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Ties for wall vertical reinforcement
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(Structural)
(OP)
17 Apr 19 14:58 )......Does anyone know of anyway (via a code anywhere) that allows you to consider a single layer/curtain of vertical wall reinforcement as "tied' via the horizontal steel? The way I've always read ACI code.....you need to have 2 layers/curtains of vertical steel, with ties between them in order to call it tied as per code.I have a feeling what the answer is on this one......but I'll ask anyway ()......Does anyone know of anyway (via a code anywhere) that allows you to consider a single layer/curtain of vertical wall reinforcement as "tied' via the horizontal steel? The way I've always read ACI code.....you need to have 2 layers/curtains of vertical steel, with ties between them in order to call it tied as per code.Basically what I have is: a wall with a single layer of vertical reinforcement (and a horizontal layer as well). I'd like to use that steel as compression steel (for a vertical load on the wall).....but it's not tied. It's a pretty short wall (4' high, 10" thick).
(Structural)
17 Apr 19 15:111) I'm not positive but I suspect that you're right in that you do need a transverse tie to be considered tied from a code perspective. That said, it's pretty hard to see an interior bar buckling out with 5" of cover.
2) You can use untied compression bars if the area of the bars is less than 1% Ag. Unless you've got a lot of reinforcing, this is probably your out.
3) I'm surprised that a central mat would actually benefit you much in a 10" wall system. Is it more for axial resistance or flexure? How much reinforcing are we talking about?
(Structural)
17 Apr 19 16:062) per KootK is what we almost always do - keep the wall reinforcement below 1% whenever we can.
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(Structural)
17 Apr 19 16:39I'd just bump up the concrete strength so you don't need the steel to carry compression.
(Structural)
(OP)
17 Apr 19 17:15Quote:
2) You can use untied compression bars if the area of the bars is less than 1% Ag. Unless you've got a lot of reinforcing, this is probably your out.
Quote:
3) I'm surprised that a central mat would actually benefit you much in a 10" wall system. Is it more for axial resistance or flexure? How much reinforcing are we talking about?
I've always wondered about that section of ACI 318. (Sect. 14.3.6 in the 2011 code.) It seems to green light it.....but Chapter 14 refers you to Chapter 10 which requires ties....so I've never been 100% sure there.It's got #9's @ 12" (vert.). So that's less than 1%. It had something else (that is gone now) sitting on it at one point.And to answer your question: yes, it is more for axial resistance than moment......as the new load will be concentric but heavy. Thanks.
(Structural)
17 Apr 19 17:20Quote (WARose)
It's a pretty short wall (4' high, 10" thick).
Quote (WARose)
It's got #9's @ 12" (vert.).
You'll be pretty close to the bottom of the wall before you even develop those bad boys.
(Structural)
17 Apr 19 17:50Can you do a 250 wall with a single layer?
I'm certain the CSA code mandates two mats for walls greater than 8"
(Structural)
17 Apr 19 17:52Quote (KootK)
2) You can use untied compression bars if the area of the bars is less than 1% Ag. Unless you've got a lot of reinforcing, this is probably your out.
Unfortunately this doesn't appear to be true anymore. Depending on who you ask it may have never been true but code language was fairly confusing.Screenshot from ACI 318-14 below. This language is different from previous renditions.
(Structural)
17 Apr 19 17:53Do you really have enough load to need compression steel?
(Structural)
(OP)
17 Apr 19 18:02Quote:
I'm certain the CSA code mandates two mats for walls greater than 8"
Quote:
Screenshot from ACI 318-14 below. This language is different from previous renditions.
Quote:
Do you really have enough load to need compression steel?
I am using ACI 318-11. And section 14.3.4 mandates 2 layers when you get more than 10".Thanks for the info Mr. H. 318-11 words it this way:So newer codes are chopping that one off at the knees.Yes sir. We are talking Heavy with a capital H here.
(Structural)
17 Apr 19 18:17Wow! We don't see line loads like that even on our bridge piers.
What about higher concrete strength?
(Structural)
17 Apr 19 18:18Quote (MrHershey)
Unfortunately this doesn't appear to be true anymore.
Wow... thanks for bringing that to my attention. Some thoughts:1) If the old interpretation was incorrect, there must be a whole lot of improperly designed bearing and shear walls out there. Lot's of folks have leaned on this.2) I'm not sure that I understand what reinforcing this provision is aimed at now. Is it out of plane, flexural compression, wall bars that don't need ties? Gosh... thanks. Or is it meant for flexuralbars assuming that you wouldn't want them to buckle under axial/creep before you get a chance to use them in tension?
(Structural)
(OP)
17 Apr 19 18:19Quote:
What about higher concrete strength?
May test to get that. (Remember: this is a existing wall.)
(Structural)
17 Apr 19 18:21I would have been hesitant to use the vertical bars for compression prior to the rewording at the less than 1% anyway. There is no mention of confining cover required so the bars could have been placed close to the face of one side of the wall without consideration of buckling blowout of the near face.
(Structural)
17 Apr 19 18:21Oh, sorry, I missed that it was existing. Yeah, can't very well spec. higher strength now...
(Structural)
17 Apr 19 18:57That new section 11.7.4.1 in ACI 318-14 is STUPID. There are millions of square feet of reinforced concrete wall out there that takes axial load and have no lateral ties.That paragraph, in my view, is a perfect example of how utterly inept some of our code writers are.I realize that there was public review, etc. but to write this in with NO commentary as to the change is unbelievable.
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(Structural)
17 Apr 19 19:06Quote (JAE)
but to write this in with NO commentary as to the change is unbelievable.
X2. First thing that I did after Hershey's post was go hunting for that non-existent commentary.
When I get to 1000 stars, I get to meet BAretired for lunch. Current start count = 790. Just sayin'...
(Structural)
(OP)
17 Apr 19 19:16Agreed JAE. You'd think they would (at least) reference some testing in commentary.
(Structural)
17 Apr 19 19:17I fear that someone re-wrote the paragraph in a reverse order and then forgot to change and "or" to an "and".I'll post a question to ACI and see what they say.
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(Structural)
17 Apr 19 19:41Quote (JAE)
That paragraph, in my view, is a perfect example of how utterly inept some of our code writers are.
I realize that there was public review, etc. but to write this in with NO commentary as to the change is unbelievable.
Will editorialize a bit here. But in my discussions with a member or two of ACI 318 and the fact that I've not seen this called out as a change in any of the educational material I've reviewed, I get the sense that they believe: a) it was a grammatical change and thus not substantive enough to highlight or comment on, all that was done was fixing the double negative from the previous codes; and b) it has always been required to tie any bars you're using in compression.I don't think I agree with either point, but that's the sense I've gotten. Probably bolstered by the fact that very few people have noticed the change or made a stink about it (though them not highlighting it certainly doesn't help). The individuals I talked to did acknowledge that the language should probably say 'compression strength' instead of 'axial strength'. I don't believe this was updated in the ACI 318-19 public draft though.And speaking of ACI 318-19 public draft, I believe they added an exemption for basement and retaining walls to get them out of some of the wall requirements, including this one.
(Structural)
17 Apr 19 19:49Basement walls and retaining walls are fine - but think of the immense numbers of precast or tilt-up walls out there that have axial load on them with a single mat of rebar.
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(Structural)
17 Apr 19 19:49...and no transverse ties...
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(Structural)
17 Apr 19 19:54I don't see how the second part can be correct, that if the longitudinal bars exceed the 1% then they have to be tied. This reads as if it is independent of the bars taking axial loads or not. The first part would seem to be now more in line with masonry.
(Structural)
18 Apr 19 14:06In earlier sections of 318 (such as 318-11) there is a section 14.3.6 which allows a designer to avoid transverse ties in "vertical" wall reinforcement as long as EITHER of two separate conditions occur: 1. As required is less than 1% of Ag - OR
2. Where vertical reinforcement is not required as compression reinforcement.
This has been interpreted as a means for a designer to avoid transverse ties - especially in walls with a single mat of reinforcement.
However, 318-14, paragraph 11.7.4.1 seems to change this. It reverses the wording but fails to change the "or" to an "and" thereby now requires designers to have transverse ties in ANY case where the reinforcement is provided in axial conditions.
The words "longitudinal reinforcement" is not defined in the case of a wall - is it vertical or horizontal?
The condition "required for axial strength" is also rather vague.
Can you clarify if the millions of square feet of single mat reinforced concrete walls out there, with no transverse ties, are now in violation of 11.7.4.1 and a structural danger?
Finally - this appears to be a significant change in the code yet no commentary is provided and I find no discussion online or on your website about it. Is there a reason for this? Was the wording changed but no one realized the vast difference it makes in wall design?
Here's the question I sent to ACI:
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(Structural)
18 Apr 19 14:55@JAEThe attachment isn't exactly the point being discussed here, but I had reached out to ACI a while back about the issue of wall ties and attached is their response. I will be curious to see what they respond back to you.
(Structural)
18 Apr 19 15:37Interesting reading slickdeals; thanks for posting.
The way it looks to me , by a strict reading of the code provisions, it would seem that the vertical bars cannot be counted as compression steel, since they are not restrained from buckling by transverse reinforcement.
However, as a practical matter in your situation, WARose, if nearly half the concrete in your wall breaks off, which is what it would take to allow the bars to buckle, the vertical steel will not be enough to keep the wall standing, anyway. So, from that perspective, you ought to be able to count it.
If that isn't an option you're comfortable with (I can't say I would be), if the heavy loading is only in discrete locations along the wall, you could consider local external confinement (anchor plates on the faces, bolted through the wall, etc.). If the load is uniform, testing the actual strength of the concrete may be the best way to determine if it's sufficient or not.
(Structural)
18 Apr 19 15:52slickdeals,
Your basement wall question is exactly what I was interested in.
(Structural)
18 Apr 19 15:56Quote (HR10)
if nearly half the concrete in your wall breaks off, which is what it would take to allow the bars to buckle, the vertical steel will not be enough to keep the wall standing, anyway. So, from that perspective, you ought to be able to count it.
I believe that there's a logical inconsistency in that statement. Since the tendency of the bars to buckle would be one of theof half of the wall breaking off, I don't think that we can claim that the bars can be relied upon to not buckle because of a perceived hierarchy of failure. There's interplay and feedback involved.I do, however, share your sense that the concrete mass surrounding the bars would likely be enough to brace them against buckling. And I wish there was a formal way to check that. I've attempted it in the past looking at the force required to brace a bar and checking that the concrete splitting capacity exceeded that value. Unfortunately, it leads to difficult questions about how much concrete section contributes to the resistance and whether or not we should rely on it being uncracked.
When I get to 1000 stars, I get to meet BAretired for lunch. Current star count = 790. Just sayin'...
(Structural)
18 Apr 19 16:24slickdeals,Thanks for that posting. They appear to first reply on the concept of an assembly of bars near the end of a shear wall. I can see that situation and understand the need/desire to require ties at the wall ends.Their other reply on the basement wall is consistent with 318-11 and earlier codes - they suggest getting below 1% by thickening the wall to avoid ties...but they then don't talk about 318-14 where even if you have < 1% steel - if you have bars for axial capacity you need to tie the bars.Your inclusion of an older document shows that the key for ties is if. This is at least a way to measure whether you need ties or not from the older codes....and perhaps 318-14.
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(Civil/Environmental)
18 Apr 19 16:43Quote (However, 318-14, paragraph 11.7.4.1 seems to change this. It reverses the wording but fails to change the "or" to an "and" thereby now requires designers to have transverse ties in ANY case where the reinforcement is provided in axial conditions.)
I might be in the minority here, but I don't see any difference in the 2011 and 2014 code provisions. Yes the wording has changed, but I don't see any difference in the intent.My interpretation differs from yours in that you read it as a requirement triggered when a wall has axial load, but I read it as triggered when the vertical reinforcement is being counted on for axial strength by the designer. To me, that is a totally logical code provision because the bars will be seeing higher percentage of the transformed section stresses and could be susceptible to buckling with no redundancy from the brittle concrete component.The 2014 version says "If longitudinal reinforcement is...". To me that means the designer is relying on the bar's compression strength to resist part of the load rather than the concrete alone. It does not indicate that it applies to any wall simply containing rebar that has an axial load. We just have to design single curtain reinforced walls using concrete strength alone, which is consistent with tradition. That's my take at least.
(Structural)
18 Apr 19 16:45Agreed KootK. I approached that very poorly. I was thinking more of the effects of external forces, such as seismic damage, when I wrote it. If the stress on the wall causes buckling of the steel, because the concrete is not adequate to confine it, then it fails in spectacular fashion.
There should be a way to determine if the concrete confinement is adequate to ensure yielding of the steel, rather than buckling, but there doesn't seem to be any that we've found so far.
(Structural)
18 Apr 19 17:15Quote (Bones206)
To me that means the designer is relying on the bar's compression strength to resist part of the load rather than the concrete alone. It does not indicate that it applies to any wall simply containing rebar that has an axial load. We just have to design single curtain reinforced walls using concrete strength alone, which is consistent with tradition. That's my take at least.
Expand that a little further and imagine a wall with a single layer of reinforcement (or two layers for that matter) and the reinforcement is primarily provided for flexural tension and exceeds 1%. You will end up with a wall needing ties in the compression zone because the code does not appear to give you an out if you are more than 1% (regardless of whether you are counting on the compression reinforcement or not).
(Structural)
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18 Apr 19 17:27You will all find this Q&A interesting as well.I don't believe anyone is arguing that if compression reinforcement is needed for strength, then it must be tied. However, many shear walls have boundary zone reinforcement triggered by flexural tension and often can end up exceeding 1% measured in the boundary zone of the wall. A case in point could be an 8" thick wall with (2)#7 each end spaced at 6" o.c. (about 1.25%). Strictly speaking, the code would require this to be tied since it exceeds 1%.
(Structural)
18 Apr 19 17:43less than or equal to 1%
OR
Vertical reinforcement is NOT required as compression reinforcement
greater than 1%
OR
Vertical reinforcement is required as compression reinforcement
OR
in there - so you have to satisfy both provisions.bones206,I disagree with you and here's why:Take a wall you have with one layer of vertical reinforcement in it and with a situation where reinforcement is required for compression load AND you have LESS than 1% reinforcement.Under 318-11:The provision states that ties are NOT required if you areWith that wall you have - since you are less than 1% the second provision doesn't matter. It says "OR". So if either one of those are true (not both) you can avoid transverse ties.Under 318-14:The provision states that ties ARE required if you areWith that wall you have less than 1% and you satisfy the first provision - but there's anin there - so you have to satisfy both provisions.Since you DO NOT satisfy the second provision you must provide transverse ties.So with the same wall situation - each code is a different result.
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(Civil/Environmental)
18 Apr 19 18:21Ok, I see the distinction now. Thanks JAE for clarifying. But in the example you give, I think it’s proper that the code wouldn’t allow that design scenario.
I think the new wording clarified the original intent and seems consistent with that commentary snippet that you posted earlier.
4
KootK(Structural)
18 Apr 19 18:43I believe that I know the answer to the question of what the code intent is. And, like most things, it's best sorted by tracing it back to the theoretical fundamentals that underpin the provision in the first place. I'll never be able to prove this to any doubters so let's just call this the KKT (KootK Theory). I put it forward for consideration and discussion, not as a statement of fact. It's going to be a bit of a journey but, for those interested enough to tag along, it may be worthwhile.
1) Why are columns required to have 1% reinforcing? The reason is to prevent passive yielding of the bars under conditions of concrete creep. Effectively, you are providing enough steel that creep strains, and thus bar strains, are keep below the yield strain of the rebar.
2) I submit that the 1% requirement also serves as a demarcation point of a different, but related sort. Another way to limit creep strain is to simply keep concrete stresses low enough that you don't get much creep tendency in the first place. I propose that the load limit below which creep strain is considered small enough to prevent passive bar yield is thought to be the point at which a designer would require 1% reinforcing for the purpose of resisting axial compression.
3) I submit that the 1% requirement only applies when there are net axial forces applied to the cross section. Flexurually induced compression does result in creep in the compression block but it is not as severe as in true compression members because the creep strain is partially restrained by the horizontal shear connection to the parts of the cross section in tension and, even, lesser compression (strain gradient effect). I believe that this is why you can have incidental bottom steel near the columns of two way slabs that will be highly compressed yet still not blow out despite the lack of ties and 3/4" cover.
4) If you take the three points above, and apply them to walls in an identical fashion, I believe that it leads to the following, rational interpretation of when ties would be required within a wall:
A) When there is a net axial compression on the cross section AND;
B) when the net axial compression load is sustained AND;
C) when the resistance of the net axial compression load would require reinforcing in excess of 1%.
5) Applying this to some common situations, I get the following:
i) Basement & retaining walls. No ties. These elements fail A and C. They may well pass B as much of the load may indeed be sustained.
ii) Axially loaded walls where design for the sustained axial load alone would NOT require reinforcement in excess of 1%. No ties as this fails C.
iii) Axially loaded walls where design for the sustained axial load alone would require reinforcement in excess of 1%. Yes to ties as this passes A, B, & C.
iv) Shear wall compression zones where rebar exists primarily for load reversal induced tension and design for sustained axial compression would NOT require reinforcement in excess of 1%. No ties as this fails C.
v) Shear wall compression zones where design for sustained axial compression would require reinforcement in excess of 1%. Yes to ties as this passes A, B, & C.
vi) The last two were tricks. Technically, other than where seismic ductility is required, no shear wall compression zone would EVER require ties as it would fail the test for sustained load (B). Kinda by definition, lateral loads are not sustained. I know, CRAZY!! And yes, I realize that this would not be kosher according to code compliant design.
6) I believe that ACI provides an alternate method for determining the need for ties based on calculating the expected strain in the reinforcing. I feel that this method is inherently more rational than the 1% business. Unfortunately, it's much less production office friendly.
When I get to 1000 stars, I get to meet BAretired for lunch. Current star count = 790. Just sayin'...
(Structural)
18 Apr 19 18:50Why not just analyze the wall as “plain concrete”? ACI does have a Plain Concrete section. You only need to calculate 3 points for a simple interaction diagram. You will get very little moment capacity though.
(Civil/Environmental)
18 Apr 19 20:45I think the ACI 318 committee can just cut and paste KootK’s post into the commentary for the next edition...
(Structural)
19 Apr 19 00:04Quote (JAE)
Can you clarify if the millions of square feet of single mat reinforced concrete walls out there, with no transverse ties, are now in violation of 11.7.4.1 and a structural danger?
Settle down, JAE. Structures fall out of compliance with each code revision. Assuming this change was intended, it's probably the step from good-enough to preferable on the code development journey. I know some would prefer the former to be the end of the line but that doesn't always happen.I like to keep in mind that the ACI doesn't have the power to crash the economy, which is what it takes to cause the sky to fall on the construction industry.
(Structural)
19 Apr 19 00:29Hey - just adding a little hyperbole to get their attention never hurts.I'm not worried. Just pissed.
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(Civil/Environmental)
19 Apr 19 00:48I want to circle back to the original question regarding the horizontal bars acting as ties to restrain buckling of the verticals. The first images that came to mind were all the wall failures in the 2010 Chile earthquake. Check out some of those reports and photos and you can see that the horizontals did not provide much in the way of lateral restraint.
(Structural)
19 Apr 19 02:09Koot - great post. I second bones on copying this into the ACI commentary
(Structural)
19 Apr 19 03:35JAE, I understand the frustration when these apparent 180s slip in without any commentary. Leaves you wondering whether they mean what's printed or
(Structural)
19 Apr 19 12:43I received the following reply from ACI.It confirms that the language in 318-14 was in error (“or” should have been an “and”).
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(Structural)
19 Apr 19 12:44Check out Eng-Tips Forum's Policies here:
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(Structural)
19 Apr 19 13:27This seems to be an interesting departure from previous editions of the code where the language seemed to imply that if you have reinforcement of 1% or more at wall ends, then you would have to tie them regardless of whether it was being used for compression or not.
I don't think current software have an ability to turn off reinforcement in the compression zone in strain compatibility calcs. I have a wall design spreadsheet that can do it, but I don't think commercial programs do it. The difference in some of the test cases I have run for shear walls of normal proportions has been around 3-5% (lower capacity without compression zone reinforcement).
(Structural)
19 Apr 19 14:43ACI seems to be struggling to make up their mind on this. This is from the Q&A (January 2019)
"Regardless of whether the reinforcement is required for tensile capacity, compression capacity or both, note that lateral ties are required if the area of longitudinal reinforcement exceeds 0.01 times gross concrete area".
The clarification in ACI 318-19 seems to imply that you can have 4% reinforcement in the boundary zone of a wall but as long as you are not counting on it for compression, it doesn't need to be tied.
(Structural)
19 Apr 19 15:39slickdeals - yes, tension rebar doesn't need transverse ties. Or am I misunderstanding you?
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(Structural)
19 Apr 19 15:54JAE - I agree from a behavior/mechanics standpoint that tension rebar doesn't need to be tied and I think the modified 318-19 language clarifies that in a much better way.
The way 318-11 and earlier were written (IMO and based on other articles/literature) was that 1% was the trigger for transverse ties regardless of the following:
1. The reinforcement was in tension
2. Reinforcement is not counted on the compression side
(Structural)
19 Apr 19 16:01I think you are correct.
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(Structural)
19 Apr 19 16:29 needed for compression. It's not as though they'll refuse to absorb compression just because they've been told to. In a ULS sense, I suppose that you could buckle the bars and then just straighten them out with the load reversal. But then that raises all kinds of questions about aesthetics, lap splice performance, and overall integrity. As I mentioned above, I think that one could make a theoretical argument for not tying any zones, compression or tension, other than in seismic hinges etc. That said, I wouldn't be willing to rely on that in practice myself.@slick: your primary interest here seems to be the shearwall aspect. You're not actually hoping to NOT tie tension only boundary elements in practice are you? Just an academic inquiry? For something with reversible demand, I live in fear of buckling the bars when they see compression, even when they're notfor compression. It's not as though they'll refuse to absorb compression just because they've been told to. In a ULS sense, I suppose that you could buckle the bars and then just straighten them out with the load reversal. But then that raises all kinds of questions about aesthetics, lap splice performance, and overall integrity. As I mentioned above, I think that one could make a theoretical argument for not tying any zones, compression or tension, other than in seismic hinges etc. That said, I wouldn't be willing to rely on that in practice myself.I'd like to chase down what level of bar strain we feel is appropriate for the expected. I know that I've seen this before but I can't recall where. As with piles, I suspect that it takes shockingly little to brace a bar in practice and that a very high level of strain is required to produce a buckle/blow out. It would be informative to know how that buckling strain compares to, say 0.0035 etc. That way, one can gauge whether a tension bar falling within a concrete compression block can be expected to buckle or remain stable in the absence of ties.
(Civil/Environmental)
19 Apr 19 16:49Some research: Link
(Structural)
19 Apr 19 16:54@Bones/CURVEB: thanks for your kind words regarding my previous post. When I dive deep like that I always fear that I've wasted 45 minutes of billable time -- and my life -- to produce something that's too oppressively long for anybody to bother reading (internet age etc). It's a comfort to know that the effort was not for naught.
(Structural)
(OP)
19 Apr 19 17:16Quote:
(Kootk)
It would be informative to know how that buckling strain compares to, say 0.0035 etc. That way, one can gauge whether a tension bar falling within a concrete compression block can be expected to buckle or remain stable in the absence of ties.
New Zealand code (NZS 3101; which I think is available on-line for free) seemingly addressed this with some of their codes in the past. And that has been reproduced in some texts I have. In the NZS 2006 equation it is Eq. 10-40 & 10-41 for plastic hinge regions. If you'll notice, 10-40 includes axial load as a variable.You might could back out of that with a strain.
(Structural)
19 Apr 19 18:52So why wouldn't this same 1% rule apply to masonry?
(Structural)
19 Apr 19 19:00you'd probably be violating the bar clearance requirements before getting to 1% steel in a masonry wall.
Open Source Structural Applications: https://github.com/buddyd16/Structural-Engineering
(Structural)
19 Apr 19 19:04I mean if the reinforcing is less than 1% then why can it be counted on for compression in concrete without ties but not in masonry? ACI 530 requires ties for rebar anytime it is being counted on for compression regardless of percentage.
(Structural)
19 Apr 19 20:26haynewp - ACI 530-13, section 5.3.2 allows for "Lightly Loaded Columns" where lateral ties are not required.No mention of lateral ties in walls that I can see - except for pilasters. Am I missing it?
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(Structural)
19 Apr 19 21:13JAE
I am out of office now, the version I have at the moment is 2005. It has the below:
2.3.2.2 Compression
2.3.2.2.1 The compressive resistance of
steel reinforcement shall be neglected unless lateral reinforcement is provided in compliance with the requirements of Section 2.1.6.5.
(Structural)
19 Apr 19 21:20JAE
ACI 530-13 9.3.2 e
Axial capacity of reinforced masonry walls ignore any contribution which would be provided by vertical reinforcement.
(Structural)
19 Apr 19 21:23Yes - I see it. Seems like that's been now relegated to only columns and pilasters (vs. walls) in later editions while the 05 edition simply refers to compression in masonry.
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(Structural)
24 Apr 19 20:18Did the OP’s question ever get answered?
(Structural)
24 Apr 19 20:42Well, sort of. I guess WARose should respond on that, though.
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(Structural)
24 Apr 19 21:00Koot,
That load reversal style of failure is one of the banes of concrete construction in seismic design. You get load reversal failure, then you cycle a few times and the concrete disintegrates. Then you lose the compression or shear load path because you just have a bunch of bars hanging in the air and bad things happen. This is why tie and stirrup detailing are a big deal in concrete seismic systems.
(Structural)
(OP)
24 Apr 19 21:01I consider it answered. I actually had forgotten about that section of ACI that the debate broke out about.
That reference i posted above (from the NZ code) appears in other forms in other references I have (in a more usable form).....when I get a chance, I'm going to mess around a bit and see what sort of concrete strains correspond to minimum tie areas (as per ACI 318 vs. NZ code).
EDIT: And by the way, thanks to everyone who participated.
(Structural)
24 Apr 19 21:51@TLHS: agreed. I was pretty careful to exclude seismic in all of my comments. That's actually something that I've come to resent a bit. Nowadays, I feel as though I'm obligated to preface every damn thing that comes of my mouth with "..unless it's seismic..."
(Structural)
24 Apr 19 23:39Koot, wasn't really disagreeing or pointing out a problem. Just expanding on your hinge zone caveat.
(Structural)
25 Jun 19 21:03Resurrecting this thread to close loop on the errata and code updates referenced by JAE above. Looks like things have formally changed here.Previous language in ACI 318-14:Language from ACI 318-14 errata:Current language in ACI 318-19:
(Structural)
25 Jun 19 21:20whew. All is right with the world. I can calm down now!
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