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Seismic bracing for trapeze & Strip Ltg. #154375 06/20/05 06:38 PM
Joined: Oct 2000
Posts: 2,721
Scott35 Offline OP
Broom Pusher and
Hello all;

Looking for the Group's assistance on a "California" design issue, in regards to Seismic Bracing
(AKA: "Keep stuff from swaying all crazy-like, during an Earthquake")

More directly, the better (Engineered or Scientific) methods & formulas, for bracing Suspended Conduit Racks (AKA: "Trapeze"), plus Suspended rows of Fluorescent Strip Lighting (8 foot fixtures, in long rows).

Trapeze / Racks constructed from Unistrut, suspended via Threaded Rod segments.
Strip fixtures suspended via 3/8" Threaded Rod.

All running +150' across open areas, which shall be used for General Sales to the Public.

In the past, I have done "Kickers" every 20' & at opposite sides, having one piece of strut parallel to the Trapeze, and one at a right angle to the Trapeze... alternating sides every 20'. Same with the Strip Fixtures, but instead of "Kickers" made from Unistrut, the "Kickers" were either E.M.T. or threaded Rod.

So far, no problems or correction notices.

I would like to know if there's a better way / formula, so when a large quake hits, I do not see a Live News Report showing all my Conduit + Fixtures laying on top of People!

Any comments are welcome.


p.s. We had an event last week - epicenter being apx. 75 miles from the project I am at, with a magnitude around 4.9 to 5.1.
It shook lightly for no more than 5 seconds where I was at (shook the heck out of stuff at the epicenter!), but when I looked up, the Fire Sprinkler lines + HVAC Fan Coils were doing the "Twist"!

That "Dancing" got me going on this current Tirade [Linked Image]


edited to correct spelling blunders

[This message has been edited by Scott35 (edited 06-22-2005).]

Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Building Codes & Related References
Re: Seismic bracing for trapeze & Strip Ltg. #154376 06/22/05 06:32 PM
Joined: Oct 2000
Posts: 2,721
Scott35 Offline OP
Broom Pusher and
No takers on the "Movers and Shakers" subject.


Oh well, I'll give myself an "A" for effort! [Linked Image]


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Re: Seismic bracing for trapeze & Strip Ltg. #154377 06/22/05 07:28 PM
Joined: May 2002
Posts: 1,716
Roger Offline
Scott, I didn't mean to ignore you, but even though we do have some Seismic Bracing requirements here in N.C. (yes it's true) I don't think I can meet your question with a quality answer from this side of the USA. [Linked Image]

Believe it or not, we have to have our in house engineer (likable person, as you are too [Linked Image]) actually sign off and seal our supports and sway installations on some hospital projects.

I wish I could give a more informed opinion, but I have only felt one earthquake in my 50 years, and that was hundreds of miles from here about 4 years ago, I think. (the age thing [Linked Image])


Re: Seismic bracing for trapeze & Strip Ltg. #154378 06/22/05 07:59 PM
Joined: Aug 2003
Posts: 1,374
Ryan_J Offline
I have the same feelings as Roger. I have never seen Title 24, so I am afraid I would be blowing smoke if I said anything. Sorry Scott, I think you know I would help if I could [Linked Image]

Ryan Jackson,
Salt Lake City
Re: Seismic bracing for trapeze & Strip Ltg. #154379 06/28/05 01:44 AM
Joined: Oct 2000
Posts: 2,721
Scott35 Offline OP
Broom Pusher and
Roger & Ryan;

Thanks for the replies!


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Re: Seismic bracing for trapeze & Strip Ltg. #154380 06/28/05 10:18 AM
Joined: Jul 2004
Posts: 9,558
gfretwell Offline
It is interesting that title 24 is not on the California statutes web page. It skips right over that one.

Greg Fretwell
Re: Seismic bracing for trapeze & Strip Ltg. #154381 06/29/05 06:01 PM
Joined: Feb 2003
Posts: 67
pwood Offline
The seismic restraint systems are designed by the project engineer.section 1632.A of volume #2 of the calif. bldg. code has the way to get to a designed system.i would request calculations and a system of is not like the good old days or rule of thumb world i use to work in!

Re: Seismic bracing for trapeze & Strip Ltg. #154382 12/03/05 12:06 PM
Joined: Jul 2005
Posts: 56
Paul O'Connell Offline

Might I suggest you contact your local Strut Rep. I know Bee Line does and I think Unistrut does publish a book on seismec specifications and how to do them. Great reference and design manual for sparkies in those areas requiring them.

Re: Seismic bracing for trapeze & Strip Ltg. #154383 01/08/06 01:43 PM
Joined: Aug 2001
Posts: 599
Nick Offline
Sorry for the late response. I haven't been here much lately. EMT is not sufficient under any circumstance for seismic support. The calculations are pretty complicated too. We are always responsible for the design by spec and use either ISAT through Tommarco, Mason Industries or power strut. They do the seismic design based on our rack layout and conduit quantity and sizes. Then they supply kits for each required seismic location. I can give you contact names for future reference if you would like.
We try and stay with cable bracing as it is cheaper than strut and can be used when the vertical rack length is more than 10ft. We are in a spot right now on the Orange County Water District job I am doing where cable bracing is not allowed and we have massive amounts of cable tray with vertical rod lengths of up to 15ft. Strut is only good to about 14ft on the angled bracing so we are looking at having to install tube steel bracing. It gets really expensive in situations like this. This is also a NEMA 4 area so the tube steel will probably have to be 316 stainless.
I have a couple pictures of an impressive three tiered seismically braced cable tray installation that seems to be on my work computer. I send it in Monday to be added in. It had to be hung with 3/4" rod (they originally wanted 7/8" rod)and each tier is braced with double strut.
When designing seismic bracing you have to take into account things like rack size IE: conduit count, conduit size cable tray weight per foot rack width and max load distance from support rods. Conduit weights are always calculated at max fill. You take into account rack spacing, rod length, weather you are using cable or strut. In the calcs the rack hight above grade is a factor. If you are running on the sixth floor of a building it is going to react differently than on the ground floor. I have even seen a factor for the soil condition the building is built on and most engineers want a safety factor built in on top as well.
I understand the basics of seismic bracing but am in now way qualified to officially do the calculations. The always have to be stamped by either a civil or structural engineer anyway so it always gets sent out for design. Now, if you are dealing with any hospital work where OSHPOD is involved, well that is a whole new thread!
I am going to send you an excel spread sheet one of my project managers made that I use to help in rack design and layout. It is intended to help get us going while the seismic is being designed. It helps us make sure our rod size is sufficient and that we are not overloading the strut. It also lets us know if the seismic locations are going to require vertical rod bracing among other things. I can't help designing a bracing system per California regulations but I can connect you with people that can!

Re: Seismic bracing for trapeze & Strip Ltg. #154384 01/13/06 04:35 AM
Joined: Oct 2000
Posts: 2,721
Scott35 Offline OP
Broom Pusher and

Received the Spreadsheet. Thank you for the helpful information + tool!

All others, thank you for the replies.


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
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