Software for Form-Finding & Cutting Patterns of Membrane Structures

Membrane structure after form-finding in RFEM

Calculation in RFEM

The structural analysis software RFEM designs membranes together with the supporting structure (for example cables).

Membranes can be modelled as general and quadrangle surfaces. The quadrangle surfaces are general quadrilateral surfaces whose boundary lines do not have to rest in one plane. Therefore, it is possible to model surfaces with anticlastic and synclastic curvature, which is characteristic for the membrane structures.

The surface types Membrane and Membrane-orthotropic are available for design. In the type Membrane-orthotropic, it is possible to define different stiffness properties dependent on the direction. Moreover, it is possible to define different directional stiffness properties for the surface type Membrane Orthotropic.

In addition, RFEM provides an option to model and design the connection plates, fittings, and others.

RFEM Add-on Module RF-FORM-FINDING | Form Finding of Membrane and Cable Structures

Form-Finding of Membrane and Cable Structures

RF‑FORM‑FINDING 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.

RFEM add-on module RF-CUTTING-PATTERN | Cutting Patterns of Membrane Structures

Cutting Patterns of Membrane Structures

RF‑CUTTING‑PATTERN generates and organizes cutting patterns for membrane structures. Boundary conditions of the cutting patterns on curved geometry are determined by boundary lines and independent planar cutting lines or geodesic cutting lines. The flattening process is performed according to the minimum energy theory.

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Calculation in RSTAB

In the frame & truss analysis software RSTAB, it is possible to design the primary construction of membrane and cable structures. Form-finding and framework design may be carried out in the engineering software Easy by Technet. The modular program system Easy performs especially the geometrically nonlinear calculation of membranes and pneumatic cushions. RSTAB has a special connection to this design program used for light framework structures.

The internal forces are determined in Easy by Technet where the membrane is also dimensioned. Then, it is necessary to import the data to the structural analysis program RSTAB by Dlubal Software in order to perform the design and stability analysis.

Since the stiffnesses may affect the forces in a membrane significantly, the cross-sections optimized in RSTAB are returned to Easy for recalculation during the iterative process. After the design, RSTAB can also be used as a tool for documentation of the structural analysis including tables and graphics.

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Add-on Modules for Structural Analysis of Cable and Membrane Structures

In addition to the RF-FORM-FINDING and RF‑CUTTING‑PATTERN add‑on modules for RFEM, you can find more useful add‑on modules for structural analysis of cable and membrane structures under the Steel Structures industry.

Knowledge Base | Form-Finding and Cutting Patterns

  1. Figure 01 - Basic Shapes of Membrane Structures [4]

    Specific Requirements of Membrane Structures

    This paper is focused on the specific aspects of designing membrane structures. These structures have specific requirements such as form-finding and cutting patterns generation. These topics are the focus of many research works and there are many methods proposed to achieve the desired results. However in this paper these issues will be discussed more from the practical point of view than from the theoretical one. The paper will be followed by examples, which will complement the discussed topic and show the special attention required during the design process.

  2. 1 - General Data

    Form-Finding in RFEM

    The RF-FORM-FINDING add-on module determines equilibrium shapes of membrane and cable elements in RFEM. In this calculation process, the program searches for such a geometric position in which the surface stress/prestress of membranes and cables is in equilibrium with natural and geometric boundary conditions. This process is called form-finding (hereinafter referred to as FF). The FF calculation can be activated in RFEM globally in the "General Data" of a model, "Options" tab. After selecting the corresponding option, a new load case or a calculation process called RF-FORM FINDING is created in RFEM. An additional FF parameter is available for defining surface stress and prestress when entering cables and membranes. By activating the FF option, the program always starts the form-finding process before the pure structural calculation of internal forces, deformation, eigenvalues, etc., and generates a corresponding prestressed model for further analysis.

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Product Video: Add-on Modules RF-FORM-FINDING & RF-CUTTING-PATTERN

Dlubal Webinar: Form-Finding and Cutting Patterns of Membrane Structures in 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.”

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Dlubal Software is a member of the TensiNet Association.

Screenshots and Application Examples | Form-Finding, Cables & Membranes