Abstract: The effects of visco-ealstic materialdamped joints on modal parameters of beamsare investigated. The governing equations of theimpedances at the joints for translational and ro-tational motions are given by considering springswith complex stiffness. The natural frequencies andmodal loss factors can be obtained by solving theequations. Numerical result can be represented inthree dimcnsional curves, which can be used for pas-sive vibration control design directly