DBA, Coil Rod

[KimWT]

Hi!

These questions are mainly related with precast concrete industry.

1. I wonder why DBAs are used instead of mild rebars,especially for connection hardware design.

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If a welding gun is not used or minor help with Fy, I think there is no advantage to use DBAs.

2. Does ASTM cover coil rods? Why not, if there is no ASTM spec?

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Why are coil rods/bolts used instead of threaded rods or anchor rods?

Are coil rods good for permanent structure or connections?​

Thanks for your help!

 

[RHTPE]

I think you need to clarify your question(s).

Are you really referring to DBS, as in dowel bar substitute? Or perhaps DBR, as in dowel bar replacement?
You reference welding - in what context? Welding of most rebar (especially ASTM A615) is not recommended.
I do not believe there is an explicit ASTM spec for coil rod. Dayton's coil rod is stated to have a yield stress from 85ksi to 110 ksi.
Coil rod can be used effectively as reinforcing, but would require careful consideration of the yield strength. It would prove to have better pull-out capacity than a machine thread rod.
Coil rod's use in concrete construction has evolved over time, from its use with form tie hardware to many other applications. The rolled thread, is easy to press into a smooth rod (as opposed to cutting machine thread) and has self-cleaning properties with respect to cement paste remnants. Cement paste often renders a machine thread rod or bolt totally useless.

Ralph
Structures Consulting
Northeast USA

 

[wannabeSE]

I don't do much with precast. But , DBA's are Deformed Bar Anchors. Ease and speed of welding with gun is the only advantage I know over conventional welding pieces of rebar.

 

[KootK]

It's an interesting question and I'll be curious to see what our precast experts have to say. Some additional things that I like about DBA's:

1) It's my impression that you get good quality control on them which is important in weldable bar.

2) The deformations are concave in rather than convex out (rebar) which I feel makes them more conducive to welding and there for more conducive to quality welding.

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.

 

[KimWT]

1. Efficiency and better QC?
Isn't there any movement to make ASTM standard which will cover coil rods?

2. Economy? Isn't cost main reason when a coil rod is selected instead of a thread rod of F1554 Gr.105 for precast connections?

 

[Ingenuity]

Isn't there any movement to make ASTM standard which will cover coil rods?

William Form coil rod products are to ASTM A29 and/or ASTM C1018: Link

However, Dayton-Superior makes no reference to ASTM standards for its coil rod product/s: Link

 

[RHTPE]

Dayton may be able to provide the certs for the rod used to manufacture coil rod.
Might be worth asking them.



Ralph
Structures Consulting
Northeast USA

 

[KimWT]

I know many engineers use coil rods and coil nuts for precast concrete connection design instead of threaded rods...
And, they are very popular in concrete formwork.
...
Though concrete form companies may adopt ASTM as internal standard respectively, isn't there any industry-wide agreement
to unify standards?

 

[TehMightyEngineer]

1) We don't utilize these, we would typically use welded A706 rebar. I would also agree that they only really make sense if a stud welding gun is used, which neither of our plants own. We either hand weld any studs or bar we need, or farm out any stud welding to a steel fabricator.

2) We utilize coil rod in a lot of our precast to save time in closing and opening forms, lifting and handling, and other instances where the threads may not be perfectly clean and rapid installation and removal of the nuts helps speed production. This typically means we have a lot of coil rod and coil nuts hanging around and thus utilize it in other areas in lieu of threaded rod (of which we stock relatively little compared to coil rod). It also is cheaper and generally more readily available from our usual precast suppliers.

I'm almost positive you can contact Dayton or Patterson (or whatever supplier is used) and get ASTM certifications for their coil rod. I believe we've had to do similar in the past.

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

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