Читать книгу Rethinking Prototyping - Группа авторов - Страница 91

In general, the equilibrium stability can effectively be tested with scale models (Van Mele et al., 2012). The presented structural system was tested and verified using a 3D printed, discrete, structural scale model (Fig. 12) to validate the digital results of the form-finding implementation with the physical model. The scale model is made out of discrete - unglued and mechanically not connected - 3D-printed pieces; it is not a structure by itself, but rather an extreme structural model as the pin-jointed, mechanically not connected pieces have a non-rigid (not triangulated) topology. If the solution would not act in pure compression equilibrium and tension along the tension tie, it would immediately become unstable and collapse.

Fig. 12 Structural scale model of a discrete funnel-shaped rib vault

Fig. 13 Equilibrium network G, form diagram Γ and force diagram Γ* of the discrete funnel-shaped rib vault. The colours are directly related to the length of the individual edges in the force diagram and hence visualize the magnitudes of horizontal thrust

As demonstrated by the collapse sequence in Fig. 14, the 3D-printed model is an extreme structural model, as it is made out of discrete, unglued pieces, forming unstable mechanisms, which can only be balanced if the ribs are in perfect axial, compression. The sudden collapse, when cutting the tie, is a demonstration of the structural honesty of the model. As for tree structures or any result of form-finding in general, form-found to act in compression only for a defined, dominant loading case (Lachauer &

Fig. 14 Collapse of the 3D-printed funnel-shaped rib vault by cutting the continuous tension tie

Block, 2012), this type of structures need to be realized with stiff nodes in order to resist live, non-funicular loading cases, which can be defined and dimensioned through the analysis of a materialized, form-found shape.