Selection of Retained DOF nodes

I have read through the Dynpac Manual Section 2.1 on Retained Degrees of Freedom.
I understand that Dynpac uses a set of master (retained) degrees of freedom, selected by the user, to extract the Eigen values (periods) and Eigen vectors (mode shapes).

However, I'm wondering if there is any further guidance on determining exactly which nodes should be selected for a particular structure.

Any help or helpful links would be appreciated.

Thanks

  • You typically want to select degrees of freedom which will capture the major mode shapes of the structure and also allow for a large mass participation. Usually you want to select the translation degrees of freedom along the primary legs, major bracing locations, primary deck overhangs and flare boom towers. However this is also dependent upon what type of dynamic behavior you are analyzing.

    I would recommend using Sample06 provided in the SACS installation as a good starting point for your retained degrees of freedom. Then check you mode shapes using the Postvue database to make sure that you aren't missing any modes and looking at the mass participation report in the Dynpac listing file to ensure that you have a good mass participation in each direction.