Then you have to make sure the bottom is fixed, meaning you need to make the heel & toe big enough to counteract 2x OT moment. What is your b & a anyway? are you using it to retain water or soil?
It's a basin for a wastewater treatment plant. Overall, the tank will be 90' x 190', 20' deep. There will be interior walls creating separate cells, such that 90' is the long side of each cell. When you look at the cells:
b/a = 90/20 = 4.5
c/a = 3 or less (c varies for each cell)
We design aeration tanks about that dimension. I don't think Vertical Cantilevers is a bad assumption. The wall is getting so long that you don't see any horizontal stiffness. Stiffness involves the inverse of deflection, since deflection increases so fast with beam length, you won't get much help horizontally.
Make sure you use ACI 350-01 with the correct factors. Also use the Z check.
Good Luck! Sounds like a fun project. Oh, usually the careful detailing is at the base of the cantilever. You have to develop resteel around a waterstop.
I have always followed the approach stated by JedClampett. Our tank base slabs were usually quite thick and sufficient to establish fixity. We have high water tables in NE that flucuate annually. Design criteria for most tanks, buried or subject to flooding, included empty tanks with high ground water and full tanks with no ground water. I did a couple of dozen of these over 30 years ago (ouch) with out any problems. We used very low working stresses for the steel (16,000 psi)and WSD to minimize cracks. The cost of the treatment equipment was so high that no one ever compained about the concrete and reinforcing costs.
I've posted this several times, but I much prefer the "Moments and Reactions for Rectangular Plates" by the United States Department of the Interior Bureau of Reclamation. It's out of print but someone probably has a copy in your office. The PCA reference was notorious for its typos, plus I don't like the way it's presented. Maybe later editions have straightened this out, but my old mind is made up.
The 'Moments & reactions for rectangular plates' is available on the net. I was going to send a copy of my very dog eared version for SlideRuleEra for his site but bridgebuster gave me the link. Have a look at thread256-166662 for info to download your own pristine copy.
Thanks. Everyone in our office gets a copy from the original that I stole out of our library. So we're all set. But I do appreciate the download, so the young whippersnappers can see how we did things before the finite element programs. And we could do them quicker.
