The material behind the world's largest atrium
Leeza SOHO skyscraper, Beijing, China
Zaha Hadid Architects’ new 207-metre Beijing skyscraper, Leeza SOHO, features a twisting, steel-formed atrium space, which – at 194 metres – is the world’s tallest.
The skyscraper, built in the Lize financial business district in southwest Beijing, has a combined floor area of 172,80m2 and features 45 floors or above ground office space and four floors of basement underneath – two for parking and two for shipping. Constructed over a subway tunnel which runs diagonally across the site, the tower has been designed in two distinct halves connected by the vast atrium space, with four bridges spanning the gap between the towers.
- Architect: Zaha Hadid Architects
- Consulting engineer: Bollinger + Grohmann
- Contractor: China State Construction
- Engineering Corporation
- Client: SOHO China
Bringing the pioneering project to life would have been impossible without steel. Apart from a core which contains the elevators, the whole of the unique, contemporary tower is framed in steel, which stabilises the building and forms its gently twisting elliptical shape.
Overcoming challenging site conditions
In many ways, the building’s stunning design and record-breaking atrium were a by-product of the conditions encountered by architects at the beginning of the project. Satoshi Ohashi, director of Zaha Hadid Architects explains: “We didn’t set out to break records with Leeza SOHO. As with all our projects, the building was designed in response to site conditions. As Beijing is extending its infrastructure, new subway systems are being built, and our client’s site stands above the intersection of lines 14 and 16.
“We literally had to span the tunnel by splitting the tower in half, so that the foundations wouldn’t affect the subway. The most elegant way to unify these two halves was with a central atrium, which will become a new public space for the city.”
“The tower really pushes the possibilities of construction, design and engineering, and it is steel which creates these virtually limitless possibilities”Satoshi Ohashi, Director of Zaha Hadid Architects
The footplate of the tower tapers to enable the required ratio of green space and access roads on the site, with parks and plazas surrounding the base. The building then becomes wider in the middle, and tapers again at the top. As the tower rises, the diagonal axis defined by the subway tunnel is re-aligned by twisting the atrium through 45 degrees, allowing panoramic views of the city and natural light to enter at all levels.
Perimeter columns follow the tapering form, and four structural steel truss rings tie the two halves together, creating bridges which pass across the canyon-like atrium.
Boundary pushing construction
Presenting a number of immensely complex engineering challenges, it was soon clear why no other architecture practice had attempted the construction of a 20-storey atrium before. “The tower really pushes the possibilities of construction, design and engineering, and it is steel which creates these virtually limitless possibilities,” says Satoshi.
To complete the building’s complex structural system, a combination of concrete and wide-flange steel was used. This comprised four layers of steel, a core tube wall, an outer steel frame, and a horizontal structure built into the tower after the completion of the core tube’s vertical structure.
Construction of the convex glass facade that serves to unite the two halves of the building also presented challenges. Here again, steelwork provided an answer. “For this project the geometry of the exterior cladding is complex, because of the gradually stepped windows, which create texture. Behind the cladding the steelwork needs to be very accurate, and its fabrication, welding and sequence of construction has to be carefully coordinated and controlled,” says Satoshi.
Tight construction deadlines
As well as being presented with a unique and complex set of engineering problems, the architects and contractors behind the project did not have much time to work with.
“All our projects in China are on a huge scale, but are accomplished in a relatively short time,” says Satoshi. Construction on the building commenced in 2015, and its topping out ceremony was held in September 2017. Less than five short years after building was commenced, Leeza SOHO is set to open in November 2019.
The ability to prafabricate steel sections off-site allowed for much swifter construction processes, contributing to achieving the ambitious schedule of work.
The building was also designed with sustainable construction in mind. “Sustainability was key to the design, and we are targeting LEED Gold certification,” says Satoshi. An advanced 3D BIM energy management system will monitor energy efficiency and environmental control, integrating such factors as heat-recovery from exhaust air, lighting, and water-collection for grey water flushing and landscape irrigation.
Steel sustainability credentials can also be felt in the reduced energy and resource requirements associated with off-site fabrication, combined with its impressive lifecycle performance. In addition to a high strength-to-weight ratio, steel is infinitely recyclable and can be recovered and reused once a building has entered its end-of-life stage.
The completion of such a complex build, particularly one with difficult site conditions – record-breaking construction achievements, and tight timeframes – simply would not have been possible without the use of steel.
Images: Zaha Hadid Architects