Tapering. Design for 310-m-tall tower evokes glass shards.

Engineers in London are completing preliminary design for what will be Europe’s tallest building. Depending on market conditions, London Bridge Tower could be up to its full height, just under 310 m, by 2009. If so, it will outstrip Frankfurt’s Commerzbank building by about 20 m.

Developer Sellar Property Group will not comment on how tenant hunting for the estimated $540-million building is going. But "our company is extremely firm in terms of delivering the project," says Barry Ostle, property director.

Sited on the River Thames’ south bank by London Bridge, the 130,000-sq-m tower is designed to evoke tapering shards of glass. It will have a multifaceted, glazed envelope with sides leaning inward 6 degrees. Width and height of the eight main facades will differ.

From the base to the pinnacle, there would be 26 office levels and a 15-story hotel. Levels 52 to 63 would be residential. An observation level is planned for 224 m above grade. A concrete core ends about 235 m above ground. It will be topped with 12 structural steel levels, including a two-story-deep outrigger truss.

The changing building use complicates design, says Joost Moolhuijzen, a partner with architect Renzo Piano Building Workshop, Paris. But it will enhance the tower’s energy efficiency. "We are targeting 20 to 30% better efficiency than a standard building," says Dave Richards, the project’s environmental designer with Arup Group Ltd., London.

Generally, surplus heat from office areas will be transferred to hotel and residential floors, where it is needed. To shed total surplus heat and refresh interior air, the engineer is designing water coolers, like car radiators, to be dispersed in the steel-framed levels above the concrete core. The tower-top radiators should contribute cooling for about 85% of the year, says Richards. Incorporating triple glazing with internal shading also will boost efficiency, he says.

Though the structural system is relatively simple, framing is complicated by the building’s geometry and mixed uses, says Kamran Moazami, a director in the London office of the building’s structural designer WSP Cantor Seinuk.

The tower’s core and sloping perimeter columns, spaced closer together as the height increases, will handle gravity loads. A combination of core and diaphragm-like slabs working with perimeter columns being "engaged" by the outriggers will resist lateral loads. Structural concrete with post-tensioned slabs will be used in residential levels and composite steel framing for office areas. Maximum internal floor spans drop from 14 m at the lower levels to 8.5 m above, further complicating column configurations, says Moazami.

Australia’s Multiplex Constructions U.K. Ltd., is consulting. The delivery method is likely to be a form of construction management. Procurement could start next year.

(Image courtesy of Renzo Piano Building Workshop)