2000 IBC 1708.2

[bjb]

Are the provisions of the above section meant to apply to roof top units? If the units have internal vibration isolators, then I say it doesn't apply. This is currently being debated here.

 

[JAE]

To me it looks like roof top units are what 1708.2.3 is talking about - referring to 1708.5, where there exists requirements that the units be evaluated for seismic competency....both internally (the unit doesn't shake apart or fail like a little building) and externally (its attachments are adequate to keep the unit from separating from the supporting structure.

Internal vibration isolators for these units are usually providing for vertical vibrations? correct? If so, what about the lateral forces? I'm not sure that vibration isolators always do the same thing that seismic isolators do.

 

[bjb]

A thousand pardons JAE, I mistakenly typed 1708.2, when I meant 1607.8.2. We are debating if 1607.8.2 is intended to apply to RTU's. It seems to me that an RTU with internal vibration isolators won't be transferring vibrations from its normal operation, and thus an impact allowance is not necessary. There is an internal debate going on here.

I agree with what your are saying about 1708. Again, my apologies for the bad first post, my brain apparently short-circuited when typing.

 

[JAE]

I guess I can't formulate an opinion on that section other than to say that high frequency vibrations don't usually effect structures via "impact"...only when motor-driven machinery starts up initially does there occur a torque force that would be applied to the supporting framework. However, with isolators, it seems that they would avoid that effect.

 

[bjb]

Thanks JAE, that's what I thought.