Experimental Testing of a Tensegrity Simplex: Self-Stress Implementation and Static Loading

A physical model of the simplest three-dimensional tensegrity unit was built at human scale out of aluminum. Self-stress implementation and static loading tests were performed on this model. At each step, accurate measurements were obtained for all nodal positions and element forces. For the prestressing phase, elongations were imposed, via mechanical devices, in different combinations of elements, called prestress scenarios. Experimental results are compared to the theoretical self-stress state obtained by singular value decomposition of the equilibrium matrix and to numerical simulations using the dynamic relaxation method. It is shown that internal forces follow the same linear trend for all prestress scenarios even if the geometry is significantly impacted. Compressive tests were conducted by hanging masses from the top nodes. It is shown that there exists a unique load-displacement relation that follows the infinitesimal mechanism direction for a finite distance, which depends on the self-stress level. The paper provides a detailed overview of the simplex’s structural behavior using both experimental and numerical results while discussing the limitations of the analysis methods explored.

Tensegrity structures are composed of compressive elements floating inside a network of prestressed cables. Their unique aesthetics and mechanical properties have always amazed architects, scientists, and engineers. However, the number of tensegrity structures built for civil purposes remains limited. Reasons behind this include a nonintuitive structural behavior with occurrences of insufficient stiffness and lack of robustness as well as a complex construction process that requires introduction of prestressing forces. Consequently, tensegrity structures are often distrusted in favor of other structural systems. Many studies have focused on finding the conditions required for the existence of self-equilibrated prestressing forces that provide stability and stiffness in tensegrity structures. However, few studies have focused on how these prestressing forces can be implemented in a structure, and the discrepancy between theoretical and numerical approaches. For these reasons, a full-scale physical model of a tensegrity module was built and tested with extreme care on the design and experimental testing. This paper presents a comparison of experimental results using two established analysis methods discussing the differences between experimental measurements and numerical models.