Elimination of multi-points support effects in modal testing

The measured Frequency Response Functions (FRFs) often have errors due to the support effects in free-free modal testing. In [1], elimination of support effects from the measured FRFs has been investigated and both stiffness and damping have been considered in support conditions. However, the method is only applicable for single point support occasion while the test structure is usually supported from more than one location in a practical testing. Therefore, this paper further investigates this method to extend its application to multi-points support conditions. Firstly, general formulas of removing the multipoint support effects from the measured FRFs are derived based on the dynamic substructure method. Then a simulated modal test of free-free beam with two points suspension is proposed to verify this method. Finally, the performance of the method is investigated with simulated noisy data. It is shown that the proposed method is effective in removing support stiffness as well as support damping from the measured FRFs as long as the measured data are not heavily contaminated by the noise.