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  • Answer

    For cross-section and stability designs, the Eurocode provides for different partial safety factors. It is important to note if stability analyzes are carried out by applying the second-order analysis and applying imperfections as cross-section designs. In this case, reduce the resistances with γM1.

  • Answer

    The stiffness type "Membrane Without Tension" describes the plate and block stiffness of surfaces.


    The plate stiffness including the shear stiffness perpendicular to the surface plane is linearly elastic and the plate stiffness in the surface plane is defined nonlinearly elastic with the material model according to "Drucker-Prager" depending on the defined thickness and the assigned material.


    In order to ensure that the surface behaves "Without Tension" in the pane direction, the nonlinear material model reacts with yielding tensile stress fy,t going to almost zero in tension-loaded elements in combination with a relatively small hardening modulus Ep . For compression forces, however, the elements remain linearly elastic due to a relatively high yielded compressive stress fy,c and react with an unrestricted compression transmission.


    Since the "Membrane Without Tension" stiffness type fundamentally modifies the wall-related degrees of freedom of surfaces, it is only applied to surfaces of the relevant model types 3D, 2D - XZ (uX/uZY) and 2D - XY (uX/uYZ ).

    To better describe the partial nonlinearity of this surface stiffness type, the release RFEM 5.06.1103 from 4.02.2016 renames the type from "Without Tension" to "Membrane Without Tension".

    The Knowledge Base article "Modeling Approaches for Shear Bearing Connections by FEM" shows a possible application.











  • Answer

    The most suitable combination is a member elastic foundation with nodal supports, which may fail each.

    Figure 01 - Bolted Support on a Bracket to a Member

    Figure 1 shows a model with such a support. As it is obvious from the results, the member elastic foundation absorbs the compressive forces and the nodal supports absorb the tension forces.

  • Answer

    In case of the result values are displayed in red, it refers to an error message.
    The defined thickness z is then not sufficient. The standard specifies that the thickness must be calculated up to the value where sigma_Z is ≦ 0.2* sigma_ü. In the graphic, 0.2 * sigma_ü is displayed as a gray line, sigma_Z as red.

    The layer structure should have such a thickness that both lines intersect.
    In Figure 1, the two lines do not intersect, so that the values are displayed in red and a sufficient thickness must be defined.

  • Answer

    The "Incrementally Increasing Loading" function of load cases and load combinations can incrementally increase the assigned load level and find an equilibrium for each load increment. The reference level “Load Increment 1.0 = 100% of the defined load” is the defined loading for load cases and a modified set of loads with partial safety factors for the load combinations. The detail settings of the function define the initial load increment k0 , the quantity of load increment Δk, the refinement of the last load increment, the break-off criterion, and the statical initial load situation.
    When defining the initial load step k0, the start of the process is specified. This input is independent of the simple input of the load case and load combination and can be greater than or less than 1.0. The program always displays all results on the basis of the load increment 1.0 within the regular calculation and carries out the additional analysis of the possible load increments by activating the “Incrementally Increasing Loading”.

    The the incrementally increasing loading is specified by the load increment Δk. With each process loop, the program increases the load to be analyzed by adding the increment to the previously analyzed load increment. The increment is constant until the break criterion is reached.

    Due to the constant increment size, it is not possible to determine an exact load factor according to the break criterion. Finally, the program shows the approximate load factor on the basis of the last load increment at which an equilibrium can be found for the model. After the calculation in Table “4.0 Results — Summary”, the load factor is displayed in the relevant load situation. By specifying a refinement of the last load increment, the initial increment Δk is divided by the refinement value after the break criterion is reached and the process is performed from the last functioning load increment until the new break-off again. Due to the smaller increment, the resulting load factor is more accurate.

    The break-off criterion for the process is basically the point at which the program can no longer find an equilibrium for the applied load (second-order analysis). In addition, you can specify the break-off by activating a maximum deformation on a particular node.

    Since certain force components remain constant in reality, regardless of the action (e.g. self-weight, prestress, etc.), the detail setting provides an option for the assignment of a fixed load component for the incrementally increasing load. The fixed load can either be a load case or a load combination. This load component is independent of the loading to be increased and is simply added to the variable component in the process.

    If the intermediate results of the active load increments are of interest in addition to the final load factor, it is possible to use the load case and load combination function "Save the Results of Load Increments" to display the intermediate results. Corresponding options are available in the panel window and in the result tables.

    In RSTAB, the activation for saving the intermediate results is coupled with the RSBUCK add-on module and in RFEM, the activation of the incrementally increasing load is coupled with the RF-STABILITY add-on module. In these cases, a license of the corresponding add-on module must be provided in addition to the licensing of the main program.

  • Answer

    The nonlinear contact between transverse member and membrane can be done by a set of member elements between the member and the surface. This requires that the member is situated eccentrically in the plane of the compressive force resulting from the membrane effect and the connection line of the membrane connection. The geometric distance between member and membrane itself has to be aligned to the physical distance between member axis and membrane connection.

    To ensure that the coupling runs homogeneously over the entire coupled length, it is necessary to ensure a uniform arrangement with the same number of FE nodes on the member axis and on the projected contact line on the membrane surface. This distribution and orientation of the FE nodes is achieved by placing the corresponding topology nodes on the member axis and the corresponding line of contact on the surface. The distance of the topology node should be selected affine to the selected grid mesh size of the connected membrane surface.

    The coupling itself must be designed with a rigid member failing nonlinearly under pressure load between the resulting nodal pairs. In this case, the specified nonlinearity must be implemented with a member nonlinearity "Ineffectivity During Tension". The connection of the rigid member in the area of the eccentric member is completely compatible (bending-resistant) and must be carried out with a free translational release in the y-/z-axis which is related locally to the rigid member axis in the area of the membrane.

    Due to the selected nonlinearity and existing alignment with the compression force resultant in connection with the free translational release, this contact modeling is able to transfer only compression forces to the connected cross beam. In case of a suction load, the coupling components fail and the membrane moves away from the secondary beam unhindered.



  • Answer

    The option controls applying of new structural elements in current stages to the already existing, deformed structure.

    Initial position:
    The new elements are applied with orientation to the initial position, i.e. to the provided geometry. The deformations are compensated throughout the construction process. Theoretically, there is a buckling in the geometry (Figure 02 1.)

    Tangential:
    The new elements are applied with the orientation of already deformed existing elements, that is, tangent to them. The deformations are not compensated throughout the construction process. Theoretically, there is no buckling in the geometry (Figure 02 2.)


  • Answer

    Such a connection can be created with a line release. Figure 1 shows an example model where wall 1 should transfer only compressive forces to wall 2.

    First, the dialog box for creating a line release needs to be opened (Figure 2). In the dialog box (Figure 3), you can now select the lines for release and the type. The type must also be created. The coordinate system of the line specifies the direction so that the release "If vy positive" must be selected (Figure 4). 

    Figure 5 and 6 show in two load cases, how the line release works.


  • Answer

    The module is designed for prestress in the immediate or subsequent composite. The templates for the tendon geometry are based on parabolic diagrams. This means that the modules are not explicitly designed for the calculation of flat slabs.

    Possible Figure:

    The geometric distribution for the free span of the tendon can not be determined automatically by the add-on modules. However, it is possible to use a user-defined tendon diagram as a basis. A prestress without bond could be set by adjusting the friction factors.

    The deformation analysis can not be performed in the RF-TENDON and RF-TENDON Design add-on modules . However, a deformation analysis on the side of RFEM in conjunction with RF-CONCRETE NL or RF-CONCRETE Deflect and applying the equivalent prestressing loads could be carried out here. The equivalent prestressing loads are exported without influence of long-term losses and would have to be reduced by a factor corresponding to these losses in RFEM.


  • Answer

    To consider nonlinearities in Dynamics, RFEM / RSTAB requires the addition of a Nonlinear Time History Method. This addition is different in RSTAB and RFEM by the type of nonlinearities to be applied.

    RSTAB Nonlinear Time History Method:

    Nonlinear member types such as tension members, compression members, and cables

    Member nonlinearities such as failure, tearing, and yielding under tension or compression

    Supports nonlinearities such as failure, friction, diagram, and partial effect

    Joint nonlinearities such as friction, partial action, diagram and fixed for positive or negative internal forces


    RFEM Nonlinear Time / Course Process

    In addition, you can work with nonlinear material behavior
     

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