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RE: SEISMIC: Roof Supported Equipment

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Make sure the weight of the equipment meets the 25% rule in 9.6.1 before
you take the "exception". If it does meet that rule, you do not need to
apply the provisions of 9.6.1 for local analysis of the equipment, but
you still need to include the equipment mass in the overall seismic
analysis (i.e., apply the lateral seismic coefficient to the centroid of
the mass). In this case, use the R-value for the building system.  
 

William C. Sherman, PE
(Bill Sherman)
CDM, Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)cdm.com


 


________________________________

	From: Polhemus, Bill [mailto:bill.polhemus(--nospam--at)tyson.com] 
	Sent: Wednesday, May 18, 2005 10:00 AM
	To: seaint(--nospam--at)seaint.org
	Subject: RE: 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?
	 
	Hm.

________________________________

	From: Polhemus, Bill [mailto:bill.polhemus(--nospam--at)tyson.com] 
	Sent: Wednesday, May 18, 2005 8:22 AM
	To: seaint(--nospam--at)seaint.org
	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)psm-engineers.com] 
	Sent: Tuesday, May 17, 2005 6:37 PM
	To: seaint(--nospam--at)seaint.org
	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 9.1.2.2).  

	 

	If you meet the criteria, just use ASCE equation 9.6.1.3-1 to
get the amplified lateral force that acts on the equipment at the
connection elevation.

	 

	
	
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