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RE: Vibration problems

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Vibration dampers will not eliminate the cyclic loading of the girders, but
they will limit the vibration into the girders.  A cheaper solution would be
to first try to add mass to the platform.  You are correct in that for a
given forcing function the 2 methods of control are stiffness and mass.
Vibration dampers control the stiffness.  You can add mass any number of

Harold O. Sprague

> -----Original Message-----
> From:	Gunnar Hafsteinn Isleifsson [SMTP:gunnarhi(--nospam--at)]
> Sent:	Monday, October 01, 2001 8:32 PM
> To:	seaint(--nospam--at)
> Subject:	Vibration problems
> 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
> Denmark

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