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

 

[UFT12]

Option 1:
Depth is not really regardless. You will need to compare depth with tee width. If depth > width this should be ok.

Option 2:
Same as 1. The width of the hor. obstruction joining two tees should be less than tee depth. We are still taking for concrete only.

Option 3:
Seems OK. As long as the obstruction is less than 1.2 m or 4 ft, the unwetted area is considered small btw sprinklers and the heat is expected to travel to the upper sprinklers activating them and hence control the fire. However I find your concern valid. This is one example of cases where clarification with the AHJ is worthy.

 

[Ahmedbadr87]

Hello Everyone,
I've just noticed that every one in this discussion is ignoring clause no .10.2.9.1 ( Ceiling pocket), is not it considered ceiling pockets?...

how can we define ceiling pockets?....I believe I'm missing sth here

 

[UFT12]

See 3.3.25 and its corresponding explanatory text. Based on that, it seems the structural bays shown above do not fall under the definition of 3.3.25 and therefore 10.2.9 should not apply.

 

[Ahmedbadr87]

UFT12 ,
I have already read that and i still can not get why the definition can not match the concerned structure discussed above. could u tell why it does not fall under 3.3.25 definition?

 

[UFT12]

Because the OP above talks about concrete tee construction. My understanding is that we are talking about the structural members of the building which are excluded from the definition of 3.3.25.

A.3.3.25 Ceiling Pocket. It is not the intent of this definition to be applied to structural and/
or framing members otherwise used to define obstructed or unobstructed construction

 

[Ahmedbadr87]

so you mean if any structural element which is part of the construction forms a depression , it would not be considered pocket?.am i getting it right?

just for clarification, i have just encountered a decorative wood bat installed in ceiling ( depth 50 cm and width 40 cm )

so for this it would be treated as obstruction not ceiling pockets or what do you think?

 

[UFT12]

so you mean if any structural element which is part of the construction forms a depression , it would not be considered pocket?.am i getting it right?

well, one could use the term 'pocket' but it should not be the pocket per the intent of 3.3.25. Other rules apply.

The decorative feature you show looks much like wood joist construction and therefore all the rules that apply for such type of construction have to be followed. By the way, this to me does not look like it falls under the definition of the ceiling pocket because it does not look like a 'bounded area' as stipulated in the definition. However, such features often raise debates between engineers or with the AHJ about their definition.