beam shear in walls of below grade structure

huangyhg

beam shear in walls of below grade structure
i'm designing a pumping station that will be approx. 35' below grade with high groundwater. the resulting shears at the wall corners and base are high.  to resist shear with vc only requires very thick walls (thicker than otherwise required to resist moment). are there good ways to provide shear reinforcement at the base and corners of the walls?
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try to avoid shear reinforcement to the best you can, especially in wall. the first thinking popped up is that weight is the preferred/cheaper means to resist hydrostatic uplift. the 2nd, how about increase strength of concrete mix? finally, have you analyzed the slab and wall as 2 way plate, or conservatively treated as one way element? it makes big difference.
you can reduce the shear to a point "d" from the support per code (for exterior loads only).  beyond that, i'd make the wall as thick as shear dictates.  you'll find if the wall is skimpy for shear, you end up with congested moment reinforcing (something i could never logically explain).
incremental increases in concrete thickness for walls are relatively inexpensive, once you've paid for the formwork.
i like jed's idea to provide chamfer (bull leg) at the corners, it would help, if you can.
thanks, kslee1000.
buoyancy is an issue and mass is helpful, but the foundation is on piers so i can use the piers to resist uplift so i was hoping to go with thinner walls.  i'm analyzing as 2-way plate now and have ult. shear of about 55 kips which gives 4' thick walls at the base.
stirrups seem like a big constructibility problem.  are shear studs ever used in this type of application?  the only thing i see them used for is punching shear at columns.
thanks, jed.  by aci 318/350 r11.1.3.1 don't you need stirrups to be able to move "d" away from the corner and base? or do you think this requirement is lifted for walls and slabs like minimum shear reinforcement reqts?
i defer to the figure r11.1.3.1(a) that implies that a shear failure would occur at a 45 degree angle from the support, stirrups or not.
i've used that section of the code many times and never had a problem.  once again, it's not for the loads pushing out of the box (the liquid), only the soil load pushing in.
are you using the factors from aci 350?  if you are, note that the extra factors for cracking resistance only apply to loads carried by reinforcing.
i appreciate the responses.
jed,
i have used d away from the support successfully in the past as well.  when i was digging in to this one i read the fine print in r11.1.3.1 that says "two things must be emphasized: first stirrups are required...."  made me wonder if i applied that incorrectly (although successfully - so far .  what do you think?
i'm not using the aci 350 environmental durability factor for vu when considering unreinforced shear capacity.  the high loads are coming from 95pcf efp soil pressures.
what do you think about pilasters in the walls to break up the horizontal spans?
i'd stay away from anything fancy like pilasters.  i know it doesn't seem economical, but just pour the entire wall to the thickness required by the shear loads.  pilasters end up being very heavily reinforced and then might have their own shear issues.
i never noticed that assumption in the commentary about stirrups.  but in r11.1 it says that that the concrete shear capacity is the shear causing significant inclined cracking.
have you tried eq. 11-4 to cal vc?
thanks, jed.  i'm reluctant to go with 48" thick walls. any other ideas would be appreciated.