Thin shell foundations: Embodied carbon reduction through materially efficient geometry

Abstract

Due to increasing global population, floor area is expected to double by 2060. At the same time, the building sector contributes 11% of global greenhouse gas emissions annually as a result of current construction processes. Therefore, if global warming is to be limited to 1.5ºC above pre-industrial levels, reducing embodied carbon will play a key role and business-as usual construction processes must be reconsidered. This research aims to reduce carbon emissions associated with reinforced concrete structural elements while addressing the need for a significant increase in adequate housing due to rapid urbanization.

The structural floor system, frame and foundations represent the systems with the most potential to limit emissions, as they are the biggest contributors to embodied carbon in a building. In contexts where labor costs drive construction costs, particularly in the Global North, material is consumed excessively at the expense of time. This research proposes shell foundations in lieu of spread foundations, drawing from historical applications such as Félix Candela’s Customs Warehouse, built in 1953. Shells distribute loads more efficiently through their cross-section, reducing the quantity of material required structurally which ultimately reduces their embodied carbon.

In this research, existing analytical equations are applied in a parametric design workflow to evaluate the environmental impact of conventional prismatic foundations and shell foundations for the same design load. For a 2MN column load on clay soil, shells reduce embodied carbon in foundations by 48%. By applying this approach systematically, insights are gained regarding their applicability to various building typologies and site conditions. For high applied loads, and soils with low bearing capacity, shells significantly outperform their prismatic counterparts. Foundations are then considered within the context of a whole building to determine the potential downstream savings when multiple systems are shape optimized. When floor slabs are shape-optimized in addition to using shell foundations, the embodied carbon of a building can be reduced by 72%.

Digital fabrication offers a pathway to economically build materially efficient foundations while addressing the additional time and labor often associated with more complex geometry. For example, advances in 3D printing earth suggest local soil can act as formwork if printed in the required shape to receive the shell geometry. Additionally, subtractive methods are explored, where earth is compacted and milled to create formwork for a shell foundation.