Glass Vaults

Introducing an adjustable mould for casting glass voussoirs for transparent shell structures

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Glass is a material that has a high compressive strength and a low tensile strength. While being mostly produced as flat sheets of float glass, it can also be casted into components that have a thicker geometry and thus a higher buckling resistance. These properties make cast glass components suitable for the construction of shell structures that are mainly subjected to compressive stresses. Shell structures often have the shape of surfaces with varying Gaussian curvature. When constructing such a shell structure out of cast glass components, components of varying geometries are needed. During this research, an adjustable mould was developed that can be used for the casting of glass voussoirs of varying geometries. The possible voussoirs geometries that can be cast in the adjustable mould are limited to voussoirs with planar, convex polygonal intrados and extrados. These voussoirs can be used to construct fully transparent shell structures. The voussoirs are dry-assembled with an interlayer in between that compensates for any production tolerances and avoids glass to glass contact. Furthermore, by using dry-assembly instead of an adhesive as a bonding method, the structure allows for disassembly and full recyclability. Tongue and groove shaped interfaces ensure an interlocking connection. The interlocking connection prevents any lateral movement and will guide the voussoir into the right position during assembly. By tessellating a shell structure, the shell structure is divided into a discrete number of voussoirs that can be cast in the adjustable mould. Several aspects have to be taken into account when optimizing the tessellation pattern including planarity, alignment to the flow of forces, face size, interior angle size and if the pattern is staggered or not. A comparison was made between three different regular tessellation patterns (triangular, quadrangular and hexagonal) with these aspects kept in mind. A shell structure was designed to cover a courtyard of the Armamentarium in Delft. This shell structure served as a case study used to demonstrate the design and production process developed for this thesis. The shape of the shell was generated through a form finding process and its structural performance was validated with a FEM analysis. The shell was tessellated into a triangular tessellation. An algorithm used for assigning either tongues or grooves to the interfaces of each voussoir was developed. A list was generated containing the following information for each voussoir: voussoir index number, interface types, edge lengths, voussoir joining angles and the adjacent voussoir index numbers. The data in this list serves as input data for the set-up of the adjustable mould. Furthermore, the connection between the shell structure and the existing structure was designed and an assembly method was developed.