The Skeleton of the Sand Dollar as a Biological Role Model for Segmented Shells in Building Construction: A Research Review

Concrete double-curved shell constructions have been used in architectural design and building constructions since the beginning of the twentieth century. Although monolithic shells show a high stiffness as their geometry transfers loads through membrane forces, they have been mostly replaced by the more cost-efficient lattice systems. As lattice systems are covered by planar glass or metal panes, they neither reach the structural efficiency of monolithic shells, nor is their architectural elegance reflected in a continuous curvature. The shells of sand dollars'-highly adapted sea urchins-combine a modular and multi-plated shell with a flexible, curved as well as smooth design of a monolithic construction. The single elements of the sand dollars' skeleton are connected by calcite protrusions and can be additionally supported by organic fibres. The structural efficiency of the sea urchin's skeleton and the principles behind them can be used for innovations in engineering sciences and architectural design while, at the same time, they can be used to illustrate the biological adaptations of these ecologically important animals within their environments. The structure of the sand dollar's shell is investigated using modern as well as established imaging techniques such as x-ray micro-computed tomography (mu CT), scanning electron microscopy and various optical imaging techniques. 3D models generated by mu CT scans are the basis for Finite Element Analysis of the sand dollar's shell to identify possible structural principles and to analyse their structural behaviour. The gained insights of the sand dollar's mechanical properties can then be used for improving the state-of-the-art techniques of engineering sciences and architectural design.