Hi guyz,
What does 3D Max Intensity really means?This term I found in Caeser 2 Vers.4.5 calculation output?Does it effected on our calculation if 3D Max Intensity is exceed the code stress allowable?

Thanks

This is a Von Mises summation and is not a Code Stress Summation it is an bit of more information for experienced people to ponder over and is not a B31 code stress calculation

For definition of stress intensity see ASME B & PV code SEC VIII DIV 2 APPENDIX 4.

Regards

If you want to see how CAESAR II computes these values, go to the SIF and Stress tab of the configuration module. Review the help text on the Yield Criterion directive.

Please go through the following web link previousely provided in this forum by John Breen Sir, if you can't locate your strength of materials book:

http://feaservices.com/fund_struct/fund_struct.html#General%203-D%20Stress%20State

But, as Dave Diehl had earlier opined "The piping codes have their own defined stresses and limits and I do not get uncomfortable when one of these "non-code" stresses exceed the code-defined allowable limits" - except some extraordinary situations, we should not employ Von Mises failure theory, as if the design fails we will be held responsible.

Engineers should deal tricky situations with tact, not by knowledge only.

regards,
sam

1.Von Mises stress,is used to estimate yield criteria for ductile materials. It is calculated by combining stresses in two or three dimensions, with the result compared to the tensile strength of the material loaded in one dimension. Von Mises stress is also useful for calculating the fatigue strength. Stress is in general a six-dimensional tensor quantity (a symmetric 3×3 tensor). Von Mises stress reduces this to a single number (a scalar) for the purposes of calculating yield criteria.
σ1,σ2,σ3, are the principal stresses. In the case of plane stress, σ3 is zero.
Finite element analysis results are typically presented as Von Mises stress.
The von Mises criterion states that failure occurs when the energy of distortion reaches the same energy for yield/failure in uniaxial tension.
2.Definition of stress intensity see ASME B & PV code SEC VIII DIV 2 APPENDIX 4.


Best regards,

We are making the same mistake as the followers of King Canute aka B31.3. (He or his followers thought he could command the tide to turn). He got his feet wet. Just because codes exclude something it doesn't mean it doesn't exist in the real world. 3D max intensity is put into the output because the code only requires certain forces to be included in the analysis. Most of the time this is not unreasonable. 3D Max intensity is included to cover those instances where the code simplification are inadequate. It is not just something for experienced stress engineers to play with.

Mizstress81, the only option is back to the code and text book.

Andrew,

Yes and No... when you look at the "quality" of some of the inquiries on this board and other places on the world wide web it seems to me just getting the work qualified to a code in a reasonable manner with a model that is accurate seems like more than one could hope for.

So what do you tell someone if the Von Mises stresses exceed the yield of the material???? and yet the calculated code stress meets code allowables.

Some of the following comes to mind with Von Mises Stresses...
Do you have an elastic followup problem i.e., an unbalanced system... then the next question you will hear is whats an unbalanced system?, etc. etc., so my reply stands any engineer that knows what a Von Mises stress is, will most likely have a grasp on what it really means and what to do with it...

I wonder if the model that stemmed this question is detailed enough? Does it take into account beam element short comings? Are all the SIFS correct? Are the bounday conditions correct? Is the temperature,displacements and pressure data correct or is this being simply analyzed to a "design temperature" based upon a pipe spec rather than the maximum or minimum operating conditions temperatures. And last but not least are the load cases set up correctly?

So Von Mises stresses are way down on the list of concerns... its kind of like the old saying if you have to ask about how much a luxury is perhaps you can't afford it.... yet.

Interestingly enough Von Mises was a fellow Austrian see ... http://en.wikipedia.org/wiki/Richard_von_Mises

Sir,
Customer gets what he pays for;'quality' is also factored in it. In Wal-Mart, don't you pay for the smile of the sales person, too ?

So, if a client replicates 15 MW unit Biomass based power plant for 3 identical twin-unit captive power stations in his own cement plant hoping for Climate Change CDM benefits, he gets the quality of the order you write for the reference plant design of steam piping. But, the same analyst gives an over-simplified print-out for a much serious service handling flammable fluid, if the deal needs up to that detail only. If client pays more, he can get more,too.

Moreover, to take credit for value addition, today's front-end smarts define small bore pipe thickness at sch 40, while raising corrosion allowance from 1.0 mm to 3.5 mm, retaining the original specification's design pr/temp & piping thickness. Everything is possible in Harry Potter's age, why to blame us, the piping analysts only , why don't we go to sufficient detail, when such situation arises ?

regards,
sam