From tensegrity grids to cable-strut grids

Abstract

In this paper, tensegrity grids are extended to cable-strut grids as supporting structures. Can tensegrity structures replace the familiar forms? If not, why? How to achieve the goal? These questions are discussed in detail. Following a review of tensegrity concepts, various forms of non-contiguous strut and contiguous strut tensegrity configurations especially the geometrically rigid forms are presented and analysed through real-scale structural design. Analysis shows that the strut-to-cable connection among simplexes inherently induces low structural efficiency, because of the mechanisms produced at the connected vertices and especially cables in the compressive layer sustaining tensions, which result in low stiffness and much reduced structural depth. Contiguous strut configurations present much better properties, but as struts are still isolated in simplexes, they are much heavier than space trusses owing to excessive bar length and reduced structural depth due to bar inclination. All these drawbacks stem from the introduction of "islands of compression in a sea of tension" in simplexes and free-standing grids. Based on the analysis, lightweight forms are geometrically rigid and of improved structural depth, and above all, based on contiguous and short struts in both simplexes and grids. Tensegrity concept is accordingly transferred to cable-strut structures, and cable-strut concept and the principles of designing cable-strut simplexes are summarized. Some lightweight cable-strut grids, including AP (anti-prism) & ATP (anti-truncated-pyramid) grids developed from the bar-intersecting method to stabilise tensegrity simplexes, and RP (reciprocal prism) grids and CP (crystal-cell pyramid) grids based on novel simplexes, are introduced and their configurations and performance is illustrated. Their high structural efficiency, especially high stiffness and outstanding weight savings over space trusses is proved in case studies. The economical value of lightweight cable-strut grids is discussed finally.