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Tower with “Floating” Podium Built in Shenzhen
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Night view exterior rendering of the new-glass-and-metal Shenzhen Stock Exchange
The new-glass-and metal Shenzhen Stock Exchange was completed this month. Its three-story “floating” podium is raised 36 m above the ground. Image courtesy of OMA; photography by Phillippe Ruault

This month, the new headquarters tower for China’s Shenzhen Stock Exchange was completed. The building boasts a ‘podium’ that appears to float 36 m above the ground.

October 22, 2013—Located a scant 1 km from Hong Kong, the new 245 m tall, 180,000 m2 glass-and-metal Shenzhen Stock Exchange tower was completed this month. The building joins the cityscape with a twist on the expected: a ‘podium’ that appears to float 36 m above the ground, surrounding a typical rectangular office tower. A clear glass curtain wall is recessed behind a textured glass-clad grid to form the facade of the tower, which responds in appearance to the amount of daylight and climate conditions, altering the viewer’s perception of its texture.

The architecture firm OMA, based in Rotterdam, the Netherlands, created the concept of the building, winning a design competition in 2006. The Beijing office of the global engineering firm Arup, in collaboration with local engineering firm SADI—the Shenzhen General Institute of Architectural Design and Research—were responsible for the engineering of the structure and the facade, mechanical and electrical services, fire safety systems, vertical transportation, building intelligence systems, geotechnical engineering, and lighting, as well as for project management.

The building contains three distinct visual elements: a 36 m tall rectangular base; the 24 m tall floating podium that measures 160 m by 100 m on plan and rests atop the base, cantilevering 36 m in the east and west directions and 18 m to the north and south; and a 54 m by 54 m square tower that extends approximately 185 m in height above the floating podium level.

“We worked with OMA right from the very beginning, during the competition, as they were developing this concept for a very regular square office tower with a podium, but [with] the podium raised up from the ground,” says Chas Pope, CEng, an associate director of Arup and the firm’s project manager and lead structural engineer for the building. “And that led to a decision fairly early on to tie the podium and the tower rigidly together.” Doing so provided the robust structural support needed to support the podium, he explains. 

Exterior rendering of the Shenzhen Stock Exchange building which contains a rectangular base, a cantilevering podium; and a square tower block

The building contains three distinct visual elements: a rectangular
base; a cantilevering podium; and a square tower block that
extends upward from the podium. A textured glass curtain wall
that is recessed behind an extruded matte metal cladding grid
forms the facade of the tower. Image courtesy of OMA;
photography by Phillippe Ruault

Pope explains that the lateral and gravity strength for the building comes from a three-part structural system, the parts working in concert. While the building has been designed for the seismic loads required under the Chinese building code, the typhoons that occur in the area make wind the controlling design factor for lateral loads, he says.

A typical reinforced-concrete core with a perimeter moment frame system extends from the foundation of the building up to the top of the tower, forming the first element of structural system. The use of a lightweight composite steel-and-concrete floor system enables the beams to span directly from the facade to the core, so there are no internal columns within the tower’s footprint, Pope says.

While the square tower forms the building’s silhouette above the floating podium, beneath the podium two 20 m wide glass atria—one located to the east, and one to the west—expand the tower’s footprint to form the rectangular base of the building.

The floating podium is formed by a series of robust three-dimensional full-depth steel transfer trusses, according to David Gianotten, the partner in charge of the project at OMA, who wrote in response to questions posed by Civil Engineering online. The floors are formed with secondary trusses that work compositely with concrete slabs framed with steel floor beams. This megatruss system forms the second element of the lateral and gravity structural system, according to Pope.

The third element of the lateral and gravity structural system is located around the perimeter of the rectangular base of the building: a series of trussed tubes formed with 2 by 2 m concrete-filled steel box corner columns supported with V-shaped diagonal braces for lateral stability. The corner columns “collect the forces at concentrated places from the [podium’s] trusses and get them down to ground as quickly as possible,” Pope says.

Diagram of the Shenzhen Stock Exchange building which displays a three-part structural system

A three-part structural system provides the lateral and gravity
strength for the building. A typical concrete-core and
moment-frame system is used for the tower, while a trussed
tube system located at the perimeter of the building’s rectangular
base, supporting the cantilevered podium and its megatruss
system. © Arup

The building is located on an array of caissons up to 3.5 m in diameter, according to Pope. This is a typical foundation for the Shenzhen region, due to its fairly soft soil and shallow layers of hard rock, according to Pope. The columns located at the atria’s corners “take the lion’s share of the podium loads, so there are very concentrated forces coming down in small areas,” Pope says. A caisson-based foundation system proved beneficial because the forces from the atria’s corner columns “could all directly go through a handful of caissons rather than having to spread out through a larger number of piles,” he says.

Identifying—and keeping separate—the load paths from the tower and podium proved tricky, according to Pope. “Once you do tie [the tower and podium] together, you have to make sure you really understand where the forces are actually going because the truss system becomes very stiff due to the gravity loading demands on it—thus tending to attract lateral forces from the towers,” he says. “So we did a number of rounds of optimization of the truss layouts to make sure we had an arrangement that was robust, but could effectively minimize the lateral stiffness of it [and] keep any load-path transfers from tower to podium to a minimum.”

Load paths during construction of the podium also had to be carefully managed. “The top and bottom floors of the podium act as the top and bottom flanges of the cantilever, so any concrete on those floors would try and attract in-plane forces,” Pope explains. “We wanted to make sure those forces were diverted into the steelwork, which was the appropriate material to carry those forces. So the slabs were constructed later [and] they were also jointed to make sure that the loads would flow elsewhere.”  

“The biggest challenge in China, still, is to maintain the quality of construction,” Gianotten noted. “Quality can only be ensured by being involved in the project from the beginning until the end.” For China, OMA’s close involvement with clients and contractors through the construction of its designs is unusual. “Many international architects give over their responsibilities to local design institutes during the documentation and realization phase of buildings in China,” Gianotten says. “OMA stays actively involved, working very closely with the client and contractors on-site until the end to maintain the best possible quality. In the end the result is much better.”

Exterior rendering of the Shenzhen Stock Exchange, which displays the building's floating podium that offers a rooftop garden

The building’s floating podium offers a rooftop garden, complete
with walking path and numerous covered spaces.
Image courtesy
of OMA; photography by Phillippe Ruault

OMA Asia’s Hong Kong office oversaw construction, while the firm’s on­site office in Shenzhen worked with the client and contractors day-to-day.

Roughly 60 percent of the building will be used for the stock exchange, including the 28 m tall floating podium, which offers three full floors and a mezzanine level. The remainder, including the majority of the tower, is rentable office space. A club space is also available at the top of the tower.

“One of the most important aspects of the Shenzhen Stock Exchange is the fact that it is a public building,” said Michael Kokora the associate in charge of the project for OMA, in written responses to questions posed by Civil Engineering online. “It is a building for the people to engage in the market and the act of exchange; it is also an urban building that is meant to engage and interact with the space around it.”

The public’s experience of the building will include an exterior public plaza and the view of the building among the growing city’s skyline. The mutability of the building’s three-dimensional facade, as well as the trading information that will be displayed digitally on the sides of the floating podium, will make viewing the building an active, ever-changing experience.

The building is the second OMA design to be completed in China, the first being the CCTV headquarters in Beijing. (See “Chinese TV Headquarters Will Feature Braced Continuous Tube Structure,” Civil Engineering, November 2006, pages 12-13.)


 

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