Analysis of clustered tensegrity structures using a modified dynamic relaxation algorithm

Tensegrities are spatial, reticulated and lightweight structures that are increasingly investigated as structural solutions for active and deployable structures. Tensegrity systems are composed only of axially loaded elements and this provides opportunities for actuation and deployment through changing element lengths. In cable-based actuation strategies, the deficiency of having to control too many cable elements can be overcome by connecting several cables. However, clustering active cables significantly changes the mechanics of classical tensegrity structures. Challenges emerge for structural analysis, control and actuation. In this paper, a modified dynamic relaxation (DR) algorithm is presented for static analysis and form-finding. The method is extended to accommodate clustered tensegrity structures. The applicability of the modified DR to this type of structure is demonstrated. Furthermore, the performance of the proposed method is compared with that of a transient stiffness method. Results obtained from two numerical examples show that the values predicted by the DR method are in a good agreement with those generated by the transient stiffness method. Finally it is shown that the DR method scales up to larger structures more efficiently. (C) 2010 Elsevier Ltd. All rights reserved.

Configuration of control system for damage tolerance of a tensegrity bridge

Nizar Bel Hadj Ali, Sinan Korkmaz, Ian Smith

Tensegrity structures are spatial, discrete, and lightweight structures that are composed of struts in compression and pre-stressed cables. Stability is provided by the self-stress state between elements independently of external actions. Tensegrity structures are attractive due to their potential for deployability, ease of tuning and high precision control. Since tensegrity structures have highly coupled behavior, placement of actuators is a primary concern when designing active control systems. This study investigates the active control performance of cable members of a tensegrity bridge. The actuation efficiencies of cable members are evaluated through a multi-criteria approach. The configuration of the control system is thus identified through outranking candidate active members. A multi-objective damage tolerance strategy is then proposed and optimally directed control solutions are identified using stochastic search. Case studies for several damage scenarios are examined to validate results. The most efficient active cable configuration is compared with that needed for deployment. This study is divided into two phases. After the description of a 16 m-span tensegrity bridge, optimally directed locations of active cables are determined in the first phase. Secondly, a procedure to ensure damage tolerance of the structure is proposed. The multi-objective self-repair procedure provides damage tolerance minimizing both maximum deflections in the structure and stresses in the structural members. Results indicate that the control strategy for deployment is a near-optimal solution for damage tolerance. The proposed methodology is applicable to a range of complex active structures. (C) 2011 Elsevier Ltd. All rights reserved.

Elsevier2012

Active tensegrity structures with sliding cables - static and dynamic behaviour

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

2011

A transformable tensegrity-footbridge system

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

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.

EDITORIAL STARBOOKS2013