Designing vertical duct support between floors with interstory drift

[SoiQHoang]

I have a 120" x 60" x 18 gauge vertical duct riser running from basement to 6th floor of a seven story building. I typically design the supports for gravity and seismic loads only, and assumed the duct construction is flexible where displacement of the duct will not generate too much additional force to the duct connection to the support at each floor. Has anyone design duct support for interstory drift?

 

[ishvaaag]

It depends on the application, and what extent of relative drift you want or need to stand. A basic tenet of seismic design is that both structural and non-structural items will sustain some damage under an earthquake event akin in effects to that imposed for design in the code. So you do not have to design always for functional survival of every non-structural item, undamaged. The earthquake event of such magnitude, except where precisely and expressly mandated, or required by the owner otherwise, is a matter of survival of the people, rather than keeping the building intact and functional at the event.

So you may choose a lower level of earthquake (or high wind) loading to which you want in any case your building remain entirely functional: for these cases the drift would be certainly a requirement for anything that has to follow it. You can either check your support points only demand a bearable level of flexibility and strength of your mechanical services, or you can modify your support and tubings to roll on supports and be flexible at bends to work well at such drifts.