CMU rebar positioner conflict with wire-tie contact splice? 4

[BSPE90]

In our specs we say to use rebar positioners to center the bars in the CMU walls and also to use wire ties for contact splices. I got an RFI for a project out to bid saying that rebar positioners are designed to space the bars so they do not contact each other to allow grout to flow between the bars so wire tying would not permit that.

We never had this question come up before. My understanding is that the positioners would just be used where there isn't a splice, only to center the bars in the CMU wall and the wire ties would still be used for a proper contact splice, where required. So both would rebar positioners and wire ties would still be used in the wall construction

Am I missing something here?

 

[r13]

I would ask the contractor to submit the source that ban the use of wire ties in CMU construction. He can have his way if the document is acceptable and approved by the engineer/owner.

 

[BSPE90]

They are saying that there is nothing in the NCMA literature that suggests wire tying will gain any strength (almost verbatim). To me, they are saying the rebar positioners would act as the tie to splice/lap the vertical bars. I guess it would work if you tie the bars to the positioner itself. But I have not actually seen rebar positioners used in person. All I know is that they are used to correctly locate the bars in the CMU but not sure if they have the capability to "tie" two bars together.

 

[r13]

1) The contractor's claim on strength gain by use of wire ties is correct - no gain, no harm.
2) Depending on the add'l spacing between bars, it might trigger the non-contact splice requirement, which results in longer splice length. But again, it is a no gain, no harm situation, if the bar can be properly positioned per code requirement (will it result in less side cover distance?).
3) The contractor seems playing a game in effort to discredit the correctness of the designer. Be careful.

 

[BridgeSmith]

The wire ties don't make the splice; the concrete does. As long as the lapped bars are not farther apart than what is allowed (in CIP concrete, it can be up to a few inches), the lap is acceptable. The wire ties are just a convenient way to keep the bars together while the concrete is poured.

If the positioners are sturdy enough to keep the lapped bars close enough together to be considered lapped while it's grouted, it shouldn't be an issue.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[r13]

Ask the contractor to submit the spec of the spacer to be used, and sketch the detail of the application to ensure the case in the middle of the sketch below will not occur. The detail on the right is another argument against the contractor's claim on strength gain through add'l bonding, unless the thickness of the spacer is negligibly small.

 

[bones206]

I think they are trying to say that the bar positioner creates a gap between spliced bars, but the spec calls for a contact splice with bars wire-tied together. You can have one or the other, but the gap caused by the positioner precludes a contact splice. They are probably envisioning this type of positioner:

 

[r13]

bones206's comment makes sense.

 

[dik]

bones... nice... first I've seen that. My life is becoming too sheltered. I'll use that in future.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

or maybe...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[BridgeSmith]

Looks to me like they could, and should, do both. Anyway, without tying them together, what keeps the upper bar from falling down to the bottom of the wall?

Rod Smith, P.E., The artist formerly known as HotRod10

 

[r13]

Other than bones206 provided, I guess this is what the contractor had in mind. If this is the case, I vote against it, as it could be problematic for the quality of grout around the splice.

 

[bones206]

Anyway, without tying them together, what keeps the upper bar from falling down to the bottom of the wall?

If the grout is placed in lifts, then the splice starts at the top-of-grout elevation. After the next several courses of blocks are laid, the rebar is dropped in from above and the end of the bar rests on the grout. If it is high-lift grouting, the bar is dropped in from the top of the wall but may rest on the top of foundation where it splices with the first dowel.

This figure from NCMA Tek 03-02A illustrates where you would typically see splices:

Masons have different ways of doing things, so as long as the final rebar condition is code-compliant, I’m not really too hung up on how they position the bars or hold them in place for grouting. I think the OP’s spec just has some boilerplate means-and-methods requirements that cover different scenarios and the mason is being diligent to ask the question and clarify the engineer’s intent before commencing work.

 

[masonrygeek]

A lot of this discussion is means and methods. Bridgesmith had it right by saying that wire ties don't make the splice, its for convenience. All of the sketches that show the bar being wired together are not necessary. Noncontact lap splices are allowed as long as the requirements of Section 6.1.6.1.1.3 (2016 version) are met, which includes bars in adjacent cells where bars are not more than 8" apart. So long as the mason keeps the bar in the right place, they can use whatever method they want. Some inspection during grouting (as is required by TMS 402/602) would help assuage any fears.