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Re: 3X Plates and Washers on Intermediate Anchors

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Chuck-

Trust me, we tested LOTS of conditions; per code & non-conforming. 

Wet at the time of construction OR e/q?

They don't fail from the load applied from  / through the AB; they fail from cross grain bending due to uplift allowed by wimpy HD's

But we do agree on.........

"The solution is good tie downs"

If you've got good HD's you won't fail the sill even if the AB holes are sloppy / over sized; it would pretty had to get only a single AB to bear.

btw you need to apply ~5000 lbf on a 5/8" AB to split a sill with properly sized hole (11/16")

again WAY more than a shear wall can deliver to a single AB.

Was the upgrading to 3x sills meant to address anticipated loads or sloppy construction practice?  My recollection that the CoLA changes were introduced address perormance deficiencies observed in Northridge structures not construction defects.

The engineers behind those changes mistakenly thought that the sills weren't strong enough.  They didn't (at the time) consider or even understand the role of that wimpy HD's played.  The were thinking "strength"  and failed to consider "stiffness"

IMO it was a case of "right answer"...... thicker sills but for the wrong reason  :)

fyi shear walls with sturdy HD's work just fine w/ AB's w/o nuts

over sized AB holes just allows the wall to slip until the AB's bear...............poor man's friction pad base isolators

Bottom line..............the HD is the key, all other issues are secondary.

Also Chuck if you read my original post, I only advocated leaving nuts of AB's "near" HD's (the ones within 12" of the wall end) so that the unintended uplift load path was reduced in stiffness so that it would not compete with the HD for uplift load. 

cheers
Bob

On 3/3/06, chuck utzman <chuckuc(--nospam--at)pacbell.net> wrote:
I'd intended to sit this one out....oh well. :o)

Bob, I think if  your test walls were representative of actual field construction you might have a different opinion.

Around here a real wall often has very wet plate stock with AB holes grossly oversize.  IMHO if & when the wall tries to resist sliding by bearing at the AB only, one or two bolts will bear.  As they fail in bearing/splitting, the load then transfers to one or two more & the sill begins to split along its length.

A well tightened AB with a square edged plate washer can bite into the sill & resist sliding.  The solution is good tie downs not loose AB.

YMMV
Chuck Utzman, P.E.

Robert Kazanjy wrote:
>>>Regarding the longitudinal splitting, what do you think caused that?<<<<

Inadequate hold downs..................

Slot cuts & overdrilling are already prohibited.

#x sills are overkill but a modern 2x is inadequate as well.

cheers
Bob

On 3/3/06, Bill Allen <T.W.Allen(--nospam--at)cox.net> wrote:

Joe –

 

If you are suggesting that the plate washers and/or the 3x sill plates are a result of such a practice, then you are saying (the way I'm reading your remark) is that it is O.K. to slot cut the sill plate and over drill the holes for the anchors IF one uses plate washers and/or 3x sill plates. Wouldn't it be better to prohibit slot cuts and over-drilling instead?

 

Regarding the longitudinal splitting, what do you think caused that?

 

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

ALLEN DESIGNS

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

-----Original Message-----
From:
Jnapd(--nospam--at)aol.com [mailto: Jnapd(--nospam--at)aol.com]
Sent: Thursday, March 02, 2006 10:39 AM
To:
seaint(--nospam--at)seaint.org

Subject: Re: 3X Plates and Washers on Intermediate Anchors

 

Bill:

You have probably see several of the Orange and LA County housing tracts that were done piece mill by the framing contractors.  Remember how they use to and sometimes slot cut the sill plates because it was faster to erect...time is money one house a day...

That; along with laborers that were told not to or were to lazy to change drill bits as they were drilling away on wood members.  Holes around sill plates were usually 3/4 -1" while using 1/2" anchor bolts.  This was confirmed after Northridge during site visits by several people..............so new City of LA interim memo.....now code.

 

Also at several apartment projects I and others investigated in the San Fernando Valley found sill plates split lengthwise along the AB line.

 

Joe Venuti
Johnson & Nielsen Associates
Palm Springs, CA