Combine Trapeze Hanger and Seismic Brace?

7/8/2022

I am planning a sprinkler system for a warehouse which is in a seismic area.

Because of the ceiling structure, we need to use trapeze hangers, and possibly combine it with the seismic bracing.

We are planning to use steel angles attached to concrete purlins, based on the sketch below, and put the seismic bracing to this steel angle (like we usually would do with a trapeze hanger).

Is something like this allowed?

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8 Comments

Dan Wilder

7/8/2022 07:45:45 am

This would be a question only a structural engineer can answer. The lateral & lower shearing/twisting forces hitting that lower purlin are a big question along with sizing of both the angle iron and the attachment hardware to/through to the purlins to the adjacent secondary structure.

Glenn Berger

7/8/2022 08:11:33 am

My gut reaction is that this would not be allowed.

David Kendrick

7/8/2022 08:31:11 am

NFPA 13 is published with the engineering using best available technology and consensus of the industry for product application.

When you step away from what is printed you have the privilege of pursuing your own engineered product and application.

There is a huge responsibility to interpret without the proper credentials and appropriate liability insurance.

Difficult as it may seem using the listed products and standards available is the cleanest approach.

James Phifer

7/8/2022 08:41:28 am

I believe NFPA 13: 9.3.5.1.4 (2016 ed) addresses this but you would need to prove the angle iron is capable of meeting your seismic needs.

David Pitts

7/8/2022 08:47:53 am

Looks like you would be better off attaching the seismic bracing directly to the concrete tee with a Hilti Kwik Bolt. Like Dan Wilder said this would be a question for the structural engineer.

Cliff Schulze

7/8/2022 08:58:29 am

I would be concerned about drilling through the bottom of a concrete joist like that. I've worked on projects where they wouldn't let us connect to the bottom third of a concrete joist because that's where they have rebar installed.

Ryan Hinson

7/8/2022 09:33:50 am

While your approach would appear to be feasible, as previously stated, you are now in the structural engineering realm. I would also wonder the following:
- Why not use the trapeze for its prescriptive sole purpose of supporting the weight of the water-filled pipe?
- Why not use the allowed designer-chosen L/R up to 300 on the sway braces used for their intended purpose to resist lateral loading by extending the bracing to the top of the concrete tee?
- What is the depth of the depth of the tee/purlin?
- Are you intending for only lateral braces off this configuration or longitudinal as well? Note that the required longer leg being vertical for the trapeze member is good for vertical loading but is less conducive to a longitudinal brace where the loading is directed across the member in the orientation where the section modulus is reduced.
- Would you be planning on bracing multiple mains off the same trapeze member? If so the accumulative loading of the trapeze member would have to be verified both in a vertical load for each water-filled pipe AND in horizontal loading from each pipe braced in this trapeze section.

Without a structural engineer's buyoff, I would recommend using the prescriptive methods already in existence separately and move on.

Anthony

7/11/2022 08:56:28 am

Per NFPA 13-16 9.1.1.3.1 and 9.3.5.1.4 you can in fact use the same support for both sway bracing and gravity load support.

However, as most have mentioned above this is a bad idea from a liability standpoint.

Some thoughts on the proposed hanger detail:

1) You're placing the pipe through the T in what appears to be a lower third. That's where the T experiences the highest tension forces (If I can remember back 14 years to statics.) So you're putting a hole where structural forces are high with out know how the building was designed to carry the load.

2) You're asking a pipe to hold the load in shear on its side. So your using the thinnest and weakest part of the pipe to hold the load. There will also be a bending moment on that pipe and I'm assuming ATR also? ATR is designed to hold a load axially in the vertical through tension not horizontally in bending.

I agree with David Pitts that several Kwik bolts would be better for this application. I'd avoid putting holes the the concrete purlins If you can. If you have to use the tee get the buildings structural engineer signing off on any proposed drilling.

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Combine Trapeze Hanger and Seismic Brace?

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