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RE: SEISMIC: Roof Supported Equipment

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Title: SEISMIC: Roof Supported Equipment
Further on this particular situation:
At worst, this equipment would be assigned a Seismic Design Category of "B".
According to ASCE 7-02 Sec. 9.6.1 (ref. page 158, left-hand column), mechanical and electrical components in Seismic Design Category B are exempt from the design requirements of Section 9.6 in toto.
But what bugs me is that I get a seismic force that is considerably greater--as much as four times greater--than the wind load. When all is said and done I get a pretty hefty force at the base of one of the corner columns of the support structure.
But I guess I just don't worry about it, per the code?

From: Polhemus, Bill [mailto:bill.polhemus(--nospam--at)]
Sent: Wednesday, May 18, 2005 8:22 AM
To: seaint(--nospam--at)
Subject: RE: SEISMIC: Roof Supported Equipment

I'm really not worried about the building--I figure the diaphragm is more than adequate to take it.
I'm actually concerned about the equipment itself, along with the platform. Wouldn't want to see it go rolling in a hypothetical seismic event.

But with it being on a roof, and the Site Classification being probably a "C", I just don't think there's going to be much "there" there.

From: Eli Grassley [mailto:elig(--nospam--at)]
Sent: Tuesday, May 17, 2005 6:37 PM
To: seaint(--nospam--at)
Subject: RE: SEISMIC: Roof Supported Equipment

If you are confident that the weight of the additional equipment is just a drop in the bucket as far as the overall building structure is concerned, then you really only need to design the attachments of the new equipment to the existing (refer to ASCE7-02, section 


If you meet the criteria, just use ASCE equation to get the amplified lateral force that acts on the equipment at the connection elevation.


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