Digital fabrication as a tool for investigating traditional Chinese architecture A case study of the dou gong Di Li1, Michael Knight2, Andre Brown3 1,2,3University of Liverpool, UK 1,2,3{di.li2|mknight|andygpb}@liverpool.ac.uk This paper presents part of a broader research project in which a set of complementary computational techniques have been applied to investigate and interpret traditional Chinese architecture. The techniques involve digital modelling, algorithmic representation and digital fabrication. The ancient rule books that describe the traditional Chinese design styles and construction technologies are the basis for the parametric rules and algorithms and the application to the modelling and fabrication process. The focus of this paper is the study of a typical Chinese joint structure, the dou gong. The precedent case study and the components of the dou gong are reviewed and analysed. Then the digital representation and fabrication processes that have been employed are demonstrated. Practical problems were found in this process and modifications were consequently made. At the end of the paper, we discuss the achievements and benefits that arise from this investigation, and potential applications in practice. Conclusions from work presented in this paper and for the broader research are drawn respectively. Significant prospective work is suggested. Keywords: dou gong, Ying Zao Fa Shi, digital fabrication, traditional Chinese architecture INTRODUCTION With the rapid development of digital tech- China is one of the Four Great Ancient Civilizations niques in architecture over the last 25 years, it is possi- which has a span of over 5000 years and its traditional ble to re-discover the value of the lost or damaged ar- Chinese architecture plays a significant role in the chitecture by transforming two dimensional physical world's architectural heritage. Unfortunately, almost information recorded in the historical literature into all the buildings constructed before the Tang Dynasty three dimensional digital representations (Webb and (618-907) have disappeared. However there are Brown, 2011). Using parametric and shape grammar some buildings from the period from the Song Dy- techniques (Li, 2001; Wu, 2005) it has been shown nasty (960-1279) to the Ching Dynasty (1616-1912) possible to describe the relationships in a digital de- remaining, but in differing states of repair. sign environment that describe the traditional de- Digital Heritage 1 - Volume 1 - eCAADe 32 | 623 signs in an algorithmic way (Li et al. 2013). Conse- historical period. The joint plays a multi-functional quently, further analysis can be made together with role that covers structure and construction require- a better level of understanding and interpretation. ments as well as being an essential component of In turn, this can significantly aid understanding, in the aesthetic qualities of the whole construction. As restoring and recreating examples of traditional Chi- Liang (1985) points out, "the dou gong plays the lead- nese architecture, or in designing contemporary ex- ing role, a role so important that no study of Chi- amples that respect traditional geometries and val- nese architecture is feasible without a thorough un- ues. derstanding of this element, the governing feature of the Chinese 'order'." Figure 1 dou gong (Liang, CASE STUDY OVERVIEW AND PRECEDENT 1985) There are the only two surviving ancient rule-books: Ying Zao Fa Shi (Building Standards) from Song Dy- nasty (960-1279) and Ching Dynasty: Kung-ch'eng tso-fa tse-le (Structural Regulations) from Ching Dy- nasty (1616-1912), which are referred to as the "two text books of Chinese ancient architecture" by Liang (1985). According to Li (2001), Ying Zao Fa Shi is rule- based and indicates parametric characteristics. The joint, called the dou gong, is described in one of the carpentry volumes in Ying Zao Fa Shi (Li et al. 2013), which is the bracket set on top of the columns and under the beams and the roof. To understand the dou gong parametrically, two approaches can be taken. First, the dou gong is treated as a whole rather than focusing on each in- dividual element and the modelling process concen- trates on building up the whole structure and set- ting up the position of all the elements. Then de- This paper is part of a broader research investiga- tailed elements are dealt with later. This is the top- tion into the digital interpretation and recreation of down method. The second involves the construction traditional Chinese architecture. We do so by turn- of each element first and then connecting them to- ing ancient rule book information into algorithms gether. This is the bottom-up method and the con- and applying these in a contemporary parametric centration of this paper, which will be discussed in modelling environment. This paper concentrates on detail in the following sections. the understanding, representation and digital fabri- Following the first approach, a graphical rep- cation of a typical Chinese joint structure, the dou resentation is made as shown in Figure 2 using gong. This is a particularly complex aspect in the de- Grashopper. Since the main structure of dou gong is sign of traditional Chinese architecture, as there are doubly symmetric, in order to construct the model ef- many elements to the joint that have a sophisticated ficiently, one fourth of a complete dou gong is built relationship with each other, as shown in Figure 1 up. By mirroring twice, a complete dou gong could (Liang, 1985), and there are many variations accord- be carried out. This is a conceptual model which ing to the scale, location, function, decoration and is based on a commonly used concept of the tree 624 | eCAADe 32 - Digital Heritage 1 - Volume 1 branches. Several layers of the tree branches grow rameters. This enables the possibility of the achieve- and expand outwards, which generates the extended ment of the aesthetic function of the joint, that is, to tree canopy. In this process, the iterative layers and treat the joint as a pure classic decoration. And in- extension of each layer are the key factors for sim- deed, since the Ming Dynasty, the structural function ulating the bracket set. To achieve this, first of all, has become less important due to the development a series of points are set up along the Z axis. This of other constructional technologies while the aes- provides the initial partition of the layers, which are thetic value became more emphasized. the basis for gong (the long arms). The number of On the other hand, several problems were ob- the layers is controlled by an input slider which can served. The accurate shape of the joint is not repre- be changed based on the need of layers. The Graph sented well in the experiment; as well as its volume, Mapper is an effective method in the controlling. an extra set of logic relationship which defines the Then the parabola function is selected to generate all precise shape and volume of the joint is needed. This the points locating the tree branches (representation is necessary to guarantee the achievement of other of gong). The strongpoint of parabola function is to important functions of the joint (which will be intro- be able to easily define all the layers together. But duced in the following sections). In addition, the ac- from the later process, it is found that this might lead curacy of each element of the joint is also omitted. to the loss of control of the branches shape within Apart from these matters, there is a key component each layer. To improve this shortage, the Gaussian which acts as a lever in the function, omitted from function is introduced to replace the parabola func- this model. The above problems lead to the adop- tion in this process. As shown in Figure 3, the shape tion of the second approach described in the follow- of the branches is closer to the gong described in the ing sections. rule book. Following this, a rectangular grid of points Figure 2 is set up within each layer. The area of layers reduced The top-down gradually from the top to the bottom alone the Z axis. approach of dou Here Path Mapper is used to arrange the location of gong points within each layer. Then, building up all the branches by lofting the curves based on the grid of points. In this process, it is noticed that although the position of the gong (tree branches) is defined, the position of the dou (the small rectangular blocks) is omitted without a clear definition and consideration. But actually from Figure 2 (top view), it is shown that Figure 3 the small square of grid within each layer could be The top-down used as the position of dou. approach of dou From this experiment, we note three points of gong using the merit. First, the layers and extension within each Gaussian function layer are achieved. This is a basis to recreate differ- ent scales of the joint without the need for another set of logic definitions. In addition, this attempt can fulfil some of the main functions stated in the rule book, such as the potential to enlarge the roof area both outwards and inwards. Thirdly, the configura- tion can be adjusted by controlling all the input pa- Digital Heritage 1 - Volume 1 - eCAADe 32 | 625 DOU GONG (THE JOINT) the roof as shown in Figure 1, transferring the roof In order to investigate the detailed elements of the load evenly through the column to the foundation. dou gong, an understanding of its development and Second and most distinctive one is to provide an structure is helpful. From the first appearance of dou earthquake-resistant function. Since all the horizon- gong in period of the Warring States (approx.