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Canteliver Retaining Walls reinforcement
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picajol
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PostPosted: Thu Mar 09, 2023 8:20 am    Post subject: Canteliver Retaining Walls reinforcement Reply with quote

Hi all!
Please see the sketch attached.
This is an canteliver retaining wall 3m high with an wall thats 20cm thick.
It will be 60m long.

How much of the horizontal reinfrocement on the front face of the wall would you apply to control the vertical cracking due to restrain of the foundation to wall connection?

Also at what distances wozld you provide contraction joints and how horizontal reinforcement would you provide in that front face?

There seems to be a lot of debate on this and also people seems to get confused on wich reinforcement controls what.
Im interested to hear your thoughts.


Thank you



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vikram.jeet
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PostPosted: Thu Mar 09, 2023 3:32 pm    Post subject: Reply with quote

Dear Er

Please see any text book on structural design  Retsining wall desin is covered in all str design booksin much details,,

Still some points :
An rcc cantilever retaining wall derives itd stability from its base ,, which on heel side hass backfill weight over it preventing it from overturning, sliding,,

The very backfill which exert earth pressures,, is also a stabilizing item,,

The wall and base slab shall be monolithic,,

In design
check overturning,,  ( FOS > 2.0 normal and 1.5 wind /eq)
Check Sliding  ( FOS >1.5 normal and1. 25 wind/eq)
Check Base pressures (max within SBC,, minimum preferably +ve)
If min base pr is negative ,, carry out redistribution as per given jn text books,  but see upliftment area is less than20% for normal case and 33% in wind/eq)

Other finer points :
Provide weep holes in wall to dissipate water pressures due to backfill charged conditions

In case water table of area is high (during monsoon)  ,, take effect of uplift  along with hydrostatic pressure on wall

Kindly see a text book to get design philosophy
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vikram.jeet
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PostPosted: Thu Mar 09, 2023 3:43 pm    Post subject: Reply with quote

Expansion joint - yr wall is 60m ,, provide one expansion joint
Construction joint : Max casting length ,, if 7.5m ,, minimum horz reinf will  suffice,,
If casting length is higher,, horz reinf can be increased as per
But if wall is not a water retaining structure,, this csn be relaxed,,
Reinforcement :
Main reinforcement in wall : Vertical reinf on earth side, on front side minimum reinf

Horz reinf is distribution reinf
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picajol
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PostPosted: Thu Mar 09, 2023 9:53 pm    Post subject: Reply with quote

Dreak Virkam "horizontal" reinforcement is fot temeparature and shrinkage, and this is the subject thats very interesting and I also think that amount of it deppends on the distance between the expansions joints.
Can you comment
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vikram.jeet
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PostPosted: Fri Mar 10, 2023 4:40 am    Post subject: Reply with quote

Horizontal reinforcement :

For water retaining walls of reservoirs,, provision of horizontal reinforcement needs special attention and latest IS3370 part 1 &2 have given% horz reinf depending on const joint (also contraction jt) spacing,
You can also refer Fintel Handbook,, providing a curve giving distance between contraction joints vs% horz reinf,,


But for Retaining  wall s not water retaining,, Minimum reinforcement as per IS 456 suffice ,,

For Rcc ret walls expansion joints can be taken max 30m ,,
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picajol
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PostPosted: Mon Mar 13, 2023 8:02 am    Post subject: Reply with quote

Just to be 100% certain.
Expansion joint are not same as control joint.
Control joint are to control the effect due to shrikage
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vikram.jeet
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PostPosted: Mon Mar 13, 2023 9:38 am    Post subject: Reply with quote

Just to elaborate :
Expansion joints at 30 m spacings are for thermal  effects.
Reinforcement and concrete  - complete  discontinuity,, with a gap to be treated as per specs.

Control joint -  Also csn be construction joints  as well ad contraction joints ,, where construction can be stopped  but casting Length affects horz reinf provision,,
These are for shrinkage effects of conc,,
Full reinf continuity,, but casting of adjacent lengths can ne staggered,  

For water ret structures, crack control as per IS 3370 must ,,

For others min horz reinf as per IS 456 ,, ok
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picajol
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PostPosted: Tue Mar 14, 2023 9:06 am    Post subject: Reply with quote

As previously said, construction joints are to allow shrinkage cracks at the joint location. I understand. But this 7,5m distance that you mentioned  is a very short distance. I must say Im a bit suprissed

One question, if you provide an control/contraction joint, you basicaly cut every other horizontal bar/reinforcement in the wall at that joint location, correct?

For expansion joint, that are placed every 30m, you need to provide somekind of "dowel bars" (full discontinuity in concrete and rebar section) as on slabs on grade, correct?
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vikram.jeet
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PostPosted: Wed Mar 15, 2023 3:24 am    Post subject: Reply with quote

picajol wrote:
As previously said, construction joints are to allow shrinkage cracks at the joint location. I understand. But this 7,5m distance that you mentioned  is a very short distance. I must say Im a bit suprissed

One question, if you provide an control/contraction joint, you basicaly cut every other horizontal bar/reinforcement in the wall at that joint location, correct?

For expansion joint, that are placed every 30m, you need to provide somekind of "dowel bars" (full discontinuity in concrete and rebar section) as on slabs on grade, correct?


There is need to differentiate  Structures of water retaining  and structures - not retaining water,,
Water Retaining Structures :
Shrinkage cracking needs to be addressed. As per Earlier  version of IS 3370 (prior to 2009) ,, the Code provides minimum reinf in these rcc structure with limitation on casting length of 7.5 m,,  The newer version of IS 3370 has now recommend ed minimum reinf% based on casting lengths upto 15m  ,, Fintel HB was earlier refered for this,,

It is again  reiterated that Reinforcement is never cut at Construction/Contraction/Control joints. Reinf id cut only at expansion joints. But in water R Strs ,, there is need to provide Water stops at these joints,, weather reinf is continued (Contro/contraction/const joints) or cut (at exp joints).

For non water structures -
Concern is not much on shrinkage cracking which I s taken care by min reinf
The main concern is thermal effects for which expansion joints are recommended at max 45 m,,
Limit of provision for rcc structures is 45 m as per IS 456 .
But for ret walls it is wise enough to reduce this as per as per ID code on provision of exp joints

Request other experts to air their views if convenient
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picajol
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PostPosted: Wed Mar 15, 2023 7:44 am    Post subject: Reply with quote

Dear Virkam.jeet, I thank you VERY VERY much for the info you gave here. I will look for the FINTEL book and get back here soon Smile
One more time, thank you very much!
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