a column at center of tank bottom plate
a column at center of tank bottom plate
(OP)
While reviewing vendor's calculation, I found I am not familiar with their equations although I used computer element modeling.
Can anybody advise the equations (or where to find) to calculate the bending stress of a tank bottom plate under a point load when the allowable soil pressure is given? A circular baseplate is used under the column, which is much larger than the cross-sectional area of the column and welded to the bottom plate.
Thanks.
Can anybody advise the equations (or where to find) to calculate the bending stress of a tank bottom plate under a point load when the allowable soil pressure is given? A circular baseplate is used under the column, which is much larger than the cross-sectional area of the column and welded to the bottom plate.
Thanks.






RE: a column at center of tank bottom plate
RE: a column at center of tank bottom plate
RE: a column at center of tank bottom plate
Roark's "Formulas for Stress and Strain" includes design equations for circular flat plates, which would typically be used for this type of application.
RE: a column at center of tank bottom plate
The plates themselves, typically 1/4", will just plastically deform until bearing capacity is developed in the granualar fill.
RE: a column at center of tank bottom plate
With this equation and computer modeling, I found that the tank bottom plate bending stress is allowable (the base has no footing under the central column). The vendor claims that the footing is detrimental to the bottom plate. This sounds odd to me.
RE: a column at center of tank bottom plate
With the flat plate formulas in Roark, you can superimpose the loadings for many cases that are not specifically tabulated. For example, a simply supported plate with uniform pressure up and a line (circular) load down will give a result similar to the one needed here. Adjust the loads so that the reaction at the edge is zero and you then have a free edge. That may not be what the vender did, but it is one approach.
Concrete footings are very seldomly used under tank columns.
Have you checked with the vender concerning the source of their equations?
RE: a column at center of tank bottom plate
RE: a column at center of tank bottom plate
RE: a column at center of tank bottom plate
But the settlement at the central column is 0.35" and the corresponding subgrade pressure is about 7ksf. These seem excessive from geotechnical point of view.
RE: a column at center of tank bottom plate
RE: a column at center of tank bottom plate
RE: a column at center of tank bottom plate
RE: a column at center of tank bottom plate
The spring constants are calaculated based on the tributory areas. I generated a fan of elements first, assigned everything (spring constants, loading, etc), and cloned these elements with a rotation.
The modulus of subgrade is about 150pci. I tend to consider the subgrade is acceptable for the loading although the deflection at the center (0.35") is beyond the typical 0.25" and the corresponding soil pressure is higher than the allowable. This is an issue with very localized high soil pressure (the stress in base plate is however well within the allowable).
RE: a column at center of tank bottom plate