Stairway forces on Shell 1

[BR0]

Hi All,
I think this may be an easy answer for a tank designer. I found a few other threads with similar questions, but didn't see an answer.

On water tank projects, our company would typically provide the civil engineering and the foundation design. However, the tank design is a delegated design by the contractor/tank manufacturer.

The calculation submittal will have calculations for the various appurtenances, such as stairways and guardrails. They are usually very complete, but they never check the stress on the tank shell.

Is this just considered to be not required? Is this a case where the loads are so small compared to the normal loading on a tank that it doesn't need to be checked? Or have they checked it so many times before that they know it will work? I did look in AWWA D100 and API 650 and didn't see specific design guidance.

Does anyone know if there are simple checks for plate stress that can be done?

Thanks for any help.

 

[JStephen]

I think all of the above.
Normally, when I put together a calculation package, I include major items, but there are a lot of little items that I either know don't really need checking or that I have design spreadsheets for but don't include them in the package.
There are ways to check stresses under reinforcing pads and more approximately under linear clips. So if you really need to see that, let the designers know.
Keep in mind, that anything that can be analyzed can be analyzed to a greater or lesser extent, and that extent is usually adjusted based on the how major the component is. So in that knee brace, I would expect that the fixed joints would be treated as pinned, radial and vertical deflections in the tank shell would be neglected, wind and thermal effects neglected, etc.

 

[BR0]

JStephen, Thanks for the response, and I guess I figured most of what you said is occurring as I do the same in my calculations. Interesting thing about delegated designs is that they typically are for the portions of work that may not be the EOR's own specialty.

I usually only review the calculation submittals to the extent that they appear to be complete and have checked the relevant items, used the correct standard, wind loads, eq loads, etc.

The most important thing that I check is that the reactions from the tank design are within what I assumed for my foundation design.

I do have the Blodgett book that covers the design of hangers and supports, but that is the linear clips you mention. It might be a bit of a trade secret, but is there a good source for the stresses under the reinforcing pads?

 

[HTURKAK]

I have pondered this problem of spiral stair tread loads on a tank shell and checked the stresses for one case probably more than thirty years ago.
Common practice in this case is the steel design of knee brace elements and fillet welding check for base plates.
If you want to see the effects on the tank shell , IMO , the best option is to develop FEM and see the effect of platform pads.
In order to get some insight you may look to the following docs;
- PRESSURE VESSEL HANDBOOK by Eugene F. Megyesy
- TUBULAR STEEL STRUCTURES Theory and Design (by Troitsky )
- PIP STF05535 Vessel Circular Platform Details,
- AISI; Steel Plate Engineering Data Vol. 1 & 2

I know also some clients have typical drawings .

 

[BR0]

HTurkak, Awesome. I will look into those resources.