Hello Victor!
Thank you very much for your reply. I’d like to tell you about my findings:
Step 1: I created two exactly identical models (mesh refinement, stiffness model, support conditions), and, as expected, both have the same mode shape. Attached are the model with the top load for comparing the displacements, as well as the modal analysis for the 1st mode shape.
Step 2: Differences arise when the rigid diaphragm is added to the building model. Here is an example of how the natural frequencies change. In ETABS, I used the “rigid diaphragm” options and applied a stiffness modification of 0.001 to the slab’s “out-of-plane” stiffnesses to approximate the changes the slab undergoes in RFEM 6.
The model behaves much more rigidly in ETABS than in RFEM 6, so I’d be interested to know what changes to the rigid diaphragm cause the stiffness of my model to decrease so significantly.
Best regards!
Frank
Test Kern - ohne Starre Kopplungen.rf6 (1.5 MB)