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Vibration problems

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This isn't actually my problem but one of my colleague's, but here it goes:

In an existing structure, consisting of steel roof girders, some transverse beams are to be installed in between the girders. From these secondary beams, an access platform is to be suspended by steel rods. Analysis indicates that the lowest eigenfrequency, for the whole assembly, is 1.5 Hz, due almost entirely to vertical vibrations of the roof girders. The frequency of the access platform has to be raised to at least 3 Hz, and stiffening the girders is not an option.

What possibilities are there. What effect, if at all possible, will it have on the eigenfrequency to install vibration dampers in the suspension rods. Does this make the roof girders and the transverse beams "think" that they are statically loaded, and thus the eigenfrequency is solely dependent on the mass and stiffness of the access platform itself. Or am I totally missing something essential here.

With best regards,

Gunnar Hafsteinn Isleifsson

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