Vertical Wind Load Distribution

[mjs611]

I am discussing how to find the reactions at each diaphragm over 2, unequal stories. When finding the reactions at each diaphragm, do you analyze as a continuous member or do you use simple span analysis?

i.e. 20 psf wind load; first story height=20', second story height=10'. With simple span the reaction at the top and middle is 20psf*10'/2=100 plf and 20 psf*(10'/2+20'/2)=300 plf. Using continuous beam analysis, the reaction at the top & middle are 25 plf & 412 plf, respectively. It creates a significant difference.

Thanks for your input on what should be an easy question!

 

[Once20036]

I think it's going to depend on your façade.
If you have brick supported on a shelf angle at every floor, you don't have any continuity across diaphragms and I would use a simple span analysis.
If you have a fancy curtain wall that's continuous over 5 stories, I'd analyze it as a beam with six supports.

 

[jayrod12]

Agreed with Once20036, it depends on the framing details.