The Modal Analysis add-on determines the lowest eigenvalues of a structure. You can specify how many eigenvalues are to be determined. Masses are directly imported from load cases or load combinations (with the option to import the total mass or only the Z-component of loads). You can manually define additional masses at nodes, lines, members, or surfaces. Furthermore, you can influence the stiffness matrix by applying axial forces or stiffness modifications of a load case or load combination.
The main features of the "Modal Analysis" add-on are:
- Automatic consideration of masses from self-weight
- Option to import masses directly from load cases or load combinations
- Preset combination coefficients for various standards (EC 8, SIA 261, ASCE 7, ...)
- Optional definition of additional masses (nodal, line, member, and surface masses as well as mass moments of inertia) directly in the load cases
- Option to neglect masses of any object in the model
- Masses in mesh points displayed in tables and graphics
- Option to define several modal analyses (for example, to analyze different masses or stiffness modifications)
- Various mass matrix types (diagonal matrix, consistent matrix, unit matrix), including user-defined definition of translational and rotational degrees of freedom
- Optional import of initial states (for example, to consider prestress and imperfection)
- Structure modification
- Optional consideration of failed supports or members, surfaces, and solids
- Output of eigenvalue, angular frequency, natural frequency, and natural period
- Determination of mode shapes and masses in nodes or FE mesh nodes
- Output of modal masses, effective modal masses, and effective modal mass factors
- Output of participation factors
- Visualization and animation of mode shapes with scaling options
- Export of result tables to Excel
- Result documentation in a printout report
The "Modal Analysis" add-on for RFEM 6 includes three eigenvalue solvers:
- Lanczos
- Root of characteristic polynomial
- Subspace iteration
The "Modal Analysis" add-on for RSTAB 9 includes two eigenvalue solvers:
- Subspace iteration
- Shifted inverse power method
The selection of the eigenvalue solver depends primarily on the model size. You can find the recommendations in the chapter Modal Analysis Settings.