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RE: SEISMIC: Roof Supported Equipment

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Please clarify if the steel platform is on a concrete roof:
"all precast concrete" 
"on a steel platform which in turn is place on the ROOF of an existing
Also, is your equipment sensitive to deflections?

 -----Original Message-----
From: Polhemus, Bill [mailto:bill.polhemus(--nospam--at)]
Sent: Tuesday, May 17, 2005 4:14 PM
To: seaint(--nospam--at)
Subject: SEISMIC: Roof Supported Equipment

Because you evil Left-Coasters have foisted this upon us, I now have to
foray into the "dark side" of structural engineering, calculating seismic

My untutored brain does register grudging respect that the ICC (in reality,
many of you SEAOCers) have done a creditable job digesting all this NEHRP
stuff for me, but I'm still agog at the sheerness of the learning curve.

Anyway, I've got a situation that would be a no-brainer if it were just a
building. But instead, I've got some rather massive equpment sitting on a
steel platform which in turn is place on the ROOF of an existing building,
and I want to determine what the effect of this will be.

Again, it will probably turn out to be nothing, but I'm undecided enough
about it that I know I have to make the effort.

So instead of just a building with a site factor involved, I've got a
building with a site factor, and then the equipment on top of that. Surely
the building will act as a sort of giant energy absorber for the equipment
such that the equipment seismic effect will be much diminished.

The building is a single (high-bay) story, all precast concrete. 

Do I do this as a Two DOF system? 

What would YOU do? 

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