Restraint for Long Sprinkler Drops in Seismic Area

8/23/2019

I have a warehouse with a roof 20 feet above. The designer has branch lines hanging under the ceiling joists. He has 10 foot drops of 1-1/2" sched 40 to an ACT ceiling over office spaces. We are in a "D" seismic design category building. I am unable to find any requirements for vertical restraint in the NFPA 13 or ASCE 7-10. Can anyone direct me?

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12 Comments

Jonathan

8/23/2019 10:22:22 am

NFPA 2016 9.3.6.7 Drops and arm-overs shall not require restraint

NFPA 2019 19.6.7 States the same

I recommend providing a lateral restraint on the branch line or arm over.

jonathan

8/23/2019 10:34:13 am

New code NFPA 2019 18.6.3.1 (Restraint of Branch Lines)

The location of the restraint at the end of the line shall not be greater than 36 in. for 1in. pipe 48 in. for 1 1/4 pipe and 60 in. for 1 1/2 pipe or larger

But if your rod is less than 6 in. from top of pipe to the attachment, restraints can be omitted 18.6.5 2019 and 9.3.6.5 2016

James Phifer

8/23/2019 10:36:14 am

below is what I found from NFPA 13, 2016 edition

9.3.6.7 Drops and armovers shall not require restraint.

9.3.2.3.1 The flexible couplings shall be installed as follows:
Within 24 in. (600 mm) of the top of drops exceeding
15 ft (4.6 m) in length to portions of systems supplying
more than one sprinkler, regardless of pipe size

Don

8/23/2019 10:47:32 am

Thank you Jonathan. I fail to understand the reasoning behind this. A 4' vertical sprig requires lateral restraint but a drop of any length with a vertical sidewall head doesn't. Hmmmm...I'll have to chew on this some more.

Jonathan

8/23/2019 11:15:34 am

Yeah it's strange but I'm assuming they think since the head will be in ceiling tile there will be little to no lateral movement. I don't see grids handling to well during an earthquake. Depends on how bad the earthquake will be I guess.

Good Luck Don

Rusty Scott

8/23/2019 10:54:03 am

Normally they have one feed main pipe drop down to just above the office (which is seismically braced with four way brace) and use long hangers that use connector nuts to extend the all thread rod to make it reach the structure. They will have end of line restraints on the horizontal branch piping. I've seen seismic cable used in a lot of spaces for the mains. If you locate the main 8" above ACT they'll have normal sized drops. Also make sure they have retaining straps and surge clips.

I have a similar case to you in a school in South Carolina where it's a 15'-0" drop pendent for an office in a theater office space only needing one sprinkler. Since we have it in our company specs and install notes that they have to brace branch piping longer than 4'-0".

If you look at NFPA 13-2013 9.3.6.6 springs 4 ft or longer shall be restrained against lateral movement. In A9.3.6.6 it discusses using wire from 9.3.6.1 and the length does not include the fitting and sprinkler. We basically have adopted this code to brace drops over 4'-0". To me I don't know why a sprig would be treated differently than a drop, I don't really see the logic in it, so that's why it's in our specification and notes. Maybe it's because of the difficultly to actually brace it vs a sprig being close to structure.

Brian Gerdwagen

8/23/2019 11:32:39 am

You never want to brace drops to a single sprinkler. Drops are supposed to have flexibility so that the differential movement is absorbed. Springs are restrained so they do not fall over and twist through lever action on the fitting below. You can not equate the two.

In seismic D, ASCE 7 says you must cut an oversize hole 1" larger than the sprinkler or use a flexible drop.

Rusty Scott

8/23/2019 03:45:20 pm

The long 15'-0" drop does have a flexible hose connection at the ACT ceiling. Would it be deemed acceptable to brace the drop then?

Brian Gerdwagen

8/26/2019 08:25:05 am

Acceptable, but not code-required.

DTC

8/26/2019 08:37:02 am

Good discussions. In our area the local AHJ's have all amended NFPA 13 9.3.6.7 to state any drops and arm-overs over 10' shall be restrained.

JAL

3/5/2021 12:49:08 pm

@DTC That's great your AHJ has a clear definition!

I'm encountering this argument recently...some say the piping which feeds only one sprinkler is considered an "arm-over," therefor eliminating the requirement. Albeit, I don't agree with the way either definition is written (branchline or arm-over).

Mark S

4/5/2021 10:13:54 am

I would counter that with: Arm-overs that are more than 2' long (cumulative length of horizontal pipe) are required to be supported (steel pipe).

Restraint for Long Sprinkler Drops in Seismic Area

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