Wind Loads on Open Structures 1

[eit09]

I am interested in wind loading on open structures. I am talking about the structure only not any equipment. I apply wind load to the first member in each plane. For every member behind the first member (assuming first member is > member behind)I assume shielded so apply no wind load to those members. I was just told that I cannot assume front member shields the wind. Why can't u assume shielding from first member?

 

[JoshPlumSE]

What happens when the wind comes from a slightly oblique angle? Let's say 5 or 10 degrees. How much shielding will that front column provide? Probably not much.

That being said, I believe the standard practice for industrial structures is to assume a certain level of shielding. But, it is a greatly reduced level compared to the assumption that you mentioned.

 

[eit09]

As for the wind coming @ an oblique angle I assume that my LC's take care of condition from WL case #3 from ASCE7-05.

 

[JoshPlumSE]

The point is that a front column can only provide shielding to columns behind it if everything lines up perfectly.

That may not be a bad assumption if you can guarantee that the wind comes from one of the two orthogonal direction that define your rectangular column grid. Of course, you have not control over where the wind comes from.

If you re-define your wind loads to come from directions that do NOT line up with your project grid (say 15 degrees and 105 degrees) then the rear columns are "askew" from the front columns and you would not assume that they are shielded by that column..... Hence the reason why the codes are very cautious about allowing you to rely much on shielding to reduce your applied wind forces.

 

[eit09]

Ok thanks I will put a note on my drawings for which direction the wind can blow .

JK, thanks for the replies that makes much more sense to me now!