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RE: Is it just me?

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You're just checking for bending.  The NDS requires a bending combined with
tension through the net section unity check. Now you just gave all the new
plan reviewers something to hassle designers about until the rapture in 2012.


-----Original Message-----
From: Bill Allen [mailto:t.w.allen(--nospam--at)] 
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




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


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


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