Protection by Generative Design Designing for full-culm bamboo durability using sunlight-hours modelling in Ladybug John Osmond Naylor1 1University of Newcastle upon Tyne [email protected] High yield cultivated construction materials such as bamboo could reduce our overconsumption of concrete and sand. Full-culm bamboo has low natural durability which in construction makes it imperative that the design affords protection from rain and sunlight. This paper presents and advocates a generative design workflow for full-culm bamboo using widely applicable architectural design software. A series of trials were carried out to modify the geometry of a planar truss and gablet roof with input parameters tested to determine the optimal roof surface area which could provide full solar protection at three different sites. This algorithmic process tested both straight and curved poles. Depending on the site, when compared to a symmetrical uniform 45 degree overhang, less or greater roof surface area is required in order to provide full solar protection. The use of curved poles and an asymmetrical truss could maintain full protection yet reduce the roof surface area further. Keywords: Full-culm bamboo, Generative design approach, Ladybug, Architectural design, Digital materiality INTRODUCTION ston, 2018). Replacing conventional materials with By 2050, some 50% of the world’s population will bio-based materials that store carbon can be one so- live in the tropics (State of the Tropics, 2020). Trop- lution to help us reduce our overconsumption of con- ical Low-to Middle-Income Countries (LMIC’s) have crete and sand (Pomponi, Hart, Arehart, & D’Amico, a shortage of housing which lacks structural qual- 2020; UNEP, 2019; van der Lugt, 2017). In many re- ity and durability (UN-Habitat, 2016) yet have a la- gions of the world, timber will most likely never be tent opportunity to utilise locally sourced bamboo able to provide the sustainable alternative we need. (Lobovikov, Paudel, Piazza, Ren, & Wu, 2007). Our Given the speed of growth and quantity required, ex- global construction industry has a decisive role to traction could have a deleterious effect on ecosys- play in climate-change mitigation with annual ce- tems (Pomponi et al., 2020). Therefore we need to ment production accounting for around 8% of an- develop the use of high yield cultivated construction thropogenic carbon dioxide emissions (Lehne & Pre- materials such as bamboo (van der Lugt, 2017). Bam- Digital design for sustainable buildings - Volume 1 - eCAADe 39 | 315 boo can absorb carbon dioxide and stabilise slopes to and though there are minor amounts of resins, waxes tackle the effects of deforestation (Tardio, Mickovski, and tannins, none of these have enough toxicity to Stokes, & Devkota, 2017). provide any natural durability (Kumar, Shukla, Dev, & Dobriyal, 1994). Bamboo is hollow (Figure 1) and with typically thin walls, this means that a small amount Figure 1 of decay can have a significant effect on the bamboo Sketch section and (Janssen, 2000). There are abiotic factors which can terminology of a affect bamboo in a structure (Liese & Tang, 2015a). If bamboo culm bamboo is exposed to the sun and rain and in con- through the node. tact with soil the lifespan of the bamboo in the struc- Sketch by author. ture can be only 1-3 years (Janssen, 2000). Changes in temperature and humidity may produce steep mois- ture gradients between surface and inner layers, and direct exposure to sun causes unbalanced and re- peated swelling and shrinkage (Liese & Tang, 2015a) (Figure 2). Figure 2 Full-culm bamboo It can be a challenge however to incorporate bamboo poles cracked and into contemporary design and construction prac- showing signs of tices. This is due to the natural variability of bamboo mould due to between the over 1200 species of bamboo, individ- exposure of excess ual plants, and individual culms. Within culms there moisture and is a non-regular distribution of node locations, a ta- bleaching due to pered diameter of the bamboo culm, and a reduced sunlight exposure. width of the culm wall over the length of the culm. Photograph taken Even within the same species, mechanical proper- by author in 2020. ties can differ since bamboo grown in drier areas and on slopes may have a higher fibre density and in- creased strength properties (Liese & Tang, 2015b). One response to this has been to standardise the ma- UV and visible light radiation also causes pho- terial through the manufacture of Engineered Bam- todegradation which breaks down bonds of the lig- boo Products (EPBs) (Sharma, Gatoo, Bock, Mulligan, nocellulosic polymer causing the bamboo surface to & Ramage, 2015). However, the greater challenge turn grey and coarse (Liese & Tang, 2015a). Such pro- is to use the raw form of bamboo, full-culm bam- cesses have contributed to a societal attitude of bam- boo. In doing so, we can ensure that the most af- boo as a temporary “poor man’s timber”. When bam- fordable and sustainable form of bamboo is enfran- boo is exposed or inappropriately applied in a struc- chised (Harries, Sharma, & Richard, 2012). Another ture and degrades, bamboo will often be blamed for challenge for architects when designing with bam- the action of the architect. As Janssen writes, “No boo, and the focus of this paper, is the low natural chemical treatment will be good enough to solve the durability of bamboo (Kaminski, Lawrence, Trujillo, & problems caused by incorrect design”. (Janssen, 2000). King, 2016). Bamboo is more prone to decay than This is a rallying call for architects to make sure that timber. Bamboo does not develop reaction wood, fundamental to any design process for bamboo, the 316 | eCAADe 39 - Digital design for sustainable buildings - Volume 1 bamboo is protected from rain and UV light. This is Computational design processes and full- a concept known as protection by design. The title culm bamboo of this paper refers to this phrase. Large roof over- Generative Design refers to a design approach that hangs provide protection to bamboo members from uses algorithms to generate designs (Caetano, San- wind driven rain (Figure 3), with a rule of thumb of 45 tos, & Leitão, 2020). Such processes save time and al- degrees (Kaminski, Lawrence, & Trujillo, 2016a). The low the testing of various iterations in order to find a angle of wind driven rain is largely consistent world- more optimal design solution (Jabi, 2013). The pro- wide, however the sun angle is not. cess of form-finding emerges from analysis with the output exclusively determined by function (Laiserin, Figure 3 2008). In the case of this paper, generative design A large roof tools applied to the architectural design process are overhang provides designed to deliver an optimal design output which protection to the provides full protection from sun and rain with min- structural full-culm imal material usage and minimal cost on a site by bamboo members. site basis. A wider challenge of computational de- ZERI Pavilion, Simon In some locations and orientations the overhang of sign tools with their great accuracies and full-culm Velez, 1999. Sketch 45 degrees will always be required to protect against bamboo is the difficulty in accurately modelling an by author based on wind driven rain but this may not provide enough anisotropic material with natural variability (Crolla, the ZERI Pavilion solar protection particularly if a site is further away 2017; Qi et al., 2021). In 2005, Willis and Woodward image from the from the equator. A design decision can be to suggested design parameters such as material flaws, book, Grow your cover the bamboo behind adobe or cement mortar grain directions and inconsistent densities will make own house: Simón such as bahareque construction techniques (Kamin- it difficult to achieve a direct correlation between dig- Vélez and bamboo ski, Lawrence, et al., 2016a). However for cost, aes- ital data and a constructed building, but note this gap architecture (Vélez thetic or biophilic reasons the designer may decide to between the building and the model will continue et al., 2000). make the full-culm bamboo visible. There are impres- to narrow (Willis & Woodward, 2005). Far from try- sive examples of buildings with structural full-culm ing to bridge this gap, mainstream architectural de- bamboo visible externally such as the Amairis Fac- sign practice operates on “reduced matter-models de- tory in Puerto Caldas, Colombia, by Ruta 4 [4], or the signed to behave like pristine, controlled numerical mi- ZERI Pavilion, by Simon Velez in Manizales, Colom- lieu” (Kwinter, 1996, p. 70). Using a generative de- bia (Figure 3). Conversely, where rainfall is low and sign approach to design with full-culm bamboo is sit- characteristic of a dry steppe climate or subtropical uated in a wider discourse within architectural design ridges, this overhang can be surplus to needs. Large crystalised by two terms. Digital materiality as coined overhangs can also reduce the occupiable footprint by Fabio Gramazio and Matthias Kohler (Gramazio of a building if the necessary extension of the roof & Kohler, 2008), and digital materiallurgy coined by requires an encroachment into a neighbouring site. Adam Fure in 2011 (Fure, 2011). Kohler and Gramazio Large overhangs can also be aesthetically cumber- use the term digitalmateriality to suggest a departure some and also prone to wind uplift. Whenever bam- from the design of purely form, but a design that is in- boo is exposed, the design should afford the bamboo formed by the constructive organisations and meth- protection to maintain its structural and aesthetic ods of implementation (Willmann, Gramazio, Kohler, properties. & Langenberg, 2013). Instead of realising a design or an image, a comprehensive design and building pro- cess is conceived. Constructive principles can be de- termined that define the production of architectural Digital design for sustainable buildings - Volume 1 - eCAADe 39 | 317 components as interrelated production steps (Will- sented which use digital modelling and robotic fab- mann et al., 2013).