Long drop pipe supports

[FPE22]

Hi everyone,

I have a dinning hall that has a ceiling height of 43 ft (13 m) which requires sprinkler protection as per NFPA. Ceiling panels are suspended at a height of 13 ft (4 m) above ground. These panels have width greater than 3.9 ft (1.2 m) and therefore are considered as obstruction to ceiling sprinkler spray pattern, and need to have sprinklers installed below them. These panels are distributed throughout the middle of the hall - at least 16 ft (5 m) between one another - and far away from walls or columns. The ceiling panels are supported to the ceiling above by four 6mm rods.

My question is, if my main pipe runs below the ceiling at 43 ft (13 m), then a long vertical drop pipe - around 30 ft ( 9 m) drop - will need to come down to connect to the sprinklers installed on the ceiling panels. How can I support these vertical drop pipes assuming they are 1" pipes? My concern is the vibration that will happen if the sprinklers connected to these pipes operate.

Appreciate your feedback.

 

[MGXFP]

You don't.

Run a sub-main down longitudinal above the suspended ceiling panels and install your drops in the low ceiling from that main. If you size your pipe the same as the above you do not need a separate calculation.

 

[FPE22]

I thought about your suggestion, but if I do that then the pipe supports will extend from the low ceiling up till the high ceiling (9 m).

Is that acceptable?

 

[cdafd]

Are you in a seismic area??

Not sure drops have to be supported.

I know sprig ups, after a certain length, have to be supported.

Need to check the book.

 

[FPE22]

The project isn't in a seismic area in itself, but it's close to an active seismic area. I think it will be affected by any nearby seismic activity.

I think that if the pipe or hanger is suspended for 9 m in mid-air, it will be subject to lateral movement.

 

[TravisMack]

Forget seismic areas and zones. That is old school. What is the seismic design category determined by the structural engineer. If A or B then no bracing. If C or higher, then full seismic.

Rod is less expensive than pipe. If you can hang the pipe and running low is an acceptable option, I would run low. It seems that running a second complement of piping down low is actually less pipe than the running high would be.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

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[MGXFP]

Pipe hanger rods can be quite long, yes.

In addition I would add flexible drops to help the pendent sprinklers not sag beneath the suspended ceiling over time.

Sprigs over 4'-0" need braced against lateral forces 9.2.3.7 2013. I don't find anything about long drops needing braced. 9.3.2.3.1 (5) 2013 states to add flexible couplings to drops over 15' for seismic.

 

[SprinklerLifer]

I agree with NewtonFP. There is no real issue with long drops needing bracing, no matter how "floppy" they seem. I would use flexible drops at the bottom to alleviate any concerns about sagging and vibration.

 

[Ehendrix]

Sprinklerlifer is correct and that method works great. I designed a church that was built as A frame building, half was exposed half wasn't. At the peak there was ceilings below that called for a 12' drop. I sent the drop down 10' then used a flex drop from that point.

The ceiling brackets do a good job of helping to stabilize the drop in those situations.

Eric Hendrix, SET
NICET Certified
Design Manager

 

[FPE22]

Flexible drops at the bottom might be a good option. Thank you all for your feedback, appreciate it.

 

[MGXFP]

Also I feel it is worth noting that many times these long drops are beneficial to calculations as well. Typically for a 1" drop the pressure gain due to elevation is greater than the friction loss effectively reducing your K factor and lowering over-discharge.