Form-Finding for RFEM 6

Product Description

  • Add-on Module of Category "Other"

Form-Finding of Membrane, Cable, and Beam Structures

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."

Doctoral Thesis on Membrane Structure Design According to FEA

Rostislav Lang Master's Thesis

This doctoral thesis by Rostislav Lang deals with the design and analysis of membrane structures using FEA software.

The Form-Finding add-on finds the optimal shape of members subjected to axial forces and tension-loaded surface models. The program determines the shape by the equilibrium between the member axial force or the membrane stress and the existing boundary conditions. The resulting new model shape with impressed force conditions is available for you as a universally applicable initial state for further calculation of the entire structure.



  • Form-finding of tension-loaded membrane and cable structures
  • Compression form-finding of member-shaped supporting structures
  • Form search taking into account the entire system with subsequent design
  • High quality form-finding by using the iterative URS method
  • Pneumatic prestress by means of gas pressure loads
  • Use of an ideal gas in a membrane
  • Geometric and force-based form-finding specifications for member components
  • Isotropic and orthotropic surface prestress
  • Stabilized form-finding for conical shapes with tangential and radial prestress
  • Organization of all form-finding specifications in one load case
  • Application for isotropic and orthotropic materials with distinct warp and weft direction
  • Consideration of nonlinear material laws by means of the "Nonlinear Material Behavior" add-on
  • Staggered form-finding processes and temporary model supports by means of the "Construction Stages Analysis (CSA)" add-on
  • Output of a universally applicable form-found initial state with impressed strains
  • Graphical form evaluation by means of colored coordinate and inclination plots
  • Automatic assignment of the initial state by load combination wizards
  • Display of all results on the initial and deformed shape as well as the incremental results on the respective deformed element geometry


Once you activate the Form-Finding add-on in the Base Data, a form-finding effect is assigned to the load cases with the load case category "Prestress" in conjunction with the form-finding loads from the member, surface, and solid load catalog. This is a prestress load case. It thus mutates into a form-finding analysis for the entire model with all member, surface, and solid elements defined in it. You reach the form-finding of the relevant member and membrane elements amid the overall model by using special form-finding loads and regular load definitions. These form-finding loads describe the expected state of deformation or force after the form-finding in the elements. The regular loads describe the external loading of the entire system.



Do you know exactly how the form-finding is performed? First, 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, comply almost exactly 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 provide you with 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


The form-finding process gives you a structural model with active forces in the "prestress load case" This load case shows the displacement from the initial input position to the form-found geometry in the deformation results. In the force or stress-based results (member and surface internal forces, solid stresses, gas pressures, and so on), it clarifies the state for maintaining the found form. For the analysis of the shape geometry, the program offers you a two-dimensional contour line plot with the output of the absolute height and an inclination plot for the visualization of the slope situation.

Now, a further calculation and structural analysis of the entire model is performed. For this purpose, the program transfers the form-found geometry including the element-wise strains into a universally applicable initial state. You can now use it in the load cases and load combinations.



  • Simulation of a mechanical and pneumatic prestress
  • Consideration of isotropic and orthotropic prestresses on cartesian or radial coordinate systems
  • Finding stress-harmonic planes, synclastic, anticlastic, or combined shapes
  • Simulation of multi-layer foil cushions, considering the ideal gas law between the layers
  • Provision of the form-found overall model geometry for determining the wind loads via an optional wind analysis in the digital RWIND wind tunnel

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Dlubal Software is a member of the TensiNet Association .


1,950.00 EUR

The prices apply to the use of the software in all countries.

Cross-Laminated Timber (CLT) Building


The Multilayer Surfaces add-on allows you to define multilayer surface structures. The calculation can be carried out with or without the shear coupling.

Price of First License
1,250.00 EUR