In a static analysis, loads are defined and internal forces are determined. A dynamic analysis, on the other hand, is based on masses . For the add-on ' Modal Analysis ', there are several options for defining masses for determining the natural frequencies and mode shapes.
Import masses
You can import loads and masses from a load case to which you have assigned the analysis type 'Modal Analysis ', and thus use them directly for the modal analysis (see image image027385 Load case of the type' Modal analysis ' for direct load transfer ). You can also take over masses from another load case or a load combination (see picture image027386 Take over masses from load case and picture image027388 Take over masses from load combination ). It imports load types such as forces and moments and converts them to masses.
You can make further specifications for the masses (mass conversion type, mass matrix settings, neglecting masses) in the modal analysis settings .
Forces are converted into masses using the mass conversion constant , which is used for the model - Basic information is stored. The default setting for g is 10 m/s² (1 kN = 100 kg).
You can combine load cases in a design situation to form an earthquake/mass combination (see picture # extbookmark manual|image027382|Design situation 'earthquake/mass combination' #).
Define masses
In addition to or as an alternative to the options described for importing masses, you can manually define node, line, member or area masses in a modal analysis load case or define area moments of inertia. These possibilities are described in chapter Additional masses .
If you have set ]] a 'multiplication factor' for the load, this is not taken into account for the modal analysis. In this case, set the factor of the load case in an # extbookmark manual|LC-manually|manually defined load combination # to scale the masses.