I am a contractor located in Los Angeles,where my engineer calls for a threaded rod of 7/8" dia. placed into exiting concrete footing (24" deep) and then 6" embededment into a 12"x24"24" unpinning concrete pier with a 4"x4"x.25" washer plate attached to the end(in new pier). My question is, does the threaded rod that passes thru the existing conrete footing need to be epoxied or will the uplift force resistance by the threaded rod with the 4x4 washer on the end be enough?


   7/8" Thd. Rod            
____|__________________
    |  (e) footing    |
    |                 |
    |<- Epoxy?        |
____|_________________|
|   |                 |
|   |                 |
|  _|_                |
|   |                 |
|                     |
|                     |
|      (n) unpinning  |
|          concrete   |
|_____________________|

That is a question for your engineer.  We don't have enough information to answer, and ethics would prevent us from answering if we did.

thanks for the reply, but what does code say about this application. My building inspector say usually the epoxy is not applied.

From what I understand, you basically have a thru-bolt.  What would determine whether epoxy is required for strength reasons depends on whether the washer bearing on the new concrete is strong enough to develop the full strength of the threaded rod.  If it is not then epoxy would be needed to help distribute the load to the concrete along with the bearing of the washer on the new concrete.  Your engineer should be able to answer that for you.  

Being in Florida, I cannot help you with code requirements in California since I am not familiar with them.  I would say that if your existing footing is in bad condition, I would recommend the epoxy to help hold everything together and act as a unit.

It's easy to say that when in doubt, go stronger.  I know I have not given you a "yes" or a "no", but like I said above, we cannot do that here.  Your engineer should be able to help you out with the requirements.  These are only my opinions and things I would look at if it were up to me. Please consult your professional before taking any action or making a decision.  

I'd second UcfSE and go talk to your engineer.  The situation is unique so there really isn't a way to reference a code section.

It appears that your engineer is trying to develop the shear cone for the pullout of the rod.  I'm not sure from your description exactly where the rod is placed in the new concrete, but even if the rod was placed at the bottom of the existing footing (and it was perfectly smooth), there would be a shear cone that can be calculated for some sort of force, depending upon the existing concrete strength and the condition of the existing concrete.

As far as the epoxy grout, it may or may not have been specified, but I would only use it as a positioning tool and not depend upon any strength between the side of the drill hole and the threads of the rod.

This can also get more complicated if there are a number of rods to be placed this way and the shear cones begin to overlap.  The analysis for this is in Section 1923 of the UBC.

OldPost,
you are exactly correct, in dicussions with my engineer the epoxy of the threaded rod does not appy, he specified it only for positioing purposes with placement. no strength derived for calucating moments.
thanks