BUILDING INDETERMINACY MODELLING – COMPUTATIONAL DESIGN AND LOW-TECH CONSTRUCTION OF A HONG KONG BAMBOO GRIDSHELL Kristof Crolla 1 , Adam Fingrut 2 1) Assistant Professor, School of Architecture, Chinese University of Hong Kong, Shatin, New Territories, Hong Kong. Email: kristof.crolla@cuhk.edu.hk 2) Lecturer, School of Architecture, Chinese University of Hong Kong, Shatin, New Territories, Hong Kong. Email: adam.fingrut@cuhk.edu.hk Abstract: This paper discusses the ‘ZCB Bamboo Pavilion’ as a case study for the computational design and building information modelling of structures where both applied materials and available craftsmanship are highly unpredictable in terms of accuracy and precision. The ‘ZCB Bamboo Pavilion’ is a thirty metres spanning, light-weight, and bending-active gridshell, completed in Hong Kong in September 2015 as a public event space. It is built from unprocessed bamboo poles, hand tied together according to traditional Cantonese bamboo scaffolding craftsmanship, and covered with tensile fabric. The paper begins by describing the geometrically complex and structurally high-performing project, and illustrates the low-tech context in which it was realised. Built from flexible components, the pavilion’s tectonic system is a diagrid shell structure that folds down into three large hollow columns. It was developed using physics simulation engines and physical model prototyping. The bamboo used has widely varying geometric, dimensional, and performative properties, and the scaffolding industry, on whose principles it was based, does not use conventional architectural drawings for its intuitive construction, creating a highly indeterminate and complex field of operation. Next, the paper discusses the building information modelling protocols put in place to respond to indeterminacies. It discusses the digital design models, the abstractions, and the assumptions that were strategically applied when developing the singular digital design proposal. The paper examines ways in which the digital modelling environment played an ongoing role in design as new refined data was added to the system. It then covers the construction documentation and annotation information that were used for onsite approximation. The paper then discusses Hong Kong’s building code and architectural practice with respect to indeterminacy. The ‘ZCB Bamboo Pavilion’ highlights how conservative local building cultures can move towards more effective incorporation of natural materials. The paper concludes by discussing the necessity for digital design practice to proactively operate within a field of real-world indeterminacy. Risk, probability, and ambiguity are to be strategically balanced out against idealized digital set-ups and design priorities. Keywords: high-tech versus low-tech, protocol for error, bamboo architecture, bending-active gridshell, form-finding. 1. INTRODUCTION As global social and political attentions toward sustainability and the environment are rapidly on the rise, greater demand for responsible eco-friendly industry continues to grow. The construction industry is one of the largest consumers of global energy, water, and raw materials. It is also a major contributor to air pollution, gas emissions, and landfill waste. The search for sustainable, regionally accessible, and renewable materials plays a vital role in reducing the overall carbon footprint of global building production. In most of Asia, bamboo is a locally available natural material that grows remarkably fast with a high strength to weight ratio. It has not been adopted by the construction industry as a viable structural material. When used in architecture, it is most commonly employed similar to traditional wood or steel as a structural compression or tension member replacement instead of being used for its unique inherent bending strength. The bending of large hollow bamboo poles can be assembled into gridshell-like structures, whereby a minimal amount of materials can create large spanning spaces. The ‘ZCB Bamboo Pavilion’ research project investigates active bending properties of bamboo through the design and construction of a large bending-active structure. The pavilion was completed in Kowloon Bay, Hong 389