Building indeterminacy modelling – the ‘ZCB Bamboo Pavilion’ as a case study on nonstandard construction from natural materials
If unprocessed natural materials are the most environmentally friendly construction materials available, how do we develop and communicate design model and construction information that allows dealing with their volatile indeterminacies?
This paper discusses the design and development of the ‘ZCB Bamboo Pavilion’, a 30-metres-spanning, light-weight, bending-active gridshell from hand-tied bamboo poles, as a case study for the computational design and building information modelling of nonstandard architecture where both applied materials and employed craftsmanship are highly unpredictable in terms of accuracy and precision.
Reflective practice and participatory action research are used to extract knowledge on and challenge the environment of practice, and improve design and construction strategies. The project is used to discuss how traditional construction can be augmented through the strategic injection of computation in the design and construction process, how computation allows for a different mode of collaboration with increased impact for the designer, and how bespoke building information models enable an expanded architectural design solution space.
The paper concludes by arguing for a mode of digital design practice that more proactively operates within a field of real-world indeterminacy. The risk and ambiguity of working with indeterminacies are to be strategically balanced out against idealised digital set-ups and onsite opportunities.
KeywordsHigh-tech versus low-tech Protocol for error Bamboo architecture Bending-active gridshell Form-finding ZCB Bamboo Pavilion Participatory action research Reflective practice
Application program interface
Building information model
Participatory action research
Zero carbon building
Like the relationship between intensive and extensive logics, or the relationship between matter force logics and codification systems, architects are inevitably implicated in the tension between the generative and limiting poles of both. (Reiser & Umemoto, 2006 , p.112)
Demand for responsible eco-friendly architectural practice continues to grow. The search for sustainable, regionally accessible, and renewable materials plays a vital role in reducing the overall carbon footprint of global building production, especially in the most rapidly urbanising regions of the world. Bamboo is one of the fastest growing natural construction materials and is locally available in most of the developing world, including South America, Africa, and Asia. Certain giant bamboo species suitable for construction grow up to a metre a day and can be harvested in three to 5 year cycles, making bamboo far more sustainable than any wood species.
Participatory action research
Methodology and aim
The research component of this project’s design and construction is framed in a participatory action research based methodology. The aim is to improve strategies, practices, and knowledge of the environment of practice. This method involves combining immediate and specific project problem solution with a reflective process of progressive problem solving. Reflecting on this actively participating in a constantly changing situation is done to enable extracting future alternative guidelines or directions for best practice. Here, this methodology led to proposing new courses of action when dealing with indeterminacy in material or craftsmanship in a digital project design environment.
The project development is set up in a spiral of steps. Each step is composed of a circle of planning, action, and analysis of the results of this action, before advancing the project with more embedded detail. This spiral enabled the crucial components of the final construction to be identified, tested, and included into a flexible design model that encompassed both the digital and physical. Interactive enquiry allowed the balanced problem-solving process to result in a design model that gradually gained concreteness until it was materialised in the final full-scale prototype: the built project.
Local community of practice
This locally important and cultural identity defining craft is at risk of being pushed aside by a more easily regulated construction environment using steel scaffolding. Rather than imposing alternative techniques, this research project recaptured the counter-narratives from the bamboo scaffolding tradition and integrated them in an adapted contemporary workflow. Thus, the ‘ZCB Bamboo Pavilion’ research project investigates how, through the combination of digital design technology, a culturally valuable yet imprecise local craft and an ecologically desirable yet volatile natural material can be practically applied as structural component in light-weiht, sustainable architecture.
The ‘ZCB Bamboo Pavilion’ is a temporary public event space capable of seating 200 people, completed in October 2015 in Kowloon Bay, Hong Kong, where it was used for 8 months before being recycled. It is a bending-active gridshell structure that spans 37 meters, is four stories high, and is wrapped in a lightweight translucent glass-fibre reinforced polymer membrane. Its design development works through immediate and specific problem solution on-the-go until sufficient confidence is built up to initiate final construction.
At the start of the research project in early 2014, no building code and hardly any information were available on the use of bamboo as a structural material in architecture, especially not as a bending-active application (Rockwood, 2015). Only reference material on general bamboo architecture was at hand (Jayanetti and Follett, 1988 Janssen and Jules, 2000, Hidalgo-Lopez, 2003, and Velez, 2013).
The geometry from this first digital model was used to extract conventional architectural plan, section, and elevation drawings for client and contractor communication during public tendering and for operational license applications at a later stage. The model was also used by structural engineers to assess the viability of the project. It further served as a basis for a physical prototype at scale 1 to 30, made from two metres long bamboo sticks following the geometry axis lines. This prototype used a straightforward mark-up system in which node intersections, extracted from the digital files, were accurately marked up onto long, straight, unbent, bamboo members. Corresponding intersection labels on different members were then brought together one by one while bending the members during the assembly. As matching labels were joined, the form gradually emerged and stiffened up.
The 1 to 30 model revealed several unforeseen challenges that could problematically affect the final full-scale structure. First, in terms of installation sequence, members practically could only be laid up from the top, rather than placed from below (impossible to reach) or woven in (impossible to bend). Secondly, approximation of the layer thicknesses and member shape needed to be more accurately digitally incorporated. Lastly, the two metres length of the used bamboo sticks could not be scaled up thirtyfold onsite. Only roughly the central 12 metres of a bamboo pole is suitable for construction, meaning members would need to be assembled from separate bamboo culms.
A second digital model addressed and incorporated most of these issues. The originally idealised single surface geometry was split up and offset into three layers spaced according to anticipated average bamboo material thicknesses. All members’ axis geometry was adjusted to meandered in between only these three layers in a way that followed a carefully orchestrated installation sequence laying-up members from the outside onto previously placed members. This prevented tight bending radii while remaining as close to the original shape as possible.
Construction information modelling
Setting up a pliable digital model allowed gradual updating of assumed variables relating to physical material properties, construction techniques, detail design, and structural concerns. As data had become more specific throughout the design and prototyping process, the unpredictable nature of both material and assembly method now required for novel construction instructions to be deployed. These needed to be clear enough to minimize any misinterpretation of data, assembly technique, or order of operations, while remaining an open system that could adapt to urgent changes in detail or geometry.
The construction documents maintained a high level of accuracy in setting out the connection intersection point markings onto members of variable thickness. These markings became guides for an assembly process that included tolerances and human error, resulting in an interconnection that allowed a level of in-situ form finding. The method was straightforward enough to allow for the onsite crossing of language and cultural barriers. A certain level of self-correction took place during the installation: as the system relied on the material’s natural bending behaviour, installation errors that deviated too far from the ‘exact’ simulated digital geometry would become impossible as the real-world material would fight back to find its balance. Large human annotation errors would be spotted and corrected instantly by the spontaneously balanced construction system.
As-built vs. digital model
Building indeterminacy modelling
The ‘ZCB Bamboo Pavilion’ challenges the role building information models (BIM) can play in facilitating alternative architecture production. Although traditional architectural drawings and visualisations were extracted from earlier models for communication and licensing purposes, for construction itself the focus lay on managing selective unconventional types of data. BIM’s purpose is hereby pushed to go beyond the optimising and streamlining of generic building production. Since there will always be a gap between digital and real-world environments (Willis and Woodward, 2010), tolerances always will continue requiring being absorbed in the design somewhere. But what if these tolerances are an order of magnitude larger than what is common practice? Or what happens if the structure itself is expected to drastically move, and change during the construction process as it finds its equilibrium form?
Since a gap between the BIM and the building is inevitable and potentially advantageous, the question remaining is: how big a gap should there be? (Willis & Woodward, 2010 , p. 184)
A fully accurately detailed and precise BIM model that aligns with conventional building models could hypothetically be created for the ‘ZCB Bamboo Pavilion’, offering full control and predictability over all involved materials, components and their tolerances. To set up this model, each bamboo pole would need to be scanned and measured ahead of time at high accuracy. That bespoke data set would then be brought into the virtual environment. A live recording of the pole behaviour would feed back into the system in real-time as poles are bent and fixed in place onsite, allowing for constant re-calculation and assessment, and so forth.
There would be advantages to this hypothetical model. Embedded digital monitoring could display or predict abnormal or undesirable material deflections or deformations and could suggest in real time where adjustments need to be made. Yet, although probably technologically feasible, this level of control is currently not practical nor cost effective. More importantly, ultimately it is not necessary and redundant. The level of sophisticated and automated decision-making this model would bring is currently already to a large extend embedded in construction implementation, as the design and construction team can rely on experience, intuition, and common sense to solve unforeseeable issues on-the-go. The gap between the virtual and the real can never be fully sealed. The role of physical prototyping and material testing and the inclusion of their findings into a flexible digital model hence needs to be valued as essential.
If unprocessed natural materials are to be incorporated more pervasively in construction, then alternative design information models and implementation systems are needed that allow dealing with their volatile indeterminacies. This project eventually positioned the digital emulation model not as an exact, ideal, and finished model that needs real-world replication, but as an element in a chain of back-and-forth between simulation and prototyping. The digital model should embody variability so that its physical materialisation can lead to singular expression. Unavoidable serendipitous occurrences could thus be exposed and incorporated more effectively. This shifts the BIM model’s focus from a quantification and simulation tool to a much more open-ended environment that works with the peculiarities of the material world rather than in isolated abstraction ahead of construction.
Discussion and evaluation
Permitting natural variability
The ‘ZCB Bamboo Pavilion’ pioneers in pushing the boundary of which 3D model based data transactions are incorporated in construction. As highlighted, certain benefits can only be found in more detailed or alternative BIM models. However, the information modelling tools most commonly used in practice are not developed to accommodate the variety of material inaccuracies, tolerances, and indeterminacies faced onsite. Although digital models are commonly updated to achieve a final “as built” model, this information flow does not incorporate the indeterminacy back into the design process. This can result in a final model which potentially dramatically differs from original design intent. The assimilation of naturally variability in digital environments is not possible with conventional tools but would be a requirement if we want to use raw materials that don’t undergo extensive industrial standardisation.
Open source API
The ability for building information modelling technology to move forward and improve in areas such as indeterminacy could be facilitated by the incorporation of a more open-source application program interface (API). Such an interface can allow for greater direct access to database fields and tables, enabling designers to take more direct and spontaneous control of their model data. This open interface then allows direct access to the software for autonomous development of more accurate customised tools that could be configured with greater sensitivity toward material attributes and structural behaviour beyond convention. An open-source attitude, whereby the appropriation and sharing of content is encouraged, will greatly enhance the versatility of BIM managers in areas of design, allowing them to introduce solutions more comprehensively to construction indeterminacy by developing their own ad-hoc solutions. To some extent, this API is becoming available in the form of scripting languages such as Python®, Visual Basic® and graphical versions such as Dynamo® or Grasshopper®, which are, albeit somewhat proprietary in nature, steps in the right direction.
The developed workflow discussed in this paper provides a very timely practice-based working model to deal with unforeseen in situ occurrences. Architectural designers now globally have easy access to cheap computational power to allow its practical incorporation even in small-scale projects. Sufficiently powerful software became accessible and versatile enough to allow for bespoke customisation in one-off designs. In the meantime, today, still, the majority of onsite construction is done almost exclusively by hand, onsite, without the use of sophisticated construction and fabrication technology, relying on whatever craftsmanship or skill is locally available. These two realities need to be brought in close dialogue.
The ‘ZCB Bamboo Pavilion’ has pushed the boundaries of the design solution space of bamboo architecture. It’s mode of practice, though, could be employed into the arenas of other analogue construction systems as well. Through setting up a mutually enforcing feedback loop between the digital and physical world and relaxing the rigidity of digital design models, a geometrically, structurally, and spatially wider range of architecture will become possible.
While technological conditions continue to advance rapidly, the material and digital worlds need to be brought closer together through a balanced workflow. In this, the architect’s fundamental task is the definition within the overall design and construction process of the comfortable balance between what digital tools allow for and what is appropriate onsite.
Paramount to the project’s success was a digital configuration capable of flexibility with respect to the tolerances of real-world materials and onsite assembly techniques, as well as the conception of the final project as a self-correcting analogue material computer that takes over when the digital emulation no longer is applicable. For this, alternative types of construction documentation and reference material extracted from the complex original data needed to achieve a level of practical simplicity.
The adoption of digital tools needs to be applied sensitively to accommodate and take advantage of a wider array of raw materials and regional labour skills. The relationship between absolute accuracy and a system with indeterminacy will remain open as the adoption of natural materials and varied construction practices are further explored. Through the innovative use of computational tools in architectural practice, customised building information models can adopt an ad-hoc approach toward balancing risk, probability, and ambiguity against an idealized design.
Design research team: Principal Investigator, CUHK: Prof. Kristof Crolla; Co-Investigator, CUHK: Mr. Adam Fingrut; Research Assistants, CUHK: Mr. IP Tsz Man Vincent, Mr. Lau Kin Keung Jason; Consultants: Dr. Goman Ho and Dr. Alfred Fong (Structural Engineering), Mr. Vinc Math (Bamboo Consultant); Authorised Person: Mr. Martin Tam; Registered Structural Engineer: Mr. George Chung; Project Documentation: Mr. Ng Ka Hang Kevin, Mr. Grandy Lui, Mr. Michael Law and Mr. Ramon van der Heijden.
CIC/ZCB Client Project Team: Executive Director, CIC: Dr. Christopher To; Publicity, ZCB: Ms. Yan Ip; Technical Services, ZCB: Dr. Margaret Kam.
Construction Team: Main Contractor: W.M. Construction Ltd.; Bamboo Construction: Sun Hip Scaffolding Eng. Co., Ltd.; Fabric Contractor: Ladden Engineering Ltd.; Lighting: CONA Technology Co. Ltd. & Brandston Partnership Inc.
This Chinese University of Hong Kong (CUHK) School of Architecture project research was partially supported by a grant from the Research Grants Council of the Hong Kong Special Administrative Region China: Project No. CUHK24400114, Project Title: Architectural design and building of light-weight, bending-active, bamboo shell structures for Hong Kong, using live physics engines.
Kristof Crolla is the sole author of this paper.
Kristof Crolla is a Hong Kong-based licensed architect and Assistant Professor in Computational Design at the Chinese University of Hong Kong, School of Architecture. His research focusses on the strategic implementation of computation in architectural design. He graduated Magna Cum Laude as Civil Architectural Engineer from Ghent University and practiced in Belgium before moving to London in 2005 to attend the Architectural Association School of Architecture (AA)‘s Master of Architecture programme Design Research Laboratory. Following this, he worked for several years for Zaha Hadid Architects, while teaching in parallel at the AA and other institutions worldwide. Since 2010, he is based in Hong Kong where he set up his practice Laboratory for Explorative Architecture & Design Ltd. (LEAD). He has been invited as a jury critic, lecturer, and tutor in numerous institutions throughout Europe, Asia, Chile and South Africa. He is best known for projects such as ‘Golden Moon (Hong Kong, 2012)’ and ‘ZCB Bamboo Pavilion (Hong Kong, 2015)’, which internationally received over two dozen design awards and accolades, including the G-Mark (Japan), Architizer A+ (USA) Awards, and most recently the 2016 World Architectural Festival Award - Small Project of the Year 2016, nicknamed «The Architectural Oscars».
The author declares that he has no competing interests.
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