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RE: equipment anchorage in isolated structures

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David,
Yes, the force is reduced.  Look at Section 17.5.4.2 in ASCE 7-05 and 17.2.6.1 in ASCE 7-10. 
 
Per ASCE 7-10:

17.2.6.1 Components at or above

the Isolation Interface

Elements of seismically isolated structures and

nonstructural components, or portions thereof, that are

at or above the isolation interface shall be designed to

resist a total lateral seismic force equal to the

maximum dynamic response of the element or

component under consideration.
 
The concept is that if you are using a base isolated building, you should be able to capture the in-structure response of the nonstructural component at the point of attachment.     But you are free to use the response of a building without base isolation.  If the nonstructural component is light in mass, the effort to design the seismic restraint may be more trouble than it is worth.  If the nonstructural component requires seismic qualification, you are able to use the reduced demand. 


Regards, Harold Sprague


 

Date: Wed, 13 Apr 2011 17:11:01 -0700
Subject: equipment anchorage in isolated structures
From: d.topete73(--nospam--at)gmail.com
To: seaint(--nospam--at)seaint.org

I'm not having much luck in finding what the force demand is on equipment anchorage requirements within an isolated building structure.  wouldn't the force be reduced since the response will be (significantly) damped above the isolation plane?  I haven't found anything in either the IBC or ASCE 7-05.  Thanks in advance.

--
David Topete, SE