ISO 13725 method for determining buckling loads in cylinder 4

[vja]

hello

Any one familiar with this standard.I got a question regarding solving (critical buckling load) equation.

 

[vja]

Any help would be appreciated.

 

[vpl]

Maybe you could tell us what is your question.

Patricia Lougheed

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[vja]

I m trying to solve the equation.
what value of F is used initially in the equation as the process is iterative.
And what method is used to solve the equation.I m using excel and using goal seek and solver to solve the equation.But I m not getting the number I m looking.

 

[dhengr]

Patricia and I must be the only two people in the world that don’t have that ISO Std. or have our copy open to that formula. Could you be any less specific? I can’t see your formula from here. Maybe provide a copy of that page of the Std. so those of us who don’t have a copy might try to be of some help. Include their listing of variables and definitions thereof. Tell us a little about your problem, a sketch, dimensions, sizes, loads, etc. A 2' dia. pipe with 2" thick walls, might be treated differently than a 12' dia. tank with 1" walls. The solution for the buckling of a cylinder did not originate with the ISO, so you might get some surprisingly good advice or insight from engineers who don’t even have that cookbook. If all else fails, iterate some more.

As an aside.... does every engineering problem in this era boil down to manipulating the variables in some unknown (as to origin) formula? Is there ever any discussion about the broader understanding of the whole problem or concepts involved, and then understanding the origin of that convoluted formula, so we show a vague understanding of the problem we are working on?

 

[vpl]

I got busy yesterday afternoon and didn't bother going to look up the standard. I was going to suggest that if you don't have a reasonable value of F to srart with then you make a basic guess with which to start (Look at literature for some numbers.) Use the results to calculate a new value and plug that in. After that, either repeat, or divide your results in two and plug in an F that would be halfway between. It should converge within a few iterations. That's a pretty standard iterative method for when you don't have a computer that's willing to spend time doing gajillions of iterations.

P.S., this is presuming you are not a student and that you have a legitimate work related issue.

I'm feeling somewhat like a fossil as this was how I was taught to find to solutions to iterative problems. Don't they teach that anymore? Or is it that they just don't people to think?

Sorry madg1, not meaning to grouse at you. But if you want help, don't just say "do you have a standard," be explicit about what your question is. It further helps if you say what you've done yourself to try and solve the problem. Just because you're not getting the number you expect, doesn't mean that there's anything wrong with the equation, it may mean that there's a problem somewhere else that you need to look into.

Patricia Lougheed

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[vja]

thank u Patricia and dhengr for your responses....reg your questions about my laziness in stating the complete problem....here is my side of the story....
This standard in no longer available with ISO......but i need to use this because some other standard(API) I m using referred this....and this standard is little bit intense compared to many other standards i used...when I searched few details about this standard , I found almost none....which made me suspicious..about the standard itself..... So i just dropped a line if any one at all used the standard...
even eng tips got one only one thread mentioning about this......again which gave me a feel that use of this standard may be not a standard procedure....
Anyway I solved that equation....I know the process.....i just wanted to know how the people in industry used to deal it...if you guys got a chance to look at that standard...let me know....i can explain what i did......it included a fortan code which helped me to understand it....

 

[dhengr]

Vja:
You seem to have completely missed my point, and I suspect Patricia’s too. I don’t have that code, so I can’t even see the formula you were struggling with. And showing us a few pages of that, as I suggested in my earlier post might help us understand what you are trying to do, or what that standard was trying to achieve. Given our experience we might have some inkling of where that formula came from or what it is trying to represent. Obviously, you should also show the API section that sites the older code, so we can understand that relationship and intent too. Showing some sketches of your problem would help people understand it better too. And, that might lead to some constructive help. We can’t help you with your problem if we don’t know what it is, and you sure haven’t explained it so far, and we can’t see it from here. You are talking to a very narrow audience when all you say is how do you solve formula #738, without even showing it. You know a process for solving a formula which you know nothing about, in terms of its origin or meaning or intent, and one can’t help but wonder if you understand the whole picture. I don’t know the answer to the latter, only you can answer that. But, you might not get much more help on your problem, if you won’t flesh it out.

 

[JStephen]

Well, I've been working with cylinders subject to buckling loads for 27 years or so and never heard of that standard, if that helps any. Which API standard references it? What is the actual product form that you're working with?

 

[chicopee]

Here, try this link

http://www.excelcalcs.com/forum/con...r-critical-buckling-load,-contribution-pitch/

 

[chicopee]

F could be the factor of safety normally of 3.5

 

[vja]

Thank you guys for all of your inputs.I completed the calculation.I am scared because of the lack of its(standards) online presence ( i know it makes less sense)
if any one looking for this type of calculation, ANSI/(NFPA)T3.6.37-1991 or ISO 13725 serves the purpose.(@JStephen )
@chicopee---- thanks for the look up.F is the critical load and FOS you mentioned should work.The link your provided also refers ANSI/(NFPA)T3.6.37-1991,which helps.
@dhegr @patricia ----there are just too many variables to type in here and that is the reason I mentioned the standard name in the first place.But you guys really explained me how to approach the problem and ask a question.I will definitely implement it from the next time.

 

[dhengr]

Vja:

You say.... “I am scared because of the lack of its(standards) online presence ( i know it makes less sense).” And, well you should be..., scared, that is. You say... “I completed the calculation,” but the question is, do you have any idea what you are actually doing.

But, you can find damn near anything and everything on the internet if you look hard enough. And, I hope you know by now that you can’t believe and trust everything you find there, or here on E-Tips for that matter. What should scare the hell out of you, is if you can’t find the same information, or corroborating information, evidence, formulas and their origin and evolution, methods, etc. in any other more reliable reference source. A good text book, an engineering handbook on the subject, an industry standard that others actually recognize, etc.

You really need a local mentor or engineer familiar with this type of engineering if you are going to be doing this kind of work.

 

[vja]

@dhengr
sir
no offense but I strongly suggest you to find this standard before commenting further......this really helps reg things I m talking about...
I have complete understanding of the formulae in this standard..their origin and methods employed.. for sure my work will be validated by other tools and will reviewed...please don't miss my question...

 

[vpl]

vja who evidently used to be madgi

You need to understand that the people who respond on here don't always have a lot of time to devote to your very important questions. So give us as complete a picture as possible. Even if someone has a copy of a standard (that doesn't mean that it's at their fingertips, especially if it's obsolete. And they may not have the time or inclination to go dig it unless they know why they need to.

And please don't lecture those of us who have taken the time to try and help you. You gave us almost nothing and we still tried to help. It's not our fault that we're not mind readers. Even if we had the standard, we still would have no idea what your problem was. You noticed what I said was that I didn't have time to go look it up. However at this point I have no inclination to go look for it.

Patricia Lougheed

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