G'day folks!
Referring to the application guide, it says that in order to make Caesar 2 choose a Constant effort Hanger, one should specify a very small allowable travel. Say 1 inch (26mm). When I do enter 26mm in the "Rigid support displacement criteria", the resulting recommended hanger is a variable spring. Is there any way I can get around this?

I believe the Applications Guide says to use 0.001 inches. Basically you want a very small number that you know will be exceeded - hence a variable spring won't work.

A better way is to specify a small variability percentage on the actual spring "card" in the input. This way you do not have to mess with the general set-up. You may need variable types in other parts of the calc.

I second Bobs approach the field he is talking about is the input window that carries the springs data....

Hey guys... correction to my earlier posting... I was specifying 0.001 inch (not 1 inch) and it was still picking a variable spring.

Thanks Bob... what would you say is a small variable percentage? 5%?

try .001

The Rigid Support Displacement Criteria field is on the individual hanger auxiliary (dialog) - see the figure below.

Hey Richard, this discussion forum is just getting better and better fith more functionality such as that previous post.. What Bob is saying though... is it not regarding the tab just before what you highlighted?... the allowable load variation that is normally sitting on 25%? I thought he meant reducing this to a smaller percentage of which I am asking if 5% would be enough. Another side issue... in the application guide it says that once the predefined hanger data is completed, and say for a Constant Effort support load, this column is filled in... does the Design Data entries now become defunct and not considered during the load case calculations?

If you completely predefine a spring at "node X", then that particular spring is no longer designed by the software. So "yes", the design data for that particular spring is defunct.

Pickles,
Your question made me think for a while. Usually I am trying to avoid using a constant spring.
There is another parameter that causes a selection to be a constant spring hanger. If the available space for spring hanger is not sufficient, the selection defaults to the constant hanger. For example, if the Anvil Fig. 82 height dimension is input for the space available, but the spring selection requires a Fig. B-268, or even a Fig. 98 with double stack spring, then the selection defaults to a constant spring hanger.
I think if you input a small available space, say 4 inches, then the constant spring selection will be the result for any movement greater than the rigid support displacement criteria.

All of you are looking at the wrong field. The documentation says you should enter a very small "Allowable Travel" -- not "Rigid Support Displacement Criteria". That would be the following field, the "Max. Allowed Travel Limit". Any hanger for which the expected thermal travel exceeds this value will be designed as a Constant Spring. The "Rigid Support Displacement Criteria" is used to force a rigid rod hanger (for any hanger location where the thermal movement is less than that value).