01 Introduction 02 Physical experiments 03 Digital tools 04 Process 05 Results 06 Evaluation 07 Physical models 08 Conclusions

Slender multistress driven structures Guillem Baraut Mattia Gambardella

In 1964 Frei Otto founded the Institute of Lightweight Structures at the University of Stuttgart. Here Otto and his team undertook extensive research into natural forms and processes, generating and inspiring optimum structures. As well as shell structures, lightweight or optimum structures include membrane structures, cable-net, geodesic domes, inflatable and air supported structures, and lattice or  reticulated shell structures such as the grid shell. Otto explored several pioneering experiments in form-finding optimal structural configuration from which we took inspiration for the set up of ours: we undertook infact a series of experiments that represented the first stage to form-finding optimal structural and spatial arrangement. EXPERIMENT 1 The goal is to develop a method which is suitable to determine a connecting system for any plane point constellation having the minimum sum length. The reorganization of the wet threads, due to the capillary water tension, follows the shortest and less energy consumption (stress consumption) configuration that the physical conditions permit. In that sense, those experiments are useful in finding, in an empirical way, a suitable configuration in networks of transportation and traffic. Real systems, such as of supply, traffic or communication can be easily simulated in this way. The method is suitable both for planar and dimensional systems. The minimum path network linking three points with each other is not a triangle, but a star-shaped system. In the case of traffic systems in the form of a minimum path networks, pedestrian walkways, roads, rail paths, the land required, the material expenditure and labor costs are reduced to the minimum. EXPERIMENT 2 In order to define the overall geometry of the final structure, the span length and the height of it will be controlled by several attractors and repellors. These affections will be informed by form-finding experiments based on nested catenaries. Some experiments with catenaries in both 2D and 3D have been carried out. All the experiments have a common characteristic that is its simplicity, in order to understand the physical behaviour of the system, to facilitate its implementation into the digital model. The physical experiments started creating the simplest set of nested catenaries possible. A larger chain is attached to two shorter chains, all made of the same steel and with the same transverse section. The chains are hanged with pins on a cardboard panel with guidelines every 1.0 cm, as can be seen in figures 1a to 1d. These guidelines will be the basis for the variation of the experiments, since some geometric parameters will be modified. EXPERIMENT 3 The aim of this experiment is to explore a net system created by wool threads sank in water, in order to have a tension based structure organized near a minimum path equilibrium. This set of experiments was first developed by Frei Otto. As it is shown in figure 1 the wool threads are attached in several points to a frame, creating a complex network with lots of intersections. When the whole box is dipped into water as shown in figures the water goes into the wool threads and due to the surface tension the threads are attached one to each other. This physical phenomena creates a network of threads with some groups of them, with the characteristic that all of them are loaded in tension but not in compression. That makes the threads adopt an equilibrium shape that is near minimal paths, depending on the loose left in every single thread.