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Re: Load Capacity of a Holddown Post as a Compression Member

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Thor,
 
Some relevant pages from the Timoshenko's book can be seen at http://www.sgeconsulting.com/public/TIM.pdf.  I have to apologize for a typo in my previous post - in terms of critical buckling load, the concentrated force is almost 3 times more severe (not lighter) loading than the equivalent uniformly distributed force. 
 
With the slenderness ratio of 27, a 4x4, 8-ft tall post performs quite close to (within about 17% of ) Euler curve, so Timoshenko's findings are not that far from reality.  The shear wall end posts, most probably, are never loaded even close to the "pair of forces" level condition.  At the same time, "pure" columns are never designed as loaded with distributed forces.  So I hope we are safe - at least as far as our design is concerned.
 
I am pretty sure that somebody already has comprehensive test data regarding the actual behavior of shear walls.  Technically it is not a big deal - just put a bunch of sensors on plywood, studs, and hardware.  
 
Steve Gordin, SE
 
 
 
 
 
  
 
  
----- Original Message -----
To: SEAINT
Sent: Friday, August 06, 2004 9:18 PM
Subject: Re: Load Capacity of a Holddown Post as a Compression Member

Steve,

Wow, there's at least one under-designed column out there if what you say is
correct!

I wonder if Timoshenko's analysis that you speak of was for a "long" column
(wouldn't columns be "tall", and beams be "long"?).  My excercise in this
would have been with an 8-foot post, more of an intermediate column
(depending on cross-section of the post).

I agree that "real" shear walls act considerably differently than we
typically model them, even if they get built exactly as we think they will
(ha ha).  Someday I hope to probe into the (theoretical) case where the
average shear in a shear wall is only half of the actual shear at one end,
and the shear at the other end is zero at that time.....  This would be with
a uniformly loaded shear wall where the overturning moment is equal to the
resisting moment:  The SFD and BMD's for such a wall look exactly like those
for a cantilevered beam turned sideways.  Someday.....

Take care,

Thor

www.shearwalls.com




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