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RE: Concrete anchorage (ACI 318-99 appendix D)

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To all:

We went through this a little bit with the flexible diaphragm retrofit ordinances in the City of Los Angeles.  You are correct, the anchor sizes that correspond to the holes in the baseplates of the HDs are WAY too big!!  You are not usually going to be able to yield any of the anchors that connect to them.  A simple fix for this is to size the concrete anchor correctly (for yield) and then put a square plare washer in the base of the hold down.  We have supplied tens of thousands of our 3/8 and 1/2 inch stud DUC Undercut anchors to go into the big welded HD9s (made for a 1 1/8 anchor rod).  

However, it is probably a moot point anyway if you are using the listed capacities from the hardware manufacturers or even ICBO ES.  You are probably going to get alot of ductility (? more like deflection) even at low load levels.  Then you can use 2000 IBC 1913.3.3.3 that waives tha anchor ductulity if you can put it into the connector.  

As I recall there is no deflection limit on the testing of these connectors.  So maybe that HD 20A design capacity is based on a deflection of over an inch.  What do you think happened to your shear wall nailing and sill plate anchors at that point after you lifted that wall off the foundation for a few cycles (and watch out for the p-delta when that wall tilts like that).

Just my 10 cents..

Howard Silverman, PE
Covert Operations, Inc.

In a message dated 6/25/2003 6:40:27 PM Eastern Standard Time, "Haan, Scott M." <HaanSM(--nospam--at)ci.anchorage.ak.us> writes:

>Forrest:
>
>This is one case where I say where are the bodies? There should be an
>exception for wood shear walls.  I do not care what anyone can calculate the
>wood post with an HD20 is going to go before the 1.25" rod embedded 36
>inches in a foundation wall.
>
>There needs to be an exception in the code for wood frame construction.  I
>do not have a 2003 IBC and would like to see if an exception was added to
>IBC 1913.3.3.2.  If there is we could do a policy until it adopted in
>Anchorage.
>
>Respectfully,
>
>Scott Haan
>
>-----Original Message-----
>From: Forrest Braun [mailto:fbraun(--nospam--at)bbfm.com]
>Sent: Wednesday, June 25, 2003 1:09 PM
>To: seaint(--nospam--at)seaint.org
>Subject: Re: Concrete anchorage (ACI 318-99 appendix D)
>
>
>Jake
>
>I was hoping that there would have been some response on this issue
>following your earlier post.  The IBC section 1913.3.3 (ACI D3.3.4 and
>5) is indicating for seismic categories C, D, E, and F, that the anchors
>are to be designed for the strength of a ductile element.  It appears
>that based on these provisions, hold downs in wood shear walls will be
>impossible to use since the embedment, and edge distances will not allow
>capacities great enough to yield the anchor.
>
>> Jake Watson wrote:
>> 
>> How many people have though about the new CCD approach and its
>> integration into the IBC?  Reading between the lines I have drawn the
>> conclusion that the new CCD approach & the IBC wants us to begin to
>> think of concrete connections the same way we think of concrete
>> beams.  Connections should be designed to fail in a ductile manner.
>> We are not necessarily making a better building by over-sizing
>> anchors.  But instead, we should design the steel to yield before the
>> concrete fails similar to a concrete beam.
>> 
>> Am I on the right track?  How many people still just use standard
>> "over-sized" connections that are strong enough, but don't fail in a
>> ductile manner?  Or is this another code provision that will be
>> repealed in a few code cycles?  Any thoughts?
>> 
>> Jake Watson, P.E.
>> Salt Lake City, UT
>
>-- 
>++++++++++++++++++++++++++
>Forrest T. Braun, P.E.
>BBFM Engineers, Inc.
>Ph (907)274-2236
>Fx (907)274-2520
>Anchorage, Alaska
>http://www.bbfm.com
>++++++++++++++++++++++++++
>
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