Deployable Tensairity Structures - development, design and analysis

A Tensairity structure has most of the properties of a simple air-inflated beam, but can bear to hundred times more load. This makes Tensairity structures very suitable for temporary and mobile applications, where lightweight solutions and small transport volume are a requirement. However, the standard Tensairity structure, which is comprised of several interacting components such as an airbeam, cables and struts, can not be compacted to a small package without being disassembled. By replacing the standard compression and tension element with a mechanism, a deployable Tensairity structure is achieved that needs - besides changing the internal pressure of the airbeam - no additional handlings to compact or erect the structure. The development of such a deployable Tensairity structure is investigated in this research. Insight is gained in the structural and kinematic behaviour of this type of Tensairity structures by means of experimental and numerical investigations on small and large scale models. The first part of the dissertation focuses on the development of an appropriate mechanism for the deployable Tensairity structure. The exploration and analysis of ideas for deployable systems is presented by means of experiments on various scale models. By doing this, the boundary conditions and requirements that have to be taken into account in the design are observed and presented. These boundary conditions are imposed by the application where the structure is designed for and by the structural concept Tensairity. With this knowledge, a solution for a deployable Tensairity structure, the `foldable truss system', is being improved with regard to its structural and kinematic behaviour. As a result, an easily foldable proposal for the deployable Tensairity structure is obtained. The second part investigates the structural behaviour of a Tensairity beam by means of experiments on scale models and numerical investigations and identifies the influence of several design parameters. More precise, the contribution of hinges and cables to the structural behaviour is investigated, as well as the influence of the internal pressure, section of the strut and shape of the airbeam. Among other things is learned from the investigations that hinges decrease the structure's stiffness and that a decent structural behaviour requires that all hinges are connected with a cable. A prototype of a deployable Tensairity beam is designed, fabricated, experimentally tested and evaluated in the third part. The detailing and manufacturing of the prototype is presented, as well how the experiments are conducted. The general behaviour of the deployable Tensairity beam, such as its stiffness and maximal load, is first discussed. Then, various configurations are studied experimentally and numerically to analyse the influence on the structural behaviour of the cables and hinges. Also here, the necessity of connecting hinges of the upper and lower strut with each other is shown. During the study, the experimental results are compared with the outcome of numerical calculations on the finite element model of the prototype. Finally, the deployable Tensairity beam is compared with other (non-deployable) Tensairity prototypes. The deployable structure shows to be a factor two less stiff than the same prototype with continuous strut. This difference can be attributed to the presence of hinges in the strut of the Tensairity structure. The proposal for the deployable Tensairity beam, containing thus the cable configuration that allows complete folding, is with regard to its structural behaviour insufficient. The main re