The Modal Analysis add-on determines the lowest eigenvalues of the 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 define additional masses manually at nodes, lines, members or surfaces. In addition, it is possible to influence the stiffness matrix by applying axial forces or stiffness changes of a load case or load combination.
The main features of the 'Modal Analysis' add-on are:
- Automatic consideration of masses from self-weight
- Possibility 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
- Ability to neglect masses of any object in the model
- Masses in mesh points displayed in tables and graphics
- Possibility of defining several modal analyzes (for example, to examine different masses or changes in stiffness)
- Various mass matrix types (diagonal matrix, consistent matrix, unit matrix) including user-defined definition of the translational and rotational degrees of freedom
- Optional import of initial states (e.g. to take preload and imperfection into account)
- structure modification
- Optional consideration of failing 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 network nodes
- Output of modal masses, effective modal masses, and effective modal mass factors
- Output of participation factors
- Representation and animation of the mode shapes with scaling options
- Export of the result tables to Excel
- Result Documentation in Printout Report
In the add-on 'Modal Analysis' of the RFEM 6 program, three eigenvalue solvers are available:
- Lanczos
- Root of characteristic polynomial
- Subspace iteration
The following eigenvalue solvers are available in the add-on 'Modal Analysis' of the RSTAB 9 program:
- Subspace iteration
- Shifted inverse power method
The selection of the eigenvalue solver depends primarily on the size of the model. Recommendations for this can be found in chapter Modal Analysis Settings .