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When doing zone of influence calculations, NFPA 13 doesn't seem to be specific about whether the weight of drops and sprigs should be included in the weight of the branch line tributary to the lateral brace on the cross main. It states "The zone of influence for lateral braces shall include all branch lines and mains tributary to the brace, except branch lines that are provided with longitudinal bracing or as prohibited by 9.3.5.9.6.1" (NFPA 13, 2016 Edition, Section 9.3.5.9.6)
This ambiguity is frustrating because long drops are quite heavy and can double the weight in the calculation if they are included. It seems like some argument could be made that they aren't "tributary" to the lateral load because they can "swing" independently, but should their influence be considered negligible? Posted anonymously for discussion. Discuss This | Submit Your Question | Subscribe
2 Comments
Randy Day
11/15/2019 10:53:30 am
Looks like you've pretty clearly answered your own question here. You have to include all branch lines unless it's independently braced per 9.3.5.9.6.1.
On the Clock
11/15/2019 10:55:09 am
I once found in an NFSA informal interpretation (a useful member resource) that the answer is yes, these loads must be included. Perhaps related, In the 2007 edition on NFPA #13, the definition of branch line was amended to include reference to sprigs, drops, return bends, and armovers. Leave a Reply. |
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