Trapeze Support with 3 Attachment Points?

5/13/2025

How would you go about designing for a trapeze supporting (2 or more) 6" mains over large spans?

For example, you have a 16'-0" trapeze span, your truss is every 8'-0". Your idea is to place one long trapeze across 16'-0" to support 2-4 feed mains treeing from a riser manifold.

NFPA 13 says we double the section modulus for every pipe, but that is assuming the we are using (2) attachment points; it doesn't seem to explain different configurations like attaching at 3 or more points on the structure.

How would we go about designing for this?

Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe

3 Comments

Dan Wilder

5/13/2025 08:43:45 am

This would be outside of NFPA's scope so a structural engineer would need to be involved.

Also, I am not sure how to size the ATR for the three attachment points AND multiple 6" mains since each hanger would be required to support 5x + 250 including the allowance and equivalent length modifiers for pipes not supported from the center of the trapeze, without that performance review.

COLIN

5/13/2025 10:31:40 am

If it's a hanger configuration not covered in NFPA 13, then it needs to be designed by an Engineer to meet the requirements of NFPA 13. Those are the only two options.

I would add that I'm not sure why you'd span two structural members with your trapeze when you can just use an standard single 8-ft trapeze and remain within the requirements of NFPA 13. Seems like you're over complicating it for no reason, unless I'm misunderstanding something here.

Anthony

5/15/2025 07:26:22 am

As others have said you'll need a structural engineer. If this is for a new build your project will have a structural engineer attached to it and it should be relatively straightforward to request support for your required design. If this is an existing building and a standalone sprinkler project you'll need to retain an engineer/firm. This sounds a lot more annoying than it actually is, could be a little pricy but the only legal way to go about non prescriptive design.

I think your real answer is to span each main on a different independent traps in differing bays.

Leave a Reply.

Home
Our Cause

The Blog
The Forum

PE Exam Prep
The Toolkit
MeyerFire University

Pricing
Login
Support
Contact Us

MeyerFire.com is a startup community built to help fire protection professionals shine.
Our goal is to improve fire protection practices worldwide. We promote the industry by creating helpful tools and resources, and by bringing together industry professionals to share their expertise.

MeyerFire, LLC is a NICET Recognized Training Provider and International Code Council Preferred Education Provider.
All text, images, and media Copyright © 2016-2025 MeyerFire, LLC

We respect your privacy and personal data. See our Privacy Policy and Terms of Service. The views, opinions, and information found on this site represent solely the author and do not represent the opinions of any other party, nor does the presented material assume responsibility for its use. Fire protection and life safety systems constitute a critical component for public health and safety and you should consult with a licensed professional for proper design and code adherence.

Discussions are solely for the purpose of peer review and the exchange of ideas. All comments are reviewed. Comments which do not contribute, are not relevant, are spam, or are disrespectful in nature may be removed. Information presented and opinions expressed should not be relied upon as a replacement for consulting services. Some (not all) outbound links on this website, such as Amazon links, are affiliate-based where we receive a small commission for orders placed elsewhere.

Trapeze Support with 3 Attachment Points?

Leave a Reply.

ALL-ACCESS

SUBSCRIBE

COMMUNITY

YOUR POST

PE EXAM

FILTERS

ARCHIVES

PE PREP SERIES