Piping support question 1

[skdesigner]

Storage occupancy, with the water available I believe I can make it work without a pump.

The downside...I'm looking at 6" main and 4" branchlines. The roof structure is bent metal "z purlins", and the GC has asked for point loads to determine if the steel can support the hangers.

NFPA 13 2010 9.1.1.2 (1) Hangers shall be designed to support five times the weight of water filled pipe plus 250 lb at each point of piping support.

No problem there, using a listed hanger assembly.

9.1.1.2 (2) These points of support shall be adequete to support the system.

Does "the system" refer to the weight of water filled pipe, or do I need to include the safety factor in the dead load as well? If I trapeze the main, and have 2 hangers per length of pipe, hung with sidewinders, I should be well within the purlin limits. Unless I multiply those numbers by 5 and add 250 lbs per hanger. I just want to be sure before I submit any calcs.

Thanks in advance.

 

[SprinklerDesigner2]

4" branchlines???

The problem you are facing isn't so much on the hanger being able to support the sprinkler it's the building. You start hanging 6" and you could easily be voiding the building warranty.

Butler and American have hanging details.

Found it, from a previous thread

http://www.eng-tips.com/viewthread.cfm?qid=250479&page=18

http://www.mybuildernet.com/sedd/Erection/80/1081464.pdf

Given this how do you hang any pipe >4" from a purlin?

 

[skdesigner]

SD2, that's exactly my concern. Luckily, we're still in the design phase, and nothing is set in stone. Just weighing all options.

Thanks for the pdf, good reference!

 

[pipesnpumps]

I would be concerned with buckling and local yielding in the purlins, right where the hanger bolt goes through. They are absolutely atrocious for hanging pipe. Any load that is not completely in line with its strong axis, and they fold like a cheap suit... Notice the pdf link says don't drill the purlin.

Get advice from the structural engineer in writing is what I would do (or at least ask for it in an RFI).

6" sch40 is 19 lbs/ft. Back when I was a pipe stress engineer I would design misc. support steel for about 2 times the expected weight.. Electricians just viewed my nice pipe supports as a free conduit routing, and minor piping is always added later in the process industry. 5 times is way overkill for designing the steel.



Real world knowledge doesn't fall out of the sky on a parachute, but rather is gained in small increments during moments of panic or curiosity.

 

[pipesnpumps]

I just read the other link after posting. It makes sense that the hangers would need to be connected near the top of the purlin.. What that does is transfer the horizontal loads from the hanger into the metal roof, so that the purlin doesn't have to resist the forces (which it would not do well at all because it has very little flange in that direction).



Real world knowledge doesn't fall out of the sky on a parachute, but rather is gained in small increments during moments of panic or curiosity.

 

[skdesigner]

" 5 times is way overkill for designing the steel." Plus 250 lb no less. That was my thought process as well. We'd be using sch. 10, not 40, but can't forget that the pipe will be filled with water, giving a listed (from allied's datasheet) weight of 23.03 lb/ft. Divided by approx. 2 when trapezing, it's still going to be around 12 lb/ lineal foot along the purlin (angle iron included). No good per SD2's reference sheet.

I've sent the weights per hanger (actual, not 5x), and I will let the structural engineer give a yay or nay. In writing, of course.

 

[TravisMack]

I did a job in the past that had a similar problem. We only had 2½" branch lines, but it was a beast to hang per the metal bldg supplier allowances. We had a 6" main and had to trapeze it across 3 or 4 purlins. Also, the purlins that were carrying the main could not be used to hang our branch lines. So, we had to then run a trapeze parallel to the branch line to spread it across as well. It became quick tricky to get it all to work. But, eventually it did and the building is still standing today

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[SprinklerDesigner2]

Right or wrong here is how I hang from bent metal purlins.

These were 10" purlins.

http://img850.imageshack.us/img850/6664/purlinhanger.jpg

Years ago I had a structural engineer who worked for a metal building manufacturer tell me that was the best way. Putting it up here though I am afraid of a chorus line telling me it is the worst way but that is how I do it. I use a step drill for the bolt through.

I will do near most anything to avoid 6" without a trapeze hanger.

Last time I worked in South Carolina they would not allow hanging from the bottom lip of the purlin and if you tried they'd have you change out the hangers.

 

[TravisMack]

SD2:

We typically see those, or a sammy sidewinder for purlins. I agree that you are not going to hang 6" from a single purlin. It will usually be spanned across 2 or 3 purlins for hanging.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com