Deep Beams as Obstructed or Unobstructed?

5/8/2023

We have a project where there is a very high corridor at a high school (45-50 feet high). There are 30-inch deep steel 'I' beams spaced at around 20-ft apart.

Should this be considered obstructed or unobstructed?

Should deflectors be at 1"-12" below deck, or can they be lowered to maximum of 22" below deck? Do all deflectors need to be at the same elevation?

Since the beams are deeper than the deflector elevation, I'm looking at Table 8.6.5.1.2 for distances from the beam to avoid the beam with the sprinkler spray.

Thank you in advance for your input.

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8 Comments

Anthony

5/8/2023 07:24:14 am

Depth of the beam is only one component of obstructed construction rules. If the beans are 20' apart and that is the only obstruction then you need to use the table noted.

Pete H

5/8/2023 07:45:56 am

What's the spacing of the beams on center?

If it's less than 7.5 ft on center, this sounds like A.3.7.1(1) in NFPA 13 (2016).

Either way, I'd say try to match the accurate construction type from the Annex definitions of obstructed or unobstructed for your building to get your answer.

Glenn Berger

5/8/2023 08:15:36 am

20 feet on center is unobstructed construction.

Dan Wilder

5/8/2023 08:57:08 am

How wide is the corridor, assuming full height walls?

The only ability to utilize a lower deflector distance is keeping under the 300 sq. ft. limitation for panel construction (and its un-filled penetrations requirement).

My inclination is going to be unobstructed and the sprinklers need to be 1"-12" max deflector distance.

Kevin

5/8/2023 09:17:47 am

The walls are full height and the width varies as the walls are angled. The width dimension is between 35'-50'.

Jesse

5/8/2023 09:15:08 am

20-ft on center doesn't sound like its obstructed. Maybe I missed something

Casey Milhorn

5/8/2023 09:44:31 am

If the beams are 20' apart, what are the framing member types? Bar joist? Purlins?

Remember, when you try to use the 300 sqft exception, you can't have any openings above the beams (as in corrugated metal decking).

Alex

5/8/2023 01:51:36 pm

This sounds like unobstructed to me!

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Deep Beams as Obstructed or Unobstructed?

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