# In Search of Lightweight Deployable Tensegrity Columns
## 2 In Search for the Best Solution  
The aim of the present paper is to compare and assess several tensegrity columns and to find the best solution for the assumed application in civil engineering. In order to do so, various aspects need to be considered: the geometry of the columns, connections between the modules, the material of the structural elements, the type of analysis, etc. In this section, the authors discuss some of these aspects in order to justify the approach adopted in the paper. There are many possible ways of creating tensegrity systems. They can be based on regular modules, which have been described in numerous works [9; 10], or can be designed as entirely new systems using the form-finding process [18]. The geometry of the columns proposed in this paper is based on regular tensegrity modules, which are connected either in initial nodes or by creating extra nodes (details are given in Section 3). Similar to the geometrical aspects, various materials can be used. It is not possible to indicate which materials are best for deployable tensegrity systems as this depends on their application. The materials used in space need to be as lightweight as possible, and they have to withstand severe environmental conditions [1; 2]. In civil engineering applications, the materials depend on the scale and working environment. At the micro-scale (for example, engineering details or mechanical metamaterials), 3D printing can be adopted [19]. At the medium- and macro-scale, both conventional materials (like steel) and novel structural materials (like for example the MoNiCamaterial described in [20]) can be applied. Due to the fact that this study focuses on the columns used as additional supports of lightweight systems and no severe environmental conditions occur, the structures are made of steel: high strength stainless steel S460 (min. tensile strength 610 MPa, min. yield strength 460 MPa) is used for the cables, and high strength structural steel S355J2 (min. tensile strength 510 MPa, min. yield strength 355 MPa) is used for the struts. Out of many possible approaches to the analysis of such structures [12; 15; 21], the authors decided to use the one proposed in [17], which combines the finite element method (FEM) and the multibody dynamics (MBD) simulations. Finite element modeling enables qualitative and quantitative analyses of the behavior of deformable structures with the defined boundary conditions and loading. It takes into account structural shape changes during the simulations. Multibody dynamics simulation, on the other hand, enables fast simulations of the systems consisting of rigid bodies with any translational or rotational displacements. It does not consider the deformations of structural members, since its equations of motion are built for rigid bodies, applied forces, and physical constraints. In this paper, the unfolded columns are analyzed using FEM, and the deployment itself is analyzed with the use of the MBD simulations. A multi-criteria approach of assessment is proposed, where various aspects are considered: geometrical parameters, deployment scenarios, mechanical behavior of the systems. The analyses are aimed at finding a lightweight tensegrity structure that has a good stiffness-to-mass ratio, maintains stability during the deployment, and can be controlled using as few active members as possible. The presented analyses were carried out within the geometrically non-linear theory, which includes large deformations of the systems. The authors focused on the static calculations, as they are most important from the point of view of the considered application as a temporary support of the ceiling in the damaged building. In order to design a column for other applications mentioned in the Introduction, dynamic analyses should also be performed. The approach adopted in this study should be considered as a first step of the design process of the proposed deployable columns.