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Frequently Asked Questions (FAQ)
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AnswerThe sum indicated in this table does not reflect the correct superposition according to the standard. This is a simple summing up of the equivalent loads. A superposition with the selected superposition rule (SRSS or CQC) is not performed in this table!Furthermore, there are differences if activating the accidental torsion in the add-on module. This leads to the generation of two load cases for each mode shape. They always contain the torsional moment in the positive and in the negative direction. As a result, the equivalent loads are doubled in this table.
First, the ribbed plate should not be modeled with the classic rib member from RFEM, but with an eccentric beam member that is arranged on the bottom surface of the actual plate. Rib members cannot be calculated with RF-CONCRETE NL with regard to deformations.
The eccentric beam is then designed in RF‑CONCRETE Members. In the "Serviceability Limit State" tab of Window 1.1, you can activate the "Nonlinear calculation.". In the detailed settings for the nonlinear calculation, you can activate the export of stiffness from the nonlinear calculation.
In the example presented here, the stiffness is exported "individually" for each LC calculated in RF‑CONCRETE Members. You can find more information about the options "Individual" and "Consistent for reference load" under the link below.
After the calculation in RF‑CONCRETE Members, the exported stiffnesses of the calculated COs are available in RFEM, where you can activate them in the respective COs for a new calculation of internal forces. To do this, activate the extra options of the respective CO. In the "Extra Options" tab, you can then activate the stiffness exported from the RF‑CONCRETE Members add-on module for a new determination of internal forces.
After recalculating the internal forces of the COs in RFEM (taking into account the exported stiffness from RF‑CONCRETE Members), you can apply them for design in RF‑CONCRETE Surfaces.
The following figure shows the deformations of the ribbed plate in RF‑CONCRETE Surfaces, taking into account the stiffness in cracked state from the design in RF‑CONCRETE Members.
In comparison to Figure 03, the linear-elastic stiffness in uncracked state (state I) was applied in Figure 04 for the eccentric beam.
Notes on the procedure described above:
- In this case, the calculation was performed in RF‑CONCRETE Members first, and the resulting stiffness was exported. This approach was selected because it was assumed that the eccentric rectangular cross-section will proceed to the cracked state (state II) first.
- The procedure shown "only" describes one iteration and is therefore only an "approximation" since an uncracked plate was assumed for the calculation of the eccentric rectangular cross-section.
- The shrinkage effect is applied as an external load in the NL calculation in RF‑CONCRETE Members. This means that, for example, an unsymmetric reinforcement would result in an additional curvature, even if the cross-section remained in the uncracked state. When calculating the plate in RF‑CONCRETE Surfaces, this effect of shrinkage on the member cross-section is not taken into account anymore.
In the design modules of RFEM or RSTAB, you can define "Provided Basic Reinforcement" and perform a nonlinear calculation in the ultimate limit state for this reinforcement.
As a result, you obtain the utilization ratio from the nonlinear calculation assuming the provided longitudinal reinforcement.
The nonlinear calculation is already included in the CONCRETE add-on module for RSTAB. In RFEM, the RF‑CONCRETE NL add-on module is required.
The temperature loads as surface loads on general glass cross-sections cannot be considered by modeling them as solid elements in the program. With the default settings, the glass pane is modeled by using 3D solid elements.
However, the 2D calculation allows for modeling temperature loads as surface loads. You can set this in the details of the layer structure, so that the 2D calculation (plate theory) is performed. In this case, it is also possible to consider the shear coupling between the layers, if necessary.
Further details on calculating and using laminated glass can be found in the technical article "Calculation and Use of Laminated Glass."
After the successful calculation, you obtain the results for the respective layer structure. Figure 04 shows the results as an example of a layer structure without shear coupling.
According to DIN EN 1993‑1‑1, 126.96.36.199 (2), the reduction factor χLT can be modified by the f factor for χLT,mod. You can activate or deactivate this option under National Annex Settings.
Spatial models with several directions selected in the RF‑/DYNAM Pro - Natural Vibrations add-on module display no separate results of mode shapes for the individual directions. It may happen that one mode shape of the vibrations is dominant in one direction (thus, the mass is only excited in one direction, such as in the X-direction only). However, it may also happen that one mode shape has vibrations in several directions at the same time (that is, the mass is excited in two or more directions, for example in the X- and Y-direction at the same time). Therefore, the mode shapes are not dependent on the global coordinate system, but on the stiffnesses of the structure in the individual directions.
You can check the direction, in which the dominant vibration of a mode shape acts, by displaying the "Effective Modal Mass Factors" table and checking whether the mass was excited in the individual directions. Figure 01 shows on the effective modal masses that the first mode shape acts solely in the Y-direction, the second one in the X-direction, and the third one is the torsional vibration.
It is possible to define several natural vibration cases and to only activate the masses in one direction. Thus, the mode shapes for each direction are obtained separately in each case.
AnswerIn addition to the stability analysis in Sections 6.3.1 to Section 6.3.3 of EN 1993‑1‑1 (Equivalent Member Method), RF‑/STEEL EC3 also provides the General Method according to Section 6.3.4 of EN 1993‑1‑1.This can be extended with the following options:~ The European lateral-torsional buckling curve, which is regulated in the German National Annex to EN 1993, for example.~ Extension of biaxial bending according to the dissertation by Dr. Naumes.~ The interpolation between lateral buckling and lateral-torsional buckling.When designing sets of members according to the General Method, a window is available in the Window "1.7 Nodal Supports - Sets of Members" where the nodal supports are displayed graphically on the set of members. In this way, the General Method represents a useful supplement to the other design methods, which has proven itself, particularly when designing tapers. It is not necessary to enter effective lengths in this method.In the "Details" of the add-on module, you can select the method to be used for sets of members in the "Stability" tab (see Figure 01).The equivalent member method may only be used for straight sets of members with a uniform cross-section (that is, not for tapered joints). For members with a variable cross-section, use the preset General Method.
AnswerThere is a detailed technical article (which is linked at the end of the FAQ) for considering the second-order theory in a dynamic order in RFEM. This article mainly describes the use of the add-on module RF-DYNAM Pro - Equivalent Loads. This add-on module does not enable any consideration in RSTAB.To correctly display the second-order theory in RSTAB, you have to use the add-on module DYNAM Pro - Forced Vibrations. Because in this add-on module, the results are fully calculated within the add-on module. If you were to export load cases first, the internal forces could not be calculated in relation to the modified stiffness matrix.
AnswerIn principle, RF‑/CONCRETE Columns designs the statically required reinforcement for a buckling analysis and generates a reinforcement proposal on this basis.As an alternative to this procedure, it is also possible to specify a certain minimum reinforcement ratio before starting the calculation. The input for this can be found in the '1.4 Reinforcement' mask in the register regarding the selected National Annex of EN 1992-1-1 (e. g. DIN EN 1992-1-1).A new reinforcement concept is defined based on the entries specified here and used to perform the designs.
In RF‑PUNCH Pro, a primary and secondary load is determined when introducing a compression and tensile force at a point of punching shear (for example, a column). For example, this may be the case when calculating a result combination (RC) that results from a previous dynamic analysis with RF‑/DYNAM Pro.
In this case, the tensile and compressive forces may occur at the connection of a column to a slab. The add-on module analyzes both "punching directions" individually and displays them as "primary load" and "secondary load."
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Wind Simulation & Wind Load Generation
With the stand-alone program RWIND Simulation, wind flows around simple or complex structures can be simulated by means of a digital wind tunnel.
The generated wind loads acting on these objects can be imported to RFEM or RSTAB.
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