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Re: '97 UBC and Proprietary Shearwalls

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In a message dated 8/15/99 11:23:34 AM Pacific Daylight Time, 
chuckuc(--nospam--at)dnai.com writes:

<< Dennis --
 Why not tell the architect we now need a minimum aspect ratio of 2:1 for
 shearwalls.  >>

Chuck,
When an owner pays a million or more for a custom home on a golf course, the 
last thing they are willing to accept is a shearwall that will block their 
view. The public is uneducated in the importance of structural engineering. 
This is where the creativity of the engineer comes into play. It is simply an 
uphill battle with the engineer losing as he tries to restrict the creativity 
of the architectural industry.

I've used Hardy Frames on five homes now. On each project where plywood shear 
walls were used, the contractors simply disregarded the plywood wall's 
integrity and thought nothing of cutting through sole plates to install 
stacks, plumbing, electrical or drains. It was not a matter of what was noted 
on the plans as there were sufficient notes on every detail and sheet to 
prevent this type of damage. Care was taken to double stud plumbing walls to 
prevent damage to shearwalls and much more. Besides, there were simply not 
enough walls to relocate the plywood shearwalls so that stacks and 
protrusions could be considered.
The fact is that the Hardy Frames are more consistently constructed and 
predictable than plywood shear walls. Considering the limitations in width 
and heights, the stiffness is also predictable (if interpolation is 
acceptable).

<Sheathed shearwall's have a multitude of virtues:
a long history of good performance, great redundancy, excellent damping
characteristics, some idea about appropriate design load values, good 
economics,
and the carpenters know how to build them (more or less).  You cannot say the
same for Hardi-frames.>

I don't think you need to ignore a new product simply because it does not 
have a historic track record. The fact is that it has more tests to support 
it's performance (I believe the tests were done at U.C. Irvine) than is 
possible with plywood shearwalls due to the number of materials and variables 
to consider.
Regardless of all of the good values for plywood, the practical side is that 
the contractors destroys most of its value by overdrilling and overnailing. 
It did take contractors in my area time to get used to the Hardy Frame, but 
once they did, they believed that the installation was easier and cleaner 
than plywood - with less hassle from the building inspector.

Yes, there are other opinions on proprietary shear walls, but only time will 
really tell on these. As long as the test reports are supported in approved 
ICBO reports and City approvals, I see no reason why they should perform any 
worse than historical, conventional plywood walls.

I might be out in left field here, but I simply don't see where the holddown 
deflection (other than if installed incorrectly) makes much difference from 
one connector to another. I think that the nail elongation and wall racking 
has much more effect on the wall's deflection than the difference between 
0.0625" and maybe 0.09" for da.

What do the tests that Simpson has done show. Is the largest deformation in 
the deflection formula from holddown elongation?

Dennis