IRC Foundation Wall Reinforcing 3

[SteelPE]

In the 2009 IRC table R404.1.2(1) has requirements for horizontal reinforcing for poured in place concrete foundation walls. The requirements are as follows:

wall height less than or equal to 8'-0" 1-#4 at the top of the wall and at mid height
Wall height greater than 8'-0" 1-#4 at the top of the wall and at the 1/3 points of the wall height.

What is the purpose of this reinforcing? Is it to limit foundation cracking that tends to occur in foundation walls?

 

[hokie66]

Yes, I understand prescriptive codes, and think they should be left to the builders. Engineers should not be involved in things which may have stood the test of time, but are at odds with sound engineering principles.

 

[bones206]

If the basement is backfilled before the floor deck is installed, or without any supplemental wall bracing, wouldn't you expect there to be some horizontal spanning action going on?

If a wall doesn't have any vertical dowels, the bottom of the wall is free to rotate unless something restrains the wall against the soil pressure. Maybe that something is the horizontal bars tying into the orthogonal walls. So perhaps the code-prescribed horizontals are a recognition of the fact that some builders backfill basements before adequate bracing elements are in place. I've seen some of the basements being built in my neighborhood backfilled before even the basement slab has been placed. And the footings don't even have keyways, nevermind dowels. But they do have the #4 horizontal bars top and bottom...

 

[dauwerda]

And then they wonder why the top of their wall is bowed in 3"

 

[GWoodPE]

hokie66, in my experience, most builders have trouble even with the prescriptive code and understanding when it does and does not apply. So they still need someone like an engineer to help keep them out of trouble.
Aren't there also empirical and prescriptive sections in the IBC and other codes? I'm curious what code you fall under for residential work, and how basement walls are typically reinforced in your area.
And aren't most sound engineering principles and code requirements also based on what has worked in the past, just with more testing/research/math behind it with a few more safety factors? Actually the commentary in ACI for the slab temperature and shrinkage reinforcing also says they "are empirical but have been used satisfactorily for many years."

bones206, no question the walls span horizontally to some extent, I've seen plenty of basement wall failures when they weren't braced before backfilling and the cracks look just like you would expect with a two way span.

Maybe its also possible the horizontal reinforcing helps distribute the load to the vertically reinforced sections of wall which also don't follow typical ACI spacing requirements because the verticals can be up to 48" on center. And to the anchor bolts which just magically work at 6' on center.

My guess is all points here are valid (and others) for why there is a requirement for some horizontal reinforcing. The code requirement is probably just a happy medium between having none and trying to prescriptively provide the full ACI requirement. If anyone has access to the commentary from the 2009 version which is when it was added I think, it might give a better answer. Interestingly it was required in ICF walls in the 2006 version but not regular concrete walls apparently.

 

[KootK]

I definitely think that horizontal wall spanning of some kind is a factor in this. If I'm not mistaken, one of the limits associated with using IRC for basement walls is a limit on the plan length of the wall between returns. It really does seem quite ridiculous that this many talented engineers can gather to discuss the reasoning behind this prescriptive requirement and still not manage to come up with a definitive answer.

Engineers should not be involved in things which may have stood the test of time, but are at odds with sound engineering principles.

Well said and I agree. It's really somewhat cruel that we are expected to own things that are designed prescriptively that would not work if designed to established engineering principles. A bit like telling surgeons that they shouldn't bother washing their hands if they're only removing an appendix.



HELP! I'd like your help with a thread that I was forced to move to the business issues section where it will surely be seen by next to nobody that matters to me:

http://www.eng-tips.com/viewthread.cfm?qid=456235

 

[SteelPE]

Quote (hokie66)
Engineers should not be involved in things which may have stood the test of time, but are at odds with sound engineering principles.

Sorry, I don't know how to put quotes in this:

The issue here is that we need to move in and out of the IRC with regards to residential structures. I can't say "hey, go see the residential code for your foundation design" on my plans. I am hired by the client to provide the design of a house. The code says I can use this wall, so I put it on my drawings right next to the 50 LVL's we needed to design to support the roof/floor systems and the 8 shear walls that needed to be engineered and shown to make the house stand up to wind loads.

Again, I don't necessarily like it, but telling a client he needs to place vertical reinforcing in a wall when there are literally millions of houses in the area built without vertical reinforcing will get me and the next engineer no where.

 

[GWoodPE]

KootK
I think there used to be a requirement on the length between returns, along with more stringent requirements for top of wall anchorage, but it was removed in 2012 or 2015. The max length is/was something fairly extreme like 60' which would make the horizontal reinforcing pretty ineffective in that regard. I think it is more useful for helping the wall to span over potential soft spots and reduce differential settlement, sort of act like a grade beam.
I think the definitive answer lies with the ACI332 commentary that it is intended for crack control. But all these other reasons are just added benefit and why it is good practice to include it. It makes the structure a little more robust and redundant.

I disagree about engineers being involved in things which may have stood the test of time but don't have sound engineering backup. The codes (not just IRC) are littered with empirical and prescriptive designs and provisions that are used all the time. They are usually more conservative, but they also may just be because nobody has taken the time and resources to do the substantial research and testing required to confirm or refute the provisions. Probably because it doesn't seem necessary. Just like the horizontal reinforcing. If there were a bunch of basements with issues with vertical cracks or failing because they can't span horizontally, then someone would be looking into it and promoting code changes to require more horizontal reinforcing. However, I can't really think of a time I have seen a vertical crack in a residential basement wall be anything more than a cosmetic concern. So maybe someone said, hey we are seeing a lot of shrinkage cracks in concrete basement walls, maybe we should throw in a little horizontal reinforcing to help keep them small so that homeowners will sleep a little better at night.

 

[KootK]

I disagree about engineers being involved in things which may have stood the test of time but don't have sound engineering backup. The codes (not just IRC) are littered with empirical and prescriptive designs and provisions that are used all the time.

I think that there's a world of difference between:

1) Prescriptive because it's empirical and nobody really knows how the mechanics work and.

2) Prescriptive when we have established methods to evaluate the situation and those very methods would indicate an egregious lack of capacity.

I'm cool with #1 but not #2.

However, I can't really think of a time I have seen a vertical crack in a residential basement wall be anything more than a cosmetic concern.

You either need to get out more or your work in a desert where back-fill resembles packing peanuts.

- Yeah, a vertical crack in a vertically spanning wall is not technically a structural concern.

- Seen many vertical cracks that had NO horizontal component and were perfectly vertical?

- We all know that the wall to diaphragm connections are mostly worthless in residential and, therefore, so is much of the logic vertical spanning walls. It is a dangerous thing to not have some horizontal spanning capability.

- Most real world structural failures have a building envelope failure associated with them. As such, I'd still consider a big, purely vertical crack to be an invitation to future pain.





HELP! I'd like your help with a thread that I was forced to move to the business issues section where it will surely be seen by next to nobody that matters to me:

http://www.eng-tips.com/viewthread.cfm?qid=456235

 

[GWoodPE]

I have seen plenty of vertical cracks, and they mainly appear to be shrinkage cracks. They typically do not have a horizontal component, but if they do, its likely because of a vertical spanning issue or a top support issue, not related to the vertical crack. The vertical crack could have been there long before any other issue developed. Maybe I'm wrong or missing something. I work in the midwest, not packing peanuts, but generally not expansive clay either. Basement wall issues are not my main job, but I've been doing residential work for nearly 20 years. I would bet 90% of the time, the basement wall issues could have been prevented by better drainage because there is almost always a grading or drainage issue associated with the foundation issue. On top of that the basement walls with issues are typically CMU not concrete, probably 95%, but that could just be my experience.

The top of wall support/diaphragm support issue could be its own extended thread. Don't get me started on stair openings adjacent to exterior walls and garages which I really wish were more clearly covered in the code.

The code is saying the specified minimum horizontal reinforcing will prevent the big purely vertical cracks, are you saying it wont?

I think we agree having some horizontal reinforcing in the basement walls is a good thing for many reasons. If you are suggesting we should require minimum shrinkage reinforcing per ACI318, you'll get no argument from me, but you will from the concrete contractors and builders, and probably the homeowners too because the contractor will tell them the engineer is making them put in twice the reinforcing they normally use and it costs an extra $200 and they don't need it.

What about CMU walls? I don't think there is an IRC code requirement for joint reinforcing in CMU basement walls. Would there even be a requirement in the Masonry code?

 

[KootK]

The code is saying the specified minimum horizontal reinforcing will prevent the big purely vertical cracks, are you saying it wont?

Is that what the code is saying? I didn't know that. Regardless, I don't feel that three small horizontal bars would do anything meaningful to limit the size of restraint/shrinkage cracks. But, as always, much depends on the particular case so it's difficult to say with any certainty.

...but you will from the concrete contractors and builders, and probably the homeowners too because the contractor will tell them the engineer is making them put in twice the reinforcing they normally use and it costs an extra $200 and they don't need it.

Common knowledge that. But it doesn't make it right. Many a bad deed was undertaken by someone following orders because they were orders. At the end of the day, are your designs controlled by you or dictated to you? It sounds like the latter. And many of us have been there ourselves to be sure...

What about CMU walls? I don't think there is an IRC code requirement for joint reinforcing in CMU basement walls. Would there even be a requirement in the Masonry code?

If anything, I've heard more horror stories about unreinforced block walls than I have about CIP walls. So I'll not be using the CMU example as a justification for the CIP situation.


HELP! I'd like your help with a thread that I was forced to move to the business issues section where it will surely be seen by next to nobody that matters to me:

http://www.eng-tips.com/viewthread.cfm?qid=456235

 

[GWoodPE]

KootK,
So what are you recommending for the horizontal reinforcing in a concrete basement wall? I've always specified basically the IRC code minimum for walls 10' or less, which I feel is justifiable because its in at least three codes, IRC, ACI332 and PCA100. So I guess I just follow those like lemmings, the requirement came from somewhere, maybe pulled out of a hat. But I haven't seen justification for requiring more. Certainly I've had pushback from contractors even on that, particularly with crawlspace and garage walls, but I don't care. I tell them to save $1 somewhere else like the paint or carpet which will be replaced in a few years anyway, nobody is going to change their foundation down the road at least not without substantial cost.


ACI332-14, section 8.2.7, In summary, requires 3 horizontal bars in walls over 6', four bars in walls over 8', minimum one bar in top and bottom 24", the others evenly spaced, lapped 24" and 30db hooks at corners, but doesn't specify the size. Additional 2#4 required in upper 12" in SDC D and E. The commentary states, "Horizontal wall reinforcement is placed to reduce cracking that can result from restraint against volume changes due to shrinkage and temperature change. The serviceability requirements of residential concrete allow for crack development. The tension face is the inside face of a wall, assuming backfill is applied to the outside face. Refer to Table R4.2.1 for common reinforcing bar lengths including 30db."

PCA100 appears to be identical to IRC.

I guess I'm just curious why the empirical requirement in ACI318 is more acceptable or sound engineering compared to the empirical requirement in the IRC?

Additionally, ACI318 does state the reinforcement limits need not be satisfied if adequate strength and stability can be demonstrated by structural analysis. So maybe the residential codes are using that exception? Since the cracks are a serviceability concern which in theory is reduced in residential, then the horizontal reinforcing requirements need not be met as long as the wall is strong enough otherwise?

Is there a great benefit to specifying horizontal reinforcing at 18" o.c. vs. what would amount to about 32"-48" o.c.?

 

[KootK]

So what are you recommending for the horizontal reinforcing in a concrete basement wall?

Given my druthers, it would be whatever an analysis for flexure and/or shrinkage restraint indicated, probably 0.0018 as a minimum.

I guess I'm just curious why the empirical requirement in ACI318 is more acceptable or sound engineering compared to the empirical requirement in the IRC?

For me, 318 is preferable because:

1) I've seen little cracking issues in commercial structures reinforced to 318 and;

2) Lots of cracking in residential structures reinforced to IRC.

So maybe the residential codes are using that exception?

I couldn't say. I know that the ICF industry uses those outs to justify minimal reinforcing ratios. And I know that because I was involved in a forensic legal case where, when the insulation was peeled back, the walls were an abominable mess of cracking.

which I feel is justifiable because its in at least three codes, IRC, ACI332 and PCA100.

I, personally, would not put too much stock in the repetition because I consider all three documents to be, essentially, incestuously generated versions of the same bottom feeder engineering promulgated by more or less the same groups of industry participants.

Is there a great benefit to specifying horizontal reinforcing at 18" o.c. vs. what would amount to about 32"-48" o.c.?

Do you have some reason to think that there's not? Again, this comes back to my relative experiences with 318 reinforcing and IRC reinforcing.

HELP! I'd like your help with a thread that I was forced to move to the business issues section where it will surely be seen by next to nobody that matters to me:

http://www.eng-tips.com/viewthread.cfm?qid=456235

 

[bones206]

Out of curiosity I went by and checked out a couple recently constructed basements. The one with shorter wall segments didn’t have any visible cracking but the other one with the long wall (~30 ft) had a transverse hairline crack right at the midpoint of the wall, and similar but smaller cracks every 18” or so within the middle third. Again these 8” walls just have single #4 horizontal bars at the top and bottom and were back filled about a week after the forms were stripped. Not sure if the cracks are from shrinkage or flexure, but they seem to be holding pretty tight.

 

[GWoodPE]

SteelPE, has your question been answered? Seems like we aren't quite sure of the exact purpose of the reinforcing, but its definetely not enough.

Kootk, why .0018 and not .0025 or .002, whatever walls would require?
Are you seeing shrinkage cracks be a problem in residential?
So you are basically promoting the idea that there shouldn't be specific codes for different types of structures, if a parking garage or office building requires a specific minimum steel then a residential basement should have the same?
I do think 18" spacing is better than 36", but I'm looking for better justification. Is there some old fashioned engineering approach to calculate the minimum rather than just relying on ACI's empirical ratio and spacing requirement?

Bones206,
That's about what we would expect right? Probably a combination of shrinkage and flexure cracks due to backfilling before the floor is in place. That wall then has less than IRC required reinforcing, Does it need to be remedied at this point? I would guess not but there is a possibility the water proofing was compromised if it moved and cracked during backfilling. Was there any visible bow along the length of the wall?

 

[SteelPE]

Has my question been answered? I guess as much as I can expect. Seems no one actually knows what the reinforcing is suppose to do. I suppose I will just continue on not installing it in my foundations and stick with the 2-#5 bars horizontal top and bottom.

 

[KootK]

Has my question been answered?

I think that GWoodPE has effectively answered your question with the statement below.

The commentary states, "Horizontal wall reinforcement is placed to reduce cracking that can result from restraint against volume changes due to shrinkage and temperature change. The serviceability requirements of residential concrete allow for crack development. The tension face is the inside face of a wall, assuming backfill is applied to the outside face. Refer to Table R4.2.1 for common reinforcing bar lengths including 30db."

HELP! I'd like your help with a thread that I was forced to move to the business issues section where it will surely be seen by next to nobody that matters to me:

http://www.eng-tips.com/viewthread.cfm?qid=456235

 

[KootK]

Kootk, why .0018 and not .0025 or .002, whatever walls would require?

Again, because 0.0018 is:

1) Much greater than the three bar business and;

2) Closer to reinforcing ratios that have performed well for me in the past on commercial structures.

You seem to be rather slowly trying to make the point that the reinforcing ration chosen is somewhat arbitrary in all scenarios. If that's the case, please just say so directly so that we can acknowledge the truth of that and move on.

Are you seeing shrinkage cracks be a problem in residential?

Not necessarily shrinkage cracks but basement wall cracks in general. It seems to me that, when real issues crop up, they tend to be associated with things like frost and hydro-static pressure rather than -- or perhaps in addition to -- shrinkage cracking. Some additional comments regarding my experience with cracked basement walls.

1) When I practiced in WI, cracked basement walls were a thing. Almost a cliche really. If I'd cared to, I could have easily made a living out of just driving around looking at people's cracked basement walls.

2) In Alberta, where I currently practice, cracked basement walls are just as much of a thing as they were in WI.

3) On this forum, I have seen many, many examples of cracked basement walls all over the US and Canada in both concrete an masonry.

4) Do all, or even most, lightly reinforced basement walls crack up? Of course not. If they did, practices would change. In this context, I think that a "high risk for cracking problems" probably means something on the order of 5% of the homes that get built this way. But, then, that's still too much in my opinion and the opinion of that lucky, one in twenty home owner who has his or her basement go to hell in a hand-basket.

So you are basically promoting the idea that there shouldn't be specific codes for different types of structures, if a parking garage or office building requires a specific minimum steel then a residential basement should have the same?

Nope. What I'm promoting is this:

Where established engineering methods would predict an egregious deficiency for something constructed to prescriptive code minimums, I don't feel that the prescriptive code minimums should be allowed to stand. Obviously, my concern here has much more to do with vertically un-reinforced walls etc than it does with crack control horizontal bars.

This is just a paraphrase of my previous comment:

I think that there's a world of difference between:

1) Prescriptive because it's empirical and nobody really knows how the mechanics work and.

2) Prescriptive when we have established methods to evaluate the situation and those very methods would indicate an egregious lack of capacity.

I'm cool with #1 but not #2.

I do think 18" spacing is better than 36", but I'm looking for better justification.

In the absence of crippling market pressure, you're justification should simply be what you, as an engineering professional, feel is right. And that would seem to be this:

Seems like we aren't quite sure of the exact purpose of the reinforcing, but its definetely not enough.

Is there some old fashioned engineering approach to calculate the minimum rather than just relying on ACI's empirical ratio and spacing requirement?

I don't know about old school but there are methods available:

1) Estimate shrinkage strain potential based on geometry and expected restraint and design crack control reinforcing accordingly.

2) Design the wall as a two way plate for the flexure that you realistically expect on the critical vertical an horizontal planes.

I don't often go to this level of detail but, then, I provide meaningful reinforcing ratios whenever I can get them. And, like most everyone else, I uncomfortably bow to market pressure on many residential projects.

HELP! I'd like your help with a thread that I was forced to move to the business issues section where it will surely be seen by next to nobody that matters to me:

http://www.eng-tips.com/viewthread.cfm?qid=456235

 

[dhengr]

GWoodPE:
You said… “So you are basically promoting the idea that there shouldn't be specific codes for different types of structures…,” and I think you’ve sorta got it bass-acwards. From the engineer’s standpoint, if they are essentially the same problem, they should be treated essentially the same. There are different codes for different levels of building buyers, bldg. quality/durability considerations and different construction practitioners. If you want it on the cheap, you use the IRC, and then live with the results and outcome. After all, many times when it is unveiled it looks fine, kinda like the important structures in the area, so what could be wrong? You saved a few hundred dollars in rebar and labor, on a 15-20k portion of a 350k bldg. project. You’ll spend many times that with the first foundation movement or water intrusion problems. The structure doesn’t know the difference, what it is called means nothing to it (parking structure, house basement wall, etc.), but, if they are loaded essentially the same, they will act and react the same and should be designed essentially the same, and with some good engineering experience and judgement. Many AHJ’s have very loose code reqr’mts. for single and two family housing. There is the longstanding belief/dictum that the homeowner is the lord of his manor and should be able to do whatever he wants with his property/house, as long as his family are the only people who are at risk in a failure. There is no need/reqr’mt. for professional engineering involvement, the builder should own a pickup and a nail gun (it used to be hammer, but now they don’t need to know how to use those any longer either). This is even more true in rural areas, without much code history.

Waterproofing is another of these kinds of issues. Good waterproofing will not be harmed by the cracking the photos show. In fact, it is intentionally designed to tolerate some cracking, which we know will happen. Moisture proofing might be (probably will be) damaged since in doesn’t bridge cracks well, at all, after a few weeks of curing. Moisture proofing is cheaper and looks almost the same to a homeowner, and the builder is long gone before the problems show up.

In each case, the homeowner doesn’t know he is being screwed when the builder saves himself a few hundred dollars on some aspect of the job, until some time after the builder is long gone and probably out of business for lack of quality workmanship and actual building knowledge. We are truly spiraling to an inferior, lowest common denominator, and thinking we aren’t getting screwed in the long run. What more could you ask for in today’s world? Sometimes, we need to do a little up-selling with the homeowner to explain why the few hundred dollars is money well spent, in the long run. And, this can be tough because the builder has their ear all day and we are only there often-n-on.

 

[bones206]

Bones206,
That's about what we would expect right? Probably a combination of shrinkage and flexure cracks due to backfilling before the floor is in place. That wall then has less than IRC required reinforcing, Does it need to be remedied at this point? I would guess not but there is a possibility the water proofing was compromised if it moved and cracked during backfilling. Was there any visible bow along the length of the wall?

Yes, I went on my basement safari with certain expectations of what I'd see based on what we'd been discussing here, and I guess it pretty much was what you would expect. Nothing catastrophic, but certainly signs pointing to potential issues if conditions change in the future. Right now they have clean, dry sand backfill with some really ineffective-looking perimeter drain system and bituminous damp-proofing. But down the road if that drain system becomes ineffective or the groundwater table rises, and the damp-proofing becomes more and more brittle, those cracks will likely open wider, split the damp-proofing and become an issue with water intrusion and perhaps wall displacement/deflection. It's probably also very intolerant of frost movement or differential settlement. But right now it looks great, despite the lack of rebar and wall bracing.

I did notice an inward bow at midspan at the bottom of each wall segment. The corners all looked quite out of square as well. My guess is that has more to do with the formwork, since there would be huge cracks if that was from deflection under load.

 

[GWoodPE]

Sorry, I'm not trying to slowly make any point. I thought I stated it before when I said the ACI318 and ACI332 commentary both say they are empirical in regard to temp and shrinkage reinforcement. If both ACI requirements are empirical, then they would seem to fall more under the category of

1) Prescriptive because it's empirical and nobody really knows how the mechanics work and.

I think there are two issues here that I'm trying to resolve in my mind:
1) Is the minimum horizontal reinforcement in the IRC woefully inadequate (regardless of vertical reinforcing) (my current thought is not woefully inadequate, but could be improved)
2) Should I throw away any code books with prescriptive requirements that might be less conservative than other code books or engineering calculations. (again my current thought is no, but understand the limitations of applicability)

What I want to know is, is it within the standard of care to specify the horizontal reinforcing per the IRC? Several comments basically implied an engineer using the IRC wouldn't be acting within the standard of care. So I want to know why.
There are plenty of examples of different requirements for different structures, so what makes this one so egregiously wrong. I don't think the problem is the same as saying all basement walls should have the same reinforcing under the same loading regardless of the occupancy. The code is saying that the serviceability limits for residential are less strenuous than commercial, which is why the T&C reinforcing requirement is also smaller. So I might say the problems are essentially different. Are there not plenty of other examples of where the occupancy or use changes the requirements, regardless of the loading or material? Fire ratings come to mind, a wall doesn't know if it needs to survive a 1 hour fire, a 3 hour fire or if it can fall down anytime. We could also design a wood beam with an equivalent capacity to a steel or concrete beam and say well the beam doesn't know what type of fire rating applies to the building so why can't we use the wood beam everywhere, they are both carrying the same load. The problems seem essentially the same, but there is still a difference.

Joe homeowner reading this thread could come away with the impression that if his house was built before 2009 without horizontal reinforcing, its doomed to fail; or if it was built after 2009 by an engineer that specified 8 horizontal bars, he got screwed because he paid for a bomb shelter but only wanted a house and he still has hairline cracks in his walls. Both conclusions would be wrong.

I'm willing to be wrong too, but before I change my standard and add more horizontal reinforcing, I just want to know that the public is getting some return on the investment and I like to have an intelligent answer for the inevitable question as to why we need more. "because that is what is required in commercial structures" seems like an inadequate response, and would only reinforce the negative stereotype that engineers are overly conservative and unnecessarily drive up cost. "I'm trying to limit the quantity and width of cracks in the walls to a more acceptable standard than the code" I suppose would be a better answer if indeed the current code standard is inadequate. Certainly there are cases where the code minimum isn't acceptable, and places the code can be improved, in my experience it wouldn't seem this is one of those areas, or at least not a high priority. So I'm looking for evidence outside of my experience that it is and I should be doing better. So far all I've heard is ACI318 is better because its more, and it works in commercial structures. I agree, but is it necessary in residential structures? The loads and materials are the same, but are the performance requirements and expectations the same? It doesn't seem like there is a consensus as to what controls the design other than it being dictated by an empirical ACI requirement.

I already feel like the IRC is beyond the level of comprehension of the typical builders, and I think that may be more of the problem. They don't know when they can and can't use certain provisions and they interpret it incorrectly. Add on top of that the lax or non-existent building departments and inadequate construction monitoring and you end up with more problems than just shrinkage cracks. Wouldn't proper implementation and enforcement of the IRC be a better place to start than eliminating the code? Or do we need to do a better job marketing houses engineered/built to a higher standard than the IRC. That starts to sound like language the insurance companies don't like.

I'm just trying to avoid being a "bottom feeder of the industry" and also avoid being an egotistical overly conservative engineer. Not that I think anyone commenting here is either one.

If your real answer is, "I like using the ACI318 minimum because it feels better, but if pressured by the owner/contractor/market forces, I'd allow less after stating my case" that seems reasonable. And that's consistent with the sentiment that there are places the codes could be improved. But I don't think it requires completely discounting prescriptive codes just because some of the prescriptions aren't consistent with other codes.

Thanks for the discussion. I'm new to posting, but have read the forum many times. First time caller, long time listener I guess you could say.