Experimental Study on Dynamic Characteristics of a Tensegrity Structure Using a 3D SLDV System

Abstract Tensegrity structures have emerged as important components of various engineering structures due to their high stiffness, light weight, and deployable capability. Existing studies on dynamic analyses of tensegrity structures mainly focus on responses of their nodal points while overlook deformations of their cable and strut members. This study aims to propose a non-contact approach for experimental modal analysis of a tensegrity structure to identify its three-dimensional (3D) natural frequencies and full-field mode shapes, which include modes with deformations of its cable and strut members. A 3D scanning laser Doppler vibrometer (SLDV) is used with a mirror for extending its field of view to measure full-field vibration of a three-strut tensegrity column with free boundaries. Tensions and axial stiffnesses of cable members of the tensegrity column are determined using natural frequencies of their transverse and longitudinal modes, respectively, and used to build a numerical model of the tensegrity column for dynamic analysis and model validation purposes. Modal assurance criterion (MAC) values between experimental and numerical mode shapes are used to identify their paired modes. Natural frequencies and mode shapes of the first 15 elastic modes of the tensegrity column are identified from the experiment, which include modes of the overall structure and its cable members. These identified modes can be classified into five mode groups depending on their types. Five modes are paired between experimental and numerical results with MAC values larger than 78%. Differences between natural frequencies of paired modes of the tensegrity column are less than 15%. The non-contact 3D vibration measurement approach presented in this work can measure responses of nodal points, as well as deformations of cable and strut members, of the tensegrity column, and allows accurate estimation of its 3D full-field modal parameters.