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COEngineeer (Structural)
30 Sep 06 17:22
How do you guys justify your self when or not to use a counterfort or a buttress?  Is there a deflection limit for a foundation wall?
Helpful Member!(2)  bridgebuster (Civil)
2 Oct 06 6:53
The use of a counterfort retaining wall is usually a matter of cost. When a cantilever wall is in the 30+ foot range a counterfort could be more cost effective.
COEngineeer (Structural)
2 Oct 06 8:13
How about if the wall is long horizontally (basement wall).  When do you decide to use counter fort?
Helpful Member!  DaveAtkins (Structural)
2 Oct 06 8:55
bridgebuster is correct.  When the wall becomes so TALL, not long, that shear, bending, and/or deflection become difficult to manage (that is, the wall becomes very thick), then a counterfort retaining wall becomes more viable.

DaveAtkins

COEngineeer (Structural)
2 Oct 06 9:03
Ok, so as long as my footing can handle the over turning moment and my steel and concrete can handle the moment, I am good right?  I am just afraid theres too much deflection counteracted by the floor diagphram at the top of the wall.
jike (Structural)
2 Oct 06 10:54
Make sure you calculate the wall deflection and batter the wall if necessary. Usually, the wall will be backfilled before the framing and diaphragm are constructed so the short term deflection will already have taken place. The contractor should field measure the actual distance before fabrication of the steel. You might even want to provide a slip connection for adjustment.
COEngineeer (Structural)
2 Oct 06 11:31
we always tell them to brace all walls before back fill.  It just this one project of mine, I specified one of the foundation wall to have counterfort.  There is no good place to put a buttress and they said they dont want to deal with counterfort.  So I should just design the wall and footing to be able to handle the overturning moment right?  And i will probably design the wall as fixed fixed (sides), fixed(bottom), free(top).  Am I doing this right?
DaveAtkins (Structural)
2 Oct 06 14:09
I have designed typical (no counterforts) retaining walls for "walk out basement" situations (backfill on just one side of the building).  I don't worry about the diaphragm taking load.  I believe the diaphragm and shear walls, since they can't resist the load anyway, will deflect enough to allow the load to be resisted by the retaining wall.

DaveAtkins

Helpful Member!  BarryEng (Civil/Environmental)
5 Oct 06 18:57
I usually design retaining walls to about 6 m deep.
Buttress walls & counterfort walls beyond 6 m.

Counterfort walls have a soil load on the heel to help the FOS for overturning but the counterfort is in tension.

A buttress wall is not as efficient in overturning stability but the buttress is in compression.

I have designed several walls for dam spillways to over 10 m because a clear water way is required & buttresses would interfere with the water path.

For analysis of the face wall of either a counterfort or a buttress wall, I use 'Moments & Reactions for Rectangular Plates' by Moody - a USBR publication.  Water Resources Technical Publication - Engineering Monograph 27.  My copy is dated 1970 & may be out of print.  It has 5 sets of boundary conditions & 11 loading cases.  If a is half width & b is the depth, the range of walls is from a/b = 1/8, to a/b = 3/2.  Results are moments in x & y directions & support reactions for 5 divisions in the vertical direction & 10 divisions in the horizontal direction.

BarryEng
cvg (Civil/Environmental)
5 Oct 06 20:10
note that counterforts are often used for dam spillway training walls because of the fact that the normally dry soil over the footing may become saturated when the water level rises and is assumed to become a hydrostatic load which may then become unbalanced once the flow through the spillway decreases.  Design of these walls with standard cantilever footing becomes difficult since the footing gets very large and is often founded in bedrock.  The last one I designed ended up with a 15 feet wide footing, nearly 5 feet thick which was anchored in concrete.  This was then anchored to an existing lower counterfort wall.  For this project, an option was to use either rock anchors or deadman anchors to prevent sliding or overturning
cap4000 (Civil/Environmental)
15 Oct 06 10:12
BarryEng

Real Nice Design Info,which I found as a pdf on line.
Thanks.
bridgebuster (Civil)
16 Oct 06 6:48
BarryEng (Civil/Environmental)
16 Oct 06 21:46
To cap4000 & bridgebuster.
Thank you for the info - I was not aware that it was obtainable on the net.
I was going to send a pdf copy to SlideRuleEra for his web site because I thought that it was out of print.  I will now send him your info.

BarryEng
COEngineeer (Structural)
17 Oct 06 7:19
Bridgebuster , I was using that table to design my foundation wall as a tank.  But I found the table a little too confusing and they dont have enough points to be accurate.  Now I have been using PCA tank design book.  The tables are much easier to use.
bridgebuster (Civil)
18 Oct 06 7:38
COEngineer,

I used EM-27 to design some counterfort walls about 20 years. While trying to find those calculations, I came across a copy of PCA Manual ST-63 "Rectangular Concrete Tanks" (1951). The PCA example does seem a bit easier to follow than the EM-27 approach.
cap4000 (Civil/Environmental)
18 Oct 06 10:41
I have the Design of Concrete Structures Book 13th edition by Nilson, Darwin and Dolan and they use the Hillerborg Strip Method for their footing design. Its takes the form of a quasi two way slab type of analysis. Good Luck.
COEngineeer (Structural)
18 Oct 06 11:35
This is what i use
geoboy (Geotechnical)
2 Nov 06 11:24
Hello guys.
I've just posted a msg about internal stability in retaining walls to calculate bending moments and shear in different cases (also within tieback)
I've found your post very interesting to me and I need some pdf's you were talking about (except EM-27).
I hope u'll excuse me for my bad english and my possibly misunderstanding, I'm italian-pizza-enginner smile.
Thanks.
COEngineeer (Structural)
2 Nov 06 11:32
geoboy, this book is more for foundation wall (like a tank) not retaining wall.  I dont have the pdf.  Just buy it :)  Shipping is cheap to Italy right?  
geoboy (Geotechnical)
2 Nov 06 11:44
Thanks for your reply.
Shipping isn't so cheap; anyway last time I ordered something from outside Europe Union 3months ago), they blocked it for 2months at the dute.
I'm still browsing the web to find something but I miss the right technical words, i guess, 'cause I'm not properly an "international-engineer"... eheh.
It's obvious that i don't find anything in italian language too (books or similiare to buy).
jhoulette (Structural)
4 Nov 06 23:12
COEngineer,
My post is possibly too late but I thought I would give some comments from a Colorado residential engineer in lieu of the comments from design expierience of dams and large retainging walls as posted earlier.
For all of my builders I use counterforts at a spacing of no more than 18ft (closer as the basement wall gets taller).  The counterfort is typically 3ft (sometimes 4ft).  I use them for ftg or piers.  Becareful with piers to prevent uplift.  You may need to extend the piers another 3 to 4 ft.
This is typical of most residential builders in the Denver area.  
I'm curious if the PCA Rectangular Concrete Tanks gave you similar results?
COEngineeer (Structural)
6 Nov 06 15:21
jhoulette, I usually use it to break a wall that is 20ft+ long, sometime they dont want to deal with counterfort so I just beef up the horizontal.  So @18ft sounds pretty good.  How do you do the calc?  Excel?  How do you determine the over turning moment?  
jhoulette (Structural)
7 Nov 06 22:15
I have used RamConcept and yes I have created a spreadsheet.  Overturning is based simply on the soil pressure along the given trib area for the counterfort.  I have found that the overturning is usually the controlling factor in my spacing of counterforts/buttresses.

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