Import of Stiffness Modifications
Tips & Tricks
In RF-/DYNAM Pro - Natural Vibrations, it is possible to import axial forces and stiffness modifications from any Load Case (LC) or Load Combination (CO). You can modify material, cross‑section, member and surface properties and activate those modifications in the LC/CO calculation parameters.
It is also possible to import stiffnesses from RF-/CONCRETE. Members or surfaces can be deactivated to analyze a modified structural system in RF-/DYNAM Pro. Axial forces and failing members are imported from the set LC/CO.
All stiffness modifications are initial conditions for the eigenvalue analysis performed in RF‑/DYNAM Pro. There, a linear calculation is performed.
When you want to consider axial forces only (for example prestress in cables or consideration of the P‑Delta effect) make sure that no stiffness modifications are activated in the calculation parameters of the imported LC/CO.
When you want to study certain stiffness modifications or deactivated members only, make sure you create a LC containing no loads but the stiffness modifications you are interested in.
Do you have questions or need advice?
Contact our free e-mail, chat, or forum support or find various suggested solutions and useful tips on our FAQ page.
Models to Download
Parametrized Model for Four Different Time History Analyses of Remote Explosion | Knowledge Base Article 001660
Knowledge Base Articles
Import of Axial Forces, Stiffness Modifications and Extra Options in RF-/DYNAM Pro - Natural Vibrations
Different natural frequencies without consideration (left) and with consideration of tension members (right)
Product Features Articles
Calculation with consideration of a damping ratio (or Lehr's damping) is not possible in the direct time step integrations. Instead, the Rayleigh damping coefficients must be specified by the user.
In technical literature, the given damping ratio for specific construction forms is in many cases only a rough approximation of the real damping ratios. In RF-/DYNAM Pro - Forced Vibrations, it is possible to use the value of damping ratio to determine the Rayleigh damping. This may occur at one or two natural angular frequencies defined by the user.
Frequently Asked Questions (FAQ)
- Why do I only obtain the seismic loads calculated in one direction in the case of design with RF‑/DYNAM Pro?
- During the check in RF‑/DYNAM Pro, I get the message "No natural vibration case or dynamic load case has been selected for the calculation." Why?
- Is it possible to display natural frequencies separately for each direction?
- What is the approach for seismic design in RFEM/RSTAB?
- What do the symbols mean in the graphical representation of the mode shapes of the RF-/DYNAM Pro add-on module?
- How is it possible to consider tension members in RF‑/DYNAM Pro?
- In RF-/DYNAM Pro, I get the error message: "The assigned mass case does not exist," although I have defined a mass case. What is the reason?
- In RF‑/DYNAM Pro, the "From self-weight of structure" option is available in a mass case. Is it always necessary to activate this option in order to consider the dead load of the structure?
- How can I consider prestressed cables in RF‑/DYNAM Pro?
- How many mode shapes do I need to consider in the dynamic analysis?
Dynamic analysis of natural frequencies and mode shapes of member, surface, and solid models