Tank foundation under roof column

[monopoly]

We have a oil tanks of about some 150ft diameter and 40ft heigt, and rested on the 1m thick of 80mm minus gravel pad, and the edge is either reinforced with 1.5m thick of 40mm minus gravel ring or concrete ring wall. There also two columns support the roof of the tank. Do you think that under column, should there be a thicker gravel ring for local shear under roof column?

 

[civilperson]

No, use a concrete pad.

 

[escrowe]

Is this a 'floating roof' with adjustable columns?

 

[monopoly]

It's fixed roof and I assume fixed columns also.

 

[escrowe]

The tank bottom is considered flexible?
The columns are internal to the tank,
and the tank roof is rigidly connected to the tank walls?

I'm sure this has been considered, but just keep in mind
that flexible circular tank foundations are expected
to settle much more in the center than at the perimeter
(perhaps by a factor of 2), and that the column foundations
will likely settle right along with the local portion of
the tank subgrade. That could be a problem
if the column foundation settlement exceeds
the vertical movement of the tank roof and walls,
while the columns are rigidly connected
to the tank roof and and the column foundation.

Just saying...

 

[BigH]

You can take into account the greater settlement of the tank in the centre than the edges by cambering the tank floor initially to "even out" the anticipated settlement.

 

[IFRs]

The column loads are typically distributed over a fairly large area to not add significantly to the hydrostatic load. Often a deeper gravel pad is all that is needed. A good geotech person can give you better advice.