Boundary constrained modal test method for large scale highly flexible structures

Abstract

Traditionally, the method of low stiffness suspension is a standard method for the modal test of structures. A requirement on the suspension stiffness is that the suspension frequency should be much lower than the first flexible natural frequency of the tested structure. Nevertheless, for large scale structure with very low first natural frequency, which could be as low as 0.1 Hz, it will need very long suspension spring to achieve the required frequency. This may be not acceptable for many labs. Even if there is sufficient high room space for the suspension, the test is, strictly speaking, two dimensional, i.e. in the plane defined by the suspension. In this paper, we discuss existing methods for coping with these problems by replacing the low stiffness suspension with a group of supports that can have any stiffness. By removing the influence of the support stiffness from a later computation with measured frequency responses, the three dimension modal test can be done conveniently. Numerical examples are described in the paper. © The Society for Experimental Mechanics, Inc. 2012.