# Flexible Diaphragm-Wind Loads



## Hromis1 (Dec 30, 2009)

Hi all, I have been going over a problem in the 7th ed Timber design book by PPI. There have been several strange approaches to problem solving in this book that bother me. I wanted to get get your opinions.

The problem in question involves WIND load transfer from a FLEXIBLE wood framed diapgram to an INTERIOR shear wall. The probelm does not call the wood diaphragm "FLEXIBLE", but I have never heard other wise.

In the SOLUTION to the problem, the book appears to treat the distribution of horizontal forces to the exterior and interior shear walls as if the diaphram is RIGID. IE given that the INTERIOR shear wall is at the mid point of the building, the shears are applied using the old 3/8, 5/8 5/8, 3/8 rule.

I would have never have done the calculations this way for a wood diaphragm.

now the per the ASCE 7-05, section 12.14.8.3.1 it explicitly says that lateral forces shall be distributed using tributary area. BUT.....

I cannot locate a similiar statement with regard to WIND loads.

I think this example problem is flat out wrong! It underestimates the wind load to the exterior walls.

What is your opinion?


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## McEngr (Dec 30, 2009)

Hromis1,

I agree with you. Even though we should design the diaphragm like it's a beam, the appropriate method is pretty simplistic as you say - trib area. In practice, I simply do the 0.5wl 1.0wl 0.5wl.

My Breyer book doesn't do it this way.


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