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Useful Program Features
The Knowledge Base includes technical articles on a wide array of structural analysis and design topics.
These articles are intended to help you navigate through the Dlubal programs, learn efficient tips and tricks, and provide further insight to the program features.
Why Dlubal Software?
Critical load factors and the corresponding mode shapes of any structure can be efficiently determined in RFEM and RSTAB using the RF-STABILITY or RSBUCK add-on module (linear eigenvalue solver or nonlinear analysis).
The RF‑STABILITY and RSBUCK add‑on modules for RFEM and RSTAB allows you to perform eigenvalue analysis for frame structures in order to determine critical load factors including the buckling modes. It is possible to determine several buckling modes. They provide information about the model areas bearing stability risks.
Evaluation of Local and Global Mode Shapes Using RSBUCK for Determination of Equivalent Member Length
When performing the stability analysis of members according to the equivalent member method, considering internal forces according to the linear static analysis, it is very important to determine the governing equivalent member lengths.
The previous post on this topic describes instabilities that may occur when using tension members. The example shown refers primarily to wall stiffening. Now, instability error messages can also refer to nodes within the range of supports. Especially truss girders and support trusses are susceptible to this. So what causes the instability here?
When analyzing structural elements susceptible to buckling by using the modules RF‑STABILITY (for RFEM) or RSBUCK (for RSTAB), it might be necessary to activate the internal division of members. If there are, for example, truss members, these are not divided internally. In this way, a global buckling mode is determined as first eigenvector in the stability analysis (see Picture 1). When activating the member divisions, we see that a local buckling of the structure is governing (see Picture 2). The figure shows the option for activating the division in RF‑STABILITY.
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