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RE: aci318 app d rods vs. rebar

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Bar to concrete development depends on a mechanical lock and an adhesive bond.  The adhesive bond is a function of the surface condition of the bar.  That is why you get a different value for epoxy vs. plain bars.  The mechanical lock is a function of the deformations on the rebar or the threaded bar as may be the case. 
Look at section 7 & 8 of the ASTM A615 that defines the deformations that rebar must have for the mechanical bonding of rebar to concrete.  There is no similar requirement for threads.  Further, there is no requirement for threaded rod embedded in concrete to be of any particular kind of thread.  Granted, most will be UNC, but the threading varies with the diameter of the rod no matter what threading is specified. 
There are manufacturers that have threaded bar that comply with ASTM 615 so you get the best of both worlds.  One manufacturer is Dywidag  Another is Williams  They are commonly used for rock anchors and for box segmental concrete design. 

Regards, Harold Sprague


From: pffei(--nospam--at)
Date: Tue, 19 Jan 2010 12:06:22 -0500
Subject: aci318 app d rods vs. rebar
To: seaint(--nospam--at)

Can anyone clarify why the tension and shear development of threaded anchor bolts (aci appendix d)  treated so differently than rebar?  the calculations for rebar development for shear friction and tension are much simpler than threaded anchors.  It is seemingly much easier to develop the capacity of rebar in concrete than an anchor rod and the impacts of minimal edge distance are much less.  also, section 1908.1.16 of the cbc has a further reduction on capacity of threaded anchors if subject to seismic loads.  there does not see to be a similar provision in the code if rebar is used tor the anchor element instead of a threaded rod. 
I have found little literature on deep embedment of threaded anchors, but why couldn't depth to develop tension capacity of a f1554 grade 36 rod be treated similarly to the same diameter of grade 60 rebar?
Thanks in advance for any discussion on the matter.
Paul Franceschi

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