Design Awards: 2008

The O2 Arena, North Greenwich

The O2 Arena, North Greenwich

Architect

HOK SPORT ARCHITECTURE

Structural Engineer

BURO HAPPOLD LTD

Steelwork Contractor

WATSON STEEL STRUCTURES LTD

Main Contractor

SIR ROBERT MCALPINE LTD

Client

ANSCHUTZ ENTERTAINMENT GROUP

Situated inside the original Millennium Dome structure, the O2 is a 22,000 seat state-of-the-art multi-purpose venue, including 96 corporate suites. It is designed to be the most technically and acoustically advanced concert arena in Europe.

Built on time and within budget the O2 Arena meets the client brief in every way. The construction programme took two years from first pile to first full capacity concert, as contractually agreed, and was achieved through careful design and teamwork in a well integrated design and build team.

Successful construction was partly due to the engineering design that considered buildability from the outset, including the constraint of being positioned within the existing O2 (Millennium Dome) structure.

The complete roof system, including cladding, catwalks, ductwork and other building services, was completed at ground level and then lifted into place in one piece. Not only was this the safest strategy, but also the most cost effective. Safe erection of the roof was enabled by the use of strand jacking. The unique and innovative lifting process, including all of the method statements and safety check hold points, was agreed between the design-build team and lift specialist PSC-Fagioli.

A detailed 3D coordination process undertaken between Buro Happold, WSSL and HOK, also involved other parties, such as M-E Engineers (for ductwork layouts), to ensure the design was properly communicated to the steelwork contractor.

Combined teamwork was also adopted for the design of the temporary works required to lift the roof. Buro Happold and WSSL worked on different aspects of the lifting frames and slender cores in their temporary condition. The whole team participated in a series of risk workshops to review the methodology, agree hold points and incorporate engineering design constraints to achieve a smooth, risk-free lift process.

The roof lift included geometric constraints of local points on the roof, as well as the global positioning of the structure relative to the concrete cores. This demanded very close monitoring, and the development of corrective measures should the constraints be reached. It was essential that the lifting strands remained within 25mm of vertical, and that the roof remained within a 30mm band of true horizontal, consequently interdisciplinary teamwork was crucial.

Bespoke brackets were used for each purlin pick-up connection to account for the spherical geometry of the roof with standard detail brackets used on the main trusses to reduce complexity.

Considerable skill and workmanship was also required to achieve the construction of some elements to within 2m of the dome fabric, without a single perforation to the existing structure.

Corrosion protection was arranged by dividing the steelwork into five distinct areas, and defining the performance criteria and environment for each. This led to an efficient corrosion protection scheme for the overall roof. Fire protection to the roof was not required.

The positioning of the 4,000 tonne roof in a single lift involved the use of multiple capacity strand jacks that were monitored by both position and load. A bespoke computerised surveying technique was used, which allowed designated positions to be observed in real time.

The design and construction sequence of the core structures allowed this to happen. The quadruped structures were fixed to the roof prior to its lift and then positioned to full height with the main roof inside the core walls. The bearing allowed these quadrupeds to be rotated into their final position.

In two of the cores, structural floors and walls were only constructed once the roof was in position to enable a vertical route for the roof lift. The design and construction of the concrete cores also had to accommodate the temporary lifting frames. The combined steel and concrete structures were assessed for stability and buckling behaviour and monitored during the lift. ‘Stressed skin’ diaphragm action in the deep profile cladding was utilised to gain maximum efficiency in the steel components.

The positioning of the temporary supports was coordinated and analysed from fully supported to lift conditions, to avoid overstress at all times.

The 2,700 tonne roof structure has a design life of 60 years. The design of the structure allows for the possibility of the enveloping main dome structure being removed. It allows for easy replacement of the main bearings at the eight support positions using temporary jacking points, facilitating efficient, effective and safe maintenance. Also, a variety of paint systems were designed to suit the different exposure conditions throughout, and the design incorporates full external snow and wind load allowances.

Judges’ Comment

s:

This is a complex and substantial building in its own right, but made more so by its location within the Millennium Dome, presenting huge challenges. The chosen solution involved raising the 4,000 tonne steel structure, with its cladding, in one lift of more than 40m high to within 2m of the Dome’s roof.

This is a triumph of planning, design and engineering, and a fine example of integrated team working.

National Tennis Centre, Roehampton

National Tennis Centre

Architect

HOPKINS ARCHITECTS

Structural Engineer

ARUP

Steelwork Contractor

ROWECORD ENGINEERING LTD

Main Contractor

ISG

Client

LAWN TENNIS ASSOCIATION

The Lawn Tennis Association (LTA) had long identified the need for a centre of excellence, to provide a world class facility for players and coaches and to be its administrative headquarters. In 2002 the LTA purchased a section of the Bank of England sports ground in Roehampton, and work on site commenced two years later..

The National Tennis Centre (NTC) comprises six indoor courts, 16 outdoor courts (with grass, clay and acrylic surfaces), player training facilities including a gym and a hydrotherapy pool, sports medicine/science facilities, player accommodation, a cafe, teaching spaces and office accommodation.

The LTA brief for the project was that it had to be environmentally friendly, robust and durable, cost effective but, above all, be a facility where the users will be inspired to work and train. The LTA, with its design team, strove to achieve a building that respects the need for sustainable development, whilst preserving the ability to adapt to future needs. Examples of sustainable features include:

  • Low energy design – maximising the use of passive environmental control and using low energy delivery systems
  • Sustainable urban drainage system
  • Rainwater collection and attenuation
  • Appropriate use of low embodied energy materials including recycled and recyclable components
  • components, such as exposed structural concrete, in lieu of separate finish systems
  • Layout and construction schedule designed to minimise disturbance to wildlife
  • A robust and adaptable building suited to future layout changes

In order to satisfy planning requirements the NTC had to be very sensitively integrated into the site. The design minimises the visual “bulk” of the building by keeping the overall height of the roof as low as possible, and by shaping the building envelope to blend into the site.

The roof is curved in section and has a column-free span of approximately 40m courts must conform to strict requirements for plan dimensions and for the height of the roof at key points above the net line and at the back of the court – these rules effectively define a 3-dimensional envelope. The design for the NTC took a different approach, combining simple circular arcs to give an elegant sweeping roof profile. The resulting geometry delivers the required tennis playing envelope whilst minimising the overall height of the building.

During the design phase a number of structural options were considered for the roof. The choice was driven by cost, ease and speed of erection, aesthetics, functionality and durability. The chosen solution comprises pairs of steel arches, spaced 17.4m apart, and spanning 40m across the courts. Each arch consists of three curved “I” beam sections, with the central portion bent to a constant concave radius and the outer portions constant convex radii. These arches are supported by pairs of concrete shear walls in the side blocks. Tapered, raking steel struts prop the beams above the court baseline and are attached into the side block structures at first floor level. These struts, together with the central portion of the curved roof beam, act as a structural arch thrusting between the concrete abutments. The outer portion of the curved beam spans in bending between the prop and the adjacent side block roof level.

In this way, the steel roof structure, acting partly as an arch in compression and partly as a beam in bending, provides a structurally efficient solution for the long span roof. The beam section is only a 533 x 210 x 109 UB which plays a significant part in minimising the overall height of the building. Secondary beams span approximately 14.6m between the paired arches and carry the roof finishes. By using standard beam sections and repetitive connection detailing an economic structure has been achieved.

The overall size of the court building is such that, conventionally, the roof would be divided up by movement joints in order to control in-plane movements generated by temperature changes causing the structure to expand or contract. However, this poses many difficulties in terms of architecture and waterproofing, and is costly. The design team sought an innovative solution, allowing the roof structure to “float” with horizontal restraint provided only at key locations. The team worked very closely with the contractor to develop connection details and an erection sequence that allowed the successful implementation of this ambitious strategy.

The reception building connects the court buildings to the offices. It is covered with a PTFE coated woven glass fibre roof. Two steel masts support a catenary cable with the fabric suspended via a series of steel ‘coathangers’. Boundary cables maintain tension in the fabric, so that the roof forms a double curved surface.

Judges’ Comment

s:

Structures for covered tennis courts have taken many forms, sometimes mundane. The National Tennis Centre, with extensive courts and administrative facilities, is well planned and deceptively simple but effective. The sweeping steelwork in the court roofs and the well developed office structures are both economical and elegant, showing great care and attention by the team.

The nurturing of national tennis talent benefits from the fine environment in this impressive facility. Game, set and match to structural steelwork!

Terminal 5, Heathrow Airport

Terminal 5, Heathrow Airport

Architect

ROGERS STIRK HARBOUR & PARTNERS

Structural Engineer

ARUP

Steelwork Contractor

WATSON STEEL STRUCTURES LTD

Main Contractor

LAING O’ROURKE LTD

Construction Manager

MACE LTD

Client

BAA PLC

BAA commissioned a new terminal, T5, to handle an additional 30M passengers per annum. The design was a direct reaction to BAA’s desire to create a building that would be an aviation landmark and could adapt over time to the ever-changing requirements of the industry. The single span provides a coherent building envelope while remaining independent of the building’s internal superstructure.

The roof has a span of 156m and is 396m long. It is supported by 22 pairs of 914mm diameter steel legs that reach down to apron level in dramatic full-height ‘canyons’ just inside the façades. The scale of the roof’s structural components clearly pointed to the use of steel as a way of creating the simple, independent building enclosure. Building movements and deflections for this type of span suggested that only steel construction would be suited.

One of the main drivers was to reduce site work and this was achieved by providing large pre-fabricated units of up to 55 tonnes each that were bolted together at low level to form the central section of the roof. The central arched section of each phase of the roof build was assembled, clad and prestressed at ground level and was then strand jacked 30m vertically into position and bolted to the abutment steel. Once each phase was complete the temporary works frames that had been used to assemble the abutments were rolled north by 54m ready for the next phase. Prior to the work commencing on site a full sized trial erection was constructed to refine the fabrication and erection processes and increase the efficiency of both on site.

The arch is formed from steel box girders at 18m centres: 800mm wide and up to 3.8m deep. These are tied at high level by pairs of 115mm diameter pre-stressed steel cables. 914mm diameter steel arms reach up from the tops of the legs to support the rafters, and solid steel tie-down straps from the frame structure. The splices in the central arched section of the rafters always carry net compression. Therefore, they can transfer forces from section to section in bearing. No welding is required. 120mm diameter “male” and “female” shear connectors interconnect during erection so that the whole rafter fits together like giant Lego bricks. As a result the splice is almost completely invisible but is very quick and easy to build.

Fully glazed façades engage the passenger with the romance of air travel but, at the same time, the brise soleil that are used to reduce cooling loads and the heavily insulated Kalzip roof minimise energy use and achieve carbon emissions superior to Part L requirements.

The building’s beauty is defined by the simple clear span of the roof which soars 156m from the east side of the building to the west creating two separate “canyons” – each of which responds to the building’s functions relative to passenger usage and airport brief. At these areas the roof structure is used to define passenger movement systems and provide scale. Within these spaces the roof supports also act as the façade’s lateral support members, creating an integrated building envelope.

The assembly of the huge connecting plates that made up the nodes was a feat of accuracy and materials handling, and the node castings were beautifully patterned and fettled by hand. The finish of both of these was not ground or polished and all the welds were left as laid. This gives the structure a scale and a grain and speaks of the human craftsmanship that has formed it.

The nodes are made from pieces of steel plate that are flame cut to shape and slotted together to avoid site welding and allow a speedy fit up on site. The loads are (almost) always compressive, so direct bearing of steel on steel is an efficient way of transferring forces. However, any angular discrepancy in the fit up could throw the far end of a 22m long member seriously out of position. The bearing surfaces were made cylindrical to allow perfect fit over a range of angles. The geometry and fit of the parts that made up the node were also optimized. For instance, the “teeth” that bear on the central pin are 150mm thick but they are set out at 154mm centres. The nominal 4mm gap allows for the standard supply tolerance on the plate thickness and removes the need for the plates to be machined thus saving time and money in the workshop.

The construction planning and the structural engineering of this project were so interweaved that it is hard to pinpoint where “design” ended and “construction method” began.

The vast majority of the steelwork is within the building envelope where it is kept dry and at a reasonably constant temperature and so, theoretically, there is no limit to its durability. The roof, by nature of its independence from the building’s superstructure, will provide for a fully flexible and adaptable internal space.

Judges’ Comment

This major airport terminal has achieved enormous public recognition for a variety of reasons. The soaring roof, spanning 150m to a height of 40m and 400m long, is truly spectacular. The plated steel roof beams, supporting “trees” and the enormous glazed façades, all show rigorous care and detail control, as well as quality of fabrication.

This well demonstrates the outstanding skills of British construction, and successful structural steelwork.

Bourbon Lane Housing, London

Bourbon Lane Housing

Architect

CARTWRIGHT PICKARD ARCHITECTS AND B+C ARCHITECTS

Structural Engineer

CAMPBELLREITH

Steelwork Contractor

BILLINGTON STRUCTURES LTD

Main Contractor

COMO GROUP

Client

OCTAVIA HOUSING AND CARE

Bourbon Lane is a landmark, Anglo-French affordable housing scheme in West London, heralding a radical move for housing design in the UK.

Bourbon Lane provides 78 much needed affordable homes for families and key workers. The development contains semipublic open courtyards in the style of a traditional London mews. This creates a sense of place and identity, and integrates the scheme with the adjacent shopping centre and existing listed housing.

It was a challenging site which had to provide a wide range of house types that integrate well into the existing urban fabric. The result is an innovative scheme that breaks new ground in urban design and incorporates a number of fresh ideas in the provision of affordable housing, and particularly the design of high density family homes. The aim was to create a thriving and interesting neighbourhood, without the appearance of conventional social housing.

Structural steel was selected for the frame of the buildings following an option study which included solutions in pre cast concrete and timber. The steel solution was preferred as it enabled the 6m cantilevers which are a principal feature of the blocks to be accommodated without imposing significant constraints on the architectural expression of the scheme.

To create the cantilevers and provide sufficient stiffness such that the habitable environment both within the flat unit and the terrace over would be acceptable. A number of models were analysed incorporating different arrangements of vertical members in order to optimise the dynamic characteristics of the structure, erection was fast and accurate.

The Vierendeel frames generally use 254 UCs whereas the rest of the frame uses a 203mm beam and column in conjunction with a 150mm pre cast hollow core floor and 50mm insitu structural topping to create floor plates with few downstands.

The overall stability of the blocks is provided by a sway frame in the longitudinal direction and cross bracing in the transverse direction. Ties and connections were provided between members to achieve robustness and guard against progressive collapse. All exposed structural steel was protected from fire with intumescent coatings with fire boarding being used for the casing in party walls situations.

The project has also used pre fabricated light gauge steel wall panels manufactured off site incorporating windows and doors. The external panels have been clad in Siberian larch.

Judges’ Comment

s:

This is “affordable housing” on a challenging site. A simple but innovative and rational steel frame supports a French prefabricated housing system. The site lies between Victorian terraces and the White City shopping centre, but this project enlivens the community. The concealed steel frame enables dramatic cantilevered accommodation on each block, with balconies and terraces enriching a tightly cost-controlled scheme.

The estate is popular, and the Housing Association plans more developments using the combination of steel frame and system building.

Killanin Stand, Galway Racecourse

Killanin Stand

Architect

EPR ARCHITECTS

Structural Engineer

CAMPBELLREITH

Steelwork Contractor

BALLYKINE STRUCTURAL ENGINEERS LTD

Main Contractor

MICHAEL MCNAMARA & CO

Client

GALWAY RACE COMMITTEE

Galway Racecourse plays host to one of Ireland’s most popular and historic race meetings. With attendees increasing year on year, the Course’s old west stand was deemed to be too small and the only feasible option was to construct a new grandstand to satisfy this growing demand.

The Killanin Stand was built at a total cost of €22 million and has a capacity of 6000 people. The two lower levels offer 700 free seats, bar facilities, snack areas, restaurants, tote hall and toilets, while the top two levels consist of corporate hospitality.

Work on site began in August 2006 with an 11 month window effectively in place as the new stand had to be ready for the 2007 festival which began on 31 July 2007. This timetable was one of the biggest challenges associated with the project. Including ground level, the new steel framed grandstand is a four storey structure, topped with a 14m cantilever roof with pre-cast concrete terracing.

Once the foundations had been completed in autumn 2006 erection of the structural steelwork began and was predominately finished within a 12 week programme – this included the application of intumescent paint which was applied in the workshop and also approximately 4,000m2 of metal decking.

A lot of pre planning was necessary because of the tight schedule. Each party to the design team had to liaise closely with other trades working on the project. For instance, as the majority of the steelwork had intumescent paint, elements such as glazing support brackets had to be welded in place in the workshop as site welding would not have been possible. The grandstand roof had a total of 67 trusses, most of them different sizes and very labour intensive to produce.

Column and beam steelwork for the first, second and third levels was erected in predominantly 7m x 4.5m grids, being replaced with double space 14m x 9m grids at the front of the grandstand on the upper two storeys. This design was to ensure better views of the racecourse from the upper floors by erecting fewer columns. To support these floors 10 large trusses on two levels had to be installed. These 1.6m deep floor trusses were erected parallel to the course and had to match the profile of the glass elevation. A similar approach was adopted for the curved glass drum where a 4.5 m cantilever was utilised at second and third floors in order to eliminate the need for columns, thus providing unobstructed views of the course.

On the plan the roof is not symmetrical. The roof structure itself is a very complex and irregular shape being 92.5m long, 31.25m wide and 20.5m high curving longitudinally and transversely with a 14m cantilever to the front elevation. It is this curvature that made the detailing/fabrication and construction time consuming due to the individual variations of each truss.

Judges’ Comment

s:

This elegant new stand provides an excellent addition to this popular racecourse.

The swooping doubly-curved roof cantilevers over the terracing, and the steelwork is extensively exposed to view. The geometry required intricate fabrication and erection, and the numerous cladding fixings are neatly expressed. The full construction process was completed within the closed season, over a very wet and windy winter.

Altogether this is a fine example of intelligent cooperation between the design team and the contractors.

14 Cornhill, London

14 Cornhill

Architect

DLG ARCHITECTS

Structural Engineer

RAMBOLL WHITBYBIRD

Steelwork Contractor

GRAHAM WOOD STRUCTURAL LTD

Main Contractor

ISG INTERIOR EXTERIOR PLC

Client

IVG DEVELOPMENT (UK) LTD

This project is about engineering to save a grade II* 1920s cellar building, and to transform it into a fully open plan and highly serviced building. The listed features include a triple height banking hall and a period fifth floor panelled boardroom. The building had to be ‘re-built’ underneath the boardroom, which involved opening up the honeycomb of small cellar offices and replacing thick columns with thin ones, one at a time. Two additional floors were also hung above the top of the old building. A complex series of transfer beams had to be devised to hang the new floors.

Working within tight floor to floor heights meant a high level of structural and services integration. The existing 100+ riveted plate beams had to be notched – all of which had different cross-sections – to fit the services in.

With the exterior of the building already determined the architectural focus looked inwards, including an iconic staircase in the glazed ‘prow’ of the building, finely detailed and engineered it works as a ‘restrained’ cog.

The foundations have been re-used which meant the weight of two new floors had to equal the weight of the removed thick columns and associated masonry. Steel was the only usable material to bridge the 15m wide lightwell. Tight construction depth within the existing floor to floor height meant only composite steel could be used, which had the added benefit of integrated service provision.

The roof construction sequence was critical as the existing structure could take the weight of the steelwork for the new floors but not the weight of the steel and floor concrete unassisted. A sequence was used whereby the steel for the two floors and the roof was put in and then connected to a number of new mega columns running through the lightwell – it was then possible to disconnect the weight of the new floors from the existing structure. With the mega columns taking the weight of the new floors the floor concrete could be poured.

The big challenge in designing the roof truss was to understand the complex range of movements and consequence deflections involving the floor beams, cantilevered trusses and hangers that could result from different floor loadings. Part of the elegance of the engineering solution was the realisation that to make the glazing work, it was not necessary to control the building’s absolute movements, only the relative movements within each glazed aperture, thus a solution where the glass moves by 60mm in the middle of the elevation with only 10mm relative differential movement across any one bay was found, and which also gave important weight and material savings.

The anti-corrosion work was all done off site as the steel was fabricated. Fire protection was applied on and off site.

It was possible to re-use 75% of the existing building, including the foundations. This has conserved the embodied carbon-based energy in the existing structure and avoided additional energy expenditure in reconstruction. The fact that the building’s new elements are lightweight and steel with a recycled component both reduces further the total energy cost.

Judges’ Comment

s:

This commercial restoration has modern spaces sensitively inserted within and above the historic listed bank headquarters in the heart of the financial district. The original building had new steel members inserted to open up large clear areas in existing floor

The Sidings Bridge, Swansea

The Sidings Bridge

Architect

STUDIO BEDNARSKI LTD

Structural Engineer

FLINT & NEILL PARTNERSHIP

Steelwork Contractor

ROWECORD ENGINEERING LTD

Main Contractor

ALUN GRIFFITHS (CONTRACTORS) LTD

Client

CITY & COUNTY OF SWANSEA

The City & County of Swansea (CCoS) are committed to development of efficient and sustainable passenger transport systems to provide access to the City Centre from the major approach roads. Part of this strategy provides for the creation of out of town ‘park and ride’ facilities with dedicated express bus routes to the City Centre.

The eastern approach to Swansea is presently served by the Fabian Way park and ride facility which has been operational for four years. The associated express bus route had been partially constructed as advanced works and required the provision of a bridge crossing over the A483 Fabian Way. The park and ride scheme including the bridge have been financed by a combination of Transport Grant and Objective 1 funding sources.

The design brief for the proposed bridge was to provide an iconic and landmark structure carrying a single lane carriageway and a cycleway and pedestrian route across the A483. It was to be located on the site of a former railway Sidings Bridge demolished in 2003.

The design of the superstructure was procured externally through a design competition.

Substructure design was carried out by the inhouse Bridges and Structures Design team of CCoS, who also undertook the site supervision role as the Construction Management Team. Several consultants were invited to tender for the design of the superstructure on a price/quality basis, given the brief that the structure was to be of a cabled stayed form which reflects the long standing maritime history of Swansea.

The selected design proposal was submitted by Parsons Brinkerhoff Ltd in conjunction with Studio Bednarski of London.

The bridge has a 71m span at a skew angle of 65º. The design utilises separate vehicle and pedestrian/cycle decks segregated by a central longitudinal steel spine beam. The original design of the decks was based on traditional steel concrete composite construction.

The spine beam is suspended from eight cables attached to a tapered mast inclined forwards by 22º and supported by two splayed sets of twisted backstays giving the bridge a graceful yet striking appearance. The splayed/twisted backstay arrangement is intended to resemble the appearance of a sail.

The tender for construction was awarded to Alun Griffiths Ltd at a tender sum of £3.3m. With the consent of CCoS, Flint & Neill Partnership was employed by main contractor Alun Griffiths Ltd to prepare a value engineered “all steel” alternative design for the superstructure.

The steelwork design and details were developed in close consultation with the steelwork contractor, Rowecord Engineering Ltd, to suit its preferred method of fabrication and erection.

Judges’ Comment

s:

A strikingly elegant bridge carries a dedicated bus lane, cycleway and pedestrian route over the A483 road. The solution has a cable-stayed structure, with a single slender, sloping mast supporting an orthotropic deck. This fully meets the client’s brief to provide a landmark economically which reflects Swansea’s maritime history.

The minimised disruption to the busy road below directly resulted from the effective use of steel. A fine example of modern bridgework.

The University of Ulster Belfast Campus

The University of Ulster Belfast Campus

Architect

TODD ARCHITECTS

Structural Engineer

BUILDING DESIGN PARTNERSHIP

Steelwork Contractor

M HASSON & SONS LTD

Main Contractor

PATTON GROUP

Client

UNIVERSITY OF ULSTER

The new 6,000m2 building provides state-ofthe- art facilities for the Department of Art & Design including a 220-seat lecture theatre, multifunction lecture and display areas, learning resource centre, CAD suite, teaching rooms, studios and workshops.

The structure consists of a 6-storey steel frame with exposed pre-cast concrete hollow core floor planks. Lateral stability is provided by cross bracing within lift and stair cores. The choice of structure maximised off site fabrication while minimising on-site disruption for the congested city centre site.

On entering the building, students pass under the sculpted lecture theatre and into the large central atrium space at the heart of the building. The protrusion of the lecture theatre into the atrium space is a particularly striking feature. The rear curved wall of the theatre hides a truss which spans across the building entrance and is supported on adjacent faces of the atrium. The long span support structure for the atrium was carefully designed to avoid any cyclical deflections developing during use.

The atrium space consists of a planar glazed vertical wall which curves over the top of the building forming a horizontal glazed roof which allows natural light to flood into the building. The vertical glazed wall is supported by steel oval sections spanning from one side of the atrium to the other. An exposed steel link bridge is provided at each floor level adjacent to the glazed wall. Horizontal brise soleil are fixed to the vertical glass wall to prevent glare and excessive solar gain while maximising the passage of natural daylight.

The atrium roof structure consists of a series of elegantly detailed bow string trusses which span just over 14m. The top chord of each of the trusses is formed from an oval section which provides an ideal balance between aesthetics and structural efficiency. The ends of the ovalised top chords are terminated in an expressed pinned connection.

Natural ventilation is employed, using automatically controlled louvers on the façade, providing cross flow ventilation via the atrium. This natural ventilation is used in conjunction with the high thermal mass structure using exposed pre-cast concrete slabs into which are integrated the lighting, fire alarm and PA systems.

The floor beams had to blend seamlessly into the circular hollow section columns. This required the columns to be fabricated with small stubs, mirroring the connecting beam, and allowing a perfect flush fitting. All exposed steelwork was treated off site with intumescent paint.

A 27m long footbridge glazed on two faces links the new building to another part of the faculty on the other side of a busy road. The footbridge’s structure consists of a pair of Vierendeel trusses which are separated from the curved glass façade to create a sense of space and lightness.

With its low energy footprint, the campus is considered to be one of Northern Ireland’s finest new buildings.

Judges’ Comment

s:

This neatly engineered and constructed project forms an extension and recladding of a 1960’s concrete building. The steelwork structure with hollowcore floors compared favourably with many alternatives, assessed against 12 parameters, crucially including safety.

A shining example of steelwork’s economic case, and a credit to all concerned.

The Worrell, Weekes and Walcott Stand, Kensington Oval, Bridgetown

The Worrell, Weekes and Walcott Stand

Architect

ARUP ASSOCIATES

Structural Engineer

ARUP ASSOCIATES

Steelwork Contractor

LARSEN & TOUBRO LTD

Main Contractor

TUBEWORKERS LTD AND STRUCTURAL SYSTEMS LTD

Client

WORLD CUP BARBADOS INC

The Worrell, Weekes and Walcott Stand (3Ws) is the largest and most ambitious structure within the re-developed Kensington Oval. It provides seating for 4000 spectators in two radial tiers surrounding the ground, as well as housing the president’s suite and VIP boxes.

The design concept is derived from the necessity to provide uninterrupted column free views of the cricket in a light and comfortable atmosphere. Local conditions, including seismic activity, hurricane winds, heavy rainfall, tropical temperatures and humidity, and extreme light levels, had to be taken into consideration.

The 3Ws stand combines reinforced concrete for the stand structure with lightweight steel framing for the roof canopy. Concrete could not offer the strength to weight ratio or stiffness of structural steel, essential characteristics for designing a cantilever roof for hurricane conditions.

The main canopy cantilevers up to 25m to provide drip line cover and shade to all the stand’s inhabitants, whilst maintaining column free views. To achieve this, the canopy unites the radial grid of the lower tiers with the orthogonal grid of the box levels through the use of steel cantilevered truss frames which vary in depth in response to the spanning requirements.

The main roof form is united with the camera gantry structure through the curved ‘cheeks’ on the two sides of the building. The geometry of this section of the roof was the most challenging section of the stand to design and construct. Each of the cheeks is made up of three cone shaped zones of cladding that overlap one another allowing air to flow between them. The front cone is cut back to form a leading edge which is defined by intersecting the cone geometry with that of a cylinder running perpendicular. This permits spectator views to the pitch boundary whilst maintaining protection from wind driven rain. The cheeks are supported by a curved steel cantilever frame which follows the cladding geometry very closely, thereby reducing the need for secondary steelwork, and is anchored into the side of the main building at three levels. The basic structural arrangement for the steel frame is made up of a series of curved universal beams, with a radius to suit the location within the cone, connected by a grid of diagonal welded tubular sections. This forms a stiff and highly efficient diagrid structure, limiting tip deflections even under hurricane conditions.

The leading edge of the cheeks required a complex double curved member that was achieved cost effectively in the steel frame by approximating the curve in six steel tubes. These were bent to specific single radii and welded end to end to form the edge beam. The tolerance was made up by welding bespoke steel plates to the beam so the cladding could be fixed in its exact location.

Kensington Oval is seen as the new standard in first class cricket and the 3Ws stand is central to this accolade.

Judges’ Comment

s:

This is a good planning response to updating this hallowed cricket ground. It gives an enhanced sense of place in the town, whilst retaining much of the former character. The design copes well with the many issues of climate, function and economy. The UK prefabricated steelwork addresses the complex geometry, and yet was constructed in the relatively unsophisticated local building environment.

The challenges were answered well, and the international work handled successfully.

Steel Wing, St Marylebone CE School

Steel Wing, St Marylebone CE School

Architect

GUMUCHDJIAN ARCHITECTS

Structural Engineer

CONISBEE

Steelwork Contractor

KL DESIGNS LTD

Main Contractor

MANSELL CONSTRUCTION SERVICES LTD

Client

LONDON DIOCESAN BOARD FOR SCHOOLS

The brief was to extend the existing school to provide a sports hall and associated arts and drama facilities on a very constrained 30m sq site. The solution was to build down instead of up with an 8m deep basement being constructed across the available site footprint. The majority of the brief was satisfied using well detailed in-situ concrete with very little in the way of finishes, which saved money but meant that every structural element was on show and required careful detailing.

The existing arts building was a 5-storey insitu concrete sway frame with 2-storeys below ground and 3-storeys above. The new east wing and the open courtyard use steel elements to maximise spans and create a lighter, more refined structure. The steel frame extends from basement level where fabricated steel box section and flat plate columns rise 11m to support in-situ concrete intermediate basement floors and ground floor structure. At ground floor the column sections turn through 90 degrees to form the cantilevered steel and ETFE canopy over the courtyard stair.

During the design of the steel wing, it was decided that a concrete prop spanning the courtyard and providing lateral support to the capping beam would be more buildable and practical in steel. By introducing a 457mm diameter tubular section this enabled ease of connectivity of the canopy support and cantilevered steel staircase to the buffer prop. Not only was this prop providing lateral support to the open courtyard capping beam, it was now supporting the entrance landing, stairs and canopy.

The canopy is supported on articulated pinned connections at two points vertically and two points laterally with stability provided by a combination of lateral supports and slender tubular bracing in plan. The main sections are supported on two vertical and two raking columns and have a 4m cantilever sailing out over the 8m deep open courtyard. The main sections consist of RHS with welded flat plate to enhance stiffness and also to form a gutter for draining the ETFE fabric which is tensioned between the main members.

The feature staircase is a double height 5m cantilevered scissor stair with one flight connecting ground to basement -1 level and then another slightly smaller flight between basement -1 to basement -2. Upper flights are detailed to dovetail with the landing structure before double continuous steel flat stringers supported by the tubular buffer prop cantilever out 8m high over the courtyard light-well. The fully welded continuous structure then returns to three 30mm diameter steel hangers which support the basement -1 landing and enable the second flight to continue down to basement level.

The stairs are deliberately designed to be independent of the main concrete frame and flow elegantly through the double height space.

Judges’ Comment

s:

This is an inner-city school with great pressure on space. The project provides a sports hall beneath the playground, and links the buildings above. Steelwork provides the unifying element in the core, balcony and link structures. Being painted orange makes it fun for the children.

The outstanding characteristic is careful foresight and detailing, and the results show they are worth the effort – and the children love it!