I have a structure with long support spans and in order to keep the vibration generated by the roof mounted equipment from causing problems, a spring with more than 2 inches of deflection is needed. However, when I put equipment on these springs , it rocks excessively in a breeze or when I push against it. What can I do to stop this?
ANSWER:
The same “softness” in the spring coil that is necessary to reduce the transfer of vibrations into the structure also will allow the equipment to rock more easily. There is nothing that can be done to prevent this. There are things that can be done to minimize the negative effects, however. These are to ensure that the isolated equipment has a low center of gravity; the isolators are spaced as widely as possible; the system is equipped with motion limiting devices; and, if exposed to wind, is protected from direct exposure. This may require the addition of an inertia mass to lower the center of gravity or a surrounding wind barrier protection wall. The use of motion limiting devices should be restricted where possible as, when limiting the motion, they can form a path for the direct transfer of vibration into the structure whenever the equipment is exposed to a sufficient lateral force.