Form-Finding | Calculation
The form-finding process of the load cases with the load case category "Prestress" shifts the initial mesh geometry to an optimally balanced position by means of iterative calculation loops. For this task, the program uses the Updated Reference Strategy (URS) method by Prof. Bletzinger and Prof. Ramm. This technology is characterized by equilibrium shapes that, after the calculation, almost exactly comply with the initially specified form-finding boundary conditions (sag, force, and prestress).
In addition to the pure description of the expected forces or sags on the elements to be formed, the integral approach of the URS also enables a consideration of regular forces. In the overall process, this allows, for example, for a description of the self-weight or a pneumatic pressure by means of corresponding element loads.
All these options give the calculation kernel the potential to calculate anticlastic and synclastic forms that are in an equilibrium of forces for planar or rotationally symmetric geometries. In order to be able to realistically implement both types individually or together in one environment, the calculation specifies two ways to describe the form-finding force vectors:
- Tension method - description of the form-finding force vectors in space for planar geometries
- Projection method - description of the form-finding force vectors on a projection plane with fixation of the horizontal position for conical geometries
RFEM 6 includes the Form-Finding add-on to determine the equilibrium shapes of surface models subjected to tension and members subjected to axial forces. Activate this add-on in the model's Base Data and use it to find the geometric position in which the prestress of lightweight structures is in equilibrium with the existing boundary conditions.
Membrane Roof and Cable Net Structures, Deformation Animation in RFEM with RF-FORM-FINDING Add-on Module.
Compared to the RF-FORM-FINDING add-on module (RFEM 5), the following new features have been added to the Form-Finding add-on for RFEM 6:
- Specification of all form-finding load boundary conditions in one load case
- Storage of form-finding results as initial state for further model analysis
- Automatic assignment of the form-finding initial state via combination wizards to all load situations of a design situation
- Additionally form-finding geometry boundary conditions for members (unstressed length, maximum vertical sag, low-point vertical sag)
- Additional form-finding load boundary conditions for members (maximum force in member, minimum force in member, horizontal tension component, tension at i-end, tension at j-end, minimum tension at i-end, minimum tension at j-end)
- Material type "Fabric" and "Foil" in material library
- Parallel form-findings in one model
- Simulation of sequentially building form-finding states in connection with the Construction Stages Analysis (CSA) Add-On
- Why do the results in a modal analysis differ between the initial prestress and the surface load?
- Although I have modeled two identical structural systems, I obtain a different shape. Why?
- How is it possible to make factorized combinations of a dead load in the context of form‑finding?
- My aim is to mesh a circular hole plate in a mapped way. Is such a meshing possible in RFEM?
- It seems that the members stay not deformed after my RF-FORM-FINDING calculation. What did I wrong?
Can I export my cutting pattern?
- How do I model a tent roof with two cone tips?
- How do I model a suspended membrane roof structure with line supports?
- I would like to calculate and design "temporary structures." What do I need for this?
- I have already divided my membrane roof into individual surfaces. Can I quickly create a cutting pattern from these surfaces?
The Form-Finding add-on finds the optimal shape of members subjected to axial forces and tension-loaded surface models. The shape is determined by the equilibrium between the member axial force or the membrane stress and the existing boundary conditions.