] [Thread] [Date] [Author]

["Swingle, Mark" <Mark.Swingle(--nospam--at)dgs.ca.gov>]

"Sorry, I might have lost my temper...."

(MS)  Dennis, I am sorry too, I do appreciate your efforts and persistence.
I guess I have just lost my patience, and I was trying to get your
attention.  However, my tone was uncalled for.
-------------------
"There can be only one answer.
1. If the diaprhagm deflection is less than 2 times the story drift the 
analyisis distribution of shear through the diaprhagm is calculated 
considering the contribution of shear from torsion in the diaprhagm.

2. If the diaprhagm deflection is equal to or greater than 2 time story 
drift, the shear may be distributed through the diaphragm by tributary area.

3. A combination (envelope) of the above."
------------------
(MS)  Perhaps it is only my inability to write clearly, because you
apparently still don't see what I am saying.  I will try again.

1.  Within item 1 above is a whole range of possibilities, not just one
answer.  The range includes 100% rigid at one extreme and 100% flexible at
the other extreme.

2.  Item 2 is one of these extremes, that of 100% flexible diaphragm
(tributary force).

3.  By item 3 I assume you mean using the highest force obtained for each
wall using each extreme method.  The code does not require this, however,
you may do it if you like.

The code says you use item 2 above if the diaphragm meets the test (>=2x).
Or use forces derived from item 1 if the test is not met (<2x), but that's
the hard part.

What I hope is that we can move the discussion beyond what the code says and
toward developing the analytical tools required to comply with what the code
says.  (I also think that we should continue to lobby to have this portion
of the code changed, with whatever means there are available to us.  That
will be a different post.)

I know you have spent considerable time in using the sw deflection formula
for wood walls.  I am interested in your thoughts and/or experience with the
use of these formulas.  The most important piece in this puzzle is the
stiffness of the WALLS, not the stiffness of the diaphragms.  I still don't
know how one can determine the forces to the walls assuming 100% rigid
diaphragm when the shear wall deflection equations are so poorly defined,
limited in scope, subject to interpretation, and non-linear.  I would be
interested in your methodolgy with regard to determining wood sw
stiffnesses.

Mark Swingle, SE
Oakland, CA

Disclaimer: these are my own opinions and are subject to change.