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  • 1.
    Dalilsafaei, Seif
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Improving bending stiffness of tensegrity booms2012In: International Journal of Space Structures, ISSN 0956-0599, Vol. 27, no 2-3, p. 117-129Article in journal (Refereed)
    Abstract [en]

    There is a high interest in employing lightweight, low-cost, deployable structures for space missions. Utilization of tensegrity structures in space application is limited, due to their low stiffness, while a number of high stiffness-to-mass truss booms have been launched. This paper aims to describe and improve the bending stiffness of tensegrity booms. Tensegrity booms of Snelson and triangular prism type are selected for the study. These structures are excellent samples of class 1 tensegrities, with a single state of self-stress and one mechanism, and class 2 tensegrities, with multiple states of self-stress and mechanisms. The stiffness modification procedure includes three steps: (Step 1) developing a strategy for a fair comparison of tensegrity booms with a high performance truss boom. A genetic algorithm is employed to find the optimum cross-section areas of the boom elements. Sources of low stiffness of tensegrities are discussed. (Step 2) an effort is made to find the optimum placement of actuators for improving the stiffness of the tensegrity booms. (Step 3) a genetic algorithm is utilized to calculate their optimum actuation. All three stages have been performed based on a link between non-linear finite element analysis and a genetic algorithm. The genetic algorithm shows high accuracy of searching non-structural space, and also dealing with above steps. Results indicate that the stiffness of tensegrity booms is highly improved by activating the structures.

  • 2.
    Dalilsafaei, Seif
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Design and analysis of tensegrity power lines2012In: International Journal of Space Structures, ISSN 0956-0599, Vol. 27, no 2-3, p. 139-154Article in journal (Refereed)
    Abstract [en]

    Overhead transmission power lines have undergone very small aesthetic and technical changes over time. Studies on mitigation of the electromagnetic field shows that utilizing a helix configuration is an effective way to reduce the electromagnetic field. This study proposes to use tensegrity structures as power lines. Tensegrity structures are composed of tension and compression elements in equilibrium. Modules, simple units with a certain rotation, are connected together to design of overhead power lines with considerable electromagnetic field reduction. A form-finding method enables the design of various free-form configurations. A parametric study is performed to investigate the influence of the module dimensions on the stiffness of the power line. A design algorithm was used for determining the optimum size of elements and the pre-stress level. The selected baseline structure was able to tolerate the wind and ice loads in severe conditions with a 50 times reduction in electromagnetic field. Finally a sensitivity analysis is performed to show the effects of element loss or damage.

  • 3.
    Pan, Danhua
    et al.
    Civil Engineering Group, Department of Applied Physics and Electronics, Umeå University.
    Girhammar, Ulf Arne
    Civil Engineering Group, Department of Applied Physics and Electronics, Umeå University.
    Effect of ring beam stiffness on behaviour of reticulated timber domes2005In: International Journal of Space Structures, ISSN 0956-0599, Vol. 20, no 3, p. 143-160Article in journal (Refereed)
    Abstract [en]

    Domes are efficient structural systems for long clear-span buildings. The introduction of laminated timber highlighted the economic advantages of this material and led to the use of timber domes even for very large spans. In this paper, reticulated timber domes of triangular network shape with decking and bottom tension ring are considered. These types of domes have high stiffness in all directions along the surface and are kinematically stable. The dome is subjected to uniformly distributed load over the entire structure. The dome model is generated with a preprocessor program called DOME-IN and analysed with ABAQUS. The focus of this paper is to evaluate the behaviour of reticulated timber domes with respect to different stiffnesses of the bottom ring beam, here defined as a non-dimensional ring beam area parameterr*, which is shown to be a very well adapted design parameter for the ring beam. As far as global buckling is concerned, the critical pressure is sensitive to the bottom ring beam stiffness only if the latter is within a certain range. In terms of design, the stiffness of the ring beam should exceed A 2* > 2 in order to utilise the full buckling load capacity of the dome system itself. The maximum deflection, normal forces and bending moments versus the ring beam area parameter are also evaluated. The maximum values of the deflection and the internal actions next to the bottom ring are very sensitive to the bottom ring beam stiffness only if the latter is less than about Ar* < 10. A recommended value for the design of the bottom ring beam is Ar* > 20.

  • 4.
    Pan, Danhua
    et al.
    Department of TFE-Civil Engineering, Faculty of Science and Technology, Umeå University.
    Girhammar, Ulf Arne
    Department of TFE-Civil Engineering, Faculty of Science and Technology, Umeå University.
    Influence of geometrical parameters on behaviour of reticulated timber domes2003In: International Journal of Space Structures, ISSN 0956-0599, Vol. 18, no 2, p. 105-122Article in journal (Refereed)
    Abstract [en]

    Domes are very efficient structural systems for long clear span buildings. The introduction of laminated timber highlighted the economic advantages of this material and led to the use of timber domes even for very large spans. In this paper, reticulated timber domes of triangular network shape with decking and bottom tension ring are considered. These types of domes have high stiffness in all directions along the surface and are kinematically stable. The dome is subjected to uniformly distributed load over entire structure. The dome model is generated with a preprocessor program called DOME-IN and analysed with ABAQUS. The focus of this paper is to evaluate the behaviour of reticulated timber domes with respect to: (a) height-diameter ratio of the dome, H/D; (b) straight relative curved types of main beams in the triangular networks versus mesh density; (c) perpendicular relative parallel types of purlin arrangements in the triangular networks versus the number of purlins; and (d) mesh density of main network members or size of triangular networks. The influence of these parameters on relative maximum deflection of the dome, relative critical pressure for global buckling of the dome, relative maximum axial forces and relative maximum bending moments in the network members, is evaluated. It is found that: (a) the optimum height-diameter ratio is H/D ≈ 0.3; (b) that straight beams in the triangular networks are preferred to curved beams, especially for higher mesh densities;(c) that purlins perpendicular to the latitudinal beams are preferable to purlins parallel to the latitudinal beams if there is a decking that provides bracing to the system; and (d) mesh densities with six sectors (n=6) (lowest number of practical interest) and as many divisions of the arc beam and of the sector of the ring beam (m = k ≥ 4), which is necessary in order to meet the design criteria for the dome, can be recommended.

  • 5.
    Russell, Colin
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Deployment simulations of inflatable tensegrity structures2008In: International Journal of Space Structures, ISSN 0956-0599, Vol. 23, no 2, p. 63-77Article in journal (Refereed)
    Abstract [en]

    nsegrity structures are attractive as deployable space structures since they are composed mainly of flexible tension members and can thus easily be folded. To automatically deploy such structures it is proposed that the tension members are replaced or enclosed by thin-film tubes, which form a continuous volume. The structure deploys when this volume is pressurised. This concept was studied by numerical simulations of the deployment process in a zero-gravity environment using the control volume method for the fluid-structure interaction. First, single z-folded and coiled tubes were analysed to determine suitable element size, number of control volumes and gas flow rate. Then one- and three-stage tensegrity masts were modelled, folded and finally deployed. The study showed that the deployment concept is feasible.

  • 6.
    safaei, Seif
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Micheletti, A.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Study of various tensegrity modules as building blocks for slender booms2013In: International Journal of Space Structures, ISSN 0956-0599, Vol. 28, no 1, p. 41-52Article in journal (Refereed)
    Abstract [en]

    This study investigates the structural performance of long and slender tensegrity booms. Previous studies show that tensegrity structures are generally more flexible than conventional trusses or space frames. The aims here were (i) to quantify how much more flexible eleven different tensegrity booms are, when compared to state-of-the-art truss booms, (ii) to find a general explanation for this. The performance criterion used for the comparison was the first natural frequency of the boom. A finite element program with truss elements was used to compute the natural frequencies around the initial prestressed configurations. The results show that tensegrity booms have between one and three orders of magnitude lower natural frequencies than truss booms. It is concluded that for the best performing tensegrity booms, the bending stiffness is independent of the level of pre-stress and the number of infinitesimal mechanisms as the bending stiffness is given mainly by the material stiffness of the tension elements and not the geometric stiffness as the infinitesimal mechanisms are not activated by bending. Thus, whereas the level of pre-stress and the presence of infinitesimal mechanisms play major roles for the stiffness of some tensegrity structures, the axial stiffness and orientation of tension elements are most important for the studied slender booms.

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