WARose
Structural
- Mar 17, 2011
- 5,594
Even though I’m a structural guy: I decided to post this question here since I figured pressure vessel designers probably face this problem on a day to day basis. (The tank I am mounting to actually has dimensions similar to most pressure vessels I’ve seen.)
I’ve got a situation where a client wants to put a pipe support on a (unpressurized) water tank’s shallow, spherical cap (actually, according to the client: the tank has been unused for sometime). The loads aren’t excessive and I have confidence in the stresses I’ve worked up (both locally and as a whole)……however: with the spherical cap I was wondering about buckling from the vertical load near the apex. (Sort of a snap-through type buckling.) One reference I have (i.e. ‘Pressure Vessel Design Handbook’, by: Henry Bednar) figures the stress from such a local load and suggests superimposing it on the other stresses (from overturning and so forth) and comparing that to an overall allowable. Some years back, I remember looking in the ASME code and most of the allowables I saw were due to overall buckling (not local).
One paper I bought over at ASME (i.e. ‘Interaction of Critical Pressures and Critical Concentrated Loads Acting on Shallow Spherical Shells’, by: Evan-Iwanowski & Loo, 1966) suggested (based on my calculations from their results) that collapse loads from such a load at the apex would be so tremendous that there would be problems with the yielding of the material and displacement long before such a buckling mode was initiated.
So I guess my overall question is this: For such localized loads on a spherical cap, is this type of buckling check not done….and if so, is it because it’s not going to control the design? And while I’m thinking on it: does the same thing apply to cylindrical shells?
Thanks in advance.
I’ve got a situation where a client wants to put a pipe support on a (unpressurized) water tank’s shallow, spherical cap (actually, according to the client: the tank has been unused for sometime). The loads aren’t excessive and I have confidence in the stresses I’ve worked up (both locally and as a whole)……however: with the spherical cap I was wondering about buckling from the vertical load near the apex. (Sort of a snap-through type buckling.) One reference I have (i.e. ‘Pressure Vessel Design Handbook’, by: Henry Bednar) figures the stress from such a local load and suggests superimposing it on the other stresses (from overturning and so forth) and comparing that to an overall allowable. Some years back, I remember looking in the ASME code and most of the allowables I saw were due to overall buckling (not local).
One paper I bought over at ASME (i.e. ‘Interaction of Critical Pressures and Critical Concentrated Loads Acting on Shallow Spherical Shells’, by: Evan-Iwanowski & Loo, 1966) suggested (based on my calculations from their results) that collapse loads from such a load at the apex would be so tremendous that there would be problems with the yielding of the material and displacement long before such a buckling mode was initiated.
So I guess my overall question is this: For such localized loads on a spherical cap, is this type of buckling check not done….and if so, is it because it’s not going to control the design? And while I’m thinking on it: does the same thing apply to cylindrical shells?
Thanks in advance.
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