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California 2016 CBC - Seismic bracing of ductwork?

JPohling

Sawhorse
Joined
Aug 16, 2011
Messages
1,188
Location
San Diego
I have a plan reviewer that is requiring seismic bracing on small cross section ductwork. They are citing ASCE 7-10, 13.6.7 Ductwork. I believe exception #2 is exactly what we have. They are saying that somehow we need to satisfy both exception #1b and #2. Our ductwork is small diameter with the largest being 24".

We are under the impression that seismic bracing is required for ductwork greater than 6 SF in area and on hangers greater than 12" in length.

What are your interpretations? Are there any commentaries on this for clarification?
 

mtlogcabin

Sawhorse
Joined
Oct 17, 2009
Messages
7,752
Location
Big Sky Country
There is also a requirement to weigh 17 lbs/ft or less. Are you meeting that?
If you are I do not see a problem if the hangers do not exceed 12 inches.
 

mtlogcabin

Sawhorse
Joined
Oct 17, 2009
Messages
7,752
Location
Big Sky Country
The issue is our hangers are longer than 12"
You do not have to meet both exceptions only one of them
You can't meet 1a because it is not a trapeze assembly.
You can't meet 1b because the hangers are over 12 inches from the support point to the structure.

That leaves exception 2 for you to use. You can meet that because the duct-work is less than 17 lbs/ft and cross sectional of less than 6 sq ft.
the plans examiner is wrong to ask you to meet both requirements.
 

Phil

Registered User
Joined
Feb 6, 2010
Messages
186
Location
California
The plan reviewer must be new. Typical ducts smaller than 6 sq ft have been exempt for decades (the actual requirements have been tweaked a little bit over the years). You might show the plan reviewer Mason Industries OSHPD preapproved details general notes which is more explicit: " . . . are not required for HVAC Ductwork and Factory Built Vent Duct where any of the following are satisfied: . . ." The pertinent page is attached. The entire document can be downloaded at https://www.oshpd.ca.gov/FDD/Pre-Approval/OPM-0043-13.pdf. This has passed the scrutiny from OSHPD. Note: CBC 1616A.1.26 revised ASCE 7's 17 plf to 10 plf.
 

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