Talk Zone – Millennium Dome, Greenwich

Citation

Jones, K. (2000), "Talk Zone – Millennium Dome, Greenwich", Facilities, Vol. 18 No. 13/14. https://doi.org/10.1108/f.2000.06918mab.014

Talk Zone – Millennium Dome, Greenwich

Keywords Structural optimisation, Design, Building

1. Introduction

The Talk Zone is one of the most striking, elegant and exciting zones within the Millennium Dome, designed as a showpiece exhibition to promote communication and associated technologies into the new millennium.

2. Spatial configuration

Talk Zone is located within an inner circumferential strip of the Dome between radii 72m to 91m, and spilling slightly beyond a segment defined by the 11th and 12th Dome mast quadrapods. The footprint size is thus approximately 19m by 65m.

In order to house the planned exhibition, it was necessary to utilise the area as efficiently as possible. To that end, additional spaces for circulation, exhibition, back-of-house and plant rooms were agreed with NMEC (New Millennium Experience Company) underneath and within the large adjacent circumferential promenade structure. This extends the Talk Zone as far as the 60m radius line in part.

A general access bridge leading to the circumferential promenade slices through the centre of the zone, splitting it into two volumes (or cores). Each volume consists of an inner core structure which houses a "black-box" environment for the main exhibition. To the outside of each core structures is a continuous wrapping of hung glazing façade. This glazed skin is offset 1.2m from the inner cores to create a "deep picture frame" effect of the entire pavilion. Within the 1.2m zone of the façade are five levels of cantilevered walkways to provide access to place monitors and mount equipment for image projection and light shows, so as to bring the whole building to life.

Part way through the design development, large atria structures were introduced at both ends of each core structure, each with sloping end walls also fully glazed. This introduced considerable "wow" factor, and was one of the significant challenges for the structural design team.

Each core contains ground and first floor of exhibition space. Inside the two cores, the height from first floor to black-out ceiling is a soaring 11m and 14m, respectively, except where there is an additional upper gallery floor deck inside the larger core.

Adorning the outside of the pavilion near the 91m radius line are lifts, escalators, spiral stairs, a link bridge and extensive sweeping external access decks.

3. Structural solution

The steelwork was separated into two phases. The two core structures are "Phase 1" (fabricated by Hares), and all of the façade, atrium and ancilliary structures are "Phase 2" (fabricated by Sheetlabs). The Phase 1 cores are stiff braced steel "boxes" with composite first floor, from which most of the Phase 2 elements are hung. The Phase 1 structure consists of a series of braced steel frames, each aligned with radial lines of the Dome, thus creating a curved inner and outer circumferential façade line. Bracing to the roof and long walls, together with the first floor diaphragm plate transfer lateral loads to the stiffly braced end walls.

Phase 2 consists of many types of structure. One of the greatest challenges was to create the cantilever atrium spaces with hung glazing positioned so far away from the main Phase 1 supporting structure. This was achieved by huge eaves-level prop-and-tie steels cantilevered from the Phase 1 corner columns, from which is suspended the entire atrium (service walkways and glazing elements). Stiffness to prevent lateral sway of each atria structure is achieved by a combination of roof level bracing and the use of each service walkway as a horizontal (hung) portal frame in tubular steel.

Another major challenge was in the geometry of the glazed envelope and the support of the immense expanse of glass. The team had to grapple with and achieve the setting out on circumferential and radial lines intersected by the inclined planes of the atria. At an early stage it was decided that the glass should be hung from a continuous eaves truss. The eaves truss is a three-dimensional (curved) "toblerone" truss bolted directly to the Phase 1 columns on the circumferential edges. At the ends, in the region of the atria, the truss becomes trapezoidal (rather than triangular) to give greater torsional stiffness and vertical bending strength for hanging the atria elements.

The external Phase 2 access deck structures and link bridge are formed in intricately detailed interlocking 3-D trusses also in tubular steel. This is supported from the ground by a line of single inclined tubular props stabilized against the Phase 1 structure. The upper gallery access deck is particularly impressive with strutting and suspension bars passing straight through the glass façade at high level, again hung directly from the Phase 1 structure.

4. Interfacing with existing structures

The foundation strategy was pre-engineered in the form of a grid of piles provided prior to the construction of the Dome envelope. A raft with occasional ground beams and thickenings spread the column loads onto the piles. Some of the steel columns were so close to the Dome mast quadrapods that the imposition of additional loads to those main piles had to be carefully considered. An area of no piles in the vicinity of the Blackwall Tunnel beneath had to be bridged.

The Dome servicing strategy was also pre-engineered using major circumferential and radial service arteries. The steel structures had to step around these arteries – for example, the whole of the inner glass façade is placed on a bridging structure at first-floor level.

Movement joints between the existing promenade/central show structures and the new pavilion had to be carefully detailed. Revisions to bracing, and structural additions to existing structures also added to the complexity of the works.

5. Programme issues

Working to the immovable deadline of the new millennium focused the mind on streamlining design and construction. For this reason, Phase 1 steelwork had to be designed and built before Phase 2 had been fully thought through. The whole team was aware of the risks inherent in this strategy. However, it was essential, in order to get the whole pavilion built (from above pile head level) in less than ten months, allowing sufficient time for services and exhibition installation. Phase 1 had to be sufficiently robust and versatile to receive the Phase 2 steels. By careful design, Phase 2 was achieved without any major restriction.

This separation of Phase 1 from Phase 2 in construction timing and responsibility created additional major challenges with respect to control of tolerances. Planar glazing requires the achievement of extremely tight tolerances at each glazing bolt. Working back from planar fixing, there were tolerance requirements at the top of the hung glazing, then another tolerance interface at the attachment between the Phase 2 and Phase 1 steelwork (at eaves level).

It became clear that although a tight tolerance for Phase 1 had been specified, the need for rapid construction precluded the instigation and achievement of a close tolerance Phase 1 structural frame. The solution lay in providing a large adjustment range (±40mm on plan and ±30mm level) at all of the Phase 1-2 interface connection points. The aesthetics of the joint were also a high priority to the pavilion architect and this led to a highly detailed engineering component.

Another location of medium-range adjustment is provided at hung glazing connection point, and then the glass-by-glass individual bolt settings which are fully adjustable in three dimensions to enable the final set and erection of the façade elements.

The programme risk associated with any failure of the system to provide sufficient flexibility to achieve the glazing erection was very significant. The total system developed allowed the timely and successful completion of the façade construction.

6. Summary

The total construction project of the Talk Zone represented a sizeable complex construction project to be completed within a short timeframe while operating in cramped conditions inside the Dome. In addition, the accuracy of fabrication and tolerance adjustment for the thousands of glazing bolt points represents a considerable challenge that was overcome by the design and erection teams. The result is a breathtaking pavilion structure for this important Millennium showcase.

For further information contact Helen Elias, Press and Public Relations Manager, Buro Happold, Camden Mill, Bath BA2 3DQ, UK. Tel: +44 (0)1225 320 627; Mobile: 0403 129 599; Fax: +44 (0)1225 320 601; e-mail: www.burohappold.com

Ken Jones MICE Senior Engineer at Buro Happold