Modal Analysis - Minimum Initial Strain
Answer
In the modal analysis settings, you can set the minimum axial strain for cables and membranes in order to apply an initial prestress to the objects and thus improve the convergence of the calculation. The initial prestress is applied to the objects in a simplified approach.
If you compare this setting with the surface load of the Axial Strain load type, you should pay attention to the fact that the two approaches differ. With the surface load, you perform a calculation in such a way that the actual prestress can deviate from the specified prestress. The calculation also takes into account other boundary conditions, such as the Poisson's ratio of the material.
You can easily check this if you vary the Poisson's ratio of the material. A Poisson's ratio unequal to 0 means that the deformation in the x- and y-direction of the surface interacts, which no longer leads to a constant stress/strain over the entire surface.
If the Poisson's ratio is 0, you obtain the same results.
Keywords
Cable Membrane Initial prestress Modal analysis Initial strain
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New
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.
New
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
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