Seismic approved, or not seismic approved? 2

[SKIAK]

I was tasked to provide details for seismic bracing for some electrical conduit runs. The situation I walked into was the new conduit had already been installed and was supported by trapeze hangars from the concrete slab above. I asked for information about the existing supports: size and span of strut support, rod diameter and length, rod attachment to ceiling, type of pipe straps, etc. Everything in the existing configuration looked okay (not considering the absence of braces and rod stiffeners, which I included in my details) except the pipe straps. I could not find any information online about the lateral resistance of the pipe straps so I called the manufacturer. The manufacturer of the pipe straps told me they were not tested for that type of loading, or loading in that direction (they mentioned a capacity transverse to the pipe of 50 lbs). In my detail package, I required that the contractor swap out the pipe straps they used for a type that had the transverse and longitudinal capacities required, but only at brace locations.

The contractor was audibly upset about having to change the pipe straps, but I maintained that they needed to use components that had been tested for the type of application they were going to be installed for.

After the contractor was almost finished installing all of the bracing and replacing the pipe straps, the owner asked me to go out and look to see that everything was installed properly. Everything looked good and I got into a cordial conversation with one of the laborers about why they needed to switch out the straps. I asked if I could see the straps they switched out and I held them up to the straps I specified, and lo and behold they were (as far as I could tell) identical, minus the manufacturer stamps.

At that point, everything was installed and there wasn't any going back, but I’m just curious, would anybody else have approved use of the other straps? They *appeared* identical when laid one on top of the other, same metal thickness and coating, there was no way to tell them apart except for the manufacturer’s stamp. In hindsight, I don’t think I would have approved them anyways, but for no other reason than the manufacturer couldn't tell me their capacity, but that is a hard sell to the contractors.

 

[BAretired]

Are you satisfied that the new straps have the required capacity based on your own calculations?

BA

 

[SKIAK]

Yes. The new straps that replaced the old straps are manufactured by B-Line (or Cooper Industries, or EATON, or whoever they are now-a-days) and have tabulated design loads. I am confident that the new straps have adequate capacity for the application.

 

[JStephen]

Possibly it's an issue of quality control, one item is tested/inspected to a higher level than the other.
Possibly it's an issue of labeling only; the overhead involved with the loading gets incorporated into only the items that require it.

 

[SKIAK]

I agree JStephen. It seems that there is one fabricator for these clips, and they get passed to different companies to be stamped and distributed. If that were true, I would think they would have the same capacity but one company paid for testing the other did not. Of course, that is an assumption.

 

[dhengr]

SKIAK:
If you are signing off on this design, you need something to hang your hat on too, w.r.t. purchased parts. Do you know that the steel strength was the same on both clips? Was the finish really the same or equal? Where the fastenings the same and approved? You should go with the supplier who certifies, tests and publishes info. and allowable loads for its products. We have certainly heard of plenty of instances where knock-off parts did not stand up to the test of time, but looked pretty much the same, and how would you know the difference? And, the biggest proliferation of these inferior parts have been exactly these kinds of misc. parts. Obviously, there are some design details where almost any grade of material would be o.k., and then you use your engineering judgement about adequacy. You do not have to stick your neck out a mile to save the contractor a buck. He could have offered to test his product and installation methods to your satisfaction rather than replace them.

 

[SKIAK]

This is true, dhengr. I don't know the material strength, or the capability of the previous clips to bite into the strut and provide the same lateral resistance. Considering these electrical cables were the main service for the entire building, I felt more comfortable going with the tested products.