A striking new addition to the Shanghai skyline is approaching completion in the heart of the city’s financial district.
The 121-storey transparent glass Shanghai Tower will twist and taper as it rises to a height of 632 metres, making it China’s tallest skyscraper. Yet despite its complexity, the design team has developed an elegantly simple solution.
Intended to be a city within a city, the mixed-use development was designed by architects Gensler with Thornton Tomasetti as structural engineers and includes commercial and retail space, entertainment and cultural venues, a conference centre, a luxury hotel, public gardens and the world’s highest non-enclosed observation deck.
The skyscraper comprises nine cylindrical buildings stacked on top of each other, all enclosed by a circular inner curtain wall and a triangular facade enveloping the entire structure.
The simplicity of Shanghai Tower’s structure is a response to multiple challenges: a windy climate, a location in an active earthquake zone, the site's unique soil conditions — a clay-based mixture typical of a river delta.
This meant supporting the tower on 831 reinforced concrete bore piles sunk deep into the ground. A 60-hour continuous concrete pour saw more than 61,000 cubic metres of concrete used to create a six-metre thick mat foundation.
Thornton Tomasetti engineered a simple, safe and cost-effective structural system that permitted the creation of an innovative architectural form. At its heart is a concrete core. The core acts in concert with an outrigger and ‘super-column’ system, with double-belt trusses that support the base of each of the nine vertical neighbourhoods.
The outrigger trusses and super columns derive stiffness from the concrete inner building, producing an effective system for resisting wind and seismic loads for super tall buildings. This approach has made for an easier and faster construction process, meaning significant cost savings for the client.
The tower’s form was refined using wind tunnel tests, which ultimately reduced building wind loads by 24 per cent. Many options were studied, but the tests pinpointed a 120-degree rotation as optimal for minimizing the wind loads. The result is a simpler and lighter structure with unprecedented transparency and a 32 per cent reduction in costly materials.
To carry the load of the transparent glass skin, an innovative curtain wall has been designed which is suspended from the mechanical floors above and stabilized by a system of hoop rings and struts. The laminated glass panels filter the sun, wind and rain, while the inner skin encloses the interior space with a unitized low-E coated insulating glass curtain wall system with integral operable solar control devices.
This double skin wall system takes advantage of the stack effect to provide natural ventilation and cooling. The buffer areas between the inner and outer skins help to regulate the environment as well as collect and recycle rain water.
The tower’s iconic twisting shape and dual-skinned facade were extremely difficult to realise using traditional 2D approaches, making model-based designs vital for the project’s success.
"We knew that if we tried to work in a traditional way, using traditional tools and delivery systems, it would be extremely difficult to carry out this project successfully," said Jianping Gu, director and general manager for Shanghai Tower Construction & Development Co., Ltd., the tower’s owner/developer.
BIM helped the team visualize the tower in 3D and analyse the design for improved decision making. For example, a Revit design model utilising the reflection analysis features of Ecotect software analysed the glare from the tower throughout the city. This helped the design team optimise the outer curtain wall, even down to the position and angle of individual pieces of glass, to minimize light pollution.
Final completion is scheduled for later this year, with the owner and design team targeting a LEED® Gold rating and a China 3 Star rating.