Hi
I want to ask about plastic hinges which mentioned in CAESAR II application guide P.3-52.My questions are:
1- When should I use it?
2- Which support needs to be analyzed by this method?
3- At which cross section of the support should i add the plastic hinge?

Thank you
Best regards

In my opinion, plastic hinges speak more of what CAESAR II CAN do rather than what a user SHOULD do.
We design systems so they do not collapse (i.e. our longitudinal stress due to sustained loads). A plastic hinge indicates such collapse.
The example you mention in the applicatin guide shows yielding due to thermal strain. Typically, an elastic evaluation (no yield) is emplyed here as it is conservative.
I see the use of this feature limit to "forensic" engineering rather than "design" engineering - that is, to evaluate what actually happened in the field, after it happens. If it yielded and you want to check the response, then try the pastic hinge.

Some more info: A plastic hinge is a type of energy dampening device allowing plastic rotation of an otherwise rigid column connection. This device is composed of a weakened portion of the column prevented from rotating by relatively small steel members. These small bars are designed to yield and allow rotation before the capacity of the column is reached,thus acting as mechanical fuses protecting the column from fatigue.

Thanks Dave; I am agree with you and that answers the question of any cross section should i add it into the model as we could know it after failure.

Thanks SJ; this point is important as it acts as fatigue protector. So we have new application for it rather than failure investigation. And we can use in design stage also, could you tell me at which cross section on the support leg should I add it? And have i to add it for any support leg exposed to fatigue? for example [ Hot bypass line have a support with leg such as trunnions ].
Thank you
best regards

To be very true, I don't find its usage in Pipe Stress analysis....This is more of a structural design concept for seismic resistant structures!!!

Strict with Dave's words...we (I mean Pipe stress engineers) don't design for collapse!!!

Thanks SJ, and i will Strict with Dave's words , again many thanks for you and Dave.