Seismic Bracing Electric Duct Trapezes

[anchorengineer]

I am trying to design seismic bracing for electrical duct trapeze supports. I have long hanging distances but mainly I have multiple levels of of trapezes. Also, the installer is hanging additional trapezes from various points along the supporting strut. There really is no rhyme or reason to their support. (See Sketch)

I want to isolate only the ducts requiring seismic restraint. I thought about adding a piece of strut above the ducts that require bracing, strap the ducts to the bottom of the new strut, and remove the existing straps holding these ducts to the existing strut below the ducts. The new rod and braces will be designed only for seismic loads. The existing will only be there for dead loads. (see sketch) Any thoughts?

Do I have to add rod stiffeners to the existing threaded rod just there for dead load or just to the new rod there for seismic bracing? Will the existing rods go into compression or do I not consider them?

Thanks!

Clarke Engineering Services, PC
Jobsite Engineering and Consulting

http://www.anchorengineer.com

 

[paddingtongreen]

If there are unimportant tiers supported by the same verticals, they will be excited by the earthquake just as much as the important ones. If the downcomers are rods,The vertical kick from the diagonal could be trouble if the aggregated horizontal force is high enough.

I don't want to go further, we did dynamic analysis for cable tray supports on the nukes. There is a danger that I might go overboard here.

Michael.
Timing has a lot to do with the outcome of a rain dance.