the shop floor.

The sculpture is constructed entirely from steel angle profiles. Every angle member is a different length and produced from steel sections ranging from 60mm x 60mm to 200mm x 200mm. Once the angles were punched and sheared to length then the highly skilled and labour intensive shaping of the sculpture began.

Full size paper templates were used to achieve the extremely complex cuts and shaping of the member ends. The welded nodes were produced from randomly rotated angles all joining together on the neutral axes of each member and, more importantly, having full member cross sectional area connection into the node.

The sculpture is made up of 547 nodes, the largest of which are the heart node, weighing 280kg and the brain node, weighing 56kg. The heart node has 29 individual members joining together in the centre. Producing these 2.5m diameter nodes was extremely time-consuming and complex. The nodes meet together to form locating points around the structure which were bolted in position.

Conventional 2D drawings were not suitable for communicating the fabrication information needed by the shop floor team. If a true view is made in 2D then there are no other members on the same plane that could be dimensioned on that true view. It is truly a 3D project that very unusually had to be manufactured on the shop floor in 3D (it would be more usual to produce pieces in the shop and then produce the 3D structure on site when it is erected).

The main key to achieving the project was the node building jig that was developed by the steelwork contractor. This is a 3m diameter ring pivoted top and bottom with graduations at every degree on the base and a clamping system around the ring. This allowed for a main member to be held in a fixed position to the centre of the ring and then members could be accurately added at any position within a complete sphere (anywhere in the world).

A total of 32,000 holes were punched or drilled in the angle profiles and the total weight of the structure was 60 tonnes.

The galvanizing of the structure, particularly the nodes, also posed some challenges. Venting of the nodes was impossible at the detailing stage as the expertise of how to hang the nodes to gain the best coating was impossible to visualise. Whichever way the node was dipped air pockets formed restricting the coating integrity. The galvanizers used an ingenious way of dipping each node into the bath on two wires and then releasing one wire while the node was in the bath, which then allowed the node to rotate and vent the air pockets, resulting in a fully galvanized node.

This is a one-off structure which epitomises the way software, machine technology and manual fabrication techniques can work together. The challenges of the design, detailing, equipment performance and quality fabrication have been extensive.

Judges’ Comment

A remarkable structural steelwork sculpture inspired by the artist’s own crouching body.

The immensely complex arrangement of hundreds of galvanized angle sections, precisely as required by the artist and structural designer, was fabricated in modules for transport and erection. The challenge facing the steelwork contractor was enormous.

This exciting work became a ‘labour of love’ for the whole team, who have achieved a high profile tour-de-force.

American Express Community Stadium, Brighton

amex_stadium_01

Architect

KSS

Structural Engineer

SKM (Europe) Ltd

Steelwork Contractor

Watson Steel Structures Ltd (Severfield-Rower PLC)

Main Contractor

Buckingham Group Contracting Ltd

Client

Brighton & Hove Albion Football Club

Brighton & Hove Albion FC kick off the 2011/12 football season with a new 22,500 seat stadium whose signature feature is a spectacular steel arched roof, engineered from the outset to sympathetically mirror the undulations of the surrounding South Downs.

The stadium comprises 4,200 tonnes of structural steelwork which was constructed between July 2009 and July 2010. The form and shape of the stadium evolved out of a direct response to the site and its topography. The curve and tilt of the roof, together with its arches, effectively replaces a mound of chalk that was scooped out to form the pitch and surrounding stands.

Efficiency and economy of operation of the stadium is key to its long term viability. To this end the stadium has been designed to respect its environment and reduce running costs by achieving a BREEAM ‘very good’ rating. This was met by minimizing construction traffic disruption by relocating spoil locally for the remediation and improvement of the adjacent arable fields, minimal environmental impact of the operational green travel plan, minimizing CO2 emissions by reducing the quantity of construction materials, optimizing insulation standards and minimizing energy consumption and waste.

The challenge to achieve an exceptionally low profile, flat arched roof to meet the visual impact needs and conceptual design ideas required entire world-class long span engineering expertise and unparalleled fabrication and construction experience.

The design trades a relatively complex, but short term, erection strategy for a long term elegance and considerable weight saving per m2. The entire structure works together and every part plays a role so that the roof only became completely self-supporting when all the pieces were in place. This minimized any redundancy and gives a structural form of breathtaking beauty and uncanny lightness of appearance for the spans and roof covering involved.

The 43m wide east roof and the 55m wide west roof are supported by 170m long arched and leaning ‘toblerone’ roof trusses, each weighing in the order of 350 tonnes. The smaller north and south roofs have more conventional cantilever roofs. All four sides of the roof are interconnected and incorporate over 1,000 sliding bolted connections to enable the roofs to continually ‘flex’ during the life of the structure.

Each roof truss is leaning outwards and thus has a natural tendency to deflect outwards and downwards effectively displacing the primary rafters in the same directions. The lateral movement of the rafters is restrained by a catenary member in the plane of the roof running between the rafters outside the line of the arched truss and transfers the tension back to bracing and foundations. To prevent the lateral loads being transferred into the terrace the rafters are supported by double pinned tubular struts.

The 20MN thrust at the ends of each roof truss is transferred to the permanent concrete thrust walls by means of bearings, each of which weighs seven tonnes and is also engineered to cater for rotation of the roof trusses as they ‘flex’ in-service. The construction method was developed alongside the design. The objective was to pre-assemble as much as possible on the ground and minimize temporary works whilst, at the same time, ensuring that the temporary stresses induced within the lightweight roof did not exceed permissible limits.

The 170m long arched roof trusses were delivered to site ‘piece small’, apart from the heavily loaded tapering end sections which were delivered as a plated fabricated section.

The individual members of each truss were first assembled into three 15m deep x 60m long sub-sections, each weighing 120 tonnes. These three sub-sections were then lifted onto a pair of 20m high temporary trestles located at ‘third points’ on the concrete terracing. The ends of the arch are supported by heavily reinforced concrete thrust walls.

Only when the entire roof structure was completed could the temporary trestles be de-jacked and removed from below the west and east roofs of the structure allowing the thrust blocks to take up the load. This process was carefully controlled with each iteration of the de-propping carefully monitored against predicted loads and movements.

Initially the weight of the entire roof was transferred onto sets of jacks installed on each of the four temporary trestles, and the ‘starting’ weight in each of those jacks recorded and compared to predictions. Thereafter the roofs were lowered in approximately 20mm increments at each of the four temporary trestles in turn. Extreme caution was required to ensure that the loads remained equally distributed between the trestles, and that temporary forces being induced into the truss members above each trestle did not approach the safe capacity.

One complication in the de-propping process was that as the roof lowered the truss deflected outwards, thus deflecting the top of the temporary tower which had to be reset to vertical using a set of horizontal jacks installed at the top of each trestle. Eventually the reactions at all four temporary trestles reached zero – at which stage the roof was free-standing and the temporary towers could be removed.

The cutting edge design has achieved a roof weight of just 101Kg/m2 which is a new benchmark for the industry for a long span roof of this form.

Judges’ Comment

This provides a long-awaited home for Brighton & Hove Albion, with community facilities.

A large structure, with curving roof and main trusses, sits comfortably into the rolling South Downs. The blue translucent roof shows off the well executed roof steelwork.

A well conceived and executed steelwork project, demonstrating close and effective cooperation in the team, bringing success for client and public.

Marks & Spencer Distribution Facility, Prologis Park, Bradford

prologis_01

Architect

Stephen George & Partners

Structural Engineer

BWB Consulting

Steelwork Contractor

Barret Steel Buildings Ltd

Main Contractor

Winvic Construction

Client

Prologis Development Ltd

Measuring 512m x 176m this is said to be one of the largest distribution centres ever built in the UK. Occupying the 90-acre ProLogis Park Bradford site, the 1.1m ft2 distribution centre represents the new logistics model for Marks & Spencer. It was officially opened by Marks & Spencer Chairman Stuart Rose in July 2010.

The design and build steelwork package consisted of steelwork for the main building, attached office blocks, stair towers and link bridge.

The 176m span of the roof is achieved through a single curved roof of 1.5km radius and is formed through a series of seven monopitch portal rafters. CA Group River Therm was rolled on site at the eaves in 178m long sheets, the longest single roof sheet ever produced. The programme for the roof installation was set at just 12 weeks. In order for this programme to be achieved it was vital that the highest quality working platform be provided.

It was quickly identified that the combination of a very shallow curved roof over a huge span allowed a unique set of design issues to be addressed by the design team:

  • The cold rolled purlins had to run straight, avoid rotation between supports, be pitched at differing amounts along the rafter, and be set vertically at exactly the correct level for 512m.
  • Each purlin would need to be set slightly different from its adjacent neighbour.
  • The roof had to remain positive under all loading conditions to avoid ponding.
  • The span is formed in seven straight monopitch rafters, each preset from the eaves to reduce dead and service load deflections.
  • The curve is formed by stooling up individual purlin cleats from the rafter backs to the line of the liner tray. This resulted in over 50 differing purlin cleat designs, some differing by only a few millimetres.

At the early stages of design the risk of getting purlin cleats in the wrong location was identified as being high, as was the potential severity of the on-site remedial work and resulting disruption to follow- on trades.

The solution was in two parts:

  1. To scribe each purlin cleat with a unique reference mark
  2. To employ unique scribe technology to not only locate each purlin cleat along the rafter, but also to scribe the corresponding purlin cleat reference mark alongside the cleat scribe location.

Innovative software enabled the close coupled drill/saw to mill unique reference and identification marks onto the steel for identification purposes.

This is taken further by corresponding scribing of the outline of the fittings for location purposes. Each rafter was delivered to the steelwork contractor’s production line with its corresponding set of purlin cleats allowing the plater/welders to easily and efficiently fabricate the rafters, enabling up to 300 tonnes of error free fabrication to be delivered to site each week.

This combination of design risk assessment and fabrication technology allowed the erection of over 7,000 purlin cleats and over 56km of roof purlins to be provided without a single instance of rectification, thus achieving a very high quality finish to the agreed programme.

The client wanted to maximize internal space and to that end no internal cross bracing was allowed. A complex system of roof bracings was designed which allowed the wind loads to be distributed to a series of side bracings, strategically positioned to miss doors, offices and windows. To cope with any possible thermal expansion the design also includes a thermal movement joint which has been positioned half way along the length of the building.

Erection of this 3,000 tonnes shed started in July 2009 and the main shed was erected in only 12 weeks. Erection at this pace demands hour by hour planning with no room for error or delay. This was achieved by detailed planning of the erection and production process. Close liaison with the client and erection sub- contractor was also key. Off site quality control ensured that virtually zero site remedial works was achieved, thereby keeping to a tight cost plan and minimizing disruption to following trades.

The frame has been designed to accept an additional three levels of mezzanine to allow future expansion by Marks & Spencer.

The building achieved ‘Excellent’ BREEAM ratings and the shell is carbon neutral thanks to the use of various organic reductions and the purchase of carbon credits.

Judges’ Comment

This state-of-the-art warehouse and distribution centre, meticulously planned and designed, was erected in 12 weeks.

The exterior conceals the sophistication of the engineering design, fabrication and erection for economy and speed. The extremely slender columns, at wide spacing, soar upwards to support a very light curved roof, avoiding valley drainage. Rooflights allow daylight to fill the cathedral-like space.

The steelwork is outstandingly light, and may well become a benchmark for such projects.

Cannon Place, Cannon Street Station, London

cannon_place_01

Architect

Foggo Associates

Structural Engineer

Foggo Associates

Steelwork Contractor

Watson Steel Structures Ltd (Severfield-Rowen PLC)

Main Contractor

Laing O’Rouke

Client

Hines

Cannon Place is a 37,000m2 ‘air-rights’ office development in the City of London above Cannon Street mainline and underground stations. The site is broadly rectangular measuring 67.5m x 87m. The brief called for a building which would appeal to financial, legal and corporate tenants, be capable of multiple sub division and optimize the quantum of lettable space on the site.

The site sits in the foreground of protected views of St Paul’s Cathedral, which has the effect of ‘capping’ the height of the scheme at 51.3m AOD. A minimum height of 5.1m above the running tracks of the mainline station had to be maintained. As a result, a height of just 32m existed within which to plan the eight floors of office space needed for commercial viability.

The site was further encumbered by:

  • the inability to found vertical structure in the London Undergound tunnels on the north elevation
  • significant existing foundations under the previous Cannon Street station facing slab block
  • the limitations on column setting out imposed by the mainline railway
  • the requirement to minimize foundations in the archaeologically sensitive Scheduled Ancient Monument.

A structural solution was devised which balances a cantilevered 21m deep ‘strip’ of office space to the north with the equivalent accommodation in the south through the use of façade deep transfer structures. This obviates the need for columns in impossible areas and transfer structures, by virtue of their location, do not eat into the development zone and reduce floor to ceiling heights.

The striking nature of the structure has been expressed by placing the fully glazed curtain wall inside the structural frame allowing the engineering to become the ‘architecture’ of the design. A plan form was devised dividing each of the floorplates into five ‘strips’ of accommodation – three of 21m deep space, separated by two of 12m. At each end of each 12m strip sits a 12m sq fire escape and service core. In the centre of each 12m zone is an atrium which allows daylight to penetrate deep into the heart of the floor plan, each atrium also contains six scenic passenger lifts.

Only columns in these 12m strips continue through the station to foundations. However, in the south atrium the number of columns passing through the station is reduced with transfer structures, a further eight columns terminate above the station acting as ‘link columns’ between the office floors above improving the floors’ dynamic performance.

Floor structures comprise 21m secondary steel beams spanning between 6m or 12m primary beams. All beams are 725 deep Fabsec beams which act compositely with a 130 lightweight concrete slab on re- entrant metal deck. The deep long span cellular beams allow the building services to pass through them maximizing floor to ceiling heights.

The north and south façade structures comprise 67.5m long deep trusses, with horizontal and vertical CHSs and diagonal ties that pick up the 21m secondary beams supporting the north and south office fingers. These trusses are supported by cantilever fabricated box section ‘X frames’ along the east and west façades, which are supported at the eastern and western edges of the two founding zones on four 12m x 14m x 1.3m wide composite steel and concrete thick-plate structures, ‘hour- glassed’ on three edges to distribute the load evenly to the foundations.

The completed structure had to be within tolerance of a pre-determined line and level to allow installation of the cladding and to align internal elements. Elastic deformations, fabrication and erection tolerances and semi-random variables were assessed and pre-set, deformed shapes were defined – a camber for the north and south façades and a trapezium for the four ‘X- frame’ cantilevers.

The huge exposed cross frame structures consist of plated box sections with plate thicknesses up to 100mm engineered to be site bolted with exposed pinned connections with just 2mm clearance holes. The accurate fabrication required was achieved with the use of 3D laser equipment and specialized jigs and machining operations. The welding processes were carefully controlled to minimize distortion and each frame was trial assembled during the fabrication process to ensure the pinned fit-up was achieved.

It would have been impossible to build the cantilever ‘X frames’ without some form of temporary support as any dead load deflection during erection would have prevented fit-up of the large diameter pins. However due to restrictions, it was not possible to provide temporary towers under the ends of the cantilever. Instead a method was developed whereby the bottom boom of the façade trusses to each elevation was supported by two sets of 12 sets of cables and strand jacks tied back diagonally to the completed central core area. As the cantilever structure was progressively erected the geometry had to be continually monitored and the strand jacks adjusted to maintain the theoretical shape. Once the frame was fully erected and all the pins installed, the strand jacks were released to allow the structure to cantilever and the floor slabs were cast.

In order to ensure the final load distribution from the ‘hour glass’ structures to the foundations was within the assumed parameters, a controlled minimum load applied through flat jacks was introduced at the base of one end of each “hour glass” structure. The jacks were then filled with resin and the bases were grouted.

The design and construction team have successfully overcome huge design and logistical challenges which would have been impossible without the use of steel

Judges’ Comment

This City site has a busy rail terminus, an Underground station and extensive archaeology!

The structural design has only four principal locations for foundations and supports. The façade structure is loadbearing, contributing to the support of the upper floors, onto four massive trunnion columns expressed externally.

The structural concept was heroic, the appearance is striking, and the site constraints were remarkable. A huge challenge, outstandingly well answered with steelwork.