Steel Tank 4

[dik]

I have a 12' dia. steel tank, right circular cylinder with an open top containing water. I want to construct a catwalk across the top and support the catwalk on the edge of the tank. The tank provides a knife edge support for the channel of the catwalk.

The load from the catwalk is relatively small. Is there a simple method of determining the effect of the point load on an unstiffened edge of a tank? The tank is constructed of 5/16 material, likely A36 or something of that ilk.

Dik

 

[JStephen]

The various tank codes (and perhaps structural codes) include formulas for allowable compressive stress in cylinders. If the width of the item supported ia enough to get bearing below this value, it should be fine.

Usually, there would be some kind of chair or stiffener at a platform support. Figure the load spreads out at, say, 30 degrees from either side, and extend the stiffener however far it takes to get the allowable load.

 

[Zhuge]

1. Compare with similar tank structure that has similar platform. Probably this is the easiest way.
2. From my past experience, for steel tank with WT 6 mm, tend to be overstressed by a platform load. assuming the platform width = 1000 mmm and LL = 2.5 kPa.
3. Another option is provide a repad on the tank surface to spread the load or remove bending moment by adding a brace instead of cantilever out (will still need a repad, but thinner than cantilever out.)

 

[ChipB]

I think JStephen is correct. I haven't done it in a long time (1996) but I did design a storage bin. If you have Gaylord & Gaylord's Structural Engineering Handbook, there is a section in there on tanks. That's where I got my info for design. I would design it similar to the support of the bin itself.

 

[dik]

JStephen... thanks for the heads up on the codes; I'll take a quick gander and see if there are any 'prescribed' approaches.

Zhuge... I was thinking of securing the platform channel to the tank with BAR 2x1/4 welded to the channel and to the tank wall. This will provide a local stiffener for the tank as well as load transfer. I don't have anything to compare it to.

ChipB... thanks for the lead re: Gaylord... I'll see if I can dig up a copy. I don't think it's a problem, but I'd like to have a methodology of checking it without resorting to a quick finite element run...

Dik

 

[sundale]

The structural engineer's standby: "Design of Welded Structures" by Omar Blodgett has a simple yield line analysis methodology for attaching a knife plate of the side of a vessel, if that is perhaps an option. You can buy still buy these classic (i.e. old school) but quite useful blue books from the Linoln Arc Welding Society for not much money.

 

[dik]

Sundale... thanks, I missed it when I tried a quick 'flip through'...

Dik