TANK WALL DESIGN
TANK WALL DESIGN
(OP)
Hi everyone,
I am reviewing a modification to wastewater existing tank by adding a dividing wall, the tank is 29' x 29' 18' high and
the dividing wall is 18' from the side wall. The structural engineer submitted a structural calculation based on 11.5'
water depth using PCA tables using three side fixed wall and came up with 14" wall with # 6 @ 12" rebars verticaly and
horizontaly. When the depth mistake has been discovered, the calculation went back to him to revise it, he did not
change the design calculation, he just used a software bending digram using wall supports fixed on one side and hinged on
the other side with hinged support at the bottom and because this case is not listed on PCA tables, he is using the
software and that he design would stay the same. Please advise if you think the wall be structurally sound and stable.
I think it is underdesigned that way
I am reviewing a modification to wastewater existing tank by adding a dividing wall, the tank is 29' x 29' 18' high and
the dividing wall is 18' from the side wall. The structural engineer submitted a structural calculation based on 11.5'
water depth using PCA tables using three side fixed wall and came up with 14" wall with # 6 @ 12" rebars verticaly and
horizontaly. When the depth mistake has been discovered, the calculation went back to him to revise it, he did not
change the design calculation, he just used a software bending digram using wall supports fixed on one side and hinged on
the other side with hinged support at the bottom and because this case is not listed on PCA tables, he is using the
software and that he design would stay the same. Please advise if you think the wall be structurally sound and stable.
I think it is underdesigned that way






RE: TANK WALL DESIGN
RE: TANK WALL DESIGN
Nader - are you "reviewing" the design to provide quality assurance? What is your role here?
If you are doing the design review and you don't know how to check a wall like this then you should get someone on board who can help you with this.
We simply cannot, here, "advise if we think the wall will be structurally stable".
RE: TANK WALL DESIGN
The minimum horizontal reinforcing, depending on the concrete strength used, would be anywhere from .003bt to .006bt. I suggest you get your hands on a copy if you are analyzing these tanks.
Mike McCann
MMC Engineering
RE: TANK WALL DESIGN
thread507-299397: Another Sewage Treatment Wall Collapsing
thread507-296127: Tank Collapses and Kills Two
RE: TANK WALL DESIGN
RE: TANK WALL DESIGN
Another point: if you design the edges as fixed, you're going to have to dowel and epoxy the reinforcing into the walls and slabs. If the reinforcing is spaced at 6 inches, you're almost certainly going to have a reduction in capacity. If they're pinned, then the shear load must be considered (actually the shear load needs to be considered in either case).
I'm not going to do a remote design (for free) for a condition I don't have all the information for. Maybe nader is not telling us the whole story. But when I hear of a design that has a fixed edge, a hinged edge and a hinged bottom, I smell a design that is being incorrectly done.
RE: TANK WALL DESIGN
Ballpark design moment based on PCA coefficients (assuming 3-sided fixed) is 1.3 * 1.7 * 61 * (18ft * 0.070 ksf) * 18ft^2 / 1000 * 12 in/ft = 660 k-in/ft.
Even assuming the PCA coefficients are conservative (which I wouldn't do), I'd treat any FEA analysis that said such a situation was ok as extremely suspect.
Brian C Potter, PE
Simple Supports - The history and practice of structural engineering.
ConstructionPic - Send annotated jobsite photos.
RE: TANK WALL DESIGN