High Strength Coil Rod 1

[astructurale]

I'm using High Strength Coil Rod for a column to beam connection. When anchoring the rod into the column I have an edge distance of 3 1/2" (round column, square rod pattern, 4 rods each 6" off CL and 90deg apart).

Since the rods are threaded they achieve better bond than a smooth bar. Can I eliminate the use of a nut at the end to anchor the rod? If so how do I calculate the embedment length needed to develop the rods? Or do I have to follow ACI 318-02 Appendix D? I would think that Appendix D does not apply becuase it applies to headed or hooked anchors only, and does not consider the bond becuase the test are for smooth rods only. Also, for just a coil rod I would assume that there is not an edge distance problem, but if I design it as an anchor w/nut at the end then I have to consider a side face blow out and concrete breakout.


Any help suggested.

 

[cap4000]

I was involved with threaded rods with no nut or hook and used Hilti's RE150 epoxy. I used Hilti's chart for their pullout values in tension. With your 4 bolt pattern there will be an overlap of the stresses and thus a reduction. Hilti has done many tests to determine the pullout values. Also, I have used a concrete bond stress of 130psi for 2 in.diameter rods and 260psi for 1 inch diameter when straight rods were just set into the concrete. Check the AISC (journal)website to verify these bond stress values. Hope this helps. Good Luck.

 

[astructurale]

Thanks cap! I appreciate the info. I've used Hilti RE150 before, but I was looking for a cast in solution. The bond stress vaules are a big help!! I'll check AISC to verify.

 

[astructurale]

I could not find the verification I was looking for in AISC. Do you have to be a memeber to find it? Write back please if you remembr or can find the name or date of the publication/article.

 

[cap4000]

Yes, you have to be a AISC member to get it for free."Anchor Bolt Design for Shear and Tension" 2 pages by Umesh Kharod in 1980 . His basic bond stress formula is:
u = 4.75 x 10*-3/2 x f'c*1/2 divided by Diameter of bolt in ksi. Tension Load (kips)= u x pi x D x Length of bolt. I hope this gets you in the right direction. Good Luck.

 

[astructurale]

Cap-

I downloaded the article. This article does not specifically address coil rods. The threads for coil rods are deeper than for normal anchor bolts, and normal anchor bolts are typically only threaded at the top for the nut. Also, I do not have a hook.

While the article is helpful, I believe that this information is likely superceeded by ACI-318-02 Appendix D, which is based on extensive research. Also, this article does not address all of the possible failure modes. You may want to refer to Appendix D for your future designs of anchor bolts.

Thanks for trying to help though.

I'm still looking for anyone who knows of any pull out tests done on high strength coil rods, to determine the applicable development length when cast in concrete without a hook, nut or washer cast in the end. I've considered using the development length of rebar comparing it to an equivalent diameter bar, but then I would be comparing a bar with 60ksi yield to one with 105ksi yield and deeper more compact grooves than the surface of re-bar.

It appears so far though that no one has done this research yet. Maybe someone will in the future...

 

[transmissiontowers]

I don't think the elimination of the nut is a good idea for smooth rods even if they are threaded. I believe the last edition of ACI 318 to give a value for pull out of smooth rods was 1963. Use a threaded rebar if you don't want a nut at the bottom. I seem to remember ACI 349 may say something?

I have designed anchor bolts out of A193-B7 (up to 3 inch diam) with a nut on the bottom for drilled shafts and the length depends on the vertical rebars in the drilled pier. You have to embed the a-bolts deep enough to fully develop the vertical bars where the 45 degree cone from the a-bolt bottom nut crosses the vertical rebar according to ACI 318 embeddment formulas.

I'm a steel guy and not a concrete guy so check my method out with a concrete guru.

You might also check out the Hilti Profis software CD that will tell you the Hilti product to use for any geometry.

_____________________________________
I have been called "A storehouse of worthless information" many times.

 

[astructurale]

Transmissiontowers-

I am not using smooth rod, but coil rod which is threaded the entire length.

Good points made!
For concrete breakout capacity you have made a point that I had overlooked. I was fixated on developing the coil rod, but I forgot that I don't have to embed the coil rod until the coil rod is developed per Appendix D design. Just embed enough to transfer the force through the cone to the longitudinal bars, since concrete breakout governs over steel failure.

Thanks...delima solved. And I'm also going to check out ACI 349 for my own information.

 

[transmissiontowers]

Oh, I see, you were talking about all-thread rod. I still think that the spacing between the threads will be too small to let them act like the deformations on a piece of rebar. If you don't like the bottom nut to initiate the cone, and the coil is a weldable grade, you could weld on a series of washers spaced a few inches apart to the rod so they would act like big rebar deformations.

Also, if the base plate you are bolting to, sits on leveling nuts rather than on the concrete, such that the anchor bolt can go into compression, you will need to make sure that you have sufficient concrete depth below the anchor bolt so you don't blow out the bottom.

_____________________________________
I have been called "A storehouse of worthless information" many times.

 

[transmissiontowers]

I googled up this on ACI 349

http://www.concrete.org/bookstore/LaunchCatalog.asp?ItemID=349297

_____________________________________
I have been called "A storehouse of worthless information" many times.