Bistable scissor structure: computational design and modelling

In many applications structures need to be easily moveable, or deployed at high speed on unprepared sites. For this purpose, pre-assembled deployable structures, which consist of beam elements connected by hinges, are highly effective: transportable with a rapid transformation and a huge volume expansion. Intended geometric incompatibilities between the members can be introduced as a design strategy to instantaneously achieve a structural stability at deployment that can be sufficient for sustaining the weight of the structure. In such bistable scissor structures, these incompatibilities result in the bending of some specific members that are under compression with a controlled snap-through behaviour. Attempts to design deployable bistable structures remain scarce, since the underlying structural-mechanical concepts are complex. Furthermore, the requirement of flexibility during deployment while ensuring some structural stability in the deployed state prevents the use of simple design methodologies relying on the structural behaviourunder service loads only. In this dissertation, computational tools are developed andapplied for the structural analysis and design process of deployable bistable structures.Computational tools are crucial for the geometrical and structural design, for the defi-nition of a rigorous design methodology and for a deeper understanding of the complextransformation behaviour of these structures.First, a geometric design methodology is proposed for triangulated bistable scissorstructures, taking explicitly the finite hinge size into account. Next, a 3D nonlinear struc-tural model is proposed to simulate the transformation of bistable scissor structures aswell as their behaviour in the deployed state. This model was used to investigate the ef-fect of geometrical imperfections in a stochastic approach during transformation. Thestructural analysis was combined with a multi-objective evolutionary algorithm to de-fine an optimisation methodology for bistable scissor structures, taking into account therequirement of a low peak force during transformation as well as the high stiffness re-quirement in the deployed state. A final design methodology is proposed for bistablescissor structures which combines a topology optimisation step with a shape and sizingoptimisation step, resulting in optimised structures. Finally, a method was proposed inwhich the optimised results of a few structures were used to obtain solutions for otherstructures by inter- or extrapolation.