ventilation vanes integrity

[altswear]

I have a wind vane that is effectively a thin sheet of stainless steel bent into a quarter circle, meant to re-direct airflow.

I am trying to figure out if there are any standards or equations for determining the longest these vanes can span before buckling. Does anyone have experience with this?

Take a look at the attachment for a better picture. Thanks for any input!

 

[berkshire]

altswear
Those things are called turning vanes or runners. /The Sheet metal and air conditioning contractors national association SMACNA has a design manual on this. The relevant section is called "Vanes & Runners" and "Vane support in Elbows". They give the maximum unsupported length for the type of vane you have as 36" for a 22ga galvanized mild steel vane. Your stainless steel turn vane drawing does not give any thickness information , so it is impossible to determine the max unsupported length. The SMACNA book is available on a subscription basis from SMACNA in Chantilly Virginia.
B.E.

You are judged not by what you know, but by what you can do.

 

[altswear]

Thanks a lot berkshire! You've given me the most definitive direction so far in all my research! The turning vane on my project is 3/8" thick, a radius of 3.25 feet and an arc length of 6 feet. It is currently being asked to a span of 16 feet. Would you happen to be able to look up the maximum span of this item? In the meantime I will see if my employer has the SMACNA book or has the means to acquire it.

 

[berkshire]

altswear
A turning vane of that size and thickness would be outside of the scope and detail of domestic ductwork. So I do not think you are going to get much help there. The only time I have encountered turning vanes of that material size and thickness, was on Boiler Breaching work. i.e. smokestack ducting. The only other place was on Peaker gas turbine generating plants, deflecting hot exhaust gas into heat exchangers, for heat recovery. The only thing I can find on this, is an excerpt from Roarks on engineers edge

https://www.engineersedge.com/column_buckling/buckling-curved-plate-loaded.htm

Since you are a structures guy you should already have this. Anyway see if this points you in the right direction. If it is not proprietary , what are you trying to do with this?
B.E.

You are judged not by what you know, but by what you can do.

 

[Stick.]

SMACNA may still be relevant in this case. The Rectangular Industrial Duct Construction Standards (there's also a similar standard for round ducting) may have what you need, but I don't have my copy accessible to verify. It does have info on ducts made from 1/2" steel plate at least, so it's in the ballpark in terms of material sizes, so it's probably worth a look. Also, be aware that if you buy a pdf copy you are quite limited on what you can do with it (DRM type security stuff), so read up on the limitations if that is your chosen route.

Also consider to possibility of adding additional support stiffeners to help carry the load and increase the maximum span. You may also need stiffeners to deal with turbulence related vibrations depending on the flow you're dealing with.