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Joined: Mar 2001
Posts: 345
tdhorne Offline OP
We were building a pharmaceutical laboratory into the shell of a tilt up warehouse. We built trapeze racks to carry the conduit but we hung the rod off of the bottom cord of the trusses. The AHJ declined concealment until we transferred the load to the top cord of the trusses. I don't doubt that some code requires this but with the largest conduit being one inch and the trapeze being one foot wide I thought it a bit petty.
Tom H

Tom Horne

"This alternating current stuff is just a fad. It is much too dangerous for general use" Thomas Alva Edison
Building Codes & Related References
Joined: May 2001
Posts: 717
A bit petty indeed. I'd fire off an RFI (Request for information) to the structural engineer. This is a new one for me. The SE may tell you the same, but I do believe they are intended to carry supplemental structure, but can not see your plans or load data from here.

May be as simple as a phone call, but could save you a lot of time and money.

Joined: Aug 2001
Posts: 599
Petty with that size rack for sure. I have run into this a number of times. Usually they will let you hang from the bottom if you make your attachments at the panel point.

Joined: Aug 2003
Posts: 1,374
I can see both sides of this issue. I agree that the weight we are talking about is rather light, but I can understand the inspector's concern. I personally would not have said anything about it if I were inspecting it.

The problem that I have is that your inspector is requiring you to go off of the top chord...did he review the truss engineering and perform the calculations to verify that the top chord could carry the extra weight? [Linked Image]

I agree with George...send the PE an RFI and he'll giggle for a minute and tell you everything is OK.

Ryan Jackson,
Salt Lake City
Joined: Dec 2003
Posts: 751
The BO is only trying to do his job. If he doesn't have the experience or knowledge to determine that the extra weight of your trapeze can be handled by the bottom chord, then he should have asked you to get your permission slip from the engineer or remove the rack. We teach that trusses are designed to carry the weight on the top truss. This BO apparently took that as meaning all weight, no matter how light, would have to be from the top. In time, this BO will understand that small weights can be supported from the bottom. Until then, get the engineer to write you up an OK.

Joined: Dec 2003
Posts: 35
We generally hang off the bottom of the truss also; But most fitters will hang off the top of the truss. I've never found out the actual reason, but I'd have to assume it's the stress loading on the truss....

Joined: Jan 2003
Posts: 4,391
You guys are spoiled [Linked Image]

99% of the jobs we are on we can not hang a 4" square off the bottom chord of a truss or I-Beam.

It is almost always in the specifications that no loads are to be placed on the bottom chord or web.

If it is an I beam structure this means using threaded rod up to the top web for even small single raceways on minnis.

It has always seemed a little extreme but it keeps it easy to enforce, no fussing around with figuring out what is to much and what is OK.

Bob Badger
Construction & Maintenance Electrician

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