For models with members, the modal analysis is influenced by the specifications for the member divisions. The settings for RFEM and RSTAB are managed in program-specific dialog boxes.
Mesh Settings (for RFEM)
The FE mesh affects the determination of the eigenvalues.
Masses are applied to the FE nodes. Members on which no FE nodes are created as a result of a division and which are also not integrated into surfaces receive only one FE node at the member start and one at the member end. In the case of a diagonal mass matrix, the masses of these members are concentrated on the two end nodes. If these nodes are supported, it may not be possible to calculate eigenvalues.
To force the member division for such members, check the network settings in the 'tab Members' Activate the Member divisions for straight members check box . For the example shown above, eleven FE nodes are created on the 5.0 m long beam with a desired FE length of 0.5 m. The masses now not only act on the supported nodes. In this way, mode shapes can be determined.
Member divisions (for RSTAB)
The member divisions affect the determination of the eigenvalues.
Masses are applied to the division points. Members for which no member division is specified have only one division point each at the member start and end. In the case of a diagonal mass matrix, the masses of these members are concentrated on the two end nodes. If these nodes are supported, it may not be possible to calculate eigenvalues (see figure 027704 Incorrect eigenvalues ).
To force the member divisions, enter # extbookmark manual in the dialog box|image034229|Member divisions for the calculation # provide a corresponding number of division points. This allows the mode shapes to be determined.
The largest value "N" of the member divisions is used for the modal analysis. The longest member of the model is divided by this value "N". This results in the maximum member division length. This length is used to determine the member divisions of all other members: The bar lengths are divided by the division length and rounded up to the next whole number.
