I have a doubt in a Stiffness - Restraint and Anchors. This may be silly for the experienced engineers, but for me its pretty tough to handle.

In Caesar, under Restraint option, we can find the stiffness option. In which the stiffness default value for restraint and Anchors are 1.0E12.

I came across one situation (i.e) due to lack of piping flexibility the pump nozzle loads are more and i considered the pump end connection to be rigid (Anchor) due to low temperature of (180 def farneheit).

In the Caesar restraint option, when i input the Stiffness value for Anchor (pump end connetion) as 1.0E10, the nozzle load decreases and less than the allowable values.

Is this way of approach is correct to reduce the pump or other equipmnent nozzle load. Also the restraint summary report shows the type of support as "Flex Anch". If this approach is wrong, can someone tell me for which case this option can be used.

Also i require some details regarding this stiffness values (i.e) for type of restraints, what will be the stiffness values ????.

Can someone clarify this issue, waiting for your kind and good reply to proceed further.

Maybe. A restraint is a boundary condition. You typically want your boundary conditions to be much more rigid than anything else in the model. "Rigid" denotes a "big" stiffness. What does "big" mean? That is a hard one to answer, "big" means different things to different peopl. I believe the value of 1E12 has its origins in the old main frame pipe stress programs of the 1970's, but someone older than I will have to confirm that.


If the stiffness of a boundary condition is less than the default of 1E12, CAESAR II will include the term "Flexible" in the description.


I can't argue (in general) with a value of 1E10 as a "rigid" stiffness. However, this is something that you would want to agree on at the start of a project, or as a "corporate" default. Changing this (or some other value) just to push a result from one side of the "pass / fail line" to the other is (in my opinion) wrong. If your system is that sensitive to the "rigid stiffness value" I'd bet you have more than one item close to its limit. Now ask yourself "how sure are you of all the other parameters (such as wind speed, or friction factor)"?

You asked what this option is for. This (Configuration Directive) was added for benchmarking purposes. We ran into a few test jobs where (believe it or not) the 1E12 wasn't sufficient. We had to actually increase the restraint stiffness to 1E15 (and in some cases 1E20) to achieve the level of accuracy we were shooting for. This was more of an academic exercise than anything else.

In general, my recomendation is to leave this alone - unless you have some project or company standard that justifies changing it.