A transformable tensegrity-footbridge system

Tensegrity structures are self-stressed pin-jointed structures composed of cables and struts. They are advantageous systems for transformable applications since structural elements and active elements can be combined. A transformable “hollow-rope” tensegrity system that has been found viable for a deployable footbridge application is explored in this paper. Its deployment requires employing active cables to simultaneously adjust several degrees of freedom. However, active elements can also be used to enhance performance during deployment and service. Although deployment is found to be feasible with a single actuation step for all actuated cables, obtaining a desired shape requires independent cable actuation. Actuation steps are thus identified with the combination of the dynamic relaxation algorithm and a stochastic search algorithm. Moreover, an experimental study was conducted on a near-full-scale physical model to validate the feasibility of the transformable tensegrity system. The scale was motivated by studying a model representative of a real civil structure having practical challenges that are similar to full-scale issues such as actuation-device constraints, joint eccentricities and friction. Although the numerical studies with dynamic relaxation reflect correctly the behavior of the idealized model, transformation of the near-full-scale transformable tensegrity model is limited by eccentricities in the joints, unwanted joint movements and friction. These results highlight the potential of this system and underline the importance of combining analytical models with large-scale physical models in the development of novel transformable structures.