HVAC Support Spacings ... can I get farther?

[RandomUserName]

I need to get a piece of duct work...

36"ø
galvanized steel
internally insulated
spiral seam
24GA
2" wc pressure rated

...from one building to another.

SMACNA "HVAC Duct Construction Standards - Metal and Flexible" states in Table 5-2 that I can support at furthest every 12 feet.

Thing is my building spacing is over 14 feet apart.

Besides building a monstrosity of a 30 ft+ tall support structure in between the buildings, is there any way I can increase the distance I can span my duct work? SMACNA "Round Industrial Duct Construction Standards" says in Table 8-1.1 That if I increase duct gauge to 16, I can span up to 20 fee, though chapter 8 says it is limited to indoor applications without weather conditions (wind, ice, and snow load). Any other ideas?

 

[Drazen]

you cannot use outside building wall as a support, duct need to be mounted loosely, and gap to be sealed, and support put nearby.

you can find detail for protrusion through building expansion joint and apply it.

as for suspension, i believe you have to make support rail all along the duct.

 

[Wilbur55]

If the walls are tall enough above the duct, think suspension bridge. A single support at center span might be suspended with a V-shaped cable affixed "high enough" on the walls.

Simple sketch linked.

Now, what about the wind that wants to blow the duct sideways?

Can you discuss with a structural engineer?

 

[msquared48]

I agree with Wilbur, but you have to think uplift as well as gravity along with wind and seismic lateral forces.

With diagonals capable of resisting tension and compression, as well as the wind and seismic, this is very doable. Incline the verticals to the sides as well as vertically, and use steel angles.

Mike McCann
MMC Engineering

 

[kacarrol]

Adding on to msquared48.....you may have to also add in snow load.

 

[Waramanga]

Add in structural engineer with appropriate expertise and PI