Modal Dynamic Analysis : P-delta Analysis

A modal P-delta analysis is similar to a modal analysis, only the deflected shape is the mode shape. The same model (with a few changes) can be used for both. The difference in the case of P-delta analyses is that the stiffness is modified to include geometric stiffness effects.

Modelling implications

A modal P-delta dynamic analysis is set up using the Analysis Wizard from the Analysis | New Analysis Task menu command. Select the Modal P-delta option. The next page is similar to the page for a modal analysis without P-delta effects with the difference in this case that a P-delta case should also be defined.

Results

The same set of results is available from a modal P-delta analysis as for a linear modal analysis.

If the geometric stiffness acts to stiffen the structure the result will be that the natural frequencies are increased, while if the geometric stiffness reduces the stiffness of the structure the result will be that the natural frequencies are lowered.