deep concrete tank wall design for shear

huangyhg

deep concrete tank wall design for shear
i am working a 40'-deep underground rectangular concrete tank. due to soil and hydrostatic pressure loading, the wall thickness is becoming over 5 feet near the bottom.  any ideas to reduce the wall thickness..?
can i use additional vertical reinforcement to help withstand the shear...?  
thank you.
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you can consider the effect of your vertical reinforcement by using equation 11-5 in aci 318-05.  just re  
thank you, i will check if this helps.  some people suggested using shear friction reinforcement, but i was not sure about that..!
i have never used shear friction but i have used "u" or "z" stirrups typically at the same spacing horizontally as the vertical reinforcing and then spaced vertically per eq. 11-15 or the minimum spacing requirements.  whichever controls.  i suppose you have considered increasing the compressive strength of your concrete as well?
yes i did (5,000 psi).  thank you again.
you could taper the wall to reduce the amount of concrete
i would recommend analyzing your wall using mcft.... with a wall that thick the crack with will be so large you will lose aggregate interlock and will likely not get the 2*sqrt(f'c) aci allows.
adding shear reinforcement is a very good idea... it's not ideal for construction, but it keeps your cracks small, and will allow you to get a thinner wall... coupled with the fact that your shear will drop off rapidly the higher up the wall you go... i strongly suggesting adding some amount of reinforcement.  
i'd just make the walls 5'-0" thick, if that's what your calculations show.  i've used shear reinforcing and tapering walls, but in the end once you have a certain thickness wall, the increases are pretty cheap, just the concrete cost.
for a 40'-0" deep tank, i'm not surprised that the walls are thick.  by the way are you using two way action?
would the tank configuration and use allow you to use mid-height struts between walls? (like what you would do to brace a deep excavation, but permanently).....
some of underground concrete structures are controled in the design by uplift (floating) if ground water is an issue.
and thick walls and slabs may be needed.
are you taking yur critical section for shear at the bottom of the wall or at a distance "d" from the bottom?