Deployment of a Pentagonal Hollow-Rope Tensegrity Module

Tensegrity structures are spatial reticulated structures composed of cables and struts. Tensegrity systems are good candidates for adaptive and deployable structures and thus have applications in various engineering fields. A “hollow-rope” tensegrity system composed of tensegrity-ring modules has been demonstrated by the authors to be a viable system for a pedestrian bridge. This paper focuses on the deployment of pentagonal ring modules. A geometric study is performed to identify the deployment-path space allowing deployment without strut contact. Two actuation schemes are explored for deployment: the first scheme employs only actuated cables, while the second combines actuated cables with spring elements. In both schemes, continuous cables are used to reduce the number of actuators required. Finally, the structural response of the module during deployment is studied numerically using a modified dynamic relaxation algorithm.

Deployment aspects of a tensegrity-ring pedestrian bridge

Nizar Bel Hadj Ali, René Motro, Landolf-Giosef-Anastasios Rhode-Barbarigos, Ian Smith

Tensegrity structures are spatial systems that are composed of tension and compression components in a self-equilibrated prestress stable state. Although tensegrity systems were first introduced in 1950s, few examples have been used for civil engineering purposes. In this paper, tensegrity-ring modules are used for a deployable pedestrian bridge. Ring modules belong to a special family of tensegrity systems composed of a single strut circuit. Assembled in a “hollow-rope” structure, ring modules were shown to be a viable system for a tensegrity pedestrian bridge. Furthermore, ring modules are deployable systems that can change shape by adjusting cable lengths (cable actuation). This paper focuses on the deployment of a tensegrity-ring pedestrian bridge. A geometric study of the deployment for a single module identified the solution space that allows deployment without strut jamming. The optimal deployment path is identified amongst hundreds of possible solutions. Moreover, the number of actuators required and their placement in the module are determined by the deployment path that is applied. Cable-based actuation often has the drawback of having to control too many cable elements. Therefore, a deployment path that minimizes the number of actuated cables was found. The number of actuated cables is further reduced by employing continuous cables. A first generation prototype made of aluminium struts and steel cables was used to verify experimentally both findings. The structural response during unfolding and folding is studied numerically using a modified dynamic relaxation algorithm. A well-known dynamic-relaxation algorithm is extended to accommodate clustered tensegrity structures (tensegrity systems with continuous cables). The deployment-analysis algorithm applies cable-length changes first, to create mechanisms allowing deployment and then, to find new equilibrium configurations. Deployment is thus carried out through an equilibrium manifold. The deployment-actuation step size is identified as a critical parameter for successful deployment. Large deployment steps lead to instable configurations while small steps are computationally expensive. Due to mechanism-based deployment, the total energy in the structural system remains nearly constant during deployment. Elastic potential energy due to cable tension is the highest energy identified while kinetic energy and the work of torque friction on strut-to-strut joints are relatively low. Finally, internal forces increase during deployment but remain low compared with service self-stress values showing that deployment is not a critical phase for the design of the bridge.

2011

Toward development of a biomimetic tensegrity footbridge

Seif Dalil Safaei, Ian Smith, Nicolas Willy Veuve

Biomimetic structures interact with their environment, change their properties, learn and self-repair, thereby providing properties that are similar to living organisms. Interactions with the environment involve unique challenges in the field of computational control, algorithms, damage tolerance, and structural analysis. Tensegrity structures are pin-jointed structures of cables and struts in a self-stress state. Tensegrity structures are suitable for active control since the shape of the structure can be changed by changing the length of the elements. Consequently, they are good candidates for biomimetic structures. This paper describes research that is moving toward a case study of biomimetic behaviour of a deployable tensegrity footbridge. This footbridge is made of four modules. Each module is composed of pentagonal circuit-pattern including interconnected struts in a ring configuration that can be folded if cable lengths are changed. Various actuator combinations can be selected for deployment. This property is particularly interesting for biomimetic structures since a single shape change can be achieved many ways. Methodologies for deployment and folding of tensegrity footbridge via combinations of spring and cable clustered actuation are described. Analytical predictions are compared with test results of a near-full-scale tensegrity footbridge. Strategies for folding and deployment are different. A continuous cable and spring configuration is feasible for deployment of tensegrity footbridge. Since the deployment behaviour is non-linear and since deformed geometry as well as joint friction influences the deployment pattern, pre-defined control commands cannot provide the desired deployed position. Active deployment control is thus justified.

International Center for Numerical Methods in Engineering (CIMNE)2014

Deployment aspects of a tensegrity-ring pedestrian bridge

Nizar Bel Hadj Ali, René Motro, Landolf-Giosef-Anastasios Rhode-Barbarigos, Ian Smith

2011