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RE: Is it just me?

• To: <seaint(--nospam--at)seaint.org>
• Subject: RE: Is it just me?
• From: "Haan, Scott M POA" <Scott.M.Haan(--nospam--at)usace.army.mil>
• Date: Fri, 9 Jan 2009 15:41:58 -0900

```There was an article about this is "Structure" magazine or "Structural
it. It is hard to make laminated studs work even with composite action.  My
spreadsheet assumed each stud just grabs an equal amount of the moment.  I
think the reason Simpson says its on the specifier because by code it hardly
ever calcs out.

I wouldn't sleep tonight if I were you knowing all the walls the are going to
crack in half at the holdowns during the next big one.

-----Original Message-----
From: Bill Allen [mailto:t.w.allen(--nospam--at)cox.net]
Sent: Friday, January 09, 2009 3:02 PM
To: Seaint
Subject: Is it just me?

When specifying a Simpson PHD hold down, one of the footnotes reads "Post
design by Specifier." In looking at the HDQ8 in 2-2x4s, the capacity is
listed as 5,715 lbs. Based on an eccentricity of 3"(CL=1.5" + 1.5" for one
2x), the weak axis bending moment due to the eccentricity is 1,428 ft.-lbs.
Assuming the 2-2Xs are face nailed adequately to transfer VQ/I stresses, this
moment results in a bending stress of 3,266 psi on the gross section. The
allowable stress on a 2x4 DF-L section is of course quite a bit lower than
this, not even considering combined stresses.

Have I forgotten how to properly draw a free body diagram or is there
something else going on here?

Otherwise, is it misleading to list 2-2Xs with a hold down of this capacity?

Regarding the VQ/I stresses, if the height of the studs are 8 feet, then the
shear on the post is Pe/h = (1428)/(8)= 179 lbs. Then VQ/I =
(179)((3.938)/(7.875)=90 lbs/in. Using 10d FN (capacity = 115 x 1.60 = 184
lbs each), the spacing would be 184/90 = 2" o.c.

This doesn't seem right to me.

If the two studs aren't nailed adequately to transfer VQ/I stresses, then the
bending stress due to the eccentricity is even higher (6,528 psi) since S
reduces to 2x1.313= 2.625 in3 from 5.25 in3.

Maybe I should put away the calculator on Friday afternoons.

If anyone would care to shed some light on the calculations, I would be most
appreciative.

Thanks,

T. William (Bill) Allen, S.E.

ALLEN DESIGNS <http://www.AllenDesigns.com>

Consulting Structural Engineers
V (949) 248-8588 * F(949) 209-2509

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