A dynamic-relaxation formulation for analysis of cable structures with sliding-induced friction

In many cable structures, special types of joints are designed to allow cables to slide freely along the joints. Thus, a number of discrete cable elements are substituted by a single continuous cable that slides over multiple nodes. Continuous cables are employed in engineering applications such as cranes, domes, tensioned membranes and tensegrity structures. Most studies involve the assumption of friction-less movement of cable elements through pulleys. Nevertheless, frictionless sliding is usually an unrealistic hypothesis. In this paper, the dynamic relaxation (DR) method is extended to accommodate friction effects in tensioned structures that include continuous cables. The applicability of this DR formulation is demonstrated through analysis of three case studies that involve both numerical and experimental investigation. Results show potential to efficiently accommodate sliding-induced friction. (C) 2017 Elsevier Ltd. All rights reserved.

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Nizar Bel Hadj Ali, Ian Smith, Ann Christine Sychterz
Elsevier, 2017
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https://infoscience.epfl.ch/record/232196?ln=fr

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Tenségrité (architecture)

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Deployment of a tensegrity footbridge

Seif Dalil Safaei, Ian Smith, Nicolas Willy Veuve

Deployable structures are structures that transform their shape from a compact state to an extended in-service position. Structures composed of tension elements that surround compression elements in equilibrium are called tensegrity structures. Tensegrities are good candidates for deployable structures since shape transformations occur by changing lengths of elements at low energy costs. Although the tensegrity concept was first introduced in 1948, few full-scale tensegrity-based structures have been built. Previous work has demonstrated that a tensegrity ring topology is potentially a viable system for a deployable footbridge. This paper describes a study of a near-full-scale deployable tensegrity footbridge. The study has been carried out both numerically and experimentally. The deployment of two modules (one half of the footbridge) is achieved through changing the length of five active cables. Deployment is aided by energy stored in low stiffness spring elements. Self-weight significantly influences deployment, and deployment is not reproducible using the same sequence of cable- length changes. Active control is thus required for accurate positioning of front nodes in order to complete deployment through joining both sides at center span. Additionally, testing and numerical analyses have revealed that the deployment behavior of the structure is nonlinear with respect to cable-length changes. Finally, modeling the behavior of the structure cannot be done accurately using friction-free and dimension- less joints. Similar deployable tensegrity structures of class two and higher are expected to require simulation models that include joint dimensions for accurate prediction of nodal positions. DOI: 10.1061/(ASCE)ST.1943-541X.0001260 . © 2015 American Society of Civil Engineers.

Asce-Amer Soc Civil Engineers2015

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Joint Friction during Deployment of a Near-Full-Scale Tensegrity Footbridge

Ian Smith, Ann Christine Sychterz

Most deployable structures, such as operable roofs and masts, move over one degree of freedom. This paper describes a structure that involves loosely coupled movement over several degrees of freedom. Analysis models of these structures are typically inaccurate. A source of inaccuracy is joint friction. Static and kinetic friction are studied experimentally and analytically. Simulations have been modified to account for these effects, and two methods are used to quantify friction effects. Friction has a significant effect on the movement of the tensegrity structure. Of two candidate parameters, cable tension and interior cable angle, cable angle is the factor that best characterizes friction effects. Values of static and kinetic friction coefficients are not significantly different in this context, and this leads to a reduction in the complexity of the friction model for simulation. Including friction effects in analysis decreases the difference between simulations and tests. Lastly, strut elements of the tensegrity structure are most critically affected by friction. (C) 2017 American Society of Civil Engineers.

American Society of Civil Engineers2017

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Dynamic behavior and vibration control of a tensegrity structure

Nizar Bel Hadj Ali, Ian Smith

Tensegrities are lightweight space reticulated structures composed of cables and struts. Stability is provided by the self-stress state between tensioned and compressed elements. Tensegrity systems have in general low structural damping, leading to challenges with respect to dynamic loading. This paper describes dynamic behavior and vibration control of a full-scale active tensegrity structure. Laboratory testing and numerical simulations confirmed that control of the self-stress influences the dynamic behavior. A multi-objective vibration control strategy is proposed. Vibration control is carried out by modifying the self-stress level of the structure through small movement of active struts in order to shift the natural frequencies away from excitation. The PGSL stochastic search algorithm successfully identifies good control commands enabling reduction of structural response to acceptable levels at minimum control cost. (C) 2010 Elsevier Ltd. All rights reserved.

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