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RF-FORM-FINDING Add-on Module for RFEM
The best I have used
“RFEM is the best I have used. I have experience with RISA, STAAD, ETABS, Visual Analysis, and others. In the tensile/fabric structure world, I've tried NDN, Forten, etc. Once you get used to RFEM's interface, it has no comparison to the others. Even with typical structures, it's much easier.”
Form-Finding of Membrane and Cable Structures
The RF-FORM-FINDING add‑on module searches for shapes of membrane and cable structures. The shape is calculated by the equilibrium of forces (specified prestress and additional load such as self‑weight, pressure, etc.), and given boundary requirements.
The new prestressed shape is afterwards used as the initial state for subsequent geometrically nonlinear static analysis. Cutting patterns for the membrane structures can be determined by the RF‑CUTTING‑PATTERN add‑on module.
- Form-finding of membrane and cable structures
- Interaction with supporting structure
- Membrane as a 2D and cable as a 1D element
- Definition of different prestress conditions for membranes
- Definition of forces or geometrical requirements for cables
- Consideration of loads (self‑weight, inner pressure) in the form‑finding process
- Temporary support definitions for the form-finding process
- Definition of isotropic or orthotropic material for structural analysis
- Optional definition of free polygon loads
- NURBS transformation for transferring model into form‑found shape
- Possibility of combined form-finding by integration of preliminary form-finding
- Graphical evaluation of the new form using colored coordinates and inclination plots
- Complete documentation of the calculation including user-defined adaptive evaluation figures
- Optional export of the FE mesh as DXF or Excel file
The form-finding function can be activated in the General Data dialog box, tab Options. Prestress (or geometrical requirements for cables) can be defined in the parameters for surfaces and beams. The form‑finding process is performed by calculation of an RF‑FORM‑FINDING case.
Steps of the working sequence:
- Creation of a model in RFEM (surfaces, beams, supports, material definition, etc.)
- Setting of required prestresses for membranes and force or length/sag for cables
- Optional consideration of other loads for the form-finding process (self‑weight, pressure)
- Setting of loads and load combinations for further structural analyses
After starting the calculation, the program performs form‑finding on the entire structure. The calculation takes into account the interaction between membranes, cables and supporting structure.
The form-finding process is performed iteratively according to URS (Updated Reference Strategy) by Prof. Bletzinger / Prof. Ramm. In this way, shapes in equilibrium are obtained considering the pre‑defined prestress. In addition, this method allows you to consider the self‑weight or interior pressure for pneumatic structures in the form‑finding process.
The prestress for membranes can be defined by two different methods:
- Tension method - prescription of required prestress in a membrane
- Projection method - stabilization especially for conical shapes
The result of the form‑finding process is a new shape and the corresponding inner forces. Usual results such as deformations, forces, stresses, and others can be displayed in the RF‑FORM‑FINDING case.
This prestressed shape is available as the initial state for all other load cases and combinations in the nonlinear structural analysis.
For more ease when defining load cases, the NURBS transformation can be used (Calculation Parameters / Form‑Finding). This feature moves the original surfaces and cables into the position after form‑finding.
By using the grid points of surfaces or the definition nodes of NURBS surfaces, free loads can be situated on selected parts of the structure.
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Interesting customer projects designed with the structural analysis programs by Dlubal Software.
Parameters for cables
Contour lines after form-finding in RFEM
Cable tensions after form-finding in RFEM
Option to export FE mesh as DXF or Excel file
Group of tents | Representation of contour lines in RFEM
Tension forces in cables and contour lines after form-finding in RFEM
Membrane structure before and after form-finding in RFEM
Form-finding for membrane-steel structure
FE mesh after form-finding
Hall with membrane roof
Contour lines after form-finding for a group of umbrellas
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