Design Awards: 2008: Award

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.