POSITION OF RE-BAR COUPLERS - ACI CODES 2

[peakpilgrim_imported]

Hi

POSITION OF RE-BAR COUPLERS - ACI CODES

I am using re-bar couplers in continuous beams. I am trying to find justification for where they are positioned in the
ACI codes but without success. I have tried 318, 315, 439.

The general concensus is that they should be staggered; top couplers between 1/4 and 3/4 of the span; bottom couplers in the first and last quarter of the span; concrete construction joints, where unavoidable, at about 1/3 of the span.

Is there any justification for this in the codes

Please advise

peakpilgrim

 

[KootK]

A mechanical lap splice is still a lap splice and, for the most part, I would think it prudent to locate them wherever one might locate a regular lap splice. I don't know of any mech splice specific code guidance however. No doubt there's something in high seismic design.

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.

 

[hokie66]

KootK,
Why do you say that a mechanical splice is a lap splice? I disagree.

There should be no technical reason to restrict the location of couplers if the full bar strength is developed. The only issue I know of is reduction of cover at the splice, as the coupler is larger than the bar. And then there is quality of installing the couplers, which is probably a good enough reason to place them other that at maximum force positions.

 

[KootK]

@Hokie:

1) A lap splice joins two discontinuous bars. Ditto for a mech splice.
2) A lap splice could be designed for full strength. Ditto for mech splice.
3) A lap splice is considered less reliable than no splice. Ditto for mech splice.

In my mind, we choose to locate lap splices so as to minimize the ratio of demand to reliable capacity. I don't see why this same logic wouldn't inform our choices when it comes to locating mech splices.


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.

 

[KootK]

Perhaps I should have simply said that a mech lap splice is still a lap splice. I simply meant to imply that similar principles ought to inform the placement of all kinds of splices. Clearly, a lap splice is a mech splice no more than a cat is a dog.

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.

 

[hokie66]

We'll have to agree to disagree. With a coupler, you don't have to worry about splitting stresses and such. Thus, couplers are allowed in tension tie members, but not lapped splices.

 

[KootK]

You can't propose a proper gentleman's disagreement and then proceed to fire one last shot over the bow Hokie. One must either set down their weapon and walk away in earnest... or debate on. Stick around. I rarely convince you of anything and it doesn't detract from my enjoyment of the attempt in the least.

There are a few code clauses, like the tension tie business, that create the impression that mechanical splices are more reliable than lap splices. I think it's misleading and a consequence of one -- or both -- of two things:

1) Usually these are situations where members aren't really being treated as true, composite, reinforced concrete. Rather, they are just steel tension members that happen to be encased in some durability enhancing concrete.

2) As a profession, I sense that we don't really trust our rank and file to properly detail these critical, zero redundancy disturbed regions. And, sadly, I agree with that position.

I think that this comes down to one question that I shall put to you. Do you believe that a mechanical splice is as reliable as continuous bar that has not been spliced in any way? My field guys have brought me two of these gadgets now that have seemingly spontaneously combusted during install. So You can guess how I feel about it.





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.

 

[hokie66]

I do have complete confidence in the couplers which I have used, Ancon and Reidbar couplers, but am not sure how available they are in your market. Would be interested to know the identity of the couplers which have failed somehow during installation.

 

[KootK]

Well darn. I was hoping that you would not feel that mechanical splices were equally as reliable as unspliced bars. My recommendations were predicated upon that. Personally, I don't see how any kind of splice could ever be as reliable as no splice. Even the mechanical splices usually introduce cold working of the rebar and additional human operations prone to error.

I'm actually going to withhold the identities of the coupler manufacturers. I don't want to be slandering them based on a couple of isolated experiences. I will say that it was neither Ancon nor Reidbar.

Some interesting, related ACI clauses:

24.5.7.3 Mechanical splices do not need to be staggered

24.5.7.3 Commentary. Staggering of mech splices is encouraged and may be necessary due to congestion. A little vague.

25.5.7.4 Tension tie splices should be staggered at least 30"

Take from that what you will.

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.

 

[TXStructural]

After typing a long explanation, I had to kill Firefox and lost it all. Koot is correct.

No requirement to stagger mechanical splices except as required for congestion or for in tension ties
318-14 Chapter 18 has requirements for seismic cases, particularly in special seismic frames and walls.

Tension splices are tested under ASTM A1034 to 1.25*fy in most cases. Because of this, while most designers keep them away from critical sections, they can theoretically be located anywhere along the length of a bar. There are no restrictions on where mechanical splices can be located in non-seismic members.

 

[hokie66]

KootK,
Maybe you can just tell me the type of coupler which failed. I don't like the tapered ones.

 

[KootK]

It was the kind where they have set screw type things coming in from the side. When we called the manufacturer about it, they made the mistake of initially insinuating that the problem might have been that it was exceptionally cold out when we did the install (it was). You can imagine how well that went over in up here in the great white north. We got kicked up to somebody more senior pretty fast and it became some plant batching, improper handling, reliability gong show that was way over my head. That or it was just bullshit.

Don't get me wrong, I like mechanical couplers and use them often. I just don't thin that their infallible.

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.

 

[BUGGAR]

Just for the record. We used Lenton taper-threaded splices on the (then) new Dumbarton Bridge. These couplers were new at that time. Specs required each coupler be observed during tightening and daily prepared samples were lab tested. In those days, slippage of the connector was the big fear. I forgot the failure rate but it was down in the 1% range. So I have personal confidence with this product if used with good quality control. That is all, carry on.

Kootk, I thought you were using a thermite splice.

 

[jdgengineer]

While I don't use mechanical splices very often, Chapter 21 has limitations on locations of Type 1 Mechanical splices but not Type 2 mechanical splices. If it's allowed in Chapter 21 in yielding areas of moment frames and shear walls the ACI code committee has pretty good confidence in their performance.