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RE: Wood Shearwall Deflection Calcs

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Paul,

The value I am looking for is for the "Tiedown Elongation" which is:

(demand force (LRFD level)/ ASD Rated Capacity of Hold Down) * Tie
Deflection @ Allowable load from ICBO Report

Then you also check for nail slip, shrinkage and crushing in the tie-down
assembly and add them together to get total tie down device deflection.

When the contractor forgets to edge nail the hold-down studs, multiply by
(2/1.4) if you are using ASD :)

-gerard
SJ, CA

-----Original Message-----
From: Paul Crocker [mailto:paulc(--nospam--at)ckcps.com]
Sent: Thursday, January 03, 2002 2:50 PM
To: 'seaint(--nospam--at)seaint.org'
Subject: RE: Wood Shearwall Deflection Calcs


I am not familiar with the manual you are referring to, but I have estimated
deflection using one of the supplements to the '97 NDS manual a few times.
For that method, my understanding is that for a rod the deflection is
basically PL/AE plus any additional deflections that may occur due to
slippage in the connections.  I have been told by an engineer working for
one of the self-compensating hold-down products companies that the
additional slippage number is nearly 0 for their products and so PL/AE is
accurate enough.  For a strap, though, I imagine that there would be
additional deflection due to nail slip and due to small kinks and bows in
the strap between adjacent nails straightening out under tension.  Any
shrinkage in the wood would only make such a condition worse, as 1/4" of
shrinkage would leave 1/4" of slack in the strap that would have to be taken
up before it would be fully activated.  Whatever you come up with, keep in
mind that straps will be pretty unpredictable in that regard and probably
don't lend themselves to being calculated to the hundredth of an inch.  I
would not be surprised if that is why tables for straps are harder to find
than for other hold-down systems.  Perhaps someone else out there can point
you to some papers on it.

Paul Crocker, P.E.


-----Original Message-----
From: Gerard Madden [mailto:gmadden(--nospam--at)duquette-eng.com]
Sent: Thursday, January 03, 2002 10:46 AM
To: SEAINT LISTSERVER (E-mail)
Subject: Wood Shearwall Deflection Calcs


Question,

I am writing a spreadsheet to calculate drift for a wood shearwall. I have a
question regarding the Tie-Down Elongation for premanufactured hardware. The
Seismic Design Manual Volume ii, page 47, footnote 3 explains how to
calculate it. The question I have is regarding straps. My Simpson catalog
doesn't give the elongation value for straps, only for obvious hold-downs
like HD's & PHD's. Yet the example in the SDM shows values for .05 and .03
for walls 3 & 5 in the table respectively.

How are they getting that value? Are the just doing Delta = PL/AE or is it
something else.?

thanks,
-gerard


Gerard Madden, PE
Design Group Manager

Duquette Engineering
10 South Third Street
San Jose, CA 95113
T: 408.494.0944 - ext 102
F: 408.494.0940
E: gmadden(--nospam--at)duquette-eng.com
w: www.duquette-eng.com



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