We provide hints and tips to help you get started with the RFEM program.
Pneumatic Membrane Structures with RFEM & RF-FORM-FINDING
Video
First Steps with RFEM
Description
Pneumatic structures are extremely lightweight air supported structures. The existing internal pressure gives the enveloping membranes structural integrity to counteract external loadings.
Utilize RF-FORM-FINDING to design air-inflated single-layer membrane systems, such as air domes, and double-layer membrane systems – including pneumatic cushions. Calculate positive or negative pressure systems or combination of both.
Typical membrane materials, including ETFE, are possible to define. Nonlinear material models capture the more realistic membrane strain behavior.
Determine the membrane shape with a permanent positive or negative pressure application within the gas solid. The prestressed shape determined with the form-finding process can now resist external loads.
Calculate all load situations for open and closed (without compressors) systems, and design the membranes for short-term and long-term loads such as wind and snow.
Additionally, design the supporting structure according to the various cross-section and stability design within a single program.
Keywords
Dlubal Product Feature ETFE Pneumatic structure Pneumatic cushions Pneu Low pressure system Tube structure Membrane structure Negative pressure Positive pressure Internal pressure Air-supported structure Pressure lock Product description for the feature Product Feature Dlubal Software feature
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The RF‑FORM‑FINDING add-on module determines the equilibrium shapes of membrane and cable elements in RFEM. In this calculation process, the program searches for a geometric position in which the surface stress/prestress of membranes and cables is in equilibrium with the 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, and 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, and so on, and generates a corresponding prestressed model for further analysis.
Compared to the RF-/ALUMINUM add-on module (RFEM 5/RSTAB 8), the following new features have been added to the Aluminum Design add-on for RFEM 6/RSTAB 9:
- In addition to Eurocode 9, the US standard ADM 2020 is integrated
- Consideration of the stabilizing effect of purlins and sheets by rotational restraints and shear panels
- Graphical display of the results in the gross section
- Output of the used design check formulas (including a reference to the used equation from the standard)
- What is the easiest way to simulate a cushion for the RF‑FORM‑FINDING add‑on module?
- When generating the FE mesh of an ETFE cushion, some problems occur. I cannot find any mistakes. What can I do?
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The limit stress is activated, but my stress ratio is “non-designable” in the Stress-Strain Analysis add-on. What could be the reason?
- How do I define a member as a cantilever and not as supported at both ends for serviceability or deflection design?
- Why do the results in a modal analysis differ between the initial prestress and the surface load?
- Where can I find the materials for the corresponding National Annexes in RFEM 6 and RSTAB 9?
- How do I apply wind load on members of open structures?
- Although I have modeled two identical structural systems, I obtain a different shape. Why?
- I encountered a sharing violation while importing a dxf file into SHAPE‑THIN. What is the issue?
- How do I define a member as a cantilever and not as supported at both ends for serviceability or deflection design?
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