Section Modulus for Trap Members 10'-6" On Center
Section Modulus for Trap Members 10'-6" On Center
(OP)
NFPA 13 gives a table of Section Modulus for varying spans of trapeze members based on 15' of water filled pipe. Not sure if anyone else installs main hangers on 15' centers but we use 10'-6" spacing and 5'-3" from each end (typical 21' lengths. 2 hanges per pipe.
Is there a formula available (maybe I missed it in 13) or another preengineered table for Section modulus based on 10'-6" centers?
Seems like I should be able to get the trapeze pipe member size down if I didn't have to use 15' centers.
TIA, ShawnO
Is there a formula available (maybe I missed it in 13) or another preengineered table for Section modulus based on 10'-6" centers?
Seems like I should be able to get the trapeze pipe member size down if I didn't have to use 15' centers.
TIA, ShawnO





RE: Section Modulus for Trap Members 10'-6" On Center
You may need to get help from a qualified (competent) engineer on this one. If you do not use the tables and parameters outlined within NFPA 13 (which many have argued contains all the engineering so you don't have to), then (as others have argued previously), you are interpretting, or worse, doing a calculation that by rights is "engineering", which is outside the scope of a NICET technician.
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RE: Section Modulus for Trap Members 10'-6" On Center
But not all is lost, there are easy and correct workarounds.
For a 10'-6 trapeze simply keep the pipe away from the center using A9.1.1.6 to find the equivalent length.
If the span is 11'-0" simply keep the pipe within 3'-9" of the left or right side for an equivalent length of 9.89'.
If the job is so big, so complex you can't offset pipe in the trapeze then pay the few hundred it will take to have a PE look at it.
RE: Section Modulus for Trap Members 10'-6" On Center
Travis Mack
MFP Design, LLC
www.mfpdesign.com
RE: Section Modulus for Trap Members 10'-6" On Center
We see a lot of companies shift cross mains to the side of the nearest truss and adjust starter pieces accordingly to maintain plan head locations. This eliminates trapezes, but I would careful if it is a large shift, so as not to affect pipe lengths too much.
RE: Section Modulus for Trap Members 10'-6" On Center
Ed Kramer
Kramer Design, LLC
RE: Section Modulus for Trap Members 10'-6" On Center
Fire Sprinklers Save Lives.
Can You Live Without Them?
RE: Section Modulus for Trap Members 10'-6" On Center
The technician was told to make the necessary adjustments.
You dont need to hire a PE to perform basic math for you.
Forest Wilson
Cherokee Fire
RE: Section Modulus for Trap Members 10'-6" On Center
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Thanks for all of your advice. I have an engineer buddy that's helping research this. I'll update as I get more information. He'll explain to me how he got there. Then we'll see if it is actually basic math or not.
RE: Section Modulus for Trap Members 10'-6" On Center
I tried and while the math was basic and easy I messed up by not knowing 1)the correct terminology and 2)where to apply the correct numbers to arrive at a correct answer.
While I would like to know more, I would like to be able to do it, I recognize it's engineering so I throw the responsibility to someone else.
It's like knowing when a 13R system becomes a full 13 through the building code. I pretty much understand it, most of the time I can get the right answer but why would I want to accept the responsibility when it's clearly the practice of engineering and architecture? I have enough responsibility without volunteering.
RE: Section Modulus for Trap Members 10'-6" On Center
Shoot me an email. I have a spreadsheet that a PE buddy of mine created a couple of years ago that calculates the section modulus for various hanger spacings and distance from side of the structural member. The table in 13 is for center loading and 15' on center.
Mine is not signed/sealed by the PE that created it. Your guy may want to use it as a starting point. He may find it is correct or needs to be changed.
Travis Mack
MFP Design, LLC
www.mfpdesign.com