In terms of function, contemporary buildings in comparison with those in the past are often faced with a higher level of uncertainties. Within the life cycle of a building, the potential for change of function and pattern of use have become the new normal state. Through a systematic approach, the Exo Towers integrates the spatial layout, structural form, building envelop and mechanical services into a whole , creating a forward-looking and universal space framework which facilitates a building with a higher degree of flexibility and adaptability.
—Yongzheng Li
Co-founder of UUA / Lead Architect
1.0 Background: An Architectural Strategy of Adaptability
With a pair of mega columns adorning the north and south facade, combined with an “exoskeleton” of structural elements, the Exo Towers is the name given to the Ruifeng Digital Finance Center as it perhaps most accurately reflects these defining structural features of this building. Located in the central position of Jinghu New District, Shaoxing, Zhejiang Province and completed in 2021, the Exo Towers covers an area of 74,000 m2. The building is comprised of two towers, being 15 and 21-storey high respectively, and linked together by a 70m-high central glazed atrium. The change of heights between the two towers not only defines a dynamic skyline, but also creates this breathtaking atrium space.
Around the same time as the project began in 2013, the nature of banking underwent a rapid transition , with mobile payments and cashless transactions from Chinese Internet companies becoming the norm. To cope with this rapid change, there was a pressing need for financial institutions to cope with new digital challenges through business adjustment and organizational restructuring. Against this background of uncertainty, to agree and design the functional layout has been a determining factor for a number of years since the initiation of the project. To allow for future changes in working patterns, the design principles of flexibility and versatility were central to the design of the office layout. Hence this building utilizes an external structural system that greatly reduces the number of structure columns of the typical floor, creating large and open office space combined with a raised floor for flexible wiring, allowing for the ongoing flexible division of functional layout in the future. In addition the external structural system not only forms the real expression of mechanic and orders the space, but also defines the scale, form and rhythm of the building, ultimately accommodating all of the unique requirements and daily activities of those people who use this space. The Exo Towers therefore derives its architectural language from the manner in which the space and structure are completely integrated.
2.0 Integrated Design: A Geometry-based Systematic Design Logic
In order to effectively organize all architectural elements and coordinate all professional parties, as large comprehensive office building like the Exo Towers should adopt a comprehensive and systematic design logic, an “integrated design” as such. Therefore, a 1.5m x 1.5m modular grid system is utilized to regulate the architectural form, position and define the spatial layout, structural form, building envelop and MEP services, facilitating mutually dependent and defined systems through collaborative interfaces.
Due to the highly prefabricated design and construction methods, the whole construction site had the appearance of a clean and well-ordered assembly line, greatly reducing the on-site wet operations. According to the feedback from the main contractor, the average number of daily workers on the site during the construction of the Exo Towers was about 80 people, which is a reduction of a third when compared with a conventional construction site of a similar scale.
3.0 Space and Structure: Mutually Defined Symbionts
3.1 Structural System
For the Exo Towers, the necessity to create open and adaptable spaces determines the idea to create an external structure system. Arguably the key factor in the confidence to deliver a building with an architectural language defined by expressing external structural elements was the decision to bring on board a structural consultant at the early concept design stage. At UUA, we believe that innovation and creative architecture is a result of an effective collaboration between architect and engineer from the project outset, as compared to a more traditional approach which sees the appointment of the structural consultant post planning permission, often to the detriment of the final outcome.
After the approval by the Planning Bureau, the structural engineers from the local design institute joined the design team formally. Thanks to the structural estimation at the beginning of the project, the structural system and the dimensions of the main components were agreed to be achievable. However, the project team was faced with a number of significant structural challenges, seeing numerous of vertical components not touching the ground combined with diagonal braces. This not only means an increase in the design difficulty and workload, but also requires extra time and effort to apply for an ‘irregular high-rise building review’. It follows to then organize experts at the provincial level to verify the seismic and fire safety of the building from a technical point of view. To avoid further complication was suggested to make the external structure a decoration and add conventional columns indoors, reducing cost and time. However as this would have compromised the whole design concept, a consensus was gradually reached with all parties: It was felt that the building will lose the most important foothold and become a posturing of ornament if it gives up structural authenticity. Fortunately we had the complete support of the client to follow our original aspiration to design an excellent landmark building with structural authenticity. The Exo Towers adopts a hybrid system of steel structure and concrete structure. The central concrete core and the external steel frame jointly constitute a supporting system. Rising up from a unified pile and raft foundation, the two towers are connected by two sets of large trusses at the top of the atrium.
3.2 Structural and Spatial Cluster of the Towers
From the 4th floor of the building, the south tower and the north tower are composed of 2 and 3 repeated structural and spatial clusters, respectively. Each cluster includes 6 floors. The cluster on the south and north facades adopts a 4+2 mode and includes a pair of 4-storey high external columns to support 4 typical floors. The load at the bottom of columns is transferred to the masts on both sides through a pair of 2-storey high diagonal braces. The double-height communal space and outdoor terrace are arranged in the position corresponding to the brace to provide a rest space for the adjacent office floors. The cluster on the east and west facades adopts a 2+2+2 mode and are composed from top to bottom of 3 groups of symmetrical hangers dropped from diagonal suspension trusses. The hung corners liberate the floor-plate edges creating column-free corners within the office spaces and offering a sweeping panorama of the city.
3.3 Entrance Hall Atrium
The 70m full-height glazed atrium between the two towers is the spatial core of the whole building. A 2-storey terraced entrance lobby is at the bottom of the atrium. The reception is on the first floor; the rest and waiting area is on the second floor. The banking hall is arranged on Floor 1-3 of the towers on both sides of the atrium. Internal office and ancillary facilities are on the 4th floor and above. Along the west facade, six sky bridges span between the two towers and in breaking down the scale of the atrium both visually and socially enhance the building's horizontal connections. Cloud-shaped perforated ceiling panels are suspended at the top of the atrium, creating a gauze-like delicate light diffusion effect. A full height cable-net glass curtain wall is used for the east facade of the atrium, reinforcing the transparency of the entrance to the atrium and the dynamic internal spaces of the two towers. The atrium spaces are flooded with natural daylight from the east and west facades, in addition to the roof lights. Every floor in each tower thus receives daylight from two directions, outside and inside, considerably enhancing the internal ambience and working conditions.
Looking upwards from the bottom of the atrium, the strong perspective relation formed by the facade grid creates a sense of movement, akin to the sensation of travelling through time and space. With the changes in light in a day, the reflection and transmission of the glass also present different tones, thus juxtaposition of cool tones and warmth is experience throughout the passing of time. One interesting view is looking eastwards from a sky bridge when you can see the real urban skyline in the distance through the cable-net facade. With an addition effect of the mirror image of the opposite skyline being reflected on the glass facades of the two towers, respectively. Like a collage, the combination of the real and the virtual reconstructs a continuous urban skyline.
4.0 Building Envelop and MEP Services: Attention to Detail
4.1Overall Strategy
In our practice, we tend to use the concept “envelop” for it includes more broadly the tectonic layer at the interface between the building’s physical entity and the space. Both the building curtain walls that are usually used for the exterior and the interior finishes with their related tectonic layers are a form of “envelop”. In addition to the envelop, aspects of the building that can be seen and touched also includes the MEP terminal devices (such as luminaires, vents, switches, sockets, sprinklers, sensors, access doors and maintenance equipment). Therefore, the details and quality of a building largely depend on the presence of the envelop and service terminals, in other words, how the two systems are harmoniously integrated into one seamless order.
As the lead architects of the Exo Towers, in addition to the conventional scope, we also guided the design of the exterior curtain wall, atrium curtain wall and the building maintenance system, delivering curtain wall drawings and digital models that provide clear guidance for the consultants. Benefited by the “internal and external” integrated design strategy we adopted, a unified design language is used in the exterior and interior envelopes, ensuring the integrity of outside and inside.
4.2 External Structure Cladding
Architectural expression and selection of materials reflect the hierarchy for the facade. The cladding of the external structure, perhaps the most characteristic part of this project, adopts a specially textured stainless steel plate called “Linen Star”. The Exo Towers is the first building in China and the second in the world to use this special material. The external structure cladded with this material can gently reflect the surroundings and interact with the light that changes throughout the day. In particular, it shows a pale gold-tone under the sun, breaking the cold impression on stainless steel materials.
The cladding of the external structure is technically the most complicated part of the entire curtain wall system, with some nodes containing up to five structural branches. In order to guarantee the upmost quality through the completion of the project, at the schematic design stage it was considered to divide the external structure cladding into separate panels based on three conditions: these being the estimated structural dimensions, stainless steel plate specification and no dead angle installation. In addition this division is also aesthetically carefully weighed to make the external structure remain consistent with the geometric logic of the whole building, akin to a “tailor made dress”.
4.3 Main Entrance and Canopy on the East
Between the two towers, a 27-metre-wide glazed canopy with a 15-metre cantilever creates a dramatic entrance experience, leading to the 70m-high atrium. The load of the canopy is borne by 2 groups of primary cantilever beams (2 beams in each group) and 4 secondary cantilever beams supported by 4 brackets welded onto the structure of the foyer. This structural strategy not only reduces the torque of the secondary cantilever beams but also shares the loads on the primary cantilever beams, reducing the heights of the cantilever beams and endowing the canopy with a sense of lightness. In order to avoid any defects from welding on the site, all of the structural components of the main entrance canopy are prefabricated in factories and bolted on the site, setting a showcase for the art and beauty of craftsmanship.
4.4 Secondary Entrances and Canopies on the South and North
The same design language is applied to the south and north entrances of the building, with a guiding entrance space being formed by a double-height glass curtain wall that retreats inwards. A screen comprised of stainless steel tubes is attached to the glass curtain wall on the 3rd floor, consisting of a super scale door frame combined with the stainless steel mega columns on both sides to form the base of the towers. By contrast, the canopy is reduced to a single-storey height, transforming the entrance space from an urban scale to a more approachable human scale. The structure of the canopy is of the combination of cantilever and suspender, again adopting the prefabricated construction method.
4.5 Underground Parking Entrance and Ventilation Louvers on the West
The two entrances to the underground parking and the ventilation louvers for building service rooms are allocated to the 1st floor on the west facade of the building. As mentioned above, the envelop division and the layout of the ventilation louvers are integrated into one geometric order.
4.6 Cable-net Glazing on the East Side of the Atrium
A cable-net glass curtain wall is used for the east facade of the atrium, creating a transparent atrium space. The load of the curtain wall is jointly born by vertical and horizontal cables. The upper end of the vertical cable is suspended from the bottom of the atrium truss by an anchor, while the lower end is fixed to the bottom beam through a spring assembly. The horizontal cable follows the same principle, being fixed between two columns. An anchor is provided at one end and a spring assembly at the other end. Finally, the glass panes and vertical and horizontal cables are fixed together by node assemblies to form a complete cable-net glass curtain wall. By hiding the anchors and spring assemblies in an ingenious way, the cable-net glass curtain wall is endowed with an extraordinary transparency and clarity.
4.7 Glass Curtain Wall and Sky Bridges on the West Side of the Atrium
The stick glazing combined with 6 sky bridges span between the two towers on the west side of the atrium. These sky bridges not only structurally bear the load of the glass curtain wall but also spatially break down the atrium into a more human scale with two stories as a group.
4.8 Ceiling System and Maintenance System of the Atrium
Suspended from the atrium, the ceiling system filters sunlight and makes the light diffuse gently, whereas at night, the integrated luminaires act as atrium lighting. The maintenance catwalks of the ceiling system provide an access to clean the glass roof and ceiling panels or replace the luminaires. The maintenance of the four curtain walls of the atrium is realized through a BMU on a horizontal track system installed at the top of the atrium.
4.9 External Facade Maintenance
The external facade is serviced by two sets of stationary crane BMUs anchored on the roofs of the two towers. The BMU has a reach of up to 35m, and can service the entire building. It is made to telescope vertically to an operating position that clears all roof obstructions, while parking below and between the obstructions in order to be hidden from sight, effectively limiting its visibility from below.
5.0 Summary: Design to Build
From the launch of the design competition in 2013 to the final completion in 2021, the Exo Towers is a project lasted nearly a decade being put in use in 2022. With more than ten rounds of major changes to the scheme, combined with to the irregular high-rise building reviews, from the confusion during the suspension of the project to the fast pace after the restart, in addition to the optimization of curtain wall feasibility to the remedy of various on-site defeats, budget restrictions, and the constraints of epidemic control policies, the Exo Towers project has experienced all the challenges and frustration of any large construction projects. However the successful completion of this project is a testament to shared passion of the design team at UUA, the client and all professional parties to find answers to all the challenges faced. It is this shared objective and perseverance by all involved to see this landmark building finished as close to the original design intent.
Team:
Architects: UUA (United Units Architects)
Lead Architect: Yongzheng Li
Client: Bank of Ruifeng
Partners in Charge: Yongzheng Li, Qizhi Li, Tim Mason
Design Team: Yanfeng Lyu, Teng Jiang, Liang Xu, Yuan Tian, Qian Lu, Jessie Millar
LDI: ZIAD
Facade Consultant: ZIAD
Landscape & Interiors: CallisonRTKL
Lighting: TORYO International Lighting Design Center
Environmental Engineer: China Academy of Building Research
VI Design: Bang
Main Contractor: Zhe Jiang Baoye Construction Group
Curtain Wall Contractor: Jangho
Fit-Out Contractor: Sundart
Photographer & Video Production: Archi-Translator
