Trapeze requirements

[AZsprink]

Hey all

Ive been reading this forum for some time and it seems that there are many knowledgeable people here. I am a fire sprinkler company owner and have seen a lot of confusion over the intent of many NFPA13 and 13d requirements. I am not an engineer, but would like know if I could post NFPA related questions from time to time to get the opinions of designers and engineers.

One issue in particular is the construction of a trapeze assembly. If I remember right, the trapeze itself is supposed to be hung with the same sized hardware as is required for the pipe that is suspended from the trapeze, “a 6inch pipe would require a ½ inch hanger rod” for example if your trapeze member is 2 inch pipe, it should be hung with 2 inch ring hangers with ½ inch buttons to accept the ½ inch ATR that is required. NFPA says that the ring hanger on the trapeze that supports the main is supposed to be the same size as the main. Example a 6 inch main supported from a 2 inch trapeze , Is it the intent of NFPA to install a 6 inch hanger to both the main and to the trapeze and shape this hanger to fulfill this requirement? Is this hanger still listed after being bent?

 

[SprinklerDesigner2]

I've never used hanger rings on the trapeze member itself.

If using pipe the three hanger rings attached to trapeze itself should be the same size as the trapeze member and should be equal to or smaller than sprinkler pipe it supports.

Bending a hanger would, in my opinion, be a violation of the listing. We're not allowed to bend hangers to make them fit.

I suppose hanging a 4" pipe from a 2" trapeze member hung using 2" rings would be fine if you found a professional engineer that would sign off on it (good luck on that one) but even then I wouldn't feel comfortable.

When using pipe I've always drilled through holes using double nuts and washers for the rod. Takes three minutes to drill the holes (do it in the shop on a bench drill) and 20 cents of nuts and washers beats $3.00 of hanger rings.

And that is my two cents worth.

 

[spkreng]

welcome AZ, as of the 2002 NFPA 13 Handbook, which I love because it explains stuff like this.

9.1.1.6.5 Where a pipe is suspended from a pipe trapeze of a diameter less than the diameter of the pipe being supported, ring,strap, or clevis hangers of the size corresponding to the suspended pipe shall be used on both ends.
Now the commentary following this, clarifies; The phrase "on both ends" refers to the top and bottom ends of the rod supporting the main. The phrase dows not mean both ends of the trapeze.The top hanger ring is being used in a position that is opposite normal use, and it must have strengh appropriate to the larger pipe size. Ideally, the ring can be shaped to accommodate the smaller pipe size. Otherwise the potential exists for the ring to elongate over time with the load, which would result in a change of pitch of the piping.

9.1.1.6.6 I'll skip to the clarification
Paragraph 9.1.1.6.6 refers to the size of hanger rods and fasteners. Each of the rods used to support the trapeze needs to be sized according to the size of the trapeze pipe in accordance with Table 9.1.2.1 (=< 4" 3/8" - 5,6 &8" 1/2") Although these rods are not sized for the larger pipe being supported, the lower safety factors relating to trapeze hangers and the shared load between two points of support are generally adequate.....Where sizing of the rods is of concern (way off center hanging point, etc.)the rod size can be selected based upon the large supported pipe size.
oh and if you just drill the "Holes for bolts shall not exceed 1/16" greater than the diameter of the bolt. Bolts shall be provided with a flat washer and nut. I assume this means rod too.



spkreng, CET

 

[AZsprink]

Thanks for the input

This is from NFPA 13 2007 edition
9.1.1.6.5* All components of each hanger assembly that attach to a trapeze member shall conform to 9.1.1.4 and be sized to support the suspended sprinkler pipe.

Doesn't this mean that all 3 hanger rods should be sized the same as the pipe being supported by the trapeze?

Example; a 6 inch pipe supported by a 1.5 inch sch 40 trapeze member. Say the 6 inch pipe is located 4 inches from the centerline of joist (the main hanger is not required to be located in the center of span is it?) wouldn't it be silly to use a ½ rod for the main and than use a 3/8 rod to support the trapeze 4 inches away?

I also don't use hanger rods for trapezes (too expensive) a lot easier to drill holes in trapeze, and don't have to argue with inspector about ring hanger size.

 

[SprinklerDesigner2]

AZsprink

"This is from NFPA 13 2007 edition
9.1.1.6.5* All components of each hanger assembly that attach to a trapeze member shall conform to 9.1.1.4 and be sized to support the suspended sprinkler pipe.

Doesn't this mean that all 3 hanger rods should be sized the same as the pipe being supported by the trapeze?"

I agree with you until someone can show me otherwise.

 

[spkreng]

I stand by the statement that 2 hanging points (on the trapeze) = enough to hang the main...SD2 what does it say in the handbook/appendix? and what you say is true than you are hanging a 2" trapeze with 6" rings all around right..someone sometime got into this and the listed hanging capability of say 2" rings does handle 6" pipe by weight, so you have the weight on the rod prob. I'll not quibble 1/2" is 50 cent more than 3/8"

spkreng, CET

 

[SprinklerDesigner2]

spkreng,

I am not sure of the answer so far as hanging with rings so I stand a chance of learning something new.

I've always drilled the holes, double nut and washer using 3/8" rod for 1 to4" and 1/2" rod for 5, 6 and 8".

I suppose an argument could be made the the 2" Tolco band hanger has a Maximum recommended load of 400 lbs

http://www.vikinggroupinc.com/usrelated/tolco/fig200.pdf

so as long as the total weight didn't exceed 400 lbs you would be ok.

But to me this determination should be made by a professional engineer but seeing how I'm not one I prefer the cookie cutter safe way.

Fact is I prefer Power Strut just to play safe. I know it's tough and bidding is competitive (an understatement) when you look at the whole scheme of things does an extra $200 on a $140k job really mean all that much?

I am hoping one of the PE's that inhabit these parts might chime in.

 

[spkreng]

Well I had nothing better to do..according to NFPA 13 2010 9.1.1.6.6 The ring, strap or Clevis installed on a pipe trapeze...just as in the 2002 edition as stated above, however the sizing of rods is absent...

spkreng, CET