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Re: Retrofit Wall Anchorage

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In a message dated 8/3/99 2:09:23 PM, you wrote:

<< On page 2-18 of the code in the right
column about 3/4 of the way down the page, the paragraph reads "Rp is the
Component Response Modification Factor that shall be taken from Table 16-O,
except that Rp for anchorages shall equal 1.5 for shallow expansion anchor
bolts, shallow chemical anchors or shallow cast-in-place anchors.  Shallow
anchors are those with an embedment length-to-diameter ratio of less that 8.
When anchorage is constructed of nonductile materials, or by the use of
adhesive, Rp shall equal 1.0"

This brings up the question of what is the difference between a chemical
anchor and an adhesive.  This is unclear.>>

Chemical anchors are drilled into the existing member, while an adhesive 
connection would be a plate epoxied to the surface of the concrete.  Also, 
you don't always have to use a rod diameter that matches the hold down 
requirements.  Conventional hold downs can experience excessive deflection, 
which is addressed in the revised LA City values for HDs when used in tilt 
ups.  This usually creates a mismatch between anchor diameter and connector 
hole size.  A plate washer with an appropriate size hole can sit in the 
bottom of the HD, enabling you to maintain that 8 diameter embedment 
requirement, and not get ridiculous with the diameter.  I've seen 1 1/8" 
diameter rods embedded 4 1/2" : ).  I find it interesting that although 9 
diameters is good for A 307 or A 36, it may not be the case for higher 
strength steels or even some of the adhesive anchor systems with lower bond 
strength materials.

Finally, be careful if you are using a pure friction type expansion anchor 
for this application. ( I have never seen this done).  An undercut anchor 
that can develop full steel strength in tension works much better.

Howard Silverman, P.E.
Covert Operations, Inc.
Anchoring and Injection Systems
Long Beach, CA
(800) 827-7229