Design of three hypar roofs made of Guadua bamboo

While seeking new ways to build inexpensive and attractive shells, designers have increasingly been exploring shells and space structures made of guadua bamboo. Guadua bamboo poles, with their relatively low mass, high strength, and great axial and bending stiffness are promising linear building components for curved grid systems. Guadua bamboo is also a sustainable building material that can be easily harvested and deployed to construct economically efficient and elegant yet durable large span roofs. However, rigorous numerical structural analyses of bamboo are not common practice. Therefore, we present the structural analysis of two roofs consisting of a set of hyperbolic paraboloid (hypars) (designer Greta Tresserra, Colombia, 2015) that are planned in Cali, a region where the giant bamboo species Guadua Angustifolia grows abundantly. Additionally, a prototype hypar built in Austria (designers Greta Tressera and Tim Michiels, Austria, 2016) is presented as well. In this study we examine the relationship between the structural behavior of hypar grids and their most critical bamboo joint. A simplified analysis, as well as a finite element (FE) analysis is performed in order to determine how the overall hypar form influences the internal loads in the bamboo. Subsequently, the most critical joints that interconnect the bamboo poles are analyzed through laboratory testing. Particular attention is given to the "fish-mouth" connection with and without mortar inserts. A better understanding of the flow of forces in the hypar grid combined with a detailed quantification of the behavior of the "fish-mouth" joint, allows for a more informed and efficient use of the bamboo material used in Cali structures. More broadly, this study seeks to demonstrate how an eco-friendly, widespread and inexpensive material such as bamboo can be used at its full structural capacity for the design and construction of hypar roofs.