Jean-François Dubé

Conceptual Design and Analysis of a Deployable Structure with Flexible Joints

The conceptual design of a self-deployable structure with flexible joints is presented in this paper. Joints store elastic energy in the folded, prestressed position and allow deployment until they are stopped by tendons. A study on a wire rope joint is first presented to determine its mechanical behavior with experimental, theoretical, and numerical approaches. An analysis is then performed on a bidimensional structure to propose the specific modeling of introducing prestress to the joints. The method is applied to a spatial system in an analysis that uses static equilibrium and kinematic deployment simulations. The results show good concordance among the different approaches.

Active control of a tensegrity plane grid

Tensegrity systems are selfstressed reticulate space structures. As lightweight frames, they are subject to deformation and vibration issues when faced to natural stimulations such as temperature gradients or wind. Classical passive solutions impose to rigidify components or to add damping in the structure using heavy devices. Active systems, mainly developed in space and seismic fields, are controlled using external energy brought by activators. We describe in this paper a mixed geometric and dynamic active control of tensegrity structures using a robust control design technique. An experiment is carried out on a six selfstress states plane tensegrity grid.

Structural design and control of modular tensegrity structures

Tensegrity systems are self-stressed reticulate structures, composed of a set of compressed struts assembled inside a continuum of tendons. This principle can be at the origin of large, lightweight and transparent structures. In practice, a few structures of this kind were built, partly because they are very demanding in design and analysis. In the wish to contribute to the development of practical structural applications, we propose in this paper a design procedure that combines form-finding and structural dimensioning under static load. To optimise the behaviour in the dynamic domain, we present a general methodology suited for the control of the first vibration modes. The case of a modular tensegrity footbridge is taken for application, taking into account different materials.

Behavior of a Double-Layer Tensegrity Grid under Static Loading: Identification of Self-Stress Level

AbstractThe determination of the state of internal stress is important to define the rigidity of a tensegrity structure and its stability. Several methods can be used; some are based on direct measurements of the forces in the elements, but are not easily transferable to a real structure. The authors opt for indirect measurement techniques, which seem more appropriate for implementation on-site. One can consider the vibratory analysis of the elements, the vibratory analysis of the whole structure, or the analysis of the structure’s behavior under static loading. Here, the node displacement fields of a tensegrity structure in different states of self-stress under several strategies of static loadings is studied by comparing the measurement obtained by a tachometer with simulations. The aim of this work is to show the feasibility of a displacement field to identify the state of self-stress by this analysis. It is shown that under certain conditions, plans can be made to replace the direct measurement of the...

Interactive Dynamic Design and Analysis of Tensegrity Systems

In this paper, an implementation of the discrete element method is presented with applications in interactive design and dynamic non linear analysis of tensegrity systems, a class of lightweight reticulate space structures. These systems are simulated efficiently using an explicit time integration scheme coupled to a 3D visualization interface, which brings the possibility to interactively model a structure, to follow its evolution in real time and to perform advanced structural analysis. To validate and justify this particular approach in the case of tensegrity systems, a static analysis comparison with other structural analysis softwares is carried out on a representative example. The benefits and versatility of the method are further illustrated through simulations of planar and deployable structures.

Study and construction of a pentagon-based tensegrity ring

ABSTRACT Tensegrity rings are composed of strut circuits and based on straight prism geometry. Recently, authors developed a general study for this kind of structure and discovered their ability of folding. In this paper, we present our recent studies on the pentagon-based tensegrity ring from a mechanical, kinematical and experimental point of view. In term of theoretical study, numerical simulations are carried out. We analyse the influence of the self-stress level and element stiffness (cables and struts) on the global system. In matter of experimentation, we present design of our first human-scaled prototype which provides a remarkable lightness. Finally, we describe the folding of this system with a comparison between experiments and numerical simulations.

Correlation between eigenmodes and the selfstress state identification of a tensegrity grid

Tensegrity systems are structures in equilibrium under an initial selfstress state. This selfstress state is a composition of elementary selfstress states, which constitute its basis. In order to identify the selfstress state of a system, we use a non-destructive method based on a vibratory analysis of the structure. The structure is subjected to sinewave excitation for a given frequency. It appears that some frequencies allow a better identification than others. This study tries to establish a relation between eigenmode, selfstress state, and the effectiveness of the identification of a double layer tensegrity grid in six elementary selfstress states. Numerical simulations validate the method proposed here for the identification of such a tensegrity grid.

Etude de la déformée d'une grille de tenségrité pour l'identification de son niveau d'autocontrainte

ABSTRACT We study the possibility to use the measurement of the displacement fields of the nodes of a tensegrity structure under static loading to obtain a new method for the identification of its self-stress state. We try to determinate the correlation between the precision of this identification and the precision of the measure. With a tacheometer we obtain a precision of identification as good as the standard method using efforts measurements.

Identification d'un modèle non local en utilisant les effets d'échelle

ABSTRACT The calibration of non local models which contain an internal length has been among the major issues conditioning the implementation of this kind of failure models. In the absence of local information on the displacement field and on microcracking in the fracture process zone, the calibration has to rely on inverse analysis. This paper presents such a procedure based on three point bend size effect tests on notched specimens. The complete load deflection curves are used for the identification of the constitutive relations. Manual calibration is discussed first and we show that Bazants size effect law, which is related to peak loads only, may serve as a helpful guide to reach the closest fit. Then, automatic calibration is described. It is shown that an optimal set of model parameters can be obtained within a reasonable number of iterations.

Corrélation entre modes propres et identification de l'état de contrainte d'une structure de tenségrité

ABSTRACT The structures of tensegrity are structures in equilibrium by an initial stress state. This stress state is the composition of elementary selfstress states which form a base. In order to identify the stress state of the structure, a nondestructive method based on the vibratory analysis has been used. The structure is subjected to a sinewave excitation for a given frequency. It appears that certain frequencies allow better an identification than others. This study tries to establish a relation between eigen mode, selfstress state and effectiveness of the identification. The article is based on a plane double layer tensegrity grid having six elementary selfstress states. The numerical simulations show the utility of the study for the identification of this structure.