Open Top Storage Tank

[99491]

Has anybody designed/fabricated an open top storage tank with a steel grill in place of the roof. I want to use 16mm round bar in mesh form but will face the obvious problem of it sagging (tank diameter at 11.5m). My other thoughts were to have just a couple of roof rafters on which the round bar mesh will form over. This would face 2 problems the first being that it is expensive and the second being that if I were to install any roof rafters I assume I would have to comply to the spacing set out in API 650 (please confirm this). My second alternative was to have a central column and plate to where all of the round bars would run to. This would sag but not to the same degree as all the way across the tank.

Does anybody have any ideas bearing in mind that it must be financially viable therefore nothing too extravagant.

Thanks and Regards

 

[IFRs]

I've never seen a grillage roof. Since you are not installing an API roof, the rafter spacing in API 650 would not apply. If you put up a center column, you might as well put in a few rafters, then lay the grid on the rafters. Or, since the tank is relatively small, put flat horizontal parallel rafters across the tank for the grid to rest on. This might be less expensive than a column with radial rafters.

 

[Bonswa]

My first thought is the same as IFR's second option. Look at it from a purely structural point of view. build parallel rafters and set the grid on top as if it were any other grated structure. I would build it to where it doesnt touch the tank at all. Put 4 columns up on the outside of the tank. Tie them in together to form a square. Then grid it out, not touching the tank at all.

 

[IFRs]

Here's another thought - span the parallel rafters with bar grating. They have strength tables. You can balance cost of grating vs cost of rafters and get the most economical design for the required loading.