A study of the geometry and structural performance of superadobe domes

Abstract

The construction of natural structures as an alternative to conventional houses has extended over recent years in response to human and environmental crisis. Superadobe is a method for the construction of self-built shelters by confining humid stabilized earthen mixture into long curved polypropylene sacks that act as formwork, stacking these long semicircular forms in a decreasing radii pattern that describe massive double curvature monoliths. Barbed wire is added between sack layers to add friction and tensile resistance, and molds placed to produce the building’s openings. This technology has a potential for sustainably reducing housing deficits in developing countries and emergency situations: It’s executable by common people, It’s economical (earth being the main material used and no heavy construction machinery is needed), and even for being a self-built technology, it has consistently exhibited good structural behavior against natural events such as earthquakes, floods, fire and high winds. This, among other self-built technologies, make it possible to build culturally sensitive shelters from ecological and accessible procedures and materials: adobe buildings, cob, bags of earth, bales of straw, among other technologies, are examples. Even if these buildings have limited or no applications in industrial areas, they have extensive applications in human activity, specifically, as a solution for homelessness. It enables the use of natural resources and avoids the need for heavy machinery and transportation of materials, because buildings are made primarily of earth. Since materials used in construction greatly impact on the economy, the environment, and on the adaptability of society, the influence that construction activity has on sustainable development is paramount. Sustainable building materials: those that are profitable, that are socially accepted and which have a low environmental impact, are the focus of many researches that back-up the use of earth inside buildings. Earth bags, whose ratio of polypropilene – to earth in the building’s total mass is small, produce lower CO2 emissions. For thousands of years, materials such as adobe, hard soil and cob have been used for shelter, and approximately 30% of the world's population and 50% of the population of developing countries live in shelters of earth, and the conscience for its use is in expansion. In this Thesis we describe social and environmental challenges that can be addressed with new self-build technologies, followed by propositions to improve them and enhance their use. We define the technology of Superadobe, Its history, its functional characteristics, structural advantages, its social and economic potential. We go through previous works that inquire about sand bag configurations and Superadobe whole building and computer model tests, we describe the construction procedure and propose new steps that can be taken both in investigation and practice to further develop it. We then present a mathematical description of the geometry of Superadobe domes, and propose a set of equations (which are solved by python script) to aid in the design of 'geometrically' functional domes. We then explain a structural assessment method to model forces, moments, tensions/stresses that form in these buildings in limit states, we incorporate the method’s and other equations into a 2nd python script, and apply it to analyze some domed designs in an attempt to predict their structural behavior. Finally, a comparison of these results with some finite element static structural analyses is done, to measure the validity of the proposed structural assessment. We seek to enhance the existing body of data on these structures to elaborate on the technology’s suitability and aid its incorporation into building codes.