All Thread A615 Rebars in Lieu of F1554 Anchor Rods?

[JennyNakamura]

I was asked to review calculations and drawings for the foundation design for an out-of-state supplier of wind turbines. I noticed on the drawings that they called for #7 A615 Grade 75 "Anchor Bolts" and immediately marked the drawings and calcs that A615 Grade 75 is a rebar designation, and that F1554 (Gr 36, 55, or 105) was the proper spec for "Anchor Rods." After an internet search, I have now seen that there are in fact A615 Gr 75 all-thread rebars, though it appears they are mostly used in soil nail and ground tie-back applications.

Is this a common anchor rod spec the wind turbine industry? Is there any reason that I should reject the calcs and ask that they be based on F1554? Is there any ACI or other code provisions that address this? If it is code-compliant and OK to use A615 all-thread rebar for anchor rods, are there any other negative things I should be aware of?

Thanks in advance.

 

[JennyNakamura]

Forgot to mention they are straight anchor rods with nut and washer at the embedded end.

 

[Lion06]

I think it should be ok (as long as the calcs check out). We recently used 150ksi all-thread bars (A615) for anchor rods on a 30-story building. The A615 designation is letting you know that the "threads" meet the deformation requirements of A615.

 

[dik]

I've used Dywidag threadbars for decades for high strength anchor rods and used the tension development length based on rebar. The only downside to using a proprietary type of threaded rebar is that the attachment nuts are quite costly. You don't normally use the proprietary nuts on the embedded end as the development length is based on the bar deformation.

Dik

 

[hokie66]

In Australia, we often use regular reinforcing bars, threaded in the shop to receive a nut. These are 500 MPa steel, about 70 ksi. You have to allow for the reduced threaded area, and also the outer part of the bar is stronger than the interior. The reinforcing steel producers publish loading data for the various sizes. For high strength bars, there are several proprietary products, e.g. Dywidag, Macalloy.

 

[JLNJ]

I have seen these commonly for large substation tower anchorages.

 

[BigH]

Question? Does the steel know that it is A615 or F1554?

Did the OP do a side by side comparison of the material properties - both mechanical and chemical to show that the steels are different?

We get this all the time when an ASTM spec is given and the contractor (we are in Asia) proposes a JIS (Japanese) or EN(European) grade instead. We then look at the steel properties - not the title of the particular "Standard."

 

[JennyNakamura]

Steel is steel - any engineer with a week's worth of experience knows that. But if the legally binding contract documents, including 3 2-inch volumes of specifications that specifically call for F1554 anchor rods and not A615 rebars, it becomes a legal question of liability, because lawyers don't know anything about material science no matter how similar (or even identical) the actual materials maybe. This is a US project, and F1554 and A615 are both US standards. I am well aware of JIS and EN standards as I work with both of them on a regular basis. I am well within my rights to reject the entire submittal without wasting any additional time on it and going home on time, but I am trying to do the contractor a favor and make sure there are no reasons based on the practical experience of others why the submittal would not be acceptable. So I spend a couple of hours on my own time without submitting a change order request to the owner like the contractor would in order to research the issue the best I can so I can accept the submittal and make everyone happy.

 

[BigH]

Didn't mean to upset but then I don't work in the States. We have far too many other problems as well . . .

 

[ToadJones]

Lion- do you mean that the threads meet the deformation requirements of A615 in terms of bond with the concrete?

 

[Lion06]

Toad-
Yes.


Jenny-
I don't think drawings and a spec calling for F1554 mean that you can't use threaded rebar. What I would do, however, is this. I would ask them why they want to deviate from the contract. You know it's about money, but get them to say it. The contract says F1554, so they bought F1554. Once they say it's the money, then ask how much of a credit the owner should expect back as a result of the change, if it can happen.
I'm sure they either 1) priced what they're proposing now or 2) priced the F1554, but can get what they're proposing cheaper. In either circumstance, they probably have no intention to credit the owner, unless you call them on it.

 

[10k]

You should be very careful with substitutions for anchor rod material. The design engineer may have (should have?) selected the material and size to provide for the recommended ductile failure of the bolt before the concrete. F1554 material has ductility requirements that even bolts made from A36 material can't match. Bolt manufacturers out there, such as Portland Bolt, will be able to comment more specifically about the comparitive ductility of A615 Gr75.

 

[Lion06]

10k. If the anchor meets A615, there is no concrete failure per App. D, because it doesn't apply to rebar. You just use the required development length of the bar.

 

[dik]

In my drawing notes, I require that anchor rods be weldable... something other steels cannot meet. Too many problems with things being out of location... just a tad.

Dik

 

[10k]

Lion06 -- You seem to be saying that ductile failure isn't a desireable failure mode. What am I missing here?

 

[Lion06]

I'm not saying that, but what else would you get with rebar in concrete. The bar will yield and that's kind of the end of the story. There is no concrete breakout with rebar.......... unless I'm missing something.

 

[slickdeals]

This has always baffled me.

Use an all-thread rebar meeting A615 specs and provide at the edge with a 2" cover in epoxy and enough development length and voila, you have the full tensile capacity of the rebar.

Then you take an all-thread rod and epoxy it in 24" into concrete with a 6" edge distance and all hell breaks loose.

 

[10k]

Lion06 -- Nothing is failure-proof. The ductility requirement is imposed to cover unexpected or unforseen overstress situations. Basically what it tells me is that we need to consider the ramifications of the mode of failure. Ductile-type failures have a degree of forgiveness that brittle-type failures don't have. That's one reason why steel is such a great building material. To read this argument from learned academics, see ACI Technical Journal Paper 92-S9 on CCD Design, Jan-Feb 1995, or PCA publication "Strength Design of Anchorage to Concrete", (R.A. Cook), 1999 (be sure to get the errata that corrects a statement saying; ..."all" typical anchor materials satisfy ductile requirements... to "about 1/2 of" typical anchor materials satisfy...

 

[Lion06]

10k-
I understand what you're saying, but please explain to me how you get a non-ductile failure of a rebar fully embedded and developed into concrete.

 

[JLNJ]

Does A615 material meet appendix D's tight ductility requirements?