Can We Over-Rule / Bypass ACI?

[BSVBD]

Please see attached...

Could ACI be considered "empirical" and therefore, could I over-rule it by providing supporting engineering data of my intent?

The general contractor wants to omit the #4 x 16" x 32" bent slab dowel at top of wall and post-install a straight bar with epoxy.

Since the tension reaction is only 567 LBS, I want to permit it, but, ACI has splice standards / formulae that I must contend with.

Can I bypass ACI with supporting data?

Thank you!

 

[JAE]

Can't seem to download your attachment - missing file extension?


Check out Eng-Tips Forum's Policies here:
faq731-376

 

[BSVBD]

Try this... please see attached...

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1542665495/tips/Wall_Footing_Section_111918_liowr0.pdf[/url]

 

[TehMightyEngineer]

ACI 318-14 1.10 is the section I believe applies. You need to submit for approval from the building official in your AHJ.

That said; this is opening you up for liability. I'd only do this if you truly have no issue with the proposed solution. I also couldn't download your pdf but to me it sounds like you should be able to justify this using ACI 318 appendix D or similar. I don't think you need to step outside the code for this.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[KootK]

I vote yes. I believe that there's a clause someplace in ACI still that says something to the tune of "a qualified professional can ignore all this stuff in favor of a rational analysis". Obviously, one doesn't want to lean on that too often as it tends to put you in an uncomfortable liability situation if there are problems. This doesn't sound like a big deal though (still can't see attachment). I got into this a bit doing some forensic work on an ICF building. That entire industry would come to a halt without such exceptions being applied to wall panel design.

 

[KootK]

Yeah, I agree with the contractor on this one.

 

[JoshPlumSE]

When I was at Fluor Daniel, we did this once or twice. Saved a lot of money for the project, I believe. It was an existing plant and we could not get the concrete columns to work for the revised loading.

The lead structural (or department head) approached Nigel Priestly (may he rest in peace) down at UCSD and asked him to take a look. He came up with a non-codified solution that justified the original design for seismic loading. I wasn't directly involved in the project. But, since he literally wrote the book on concrete seismic design, it sailed through code check.

If I remember correctly, it was a case of not quite meeting the code confinement requirements for columns. And, he justified it by demonstrating the strain demand on the concrete column with it's current confinement was satisfactory based on the concrete material models he had developed / published over the years.


So,it can definitely be done. But, it's not something that I would be comfortable doing very often. And, it may require that you have an "impressive name" associated with the calc to get the plan check department to accept it.

 

[BSVBD]

TME... what is AHJ?

Koot... or anyone else... can you direct me to that "clause"?

I really think that if i choose NOT to use the bent dowel, and design a different connection, that the splice length wouldn't even apply...

I think my over-analysis is causing others to do the same.

Thoughts?...

 

[WinelandV]

AHJ - Authority Having Jurisdiction (i.e., local building department)

If I were in your shoes, I would go with the straight bar, and make sure it's long enough for splicing to the slab r/f. Then, I'd fire up Hilti profis and verify that you can transmit the 567 lbs via epoxy. I'd wager that it should be able to. Then, you're no longer "outside the code", so to speak.

 

[BSVBD]

winelandv... I've already determined that I can accomplish this with Simpson "SET" epoxy, concluding that same, that the code would no longer apply since I'm no longer using a dowel in the manner of a splice.

I just need to convince my supervisor.

Thank you!

 

[Celt83]

If the screenshot from KootK is your detail several questions:

- Assume your using the high slab to restrain the top of the wall so it's not a true retaining wall, do you have enough friction engagement with that high slab to provide the necessary bracing force?

-What are the high #4 transverse bars and (2)#5 in the footing toe doing for you?

-If you've designed the wall restrained, as the dowel and wall vertical bar position suggests, why the longer heel on the footing?

-Would a standard hook on the dowels not provide an adequate tie, seems the detail is trying to lap the tie with the vertical bars?



Open Source Structural Applications:

https://github.com/buddyd16/Structural-Engineering

 

[JAE]

Why can't you use a "form saver" coupler at the wall face? A little more money but avoids the contractor's headaches and still follows ACI for hook development length.

Otherwise - use Profis and go on as winelandv suggests.

Check out Eng-Tips Forum's Policies here:
faq731-376

 

[rapt]

How is an expoxied straight bar going to achieve the same effect as the current detail? Lapping with the wall bars!

 

[KootK]

Koot... or anyone else... can you direct me to that "clause"?

Meh, not worth the effort as I don't think that's your answer here.

Canadian code says do whatever if you're qualified. Of course that won't help you any in the US.

ACI says that you can pitch whatever to the AHJ. Also no help to you as I can't see you going to that trouble for something as minor as this.

I really think that if i choose NOT to use the bent dowel, and design a different connection, that the splice length wouldn't even apply... I think my over-analysis is causing others to do the same.

Yeah, that. I see this as just a connection and one not requiring flexural continuity around the joint. Technically, even if you stick with the original detailing, development alone would not guarantee a successful joint. It almost certainly would work fine based on some investigation that I've done in the past on the pullout capacity of rebar but that's a tale for another day. In summary, I agree that your best bet here is to simply design the joint for the tension at the slab and not worry about bar development unless that's part and parcel with your joint design concept somehow.

 

[EDub24]

I second the formsaver. That seems like it'll solve all your problems.

 

[Sawbux]

You show an embedded waterstop right above the hooked bar. Seems to me that you will already have a split formwork at that point. So what's the problem with using hooked bar?

 

[Ron]

TME is correct. Yes, you can do almost anything you want with regard to codes; however, you have a standard of care to consider. It will increase your liability.

 

[NorthCivil]

When doing sign off for residential decks, I had a standard detail for a 24" pad footing to frost depth, with a 10" square column that rose to the base where the timber post would connect to the concrete column.

I got so sick of small contractors messing around with crooked forms, badly formed rebar. once they placed the concrete, who knows where their attempt at a rebar cage would be?

It became more a liability, a lot of work for the contractor. I just gave up and spec'd these

https://www.bigfootsystems.com/include/best_footings.htm

and told the carpenters to just drive a single #5 bar down the middle of the form when wet.

I think less rebar is better for small compression only applications, when you can't be sure of the quality of the placement.

 

[Shu Jiang PEng SE]

Clause 12.11 of ASCE 7 specifies the minimum anchorage strength of structural wall to diaphragm. Overstrength factor may needs to be applied to the design value depending the lateral seismic resistance system and sit data. Therefore you had better check the required strength before trying to over rule ACI.