# Radius Corners



## Keystone

Can someone point me to the section in ACI, think it's 318 or 315, stipulating rebar shall be radius in foundation corners?


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## Msradell

Is this what you're looking for? It's from ACI 315.


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## Keystone

Msradell, close but no cigar yet.  But I will look in that section for the requirement that rebar be radiused thru corners of the foundation vs just butting rebar ends at the corner and tying it.


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## Msradell

There isn't a requirement for that. Some engineers specify that corner bars be inserted, some engineers just let you cross tie the bars in the footings. There's nothing in ACI 315 or 318 that mandates radius is through the corners. You don't actually bought them like you mentioned, you actually overlap them and then tie them at the point they overlap.

For instance if you have 3 bars in each footing you wind up with a checkerboard in the corner where each bar ties to 3 bars going the other direction.


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## mtlogcabin

If you do not have radius corner bars installed then how do you meet the requirement of a rebar splice to overlap a minimum 40 bar diameters?


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## Keystone

Mtlogcabin, I agree. I may be making it up but I thought from my beginning days of inspecting and going through ACI levels there was a section that spelled out corner rebar radius. 
 I ran across a concrete contractor who stated, I was the first guy to ever call radius corner rebar, so I did affirm my call when asked for a code reference/section via rebar overlapping however I was also seeking clearer cut verbiage from ACI if available.


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## ICE

mtlogcabin said:


> If you do not have radius corner bars installed then how do you meet the requirement of a rebar splice to overlap a minimum 20 bar diameters?



I had the impression that the 20 bar diameter overlap was for CMU construction only.

Even with that as my reality, I always ask for a wrap around a corner.


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## conarb

ICE said:


> I had the impression that the 20 bar diameter overlap was for CMU construction only.


The 20 bar overlap and radius is usually specified by the engineer, back when I was a young carpenter we bent the rebar over our knees, once I graduated to architect designed buildings this was always specified and I bought a rebar cutter bender that bent the proper radius.  Back when we were bending it over our knees no inspector ever said anything, so I always assumed that the engineers got their radii from the ACI handbook.


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## Mark K

If the reinforcing bars are not continuous you have an unreinforced concrete section which will likely result in a crack in the foundation.  To prevent this problem you need to develop the bars which is  typically done by providing lap splices.  I forget the exact numbers but for typical foundation reinforcement I believe you need more like 40 diameters.  At corners this issue is addressed by providing hooks which are hooked around a vertical bar.

ACI 318 was written for engineers who would not have any trouble understanding that providing the hooks was necessary.

One of the problems with the IRC is that it attempts to provide  prescriptive solutions for every condition.  It does not help when you have a cheap or ignorant contractor.


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## ICE

conarb said:


> The 20 bar overlap and radius is usually specified by the engineer, back when I was a young carpenter we bent the rebar over our knees, once I graduated to architect designed buildings this was always specified and I bought a rebar cutter bender that bent the proper radius.  Back when we were bending it over our knees no inspector ever said anything, so I always assumed that the engineers got their radii from the ACI handbook.



The footings that I inspect are not engineered to that level of sophistication.  Mostly there is no engineer at all. So what I would need is a code section.  Tiger code has it but the realty is that the rebar need not be tied to each other and obviously some overlap is required or else there would be footing with no steel.  I don't measure the overlap and just eyeball it.  16" looks about right for #4 bar.


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## ICE

Mark K said:


> I forget the exact numbers but for typical foundation reinforcement I believe you need more like 40 diameters.  At corners this issue is addressed by providing hooks which are hooked around a vertical bar.



Maybe in one of the mansions that conarb built but I haven't encountered that in any residential application.  I would like to know what ACI 318 recommends for the lap splice if anyone has a copy.  Now that I think about it, I might have a copy.....it would be so much easier if someone could tell me.

In years past I did deal with hooks in a lot of places on large commercial projects.  Thankfully, the steel details were supervised by a deputy inspector.


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## mark handler

ICE said:


> I might have a copy.....


https://law.resource.org/pub/us/cfr/ibr/001/aci.318.1995.pdf


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## ICE

Thanks Mark,
I dug through it and didn't find a minimum lap splice except for spirals.


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## Mark K

ACI 318-95 is 20 years old!  The world has changed but I believe that the changes in development length have not been great.

There are formulas for developing reinforcing in ACI 318.  This document was intended for use by engineers and was intended to be used when the demand forces were explicitly defined.

The IRC refers to other ACI and PCA documents, which I do not have copies of, but which may provide the desired answer.

I believe the IBC and IRC assume that the jurisdictions enforcing these codes will have access to all of the standards referenced in the codes.  One could have an interesting discussion related to the ability of many jurisdictions to understand the codes they attempt to enforce.


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## Msradell

ICE said:


> Maybe in one of the mansions that conarb built but I haven't encountered that in any residential application.  I would like to know what ACI 318 recommends for the lap splice if anyone has a copy.  Now that I think about it, I might have a copy.....it would be so much easier if someone could tell me.
> 
> In years past I did deal with hooks in a lot of places on large commercial projects.  Thankfully, the steel details were supervised by a deputy inspector.


ICE, this extract from 318-11 says in section 7.10.4.5 the laps for spirals should be a minimum of 48d. Hope that helps.


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## Msradell

mtlogcabin said:


> If you do not have radius corner bars installed then how do you meet the requirement of a rebar splice to overlap a minimum 20 bar diameters?


The requirement for minimum laps doesn't apply for corners. I do a good bit of rebar detailing and some engineers specify them, some specify them only for the outside bars and some don't specify them at all. I'm not sure what criteria they use to make that determination but many jobs to not have them at all. I've even had just returned for corrections when I put them in and they were not called out.


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## conarb

Mark's post reminds me that the minimum has always been 40 diameters, even on the cheap stuff I did early career, the confusion with 20 diameters comes from the fact that most of those were #4 bar and 40 diameters with #4 is 20", a 10" lap has never been acceptable even in Tigerstan.


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## mtlogcabin

During a seismic event a footing will be subject to both compression and tension and we all know concrete without proper reinforcement does not react well when in tension. I do not see have four 1/2 inch laps will work that well.


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## mark handler

I don't know why you want to co through the brain surgery of ACI 318
Minimum lap splice length. the minimum required lap length for spliced reinforcing bars is determined using Equation 1
ld  = 0.002db fs, (Eqn. 1)
but not less than 12 in. (305 mm) or 40db, whichever is greater
http://ncma-br.org/pdfs/68/TEK 12-06A1.pdf




Just Splice all laps per the IRC (CBC) R403.1.3.5.4 _*Lap splices, *not just corners, all splices_


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## my250r11

*2009 IRC
R404.1.2.3 Concrete, materials for concrete, and forms.* Materials used in concrete, the concrete itself and forms shall conform to requirements of this section or ACI 318.
*R404.1.2.3.7.1 Steel reinforcement. *Steel reinforcement shall comply with the requirements of ASTM A 615, A 706, or A 996. ASTM A 996 bars produced from rail steel shall be Type R. In buildings assigned to Seismic Design Category A, B or C, the minimum yield strength of reinforcing steel shall be 40,000 psi (Grade 40) (276 MPa). In buildings assigned to Seismic Design Category D0, D1 or D2, reinforcing steel shall comply with the requirements of ASTM A 706 for low-alloy steel with a minimum yield strength of 60,000 psi (Grade 60) (414 MPa)
*R404.1.2.3.7.5 Lap splices.* Vertical and horizontal wall reinforcement shall be the longest lengths practical. Where splices are necessary in reinforcement, the length of lap splice shall be in accordance with Table R611.5.4.(1) and Figure R611.5.4(1). The maximum gap between noncontact parallel bars at a lap splice shall not exceed the smaller of one-fifth the required lap length and 6 inches (152 mm). See Figure R611.5.4(1).
*R611.5.4.3 Lap splices.* Vertical and horizontal wall reinforcement required by Sections R611.6 and R611.7 shall be the longest lengths practical. Where splices are necessary in reinforcement, the length of lap splices shall be in accordance with Table R611.5.4(1) and Figure R611.5.4 (1). The maximum gap between noncontact parallel bars at a lap splice shall not exceed the smaller of one-fifth the required lap length and 6 inches (152 mm). See Figure R611.5.4(1).
*R611.5.4 Reinforcement installation details.* *

TABLE R611.5.4(1) LAP SPLICE AND TENSION DEVELOPMENT LENGTHS
BAR SIZE NO.*

*YIELD STRENGTH OF STEEL, fy- psi (MPa)*

*40,000 (280)*

*60,000 (420)*

*Splice length or tension development length
(inches)*

Lap splice length-tension

#4-20

#5-25

#6-30

There is a table just couln't figure out how to keep the format.

If it is to be continous then it has to meet the lap with a corner bar or it IS not continous.  If an engineer designs it with out corner bars that is his ARS not mine. If you don't have corners it NEEDS to be enginneered other wize they are required. IMHO


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## ICE

I must not be paying attention because I keep seeing Masonry and CMU requirements but nothing for a footing.  Is there something out there for a footing?


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## conarb

ICE said:


> I must not be paying attention because I keep seeing Masonry and CMU requirements but nothing for a footing.  Is there something out there for a footing?


Yeah, ACI, remember our old buddy Uncle Bob screaming that the IRC was a stand-alone code?


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## Keystone

Someone will probably want to jump all over this but in non design professional opinion and in a residential application, I would consider foundation corner radius rebar to be slightly more important due to lateral/unequal pressures than a footing!

My original questions related strictly to the foundation but some are referencing footing. In residential footing applications by design professional or not I do not see radius corner rebar with a slim few who radius an outside corner I rarely see a commercial footing with radius rebar, It's typical to see a commercial grid with tied intersections.

At this point I believe I am still correct in my interpretation of radius foundation corner rebar on the basis of the overlap requirement and will continue making this call despite but ACI not appearing  to offer a clear cut requirement that spells it out as such.


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## Mark K

The IRC cannot be as complex as it desires to be and still be a stand alone document.


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## ICE

Keystone said:


> My original questions related strictly to the foundation but some are referencing footing.



Aren't they pretty much the same thing?  I understand that a foundation can have a stem wall, however most do not.  So a slab for example has a footing which is the foundation.


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## Keystone

ICE, Generally speaking yes they are the same however for structural purposes I would say each has specific purposes.  The foundation experiences vertical and lateral pressures whereas the footing and stem wall more specifically distribute incoming vertical load to the substrate. 

A stem wall while it is listed as part of a foundation is in my opinion nothing more than a vertical extension of a footing with the sole exception being the stem wall does not sit on virgin or prepared base of soil. Both the footing and stem wall have equal backfill.


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## Msradell

Keystone said:


> ICE, Generally speaking yes they are the same however for structural purposes I would say each has specific purposes.  The foundation experiences vertical and lateral pressures whereas the footing and stem wall more specifically distribute incoming vertical load to the substrate.
> 
> A stem wall while it is listed as part of a foundation is in my opinion nothing more than a vertical extension of a footing with the sole exception being the stem wall does not sit on virgin or prepared base of soil. Both the footing and stem wall have equal backfill.


Many times, a stem wall can experience significant lateral forces. It has the backfill pushing it inward and it has the reaction forces of the framing forcing it outward. Of course it depends on the height of the stem wall but many times when they get up to 3'-4' they can experience some significant forces.


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## conarb

Msradell said:


> Many times, a stem wall can experience significant lateral forces. It has the backfill pushing it inward and it has the reaction forces of the framing forcing it outward. Of course it depends on the height of the stem wall but many times when they get up to 3'-4' they can experience some significant forces.


Very true, especially with 8' high hillside foundations we can't backfill until the floor framing is in place to hold the foundation wall from moving inward, this is a PIA for us since we love to backfill before we roll joists so we aren't stepping/falling in the hole.


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## Paul Sweet

I don't think the corner of a footing or foundation wall is actually a lap splice situation.  I'm extremely rusty when it comes to concrete & reinforcing details, but if I remember right you can use a hook or turn the rebar 90 degrees for 6" or so to develop the tension.


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## eogea62

It depends on what Seismic Design Category you are located in.

2015 IBC, Sec. 1905, Modifications to ACI 318, 1905.1.7 Seismic Design Cat C,D, E or F. (c) Plain Concrete Footings...Last sentence..."Continuity of reinforcement shall be provided at corners and intersections" (2012 IBC says the same thing)

     Exceptions:
           1. In Seismic Design Cat A, B and C, detached one- and two-family dwellings three stories or less in height constructed with stud-bearing walls are permitted to have plain concrete footings without longitudinal reinforcement.

So, if its commercial under the IBC, corner bars or continuous rebar is required at corners and intersections.
If it's residential one and two-family dwellings, and you are located in Seismic Cat A, B or C, no reinforcement is required at all.  

That being said, I don't always agree with the code, but it is what it is.


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## steveray

As Mike posted...Ch4 sends you to Ch 6 and gives you the min. lap splice...From a devils advocate point of view, I can't see why it matters in the corner. Until we adopted the 2009 we had no rebar in the vast majority of our houses and have never seen a failure for this....


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## Keystone

Msradell, When a stem wall is exposed on one face yes I agree, the stem wall will experience significant outward forces however my explanation referenced equal backfill on both faces.  

Eogea62, I will read into that portion a bit more for consideration.


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## mark handler

*Failures that might have been prevented with proper reinforcing.*


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## JBI

mark h.
Nice pics. The first looks like soil lateral load was the cause, the 2nd and 3rd appear to be differential settlement. Different causes, possibly required different solutions to prevent failure.


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## mark handler

JBI said:


> mark h.
> Nice pics. The first looks like soil lateral load was the cause, the 2nd and 3rd appear to be differential settlement. Different causes, possibly required different solutions to prevent failure.


Even if it is the soil settlement, rebar *may have *and probably would have prevented the failure.




*Rebar is for tension*


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