Regarding item 1, I use my shear wall deflection program and adjust the
plywood and nailing so that the deflection (horiz.) is approx. equal
for each of the walls within the same grid line. Any
Stan Scholl, P.E.
Laguna Beach, CA
I agree; I would use
a linear interpolation for hold down deflection as long as the uplift force
was greater than zero. The problem with the bolt holes is the very reason why
I try not to use these types of hold downs anymore.
- You don’t force
deflection compatibility along a grid line? In other words, if you have a
short shear wall in the same line as a long shear wall, you let them deflect
independently? If so, how do you rationalize the difference in the
deflections? Of course, it probably doesn’t make a lot of (practical)
difference either way.
- What do you use for
the deflection of floor to floor hold downs like metal straps?
- What do you use for
the deflection of hold down systems like Simpson’s ATS, Earthbound Impasse
system and Quake-Tie cable system?
Sent: Thursday, May 06, 2004
Subject: Re: Rigid vs. Flexible
Question about calculation of the
If the holdown is rated for 2000
pounds of uplift that results in 1/8" deflection, why not consider a linear
relationship for uplift. If the uplift force is 1000 pounds than the
holdown deflection is (1000)(0.125")/(2000) = 0.0625" uplift. The
relationship most likely isn't perfectly linear, but its probably not a bad
approach. If the shear wall is a 2:1 aspect ratio, than the horizontal
deflection is (2/1)(0.0625") = 0.125" deflection.
We have written our program
using this approach which self iterates to a solution where all walls and
frames must have the same deflection (tolerance cutoff of 0.005" between
maximum and minimum shear wall deflection). Forces to individual walls
are based upon all walls having the same deflection (pure
translation). Holdown sizes are checked on each iteration, and the
sizes automatically increased to the appropriate size for the given uplift
size. The holdown contributes greatly to the shearwall drift unless you
have a very stiff holdown. But if you assume 1/16" oversized holes for a
bolted holdown, and the shear wall is 2:1 aspect ratio, than you have 1/8" of
shearwall horizontal deflection just due to the bolt holes slip in the
wood post which is about 20% of your allowable drift for an 8 foot tall wall,
and you haven't put any load on the wall yet (assumption is that any
uplift on post must move 1/16" to engage the bolts to resist the
uplift). I have found that for the short walls, the nail slip and
holdown movement are the major contributor to shear wall