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London's 'Tulip' tower structural details revealed

The technical details behind the proposed 305m high “Tulip” tower in London have been revealed.

Designed by architect Foster & Partners the structure is set to be the City of London’s tallest tower and 1m shorter than the Shard, the UK’s highest building. Developer Bury Street Properties has put in a planning application for the tower earlier this week. It is to be used as a visitor attraction without any office space. Bury Steet properties is owned by Jacob Safra, who also owns the St Mary Axe tower in the City.

At the top of the tower a dome composed of compact, exposed structural steel members with glass infill panels has been designed with a lattice frame that arches over the top structural level.

Tulip Tower

Concrete has been chosen for the shaft structure

Floors at the top of the tower will be made of composite slabs supported by a steel frame. Six inclined, round steel columns will support the outer edges of the steel-framed floor levels. The concrete lift shaft will support the inner edges of the floors through embedded plates cast within the walls.

Steel was chosen for the tower’s top framing due to its lightness and versatility to form its unique geometry.

The outer diameter of the concrete lift shaft will be14.3m while its wall thickness is 900mm.

The reinforced concrete shaft is to be vertically post-tensioned from the foundation level to reduce the potential for cracking of the concrete surface and improving the concrete’s durability.

The Tulip’s foundations will consist of a thick concrete pile cap supported on 1.8m diameter deep piles embedded into Thanet Sand. The outermost piles are designed to resist compression and tension. Additional 1.5m diameter compression piles are provided under the central lift pit and carry a portion of the gravity load of the tower.

A perimeter secant piled wall will be built to temporarily support the excavation for the new foundation. Inclined steel columns on the tower are being supported by three concrete corbels provided at the base of the steel-framed levels.

Concrete buttresses at the tower’s base are also set to stiffen the base, provide extra redundancy and reduce the bending moments and shear forces within the reinforced concrete pile cap.

A pair of tuned mass dampers will also be placed at the lower levels of the structure  to reduce the impact of wind-induced accelerations.

If planning permission for the tower is granted, construction is planned to begin in 2020 with the project due for completion in 2025. Foster & Partners said it wants the Tulip to complement the Gherkin next door which it also designed.

The Tulip will officially be known as 30 St Mary Axe, its street address.

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Readers' comments (2)

  • Do Architects usually have an in house structural design department or are they just keeping quiet about who's actually going to make this work? Bit like the Milau Viaduct, always noted as 'designed by Foster and Partners', never '....in collaboration with ....Structural design engineers and built by....'! Is it a surprise that the public have no idea what civil engineers do. They design and build the architects' flights of fancy....and lots of other useful stuff!

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  • @James Wren: Foster + Partners do in fact have a structural engineering department. https://www.fosterandpartners.com/expertise/structural-engineering/

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