The Modal Analysis add-on provides you with the option to automatically increase the sought eigenvalues until a defined effective modal mass factor is reached. All translational directions activated as masses for the modal analysis are taken into account.
Thus, it is possible to easily calculate the required 90% of the effective modal mass for the response spectrum method.
Building stone on stone has a long tradition in construction. The Masonry Design add-on for RFEM allows you to design masonry using the finite element method. It was developed as part of the research project DDMaS - Digitizing the Design of Masonry Structures. Here, the material model represents the nonlinear behavior of the brick-mortar combination in the form of macro-modeling. Do you want to find out more?
You have several options available to define masses for a modal analysis. While the masses due to self-weight are considered automatically, you can consider the loads and masses directly in a load case of the modal analysis type. Do you need more options? Select whether to consider full loads as masses, load components in the global Z-direction, or only the load components in the direction of gravity.
The program offers you an additional or alternative option for importing masses: A manual definition of load combinations as of which are the masses considered in the modal analysis. Have you selected a design standard? You can then create a design situation with the Seismic Mass combination type. Thus, the program automatically calculates a mass situation for the modal analysis according to the preferred design standard. In other words: The program creates a load combination on the basis of the preset combination coefficients for the selected standard. This contains the masses used for the modal analysis.
Automatic consideration of masses from self-weight
Direct import of masses from load cases or load combinations
Optional definition of additional masses (nodal, linear, or surface masses, as well as inertia masses) directly in the load cases
Optional neglect of masses (for example, mass of foundations)
Combination of masses in different load cases and load combinations
Preset combination coefficients for various standards (EC 8, SIA 261, ASCE 7,...)
Optional import of initial states (for example, to consider prestress and imperfection)
Structure Modification
Consideration of failed supports or members/surfaces/solids
Definition of several modal analyses (for example, to analyze different masses or stiffness modifications)
Selection of mass matrix type (diagonal matrix, consistent matrix, unit matrix), including user-defined specification of translational and rotational degrees of freedom
Methods for determining the number of mode shapes (user-defined, automatic - to reach effective modal mass factors, automatic - to reach the maximum natural frequency - only available in RSTAB)
Determination of mode shapes and masses in nodes or FE mesh points
Results of eigenvalue, angular frequency, natural frequency, and period
Output of modal masses, effective modal masses, modal mass factors, and participation factors
Masses in mesh points displayed in tables and graphics
Visualization and animation of mode shapes
Various scaling options for mode shapes
Documentation of numerical and graphical results in printout report
In the modal analysis settings, you have to enter all data that are necessary for the determination of the natural frequencies. These are, for example, mass shapes and eigenvalue solvers.
The Modal Analysis add-on determines the lowest eigenvalues of the structure. Either you adjust the number of eigenvalues or let them determined automatically. Thus, you should reach either effective modal mass factors or maximum natural frequencies. Masses are imported directly from load cases and load combinations. In this case, you have the option to consider the total mass, load components in the global Z-direction, or only the load component in the direction of gravity.
You can manually define additional masses at nodes, lines, members, or surfaces. Furthermore, you can influence the stiffness matrix by importing axial forces or stiffness modifications of a load case or load combination.
Do you want to consider other loads as masses in addition to the static loads? The program allows that for nodal, member, line and surface loads. For this, you need to select the Mass load type when defining the load of interest. Define a mass or mass components in the X, Y, and Z directions for such loads. For nodal masses, you have an additional option to also specify moments of inertia X, Y, and Z in order to model more complex mass points.
You can already see it in the image: Imperfections can also be taken into account when defining a modal analysis load case. The imperfection types that you can use in the modal analysis are notional loads from load case, initial sway via table, static deformation, buckling mode, dynamic mode shape, and group of imperfection cases.
It is often necessary to neglect masses. This is particularly the case when you want to use the output of the modal analysis for the seismic analysis. For this, 90% of the effective modal mass in each direction is required for the calculation. So you can neglect the mass in all fixed nodal and line supports. The program automatically deactivates the associated masses for you.
You can also manually select the objects whose masses are to be neglected for the modal analysis. We have shown the latter in the image for a better view. A user-defined selection is made the and the objects with their associated mass components are selected to neglect the masses.