The Impact of Pneumatic and Catenary Forms on the Design of Thin Concrete Shells
Nyema Wesley1; Ruy M. O. Pauletti2; Leila C. M. Valverdes2; Sigrid Adriaenssens1
1 Princeton University; 2 University of São Paulo
doi:10.20906/CPS/CILAMCE2017-0766
Resumo
This project encompasses the structural application and analysis of pneumatic and catenary forms in the context of large-scale thin concrete shells. Catenary shapes, which are resultant from self-weight, were traditionally desired for these structures, as the formwork could easily be derived from the hanging-membrane technique. The construction process, however, can prove to be quite tedious, especially with the presence of doubly-curved surfaces (otherwise known as non-zero Gaussian surfaces). In recent years, pneumatics has been introduced as a powerful tool to aid in the creation of these concrete shells. Using the Pneumatically Formed Hardened Concrete (PFHC) method, an initially flat plate of concrete, consisting of panels, is poured in the shape of the "flattened" final geometry. An air-tight membrane lying under the the concrete layer is then inflated to apply an outward pressure, lifting and deforming the panels until the desired shape is formed. This method is particularly novel in the sense that, regardless of the final conjoined body, the composite plates will only undergo a curvature change in one direction, which respects the deformation capacity of the material. To investigate these modern practices, including the PFHC technique and beyond, an original design for a thin concrete shell was drafted. The ANSYS finite element software was utilized to obtain both pneumatic and catenary forms from the same initial material properties and boundary conditions. From this point, a pressure was applied either as a gravity load or as a radially-emanating force to the nodes in the mesh, giving volume to the shell. Stiffness and applied loads were altered in several portions of the geometry in order to achieve aesthetic and optimal designs. We would expect both the pneumatic and catenary shapes to appear somewhat similar, yet given the nature of their respective loadings, the principal stress distribution should differ. The degree to which these discrepancies exist, and their respective implications
Palavras-chave: Finite Element Modeling; Pneumatic and Catenary Forms; Patterning; Thin Concrete Shells