Material FoS for MEP Seismic Bracing

[mikeCTE]

We are analyzing a trapeze support for MEP supports in a seismic zone. One of the elements of the trapeze is a threaded rod.

In reviewing the rod specifications, it has a safe working load of 5. (SWL = ultimate / 5)

I know that different industries and applications have minimum required FoS values. I am curious what this value is for ASCE7-16 for components supporting MEP equipment.

Our contractor is pushing us to use 3/8" rod b/c they've used it a lot in the past. Our numbers show that we would need 1/2" rod to achieve the safe working load.

For example, if the SWL is 1500lbs, we can multiply by 5 to get 7500lbs ultimate. If our demand is 2500lbs, then our actual safety factor would be 7500/2500 = 3.0. Is 3.0 acceptable?

Thanks

 

[bones206]

Try MSS SP-58 “Pipe Hangers and Supports – Materials, Design, and Manufacture”. Should contain allowable stresses for threaded rod.

Also consider that compression in the rod may require a rod stiffener to avoid buckling, depending on your bracing arrangement and relative seismic vs. dead load magnitudes.

I believe NFPA has their own design criteria that would govern for sprinkler pipe hangers.

 

[fel3]

Also check the SMACNA Seismic Restraint Manual:

https://www.smacna.org/store/product/seismic-restraint-manual-guidelines-for-mechanical-systems

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"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[mikeCTE]

Yes, we tried looking at both of those codes but do not have access (we don't own them).