Effect of Strut Geometric Imperfections on the Internal Forces Distribution in Tensegrity Structures

Tensegrity structures are valued for their distinctive look, deployability, and potential for active control, making them attractive candidates for applications in civil engineering, architectural, and space structures. Recent large-scale experiments have revealed discrepancies with numerical model simulations when significant external loads or prestress are applied. These differences can be due to initial geometric imperfections of compressed struts, which lead to an elastic bending causing a reduction in the struts’ axial stiffness. This affects the distribution of prestress and internal forces, as well as the structural stiffness and load-bearing capacity. This article focuses on the influence of the out-of-straightness of struts on the distribution of prestress and internal forces, and how these geometric imperfections should be considered to obtain more reliable models for design and assessment. The first part of this work develops a dimensionless analytical expression for the loss of strut stiffness due to out-of-straightness. The second part explains how this analytical expression can be integrated into a numerical code developed by the authors, called Muscle, for calculating tensegrity structures. In the third part, the approach is validated on two previously tested prototypes, an aluminum simplex and a 15 m bamboo footbridge, demonstrating that geometric imperfections can change internal forces by tens of percent. The proposed formulation thus provides a computationally efficient and general framework for incorporating imperfection-induced stiffness reduction into the analysis and design of tensegrity structures.