Determination of dynamic properties of nonlinear structures using thepull-release test

Abstract

For the determination of the dynamic properties-natural frequencies, mode shapes and damping-of an existing structure, a number of experimental methods are available. Among the most common ones are: the shake table test for small and medium size structures; excitation by a shaker mounted on the structure and locating the resonances by sweeping across a frequency band either slowly or in discrete steps; monitoring the ambient vibrations and determining the properties by signal analysis; and pulling (or pushing) the structure and suddenly releasing it and measuring the resulting decaying vibrations. This pull-release test is one of the simplest dynamic methods for determining a complete set of dynamic properties. While it is usually employed at low amplitudes of vibration, the method can also be employed at large amplitudes and consequently to obtain amplitude-dependent dynamic properties for structures with non-linear deformation and damping properties. This presentation focuses on the theoretical and analytical issues that have to be considered in planning such a test and interpreting the results