3.6.7: Natural Vibrations
To determine how and at what frequency a structure vibrates, use the “NaturalVibrations” component. Fig. 3.6.7.1 illustrates a simply supported steel beam (IPE100) with a point mass at mid-span in its 10th natural vibration mode.
The mass of beams and trusses is calculated based on their material weight. Karamba3D employs consistent mass matrices for beam elements, while a lumped approach is used for truss and shell elements. Additional masses can be defined at nodes (see section 3.1.9) to simulate the effect of components such as concrete slabs, which typically constitute the majority of mass in high-rise structures. These additional masses are assumed to have translational inertia only.
Karamba3D scales the resulting vibration modes so that their largest component is 1. These modes are attached to the model as result cases, which can be viewed using the “ModelView” component. The calculation of modal mass and participation factors is based on these scaled modal displacements.
The input plugs “ThII?” and “LCasesNII”, as well as the inputs under “Options”, have the same meaning as those in the “Eigen Modes” and “Buckling Modes” components.
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