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  • Answer

    Yes, because a different GammaM factor according to DIN18008 is applied for the determination of the allowable limit stress for different glasses, it is also stored in our material library. However, the consequence is that by activating this option, the stiffness of the system is reduced by this factor.
    Especially when calculating solid loads (Climatic loads), the reduced stiffness of the system also affects the calculated stresses and deformations.

  • Answer

    It is not possible to outsource the calculation to a cluster for RFEM.

    One way to relieve computer workstations of complex calculations is to:

    RFEM is installed on a terminal server with well-equipped hardware. Every member of staff who has to carry out complex calculations receives access to the server via remote desktop.

    Network licenses are required for this option.

  • Answer

    Check if you entered "Nonlinearities" in your structure. For example, "Failing supports", "Nonlinearities (compression or tension members)" or "Nonlinear material behavior" (see Figure 01).

    This warning appears as soon as you try to add load cases for result-combinations in such structures (see Figure 02).

    When adding load cases of the result combination (RC), only the results of the individual load cases are added. This means that you may not be able to represent the "Nonlinearities" correctly because a member may not be displayed correctly. For example, it fails in one load case, but does not in another load case. When using RC's, you would thus add up the results from different structural systems. This leads to incorrect results.

    In these cases, use the load combinations (COs). In this case, a large load case (load combination) will be created and this load situation combined is calculated. Allows for correct representation of nonlinearities in the structure.

    As an alternative - if a calculation with the RCs is required due to the calculation time - you can consider whether the nonlinearities will be absolutely necessary.
  • Answer

    Often, these problems can be solved easily and effectively.

    Especially in the edge areas of plates, the results often oscillate. In this case, the result can be improved by modeling a foundation collar with a negligible thickness around the surface. It is assigned the same foundation as the main plate. The support collar shows the edge area of the slab more accurately and the convergence behavior is often better.

    It is important that the foundation collar at least reaches sufficiently far that the settlement depression has subsided completely. Thus, it is also possible to graphically represent the influence of settlement on surrounding buildings graphically.

  • Answer

    First, select the type of stiffness modification to be carried out in the Edit dialog box of the respective surface in the "Modify Stiffness" tab. For example, as shown in Figure 01, by using the "multiplication factors".

    Multiplication factors can be specified for the different stiffness components (for example, membrane stiffness).

    Whether the factors or the set stiffness modification are applied in the individual load cases or load combinations is controlled by the calculation parameters. Now, this means that the modification is taken into account as soon as the check box shown in Figure 02 has been set. When you remove the check box, the modifications will not be considered for the surfaces.

    Thus, it is possible to control the stiffness modification by load case or load combination.
  • Answer

    When entering formulas with values without dimensions, it is assumed that they are SI units. Is the searched-for unit not a SI unit, but a multiple thereof (for example,? kN instead of N), the result is factorized accordingly. For the example in the figure, 1000 N / m = 1 kN / m would be the case.
  • Answer

    The asymmetrical equation solver can improve the convergence. However, it should only be activated if there are really convergence problems.

    For certain material models, you are also prompted to switch on the unsymmetric equation solver.

    For the "normal" equation solver, only one side of the matrix has to be stored because it is symmetric to the main diagonal. In the case of the asymmetric equation solver, both sides have to be stored and, of course, generated beforehand. This takes more RAM and a longer processing time.

    For a model that already converges well, the unsymmetric solver results in a longer computing time.

  • Answer

    Finite elements with plastic material are divided into 10 layers. First, a normal elastic analysis is performed in the first iteration. Then, the stress is calculated in each element according to the adjusted strength hypothesis in each individual layer. If the limit stress in one of the layers is exceeded, the stiffness of this layer is reduced. Based on the reduced stiffnesses of the 10 layers, a total stiffness is determined for each element. With this new stiffness, a new calculation iteration is started.

    Iterates until the changes are only small.

    The total stress is converted into the stresses of the individual layers by means of the laminate theory. This theory is also used for the conversion between the stiffnesses of the layers and the total stiffness.

    4 different strength hypotheses can be used as the limit stress:

    • Shape Modification Energy Hypothesis (von Mises-stress)
    • Shear stress hypothesis (Tresca stress)
    • Failure hypothesis according to Drucker-Prager
    • Failure Hypothesis According to Mohr-Coloumb

    The failure hypothesis is displayed in Figure 1.

    The von Mises hypothesis is preset because it is the most frequently used strength hypothesis.

  • Answer

    The finite element types used in RFEM are given in the following table. They are chosen automatically
    by the program according to the situation.

    Element Type Element description

    1D: beam element element with rotational degrees of freedom

    2D: plate element Lynn–Dhillon; MITC3; MITC4 – used in case of nonlinear calculation
    2D: wall element with stabilized zero energy modes
    2D: shell element shell element = plate element + wall element

    3D:  solid element element with rotational degrees of freedom; element without rotational degrees of freedom (with or without extra shape functions)
    gas element
    contact element

    Integration Procedure

    For members, analytical integration is used for linear cases, while in the nonlinear setting the two
    point Gauss quadrature is used along the beam. For nonlinear cases the following integration rule
    is used in the cross-section: 2×2 Gauss quadrature for quadrangles and 4-point selective reduced
    integration rule for triangles (3 points for 𝜖x, 𝜖y and 1 point for 𝛾xy).

    In plate elements, analytical integration is used whenever possible (in Lynn–Dhillon element or in
    a triangular element). In other cases, a 2×2 composite Gauss quadrature is used in the element
    plane (quadrangles). In solids, a 2×2×2 composite Gauss quadrature is used in hexahedrons.
    Reduced one point integration is used for some particular terms to avoid numerical problems.

    Let us focus on integration in plates with respect to their thickness, which is based on the Gauss–Lobatto quadrature. The Gauss–Lobatto quadrature is a Gauss quadrature in which boundary points
    are forced to also be integration points, which allows an exact evaluation of stresses on layer
    interfaces in case of multilayered plates. In case of linear calculation, three integration points are
    used per layer. In nonlinear calculation, nine integration points are used in the plate (nonlinear
    calculation allows one layer only).
  • Answer

    The module works according to DIN 18800 and proof with torsional forces is not possible there. An elastically plastic proof with torsion is possible with the STAHL EC3 module.

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