RINGWALL FOUNDATIONS
RINGWALL FOUNDATIONS
(OP)
I am designing a ringwall foundation for an above ground tank. I am not sure how to find the max bearing pressure on the soil due to the weight and moment of the tank. There is an equation in the api 650 which is what i am using for the design. The eqn is as follows (1.273Mrw/D^2)-(wt(1-.4Av)
where Mrw is the moment at the ringwall surface.
D is the diameter of the tank.
wt is the line load from the tank shell and roof
Av is vertical seismic pressure.
is this the correct equation to use to find the max soil pressure? Is there any other approach? Why doesn't this equation take into account the wight of the product inside the tank?
Your help is appreciated,
~Miguel Diaz E.I.T.
where Mrw is the moment at the ringwall surface.
D is the diameter of the tank.
wt is the line load from the tank shell and roof
Av is vertical seismic pressure.
is this the correct equation to use to find the max soil pressure? Is there any other approach? Why doesn't this equation take into account the wight of the product inside the tank?
Your help is appreciated,
~Miguel Diaz E.I.T.






RE: RINGWALL FOUNDATIONS
RE: RINGWALL FOUNDATIONS
RE: RINGWALL FOUNDATIONS
However,unless your tank botom is specifically designed to carry the load to the wall/foundation (a rare case), the ring wall foundation usually only supports the tank shell and its roof. The weight of the content is carried by the fill/soil material directly below (usually sloped to account for settlement).
You should consider the following load combinations:
1. Selfweight + Wind (Tank empty)
2. Tank full during earthquake.
Now you can perform simple hand calculation to get the max/min bearing pressures.
RE: RINGWALL FOUNDATIONS
RE: RINGWALL FOUNDATIONS
RE: RINGWALL FOUNDATIONS
RE: RINGWALL FOUNDATIONS
RE: RINGWALL FOUNDATIONS
RE: RINGWALL FOUNDATIONS
The anchor bolt equation does not include weight of the contents because they figure that you'll load the anchor bolts without significant movement of the shell, which will not allow any uplift resistance from the contents on the bottom plate. When you're figuring loads on a ringwall, the liquid directly over the ringwall will be included in the design, though.
Ringwalls can usually be sized using P/A +/- Mc/I. The design either needs to preclude uplift or include it in the design, and needs to meet allowable bearing criteria.
Why to use a ringwall- for a more stable foundation, basically the same reason you'd put a concrete slab under your house instead of building it on gravel.
RE: RINGWALL FOUNDATIONS
I can think of many instances where a ringwall is useful or required. So far, there has been nothing in the problem description which would indicate to me that a ringwall would add anything to the structure, except cost.
There are thousands of large, significant tanks without concrete foundations. There are thousands of smaller tanks here in western Colorado alone without concrete foundations. I know of cases where the ringwall contributed to distress after differential settlement. Actually figuring the applied loads to a ringwall and making the system work properly is a real chore, as this post illustrates.
Why use the ringwall??
RE: RINGWALL FOUNDATIONS
RE: RINGWALL FOUNDATIONS
RE: RINGWALL FOUNDATIONS
RE: RINGWALL FOUNDATIONS
RE: RINGWALL FOUNDATIONS
engphila
RE: RINGWALL FOUNDATIONS