An Active Deployable Tensegrity Structure

Tensegrity structures are spatial reticulated structures composed of cables and struts. Their stability is provided by a self-stress state among tensioned and compressed members. Although much progress has been made in advancing research into the tensegrity concept, the concept is not yet part of mainstream structural design. A design study for an active deployable tensegrity footbridge composed of pentagonal tensegrity-ring modules is presented in this thesis to further advance the tensegrity concept in modern structural engineering. Tensegrity-ring modules are deployable circuit-pattern modules that when combined form a "hollow rope". In the absence of specific design guidelines, a design procedure is proposed. Deployment is also included as a consideration for sizing. Deployment is usually not a critical design case for sizing members of deployable structures. However, for tensegrity systems, deployment may become critical due to the actuation required. The influence of continuous cables and spring elements in statics, dynamics as well as in deployment is investigated. A stochastic search algorithm is used to find cost-effective design solutions. The deployment of the tensegrity "hollow-rope" system requires employing active cables to simultaneously adjust several degrees of freedom. Therefore, actuation schemes with individually actuated cables, continuous actuated cables and spring elements are investigated. The geometric study of the deployment for a single module identifies the contact-free deployment-path space and the path with the minimum number of actuators required. The number of actuators is further reduced by employing continuous cables and spring elements. The structural response during deployment is studied numerically using a dynamic relaxation algorithm. 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 involves independent actuation in several cables. Independent actuation steps are successfully found with the combination of the dynamic relaxation algorithm and a stochastic search algorithm. Experimental studies conducted on physical models validate the feasibility of the active deployable tensegrity footbridge. Although results on the near-full-scale physical model are mitigated by eccentricities in the joints, unwanted joint movements and friction, they reveal the potential of the active deployable tensegrity system. Conclusions are as follows: Design results illustrate that the tensegrity "hollow-rope" concept is a viable system for a footbridge meeting typical static and dynamic design criteria. For the "hollow-rope" tensegrity footbridge, deployment is a critical design case when spring elements and continuous cables are employed in the system. The proposed actuation schemes successfully direct deployment and correct midspan displacements under service, but are less efficient regarding shape corrections during deployment. Future work involves studies aiming to improve the control of the structure and to employ actuated cables for damage compensation during deployment.

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