A membrane is stretched by means of isotropic prestress between two radii of two concentric cylinders not lying in a plane parallel to the vertical axis. Find the final minimum shape of the membrane - the helicoid - and determine the surface area of the resulting membrane. The add-on module RF-FORM-FINDING is used for this purpose. Elastic deformations are neglected both in RF-FORM-FINDING and in the analytical solution; self-weight is also neglected in this example.
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RFEM and RSTAB are able to cover a large number of branches in the building and construction industry with their generally usable structural frame analysis and FEM programs. Designing cable structures is thus also possible in both software solutions. Some assistance tools for modeling and design will be presented in the following text.
Cable and tensile membrane structures are regarded as very slender and aesthetic building structures. The partly very complex double-curved shapes can be found using suitable form-finding algorithms. One possible solution is to search for the form via the equilibrium between the surface stress (provided prestress and an additional load such as self-weight, pressure, and so on) and the given boundary conditions.
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Das Zusatzmodul RF-FORMFINDUNG ermittelt in RFEM Gleichgewichtsformen von Membran- und Seilelementen. In diesem Berechnungsprozess sucht das Programm für die Membran- und Seilelemente eine geometrische Lage, in der die Oberflächenspannung/Vorspannung der Membranen und Seile im Gleichgewicht mit den natürlichen und geometrischen Randreaktionen steht. Dieser Prozess heißt Formfindung (nachfolgend FF genannt). Die FF-Berechnung wird in RFEM global in den "Basisangaben" eines Modells im Register "Optionen" aktiviert. Nach Aktivierung werden in RFEM ein Lastfall beziehungsweise ein Berechnungsprozess mit dem Namen RF-FORMFINDUNG angelegt und für die Seil- und Membraneingabe zusätzlich FF-Parameter zur Definition der Oberflächenspannung und Vorspannung freigeschaltet. Die Aktivierung der FF-Option bedeutet für das Programm, dass vor der reinen strukturellen Berechnung der Schnittgrößen, Verformung, Eigenwerte etc. immer zuerst der Formfindungsprozess gestartet und für die Folgeberechnung ein entsprechend vorgespanntes Modell vorgegeben wird.
There is a known complexity in calculating footfall response on irregular floors or staircases of any type. Footfall Analysis uses the RFEM model and the modal analysis results of RF-DYNAM Pro - Natural Vibrations to predict the vibration levels at all locations on a floor. A rigorous analysis method is essential to enable an accurate investigation of the dynamic behavior of the floor.
The software incorporates the most up-to-date analysis procedures, allowing the user to select between the two most often used calculation methods available, namely the Concrete Centre Method (CCIP-016) and the Steel Construction Institute Method (P354).
- Footfall Analysis links with RFEM, using the model geometry from there, thus the user is not required to create a second model specifically for footfall analysis
- Allows the user to analyze any type of structure for footfall analysis, irrespective of the shape, material, or use
- Quick and accurate predictions of resonant and impulsive (transient) responses
- Cumulative measurement of vibration levels – VDV analysis
- Intuitive output enabling the engineer to advise improvements of critical areas in a cost-effective way
- Pass/fail limit check in accordance with BS 6472 and ISO 10137
- Selection of excitation forces: CCIP-016, SCI P354, AISC DG11 for floors and stairs
- Frequency weighting curves (BS 6841)
- Quick investigation for full model or specific areas
- Vibration Dose Analysis (VDV)
- Adjusting the minimum and maximum walking frequencies as well as the walker’s weight
- User input damping values
- Varying the number of footfalls for resonant response, user input or software calculated
- Environmental response limit based on BS 6472 and ISO 10137
- Overall maximum response factors and critical nodes
- Resonant analysis (maximum response factor, RMS acceleration, critical node, critical frequency)
- Impulsive (transient) analysis (maximum response factor, peak acceleration/velocity, RMS acceleration/velocity, critical node, critical frequency)
- Vibration dose values for both resonant and impulsive analyses
Charts
- Response factor vs walking frequency
- Mass participation vs eigenmodes
- Velocity time history
With the activated option 'Topology on Form-Finding Form' in Project Navigator - Display, the model display is optimized based on the form-finding geometry. For example, the loads are displayed in relation to the deformed system.
Although I modeled two identical systems, I got a different shape. Why?
How is it possible to make factorized combinations of a dead load in the context of form‑finding?
It seems that the members stay not deformed after my RF‑FORM‑FINDING calculation. What did I wrong?
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