Читать книгу Rethinking Prototyping - Группа авторов - Страница 84

The structural efficiency of shells comes from the fact that their dominated load-bearing is membrane action, i.e. axial compressive or tensile force flows along its centre surface, which is inherently more efficient than carrying loads through bending.

Traditional vault construction demonstrates the use of efficient structural form in combination with funnel-shaped architecture, such as the rib vault of the chapel of Cluny Museum in Paris, France (1485-1510). This masonry vault of course stands efficiently in compression due to its funicular shape (Fig. 3a) resulting in a relatively filigree structure. The contemporary installation La Voûte de LeFevre (2012) by Matter Design is based on the same structural system, featuring a more irregular geometry thanks to digital, structural form finding and CNC fabrication (Fig. 3b).

Fig. 3 (a) Rib vault of the chapel of Cluny Museum (1485-1510); (b) Matter Design, La Voûte de LeFevre (2012)

Yet, these compression structures depend on fixed boundary conditions, which usually do not allow opening up the sides. The vaults in Fig. 3a are stable thanks to massive buttresses taking the horizontal thrust of the rib structure. The openness and lightness of the installation in Fig. 3b on the other hand can only be achieved by a steel frame suspended from the ceiling of the gallery space. The structure thus depends on this continues support, in contrast to the cantilevering structures in Fig. 2. The question arises how one can use the structural efficiency of funicular shapes to create open, funnel-shaped shells without the need of a secondary structural frame acting in bending or heavy buttresses.

This paper discusses a direct form-finding approach for funicular funnel shells, and demonstrates the manifold design space of these structures. In the following section, the basic structural principle is illustrated by referring to traditional and contemporary construction techniques. Subsequently, graphic statics and its extension to surface structures, Thrust Network Analysis, are discussed. In the last section, the form-finding approach and its implementation as a design tool are tested through a digital design exploration, and finally verified using a 3D printed, structural scale model.