Raffles City Chongqing / Safdie Architects / China

Raffles City Chongqing

• Architects:  Chongqing Architecture and Design Institute; Moshe Safdie & Associates; P&T Group 
• Location:  Chongqing, China
• Owner/Developer:  Capita Malls Asia; CapitaLand Limited; Singbridge 
• Structural Engineering:  ARUP, East China Architectural Design & Research Institute 
• MEP Engineer:  Parsons Brinckerhoff Consultants Private Limited
• Project Size:  817,000 sq.m
• Development GFA:  1,134,260 m2 / 12,209,073 ft2  
• Building Height:  354.5 m / 79 story
• Building Function:  Residential, Office & Mixed-Use
• Structural Material:  Composite (Core-Reinforced Concrete; Columns-Concrete Encased Steel; Floor Spanning-Steel)
• Project Dates:  2011-2019
• Facade Engineer:  ALT Limited
• Quantity Surveyor:  Rider Levett Bucknall  
• Landscape Architect:  Williams, Asselin, Ackaoui & Associates  
• Interior Design, Hotel & Convention:  CL3 Architects Ltd.  
• Interior Design, Retail:  The Buchan Group  
• Wind Engineering:  RWDI
• Elevator Consultant:  KONE
• LEED Consultant:  ARUP
• Energy Label:  LEED Gold BD+C: Core and Shell

One of the outgrowths of dense vertical urbanism is the challenge of interconnecting tall buildings at multiple levels in the sky in order to have the super-connected urban whole, pathways between the vertical nodes must be equally advanced along with technological breakthroughs that allow towers to grow vertically. The "Conservatory" At Raffles City in Chongqing, China is a new invention of the horizontal tower. It provides a fully enclosed mixed-use program while linking vertical towers together, creating a new type of three-dimensional building matrix.

Raffles City Chongqing is a comprehensive mixed use development with an overall gross floor area of approximately 1,100,000 square meters. The development encompasses a transportation hub, luxury residential, high end serviced apartments, offices, retail, and substantive public space programs. The key tall building features are six 250 meters high and two 350 meters high towers, all curved. A 300 meter long, glazed "sky bridge" sits atop four of the 250 meter tall towers, and connects to the two 350 meter tall towers. The physical linkage in the air of these six towers creates a mini-"skyscraper city" in itself. This is a truly unique architectural topography, the design and delivery of which required new thinking and solutions to the structural engineering, as well as all building design disciplines.

In recognition of CapitaLand's drive towards sustainability, Raffles City Chongqing has been accorded the LEED-CS (Leadership in Energy and Environmental Design - Core & Shell) pre-certification at the Gold Level by the United States Green Building Council. Raffles City Chongqing is the City's largest development to receive the Gold Certification.

Tower Details -

Emanating from the podium are eight towers: six southern towers reaching 250 meter and two northern towers topping out at 350 meter. The towers are a mix of uses, comprised of residences (T1,T2,T5,T6); Luxury residences (T3N); Offices (T4N, T4S, T3S); Service apartments (T4S); and Hotel (T4N) programs. The conservatory spans across four southern towers, and links six of the eight towers.

Currently under construction in Chongqing, China, Moshe Safdie's Raffle City Chongqing features an extraordinary engineering feat of erecting a 300 meter long "horizontal skyscraper". An extensive urban district set at the meeting point between the Yangtze and Jialing rivers once constructed Raffles City Chongqing will hold the world record of the highest sky bridge linking the towers.

The Conservatory functions as a container for individual programs, as a bridge that connects the various mixed uses of the towers, as well as a horizontal city in the sky allowing for its own programs to intermingle and mix. Once established as a vital programmatic requirement and fundamental linchpin for the project, the technological and logistical hurdles for creating a horizontal tower in the sky need to be addressed.

Structure -

The first issue was how to structure the 280 meter long Conservatory deck as it links the six towers, The support system and framing concept had to be carefully analyzed to ensure that it was efficient in its design, and was not too onerous on the buildings supporting it. The key constraint was the vast differential movements between the six towers, particularly under seismic events. The city of Chongqing is in an active seismic zone, which posed a far greater challenge than the SkyPark in Singapore. Turning to engineering partners at ARUP, the team endeavored to create an innovative structural concept to solve this key constraint.

The breakthrough occurred in conceiving the Conservatory as an individual structure. Unlike the SkyPark that constituted two structural bridges linking three towers, with a large cantilevered structure at one end, the Conservatory would be one rigid element, simply supported by four of the towers. This allows the Conservatory to avoid having the massive movement joints. Under the design requirement for a level 3 seismic event, the differential movement between the towers was upwards of  +/- 3m in the X and Y dimensions, thus the concept of bridging between towers became untenable. However , by creating a rigid whole supported by the four towers, the support members were required to cater for the huge differential movements of the towers.

ARUP proposed massive friction pendulum bearings that sit on top of the tower roofs to receive the main structural supports from the Conservatory to move atop of the towers as if on ball bearings, while the four towers sway in various directions. At the same time, these bearings, as well as dampers within the support structure, help to restrict the towers differential movements. The bearings sit on huge steel reinforced concrete beams that span from the towers structural core out to a deep perimeter beam at the top of the four towers. This distributes the load of the Conservatory, transferring and sharing it equally into the perimeter columns and core, thus keeping the towers structure to reasonable member sizes.

Super-Structure and Enclosure -

As innovative and exciting as the structural design is, it only comprises the bottom half of the elliptically shaped Conservatory. However, just because the space needed to be enclosed, as its name suggested, the concept for the Conservatory was to create a rich landscaped space, with clear views across the city, river valleys, and night time sky. The driving design factor became the best way to create an enclosure that maintained maximum visual clarity with an expressive architectural character.

The first design concept was to investigate the use of a space frame structure. The rationale for the space frame concept was two-fold: it allows for the lightest weight structure and glazing concept to preserve the garden in the sky interior, while providing the needed conditioned space enclosure. Additionally, the elliptical shaped profile of the Conservatory creates an outward thrust force, which made an arch structural concept highly inefficient. As a starting point the geodesic dome design of Buckminster Fuller were studied extensively and one concept was zeroed in on, to use two layers of hexagonal shapes with tension ties coalescing at the center, creating the lightest and clearest structural construct. As the spans across the hexagon were far too great for cladding, a secondary aluminium structure of six triangular canted planes was created to complete the enclosure. The canted structure was efficient, and created a tessellated triangular surface that allowed for alternating planes of glass and aluminium to create a high performing enclosure.

Through extensive investigation, invention, and exploration into the inherent optimal buildability of the Conservatory super-structure and enclosure, a design evolved that is appropriate for the use type and is in elegant expression of its ideals.

Life Safety and Planning -

Fire and life safety codes have evolved along with the development of the high-rise over many decades, and they will need to continue to evolve with the design inventions that are created as a response to dense urbanism. As these inventions and new building typologies are created, design teams will need to think creatively and work hand-in-hand with safety officials to ensure that the highest standards are maintained and applied appropriately.

The largest issue was the requirement that the Conservatory population be counted toward the egress requirement in the supporting towers. Since the Conservatory would constitute the largest floor plate and population size for each tower, every egress stair and fire-safety lift requirement would need to be sized off of it. When calculated, the impact on the tower egress stair sizes would have required that they be tripled. As the slender towers of the project were already less than optimally efficient, this impact could not be absorbed. Hence, an alternative approach was needed.

As a whole, the major challenges of egress and life-safety became a fundamental driver of the planning for the spaces in the Conservatory. Though a mixture of invention and review process, the Conservatory was able to seamlessly integrate with the rest of the project.

Comfort and Place-making -

The design responded through a multi-tiered concept, starting with the enclosure. The glazing of the enclosure is made up of insulated double glazed unit with low-emission coating. The design for the enclosure and interior spaces within the Conservatory presented a unique challenges of developing a blend of comfort and efficiency, while maintaining an open and light filled space. The main drivers are the occupants comfort levels, the previsions required for a rich landscaped planting environment, and the efficiencies needed to maintain a sustainable design and operating cost.

The development of the interior design and architecture of the Conservatory has also created the ability to create smaller micro-climates. Common to many of the program spaces, small pavilion-like structure evolve under the larger roof enclosure.These interior spaces allow for their climate, lighting, and interiors to be isolated from the greater whole, further creating comfortable and efficient interior environments. Across the Conservatory, these pavilions create their own spaces and circulation patterns. One journeys from soaring expansive areas into smaller more intimate environments, as the building is discovered. In many respects, the Conservatory becomes its own city-scape in the sky.

Conclusion -

More than just a building, Raffles City Chongqing is a landmark urban renewal project that expressed and shpaes Chongqing's global city aspirations. As the master planner of this important site, CapitaLand fully appreciates the historical and cultural significance of Chaotianmen to the people of Chongqing. The Conservatory is representative of a new building type, spawned from dense urban environments. As a pioneering concept derived from requirements of increased density, the Conservatory is one example of a new typology. Further evolution of this typology will undoubtedly unfold, perhaps integrating itself across multiple projects and sites, and creating a true three-dimensional matrix of our urban fabric. 

Developer aimed to create a vibrant riverfront urban district that serves as a dynamic city gateway benefiting of Chongqing's growing economic influence.