[b]Stress Induced by Attachments[/b]

[jcoots]

I am trying to determine the stress induced by external attachments on large diameter tanks. In this case I have a 60' dia. x 30' tall tank. The shell plate at the elevation of interest is 3/16" thk. I need to attach a knee brace that will support a catwalk. How can I determine at what point do I need a repad, and then how do I determine what size the pad needs to be?

Any enlightenment will be appreciated!

Jacob

 

[JoeTank]

Bednar's pressure vessel handbook has a pretty good method.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[jcoots]

Thanks for the tiP. I'll be looking into it.
In the mean time I am wondering if Bednar's method takes into account the large diameters of storage tanks. I only ask this because I've used CodeCalc for this application as well as an API reference and they both give me an answer, but in the program a notice appears sayng that the application is really out of the scope of the program and the API reference is only good for tanks who's diameter to thickness ratio is within a certain small range.

 

[JoeTank]

Bednar's method doesn't have computer program-like restrictions on it. It's pretty generic and is applicable to all R/t ranges. It's very conservative though, but at least you can point to a method published in open literature if challenged.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[jcoots]

The reference will help alot!
I have a copy on the way.

Thanks

 

[JStephen]

One method is to apply a horizontal stiffener, then use shell equations from Formulas for Stress and Strain, or other references, treating the stiffener as though it were continuous around the tank (even though it is not). This may be the Bednar method mentioned above.

The program you mention quite likely uses WRC-297 or some similar method, which is intended for pressure vessels, which normally have thicker shells relative to diameter.

 

[LSThill]

jcoots (Mechanical) team member:

Why not use the templet in STAAD PRO 2005.

 

[jcoots]

To JStephen:
I just recieved Bednar's book. Come to find out its something another guy in our dept. has been wanting for a while. It seems to use the same method laid out in WRC 107 which is the methodology Codecalc is based on. However it shows much easier examples to follow and elaborates on some other items. Thanks for the ref. I have Roark's formulas, but haven't looked into the method you mentioned yet.

To Isthill:
I am completely unfamiliar with STAAD PRO 2005. But I did a quick search on-line and found out a little. I understand that using software like this can help solve these types of problems, but I don't have anything quite like that right now, but working on it. I was trying to find a way to size repads for attachments by hand. Thanks anyway.