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A research project explores techniques from the past to learn about building stronger structures in the future
Sometimes research involves destruction in the name of creation. Architects and engineers from Zurich-based BLOCK Research Group at science and technology university ETH Zurich recently teamed up to build, and destroy, a vaulted masonry structure that was designed with advanced digital fabrication methods but constructed with traditional timbrel, or Catalan, thin-tile vaulting techniques. Through its research of freeform shells, tiling patterns, building sequences, and formwork, the group hopes to construct increasingly radical forms without sacrificing efficiency.
Now rarely used, centuries-old timbrel vaulting methods were commonly employed in Spanish architecture and in many Beaux Arts landmarks. The form is known in the United States as a Guastavino vault after the Spanish architect Rafael Guastavino, who patented a version of the system in 1885. Traditionally, the vaults’ structural form followed a lightweight wooden structure that would guide the mason as he placed tiles. Using Thrust Network Analysis (TNA), a new form-finding method, the BLOCK group has created new possibilities for freeform vaulted shapes that can be constructed using a continuous cardboard formwork system. After creating irregular geometries with TNA, the researchers establish the shape of edge arches, close in the adjacent surfaces, breaking the pattern with a groin vault to begin another arch section.
The group also aims to show that recyclable and reusable cardboard formwork could dramatically reduce the material and labor costs of construction while making complex vaults possible. Fabricated with a 2-D CAD-CAM cutting and gluing process and assembled on site, the formwork for the group’s Catalan prototype was supported by a system of stacked shipping pallets. These reduced the amount of cardboard used and allowed the unrolled cardboard pattern to fit the CNC equipment’s size requirements. The team implemented custom RhinoScripts to translate the self-supporting vault surface into machine code to produce 200 cardboard boxes.
The group also discusses techniques for cutting tiles to be used in the prototype vault in its research paper, available here: “The most ideal cutting logic for the high double-curvature of the prototype vault would be a two-cut system, employing a combination of oblique and bevel cuts to ‘bend’ a surface in space.” Because of the tool constraints on this project, the team developed a simplified version of the cutting system that allowed for curvature in one axis of the tile while relying on hinging and the mortar joint to achieve a double curvature.
Removing the formwork from the surface of the shell, also called de-centering, was another critical step. The supporting structure had to be removed all at once to avoid asymmetrical loading from below, which could cause the vault to bend and crack. In order to allow the formwork to lower slowly from the masonry surface, the frame sat on a series of sealed plastic tubes containing cardboard spacers consisting of a folded stack of cardboard sheets taped together. The team calculated the dry compressive strength of the spacers to carry the load of the shell, the pallet and box framework, and the masons. But once the vault was complete, the tubes were filled with water, which saturated the cardboard and caused it to compress under the load of shipping pallets.
After successfully de-centering the structure, the team tested its strength, adding more than three pallets of sandbags to its surface before it finally collapsed. BLOCK’s future work will seek to streamline the TNA form-finding process as well as improve the efficiency of its construction techniques, ultimately working to identify design criteria like maximum vault curvatures with a range of tile sizes and patterns.