We have a doubt in the dinamic analysis.
What is the value to enter in the parameter : Stiffness Factor for Friction ?
How can i represent the friction in the dinamic modal ( Modal Analysis ) ?

Unless you are attempting to "tune" the CAESAR II dynamic results to actual measured field data, this input item should be left blank. In general, there is no way to know what value to specify for this parameter - unless attempting to match field data. This is especially true on a new system.

When attempting to "tune" the results, start with a value of "100", and then increase or decrease the value as needed to zero in on the target results. (If the pipe slides too much, increase this value, and if the {friction} load seems too high, reduce this value.) Once this has been accomplished, you can then adjust the system so that it no longer responds to the dynamic load.

You won't see any friction effects in a Modal Analysis, since this is a free, undamped evaluation.

NOTE: as other discussions (in this forum) on friction have indicated, there is no single answer to a friction problem. Even when performing a static analysis, there are multiple friction solutions. This is further complicated by the variability of the friction coefficient over time. A dynamic analysis just adds a layer of complexity and uncertanty to the problem.