NFPA 13 - Sprinkler, beams\ceiling pockets and delayed activation?

[ARss]

Hi people,
I've a problem with a "special case"; I need to install a sprinkler system on a ceiling with big "beams" (1,05m x 0,90m - about 41" x 36") - see attached file.
NFPA 13 provide some indication for beams (small beam 14") o for ceiling pocket (max volume 1000 ft3 - 28m3) but it's not my case.

So i've provided a sprinkler under beams and a sprinkler betweem beams, it is correct? - see attached file.

My question is: there is a (big) delay for the activation of sprinkler under beams? NFPA 13 give some other rules?

Thanks to all!
bye
AR

 

[cdafd]

How deep are the beams?

 

[ARss]

Beams are long about 40m (130'), with an height of 90cm (36") and a width of 105cm (41"). Between 2 beams there are 115cm (45").
All these measure is indicated in the pdf attached

Every "pocket", between 2 beams, has a volume of 41m3 (1447ft3).

thanks again!
AR

 

[TravisMack]

With beams <48" in width, I believe you can be just in the high part and not have to put sprinklers below the beams. Verify to be sure.

Travis Mack, SET, CWBSP, RME-G, CFPS
MFP Design, LLC

http://www.mfpdesign.com

 

[UFT12]

Agreed with Travis. It is also stated somewhere in NFPA 13. You dont need the under the beam rows and therefore save considerably as long as they remain under 4ft, 1.2m. If for any reason you cannot go without them, the 1.05 m should be wide enough to collect heat and therefore be of no concern. Of course, the prudent designer should consult the AHJ.

 

[ARss]

mmm, yes normally i don't need protection under beams (<4ft) but sprinkler between beams is obstructed by the same beams - see figure 10.2.7.1.2 and table 10.2.7.1.2 NFPA 13 - 2019.
so (i think) i need sprinkler also under beams.

My problem is: there is a delayed activaction of sprinkler under beams 'cause smoke and heat travel along pocket between beams? NFPA 13 or other codes, provide something for this case?

Thanks again!
AR


p.s. Also EN 12845 provide to "ask AHJ", but in Italy AHJ don't understand nothing about Sprinkler system! LoL - So I try to understand if NFPA, or other codes provide something different!

 

[UFT12]

Be careful how you read 10.2.7.1.2. You need to observe one of options 1 to 4. Per your drawing, it seems option 2 is satisfied and therefore you can disregard 10.2.7.1.2(1).

Presumably, the standard makes the convention that an obstruction up to 1.2 m is not considered large enough to impede heat traveling to the higher sprinklers and therefore the delay is considered negligible.

 

[ARss]

Maybe I didn't explain myself very well (English is not always simple!).

I'm watching Figure 10.2.7.1.2(a) (no §10.2.7.1.2) so I provide sprinkler under beams, because beams is an obstruction to Sprinkler Discharge Pattern Developmen, for sprinkler installed between beams.

 

[TravisMack]

10.2.7.1.2(2) addresses your situation. Sprinklers are not required below the beams <48" in width. If you are still going to provide sprinklers under the beam, then you are exceeding the minimum requirements of the standard and that is generally acceptable to exceed the minimum requirements.

Since you only need to meet ONE of the four options in 10.2.7.1.2 then you can disregard (1) in your situation. Again, as long as you are exceeding the minimum then you are ok.

As to your question, I don't believe those beams will significantly delay activation of the lower sprinklers. But, since they aren't required, and as long as you calculate the additional flows then no worries at all.

Travis Mack, SET, CWBSP, RME-G, CFPS
MFP Design, LLC

http://www.mfpdesign.com

 

[ARss]

Ok, thanks Travis, and UFT:
Now i read again and better §10.2.7.

If I've other dubt I will return

 

[ARss]

Hello again!

A colleague say that the case described above complies with 10.2.6.1.2 - (5) because it is like "concrete tee construction" with large legs spaced less than 2,3m on center.
If this is true, i can consider the ceiling like a unobstructed construction... and provide sprinkler only under tees (max 1") that's right?

thanks a lot!

 

[TravisMack]

My first thought when you described it, was concrete tee construction. However, seeing the section you provided, it didn't match what I am used to seeing as concrete tee construction. Generally, the stems are much narrower in concrete tee construction. But, if you can justify that as concrete tee, then you are able to be 1" deflector below the bottom of the stems.

Travis Mack, SET, CWBSP, RME-G, CFPS
MFP Design, LLC

http://www.mfpdesign.com

 

[ARss]

Yes I know, tee construction have stems narrower. That's my doubt...
From the structural point of view is identical, but i've some doubt that is identical also for "fire\smoke"; I will think about it!

Thanks Travis

 

[cdafd]

NFPA 13 does not define what a concrete tee is??? Does it? specifically the bottom width?

Past substantive changes in NFPA 13 have permitted the sprinkler deflector to be as much as 22 in. (550 mm) below the ceiling for obstructed construction. A 22 in. (550 mm) maximum deflector position for other than concrete tee construction is set in 10.2.6.1.2(1). Positioning the sprinklers more than 22 in. (550 mm) below the ceiling negatively affects sprinkler activation. While 22 in. (550 mm) is the maximum distance, the sprinkler should be placed closer to the ceiling where practical, since the activation time increases as the sprinkler is placed farther down from the deck. The goal is to optimize the sprinkler activation time while minimizing the obstructions to the sprinkler discharge pattern.

 

[UFT12]

Well, it does at it seems. Maybe not as much as I would like as the relevant section is included in the annex but at least it give us a good understanding of the standard intent.

A.3.3.41.1(2), edition 2019
Concrete Tee Construction. The term concrete tee construction as it is used in
this standard refers to solid concrete members with stems (legs) having a nominal thickness less than the nominal height. [See Figure A.3.7.1(a) for examples of con-
crete tee construction.]

With that said and per the OP drawing, it doesn't seem this can be qualified as concrete tee construction and therefore the higher sprinklers are still required. Combining 10.2.7.1.2(2), lower sprinklers are not necessary.

The OP is reminded that we are always speaking for the least but satisfactory level of protection per the standard. As always, the AHJ or insurance carrier may ask for extra requirements.

 

[cdafd]

Uft

Thanks

Could not get the computer to open the appendix the other day

The tee just has to be narrower than the height,,,

If I read it correctly

 

[cdafd]

So it looks like the op

Has the base of the tee wider than the depth??

 

[ARss]

First of all, thank you!!!

Second: what does mean "OP"?

Third: see attached handmade draw (sorry for low quality).

My question is "provocative": if Option 1 is ok, why Option 2 is not? For me Option 2 is an improvement than opt. 1... no? Less "empty volume" and less delay in activation, specially if I provide sprinkler under the concrete concrete panel.

Option 3, for me is a little bit too "dangerous" if obstruction is one, ok i will apply point 10.2.7.1.2(2). But i've 17 obstruction, so i've half of my area "not covered" by sprinkler... no?

 

[UFT12]

OP means original poster, the one that initiated this thread.

I couldn't find any handmade drawing.

 

[ARss]

I try again to attach file... strange:

i leave the link here:

https://files.engineering.com/getfile.aspx?folder=b12877d8-f451-461e-8e40-547e325fa9d5&file=draw.pdf

p.s. OP... original poster ok!