How to consider tension members in RF-/DYNAM Pro?

Answer

To study a system with tension members in RF-/DYNAM Pro it is recommended to define several Natural Vibration Cases (NVCs) and to use the stiffness modification options. The natural vibration analysis is a linear analysis of frequencies and mode shapes, tension members are considered as trusses in RF-/DYNAM Pro and can cope with tension and compression to the same degree. To estimate how the frequencies change when the tension members fail you can import this initial state into RF-/DYNAM Pro via a Load Case where you deactivate the members manually or via a Load Case where the tension members failed due to the load state. The defined NVCs can be assigned to Dynamic Load Cases (DLCs) to perform, for example, a response spectrum anaylsis with the export of equivalent loads (add-on module RF-/DYNAM Pro Equivalent Loads).

The equivalent loads that are exported into Load Cases in the main program RFEM / RSTAB are evaluated with consideration of all nonlinearities, in some cases this can lead to conflicts. One example is shown in the Figure 1. In the first case no stiffness modifications are used in RF-/DYNAM Pro and therefore all members are considered in the dynamic analysis, but in RFEM/RSTAB the tension member fail due to equivalent loads. When you want to perform a completely linear analysis you must deactivate the nonlinearities in RFEM/RSTAB. In the second and third illustrated case an initial condition is imported where the tension members are not available; the equivalent loads are therefore based on the same structure as the structure for the calculation of internal forces and deformations.

When using the response spectrum analysis in the RF-/DYNAM Pro Forced Vibrations add-on module, the modified stiffnesses of the natural vibration case (NVC) are also used for the further calculation of the results. The entire linear calculation considering the initial conditions takes place within the RFEM-DYNAM Pro add-on module.

Keywords

Tension member Tension members Nonllinear Dynamic  Response spectrum analysis  Equivalent loads

Contact us

Contact Dlubal Software

Did you find your question?
If not, contact us via our free e-mail, chat, or forum support, or send us your question via the online form.

(267) 702-2815

info-us@dlubal.com

RSTAB Dynamic Analysis
DYNAM Pro - Forced Vibrations 8.xx

Add-on Module

Dynamic and seismic analysis including time history analysis and multi-modal response spectrum analysis

Price of First License
1,120.00 USD
RSTAB Dynamic Analysis
DYNAM Pro - Equivalent Loads 8.xx

Add-on Module

Seismic and static load analysis using the multi-modal response spectrum analysis

Price of First License
580.00 USD
RFEM Dynamic Analysis
RF-DYNAM Pro - Equivalent Loads 5.xx

Add-on Module

Seismic and static load analysis using the multi-modal response spectrum analysis

Price of First License
760.00 USD
RSTAB Dynamic Analysis
DYNAM Pro - Natural Vibrations 8.xx

Add-on Module

Dynamic analysis of natural frequencies and mode shapes of member models

Price of First License
850.00 USD
RFEM Dynamic Analysis
RF-DYNAM Pro - Natural Vibrations  5.xx

Add-on Module

Dynamic analysis of natural frequencies and mode shapes of member, surface, and solid models

Price of First License
1,030.00 USD