Hey guys i was just going through the Computational control terms and their application

Can somebody answer the following question of mine:

There is a Use pressure stiffening term with the options of Default/yes and No....In the caesar built in help...it states that "This flag enables CAESAR II to include pressure-stiffening effects in those codes that do not explicitly require its use. In these cases pressure-stiffening effects will apply to all bends, elbows, and both miter types. In all cases, the pressure used is the maximum of all pressures defined for the element. Pressure Stiffening effects are defined in Appendix D of B31.1 and B31.3."

What i understood from this that this options allows the pressure-stiffening effects at the bends etc to be incorporated in our calculation...the default options means that caeser will take the bourdon effect off, and pressure stiffening as per Appendix D of above codes.....what does it mean if we select the yes and NO options???

also tell me if we are analyzing a pipeline under B31.4, then what option should we select out of these three?? Pressure stiffening effects are not defined in B31.4

Hi Umair

1) Pressure stiffening
Caesar Default --consider ASME B 31.3 Appendix D Note-7
If Select Yes----consider ASME B 31.3 Appendix D Note-7
If Select NO---- Do not consider ASME B 31.3 Appendix D Note-7

2) Bourdon Effect
Caesar Default --do not consider for metallic piping but consider for GRE/FRP.
If Select TRANSLATION ONLY --Consider only translation effect for straight pipe & bend
If Select ROTATION & TRANSLATION --translation effect + rotation for oval bend.



Regards

Habib

hello habib thank you

also tell me if we are analyzing a pipeline under B31.4, then what option should we select out of these three?? Pressure stiffening effects are not defined in B31.4??

can u please reply this one??

Also it would be a great help if you could explain and elaborate on the terms rod tolerance, rod increment and alpha tolerance....whats their usage and the effect of the change in their values

thanks

Hi Umair

I have not used B 31.4.
Yes Appendix D is not there like B 31.1/B31.3
I suggest you stick to default Caesar setting.
Whatever menu you want to know , put cursor there & press "F1" Caesar help will display the detail.

Regards

Habib

well i know that thing but the explanation for the terms i have asked for is not clear from what i get from the help so it would be very kind if you can explain these terms

Umair,

In simple terms: Imagine the bahavioural changes in a beam when it is loaded by a lateral force and when it is loaded by a tensile force as well as the lateral force. Is it not the case that it is easier to bend it with the lateral force alone? Instead of tensile force if you use compressive force the bahaviour is just the opposite ( recall bifurcation buckling) .

The above phenomenon is what is known as geometric stiffening , this is a type of non linearity knwon as geometric non linearity.The addition or reduction in stiffness is not a function of the material and dimensions of th beam while the conventional stiffness ( AE/L, EI/L^3,GJ/L etc )of the beam is a function of these parameters. Stress stiffening is this phenomenon.

Bourdon effect on the other hand is extension of the pipe due to pressure loading. A very simple case: If the pipe is a loaded with a force at each end= PXA, is its axial extension not equal to:PD/4ET ( considering poisson ratio =0)? Treat it like displacement induced loading.

Regards

... and as to the CAESAR II options on that particular Configuration Directive:

"Default" means do whatever the active piping Code says. So if you run a Code that includes pressure stiffening on bends, then CAESAR II will include pressure stiffening. On the other hand, if you are running a Code that does not include pressure stiffening on bends, then CAESAR II will not include pressure stiffening.

The options "Yes" and "No" permit you to deviate from the "Code" default - sometimes necessary when trying to match results for older systems or other applications.

In general, you want to leave this set to "Default".

Umair,
Check Note 7 in the Flexibility and SIF table of B31.4

Thank you for your support in earlier questions guys...can you please clarify me some further stuff

1. Rod increment: It is the maximum amount of change in the angle of the rod rotation between successive iterations. The default is 1.0 degree, but this number can be decreased in difficult to converge models.

question : My question is that how can please explain this term in detail to me also tell me how can decreasing the angular rotation of rods help in convergence???

2. rod tolerance: it is the maximum change in rod rotation between iterations for convergence to occur.

Question: Explain how this differs from rod increment and yet again explain how changing this value can effect the iteration issue encountered in a model with large rotation rods??

I shall be very thankful

The increment is how much the angular position will be changed in successive iterations. The smaller the increment, the longer the solution may take to converge, but there is less chance of stepping over a position that will converge.

The tolerance is the difference in positions that is acceptable to be considered converged.