How to Calculate Stress in Hanger Support?

12/29/2021

One of the consultants on my project provided a review comment requiring us to submit a calculation for stress in the hanger support.

We follow NFPA 13 here, and I've never provided something like this.

What exactly are they asking here, and is there guidance on how would I go about calculating the stress in the hanger components?

Thanks in advance.

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5 Comments

Anthony

12/29/2021 08:22:20 am

I think they'd only care about the hanging rod's stress. If they're looking for the loop hanger or say c clamp itself call Hilti, PhD ECT. They'll have material that have theses calculations all done I bet. Might be a pain to get though. It's literally their job to do theses calculations before they get the hanger listed.

Some statics review:

Stress = force/cross sectional area

Forces should be the (mass of the length of pipe + water in pipe ) x gravity.

Assuming you're hanging with all thread rod you'll need to find the minimum radius of the rod after the have been cut ie thread depth.

You'll probably want to look up the yield strength of the particular steel in the rod to calculate the safety factor.

You may also want to add the NFPA required 250lbs (weight of a man hanging on a hanger) to your initial weight/force calculation.

Jon

12/29/2021 08:23:20 am

If the hanger in question is a standard hanger and not a trapeze hanger or seismic brace, there are no calculations necessary if you are following the hanger rules set forth in NFPA 13 (Chapter 17 of the 2019 edition) and not using a performance-based approach to address an unusual application or situation. If you are using the performance-based approach option, then the hanger design needs to be certified by a registered professional engineer.

Alex

12/29/2021 08:44:42 am

If you followed NFPA 13, then no calculations should be required.

Like Jon mentioned, if you used a performance-based approach, then further calculations may be required.

For a case like this, I wouldn't be afraid to simply call the consultant and discuss what they are looking for and explain your design further. I'm always quick to getting on a phone call rather than guessing what people are looking for. Saves time, headaches, and tends to creates relationships that can be used further down the road.

Alex

Jack G

12/29/2021 09:40:08 am

I think the consultant may be looking at the narrow width of sprinkler loop hangers compared to plumbing clevis, and is concerned of " burst stress " of the supported pipe which would depend on weight supported, internal pressure and spacing.
I did these several years ago, a progresso food plant in vineland. Look up Barlows law, it might provide insight.
When i was a Chemical engineering student, we designed ,on paper, an ammonia plant in Texas, encompassing reactions, pipe hangers, supports, support structures. Barlows law was our best friend.

sean

12/31/2021 06:17:38 pm

i think they are looking for how NFPA 13 chapter 9 talks about sizing the stress of seismic hangers. also some manufacturers have these completed or simplified.

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How to Calculate Stress in Hanger Support?

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