ACI 318 Appendix D and rebar development 1

[tvar]

A question, I have been asked to review some calculations and they are using Appendix D to calculate the development length of building pier dowels into a drilled pier. I believe that the dowels don't fit the definition of an anchor so Appendix D doesn't apply the length should be calculated using Chapter 12 "Development and Splices of Reinforcement"

 

[TehMightyEngineer]

A sketch would be useful to see your forces being transferred.

My answer is if they're trying to transfer the forces into additional reinforcement via lap splices or struts. If not then I agree with their choice of using Appendix D. Further, even with force transfer to other reinforcement I still would likely check appendix D to ensure there wasn't a failure of the concrete pier (but it wouldn't likely be the controlling force in determining the tensile strength developed in the bar).

For further details I hand the floor over to KootK who will undoubtedly show up.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

http://www.americanconcrete.com

 

[jayrod12]

Have you checked out the HiltiRebar web program? It's geared towards almost this exact problem.

 

[tvar]

Thanks for the quick response I should have made my problem a little clearer. The anchor rods into building pier checked per Appendix D. The question is the splice length required for the(12) - # 11 vertical dowel bars that tie the building pier cap to the 8' diameter drilled pier and splice with the (24) - #11 in the drilled pier. There is a moment on the top of the drilled pier hence there is tension in some of the vertical dowel bars

 

[tvar]

Appendix D comes up with a development length into the drilled pier of 5'-6" and Chapter 12 7'-1"

 

[sandman21]

Per ACI 318-11 D.4.2.3 the limits on embed per Appendix D is 4d to 20d.

 

[KootK]

Check out this thread for some concepts. Based on the information that you've told us, this sounds like non-contact lap splicing in excess of 6" which is often best handled with something similar to strut and tie modelling. Appendix D would not be appropriately efficient and plain development may not be sufficient.

If Appendix D were applied properly and showed enough capacity, that would probably do on it's own. Based on the calculated length, however, it doesn't sound as though it was applied properly.

Let us know how your situation may differ from the sketch below.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[tvar]

The sketch is very close to the actual situation, the only difference is that the (12)- #11 have hooks on top in the pier and the ties in the drilled pier seem to be light at #4 @ 23" spiral. Like I said above Chapter 12 gives a minimum of 7'-2" but based on the actual geometry I think it should be more.