Which Test Weight to Use for Hanger Spacing?

4/30/2020

Many listed hanger fasteners have their own weight limits. When I calculate the allowable hanger spacing for different size pipes, should I be using the Ultimate Pullout, UL Test Load, or FM Test Load?

Just looking at the Sammys for Wood Vertical (https://www.swfastener.com/pdf/ITW%20Sammy.pdf), for instance - some of the wood screws can have three different load values and I'm not entirely sure which I should be using to determine the appropriate hanger spacing for a sprinkler system. Thanks in advance.

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4 Comments

Dan Wilder

4/30/2020 08:21:13 am

For the same MFG, please look at the more current catalog, which on Page 14 shows the listings for both UL & FM in a maximum pipe size available. Typically, anything with fire sprinkler listings or approvals are shown with a maximum pipe size but you may need to reference this based on the UL listing or FM approval sheet if the MFG data sheet does not specify. ICC-ES sheets are also very helpful with exactly how items are to be installed and in what conditions.

http://www.itwbuildex.com/pdf/updated_sammys_catalog_2018_19.pdf

For example, Caddy Top Beam Clamp indicates 2 loads and shows a UL listing and FM approval for the 3/8" & 1/2" models but no pipe sizes.

https://www.erico.com/catalog/categories/R385?pdf=1&language=en&country=US

However, digging into the general page you can get to this page which links out to both UL (Free account required) & FM and these show maximum pipe sizing for the 3/8" up to 4" and the 1/2" up to 8"

https://www.erico.com/category.asp?category=R385#catalog-documents

https://www.erico.com/catalog/certifications/FM.pdf

Most websites are setup this way and generally speaking, if the 3/8" version is UL & FM, it can handle piping up to 4", the 1/2" models can hold up to 8".

This next part is a whole 'nother Q/A itself but in a nutshell...

There are exceptions, the most notable that comes to mind being the Hilti HDI-P which shows UL/FM BUT this is based on applications using "Uncracked Concrete". I have not been on a project yet that I could get a structural engineer to sign off that the PT slab was "Uncracked Concrete" (Hilti lost their listing on this product back in ~2006 for a bit because of the cracked vs uncracked designation hence the ICC-ES came into the spotlight). However, Hilti also makes a HDI-P-TZ version that is allowed for cracked concrete and for use in seismic areas for shallow enbedment applications up to 4".

In the end, just read through the available literature on the sites if you don't see pipe size limitations in fire sprinkler applications.

Casey Milhorn

4/30/2020 10:19:58 am

I think you are asking what number to use when comparing to the weight of the water filled pipe x 4 + 250 lbs (Per NFPA 13). If that's the question, then go by the UL listing (if its a UL job), FM listing (if its a FM job), or your choice if the job doesn't have a specific listing agency in the specs. So for example, if your weight of your pipe + 250 lbs equals 350 lbs at a 10' spacing, and your UL listed test load is 360 lbs, then you are in good shape. Rarely have I ever seen an issue with the listed pullouts not being enough to space hangers to 12' or 15' per NFPA 13. But it is worth checking for when dealing with a new hanger attachment or larger pipe.

Mike

5/5/2020 10:30:47 am

In the appendix it states the 250# is a safety factor.

I don't think it should be included in the design load if applying them to a load limit for a particular structure. Instead, consult with the structural engineer to see if their safety factor accommodates the additional 250#.

Has anyone else taken this route?

Rory link

7/10/2023 05:47:24 pm

The purpose of the 250 lbs is to accommodate the weight of a single human in the event of a mishap with their ladder/lift system and they have to dangle from a single hanger until rescued. No joke. The safety factor of five on the capacity of the hanger assembly is for variances and to resist seismic forces.

Generally, the 3/8" all thread rod is the weakest piece of the hanger assembly with just a 730 lb capacity. 1/2" rod has a 1,350 lb capacity so the pull-out capacity on lag screws and the loads on your hanger rings really come into play at this point.

Generally, the permissible maximum hanger spacing in the standard is rarely achievable with ordinary hanger material, yet most designers go with the max. spacing table and don't give it a second thought. That table is a stop sign, not a starting line; start at the capacity of weakest material in the hanger assembly, then capacity of structure vs weight of equipment to determine spacing; then look at the max spacing table to make sure you don't go over.

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Which Test Weight to Use for Hanger Spacing?

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