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Frequently Asked Questions (FAQ)
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With the COM interface, you can access most operating elements as well as results of the following programs or add-on modules:
- RF- / STEEL EC3
- RF- / CONCRETE
- RX-TIMBER Glued-Laminated Beam
- RF-/TIMBER Pro
- RF- / DYNAM Pro
AnswerBefore you can start the calculation in the add-on module, you should check each tab. This message appears if you have not opened the calculation parameters of the natural mode case at least once. Although a bulk case has been defined, it has not yet been assigned to the natural mode case.
AnswerIn this case, you have the option to print the image in the timeline diagram directly into the printout report. Here you proceed as described in the picture.
Each multi-mass system can usually be represented by a single-mass system. When you do this transformation, you need the modal mass of the system. This mass is needed to generate the frequency of the equivalent single-frequency oscillator.Beiteilungsfaktor
This factor can also be negative because it is composed of the substitute mass at a node and the associated displacement due to the eigenform. If the deflection is in the negative direction, the participation factor becomes negative. The replacement mass factor is then still positive, since the participation factor is squared. (see formula)equivalent mass
The equivalent mass of a system is a part of the total mass which is excited due to the vibration of the multi-mass oscillator. The equivalent mass of a system can be between zero and the total mass. The replacement mass factor is only the quotient of the total mass to the substitute mass. As a rule, this makes it possible to check more quickly what proportion of the excited mass of the respective eigenform is. Should it happen that the substitute mass factor is greater than 1, one should check the discretization of the system and, if necessary, refine the division of the nodes or the FE mesh.For an earth analysis, the substitute mass factor and the substitute mass are usually decisive, since these values are used to calculate the dynamic equivalent loads on the building.
AnswerThis setting defines how the defined loads in RFEM / RSTAB are handled in the dynamic module, since they only have to be transformed in bulk.Z-load components: When this option is selected, only those masses that act in the Z-direction are considered. This includes the positive as well as the negative direction. This option is preset because it is required in most cases. Loads such as earth pressure defined in a horizontal direction are not taken into account.Z-load components (in the direction of the gravitational force): In this case, the loads are considered only in the positive Z-axis. If you want to use this option, you should check in which direction the Z-axis was defined. With this option, it does not matter in which direction you apply the self-weight in a load case.Full load as mass: With this option, all loads are converted into masses, both horizontal and vertical.
In RF‑DYNAM Pro ‑ Natural Vibrations, it is possible to import the geometrical stiffness matrix. You can use it to consider the second‑order analysis. The equivalent lateral loads for earthquakes generated with the RF-DYNAM Pro - Equivalent Loads add-on module take this stiffness modification into account.
In the attached file, it is described when the second-order analysis according to EC 8 has to be considered and which options are offered by the Rf-DYNAM Pro modules.
Second-order analysis.pdf (471 kB)
AnswerTo study a system with tension members in RF-/DYNAM Pro it is recommended to define several Natural Vibration Cases (NVCs) and to use the stiffness modification options. The natural vibration analysis is a linear analysis of frequencies and mode shapes, tension members are considered as trusses in RF-/DYNAM Pro and can cope with tension and compression to the same degree. To estimate how the frequencies change when the tension members fail you can import this initial state into RF-/DYNAM Pro via a Load Case where you deactivate the members manually or via a Load Case where the tension members failed due to the load state. The defined NVCs can be assigned to Dynamic Load Cases (DLCs) to perform, for example, a response spectrum anaylsis with the export of equivalent loads (add-on module RF-/DYNAM Pro Equivalent Loads).
The equivalent loads that are exported into Load Cases in the main program RFEM / RSTAB are evaluated with consideration of all nonlinearities, in some cases this can lead to conflicts. An example is illustrated in the picture. In the first case no stiffness modifications are used in RF-/DYNAM Pro and therefore all members are considered in the dynamic analysis, but in RFEM / RSTAB the tension member fail due to equivalent loads. When you want to perform a completely linear analysis you must deactivate the nonlinearities in RFEM / RSTAB. In the second and third illustrated case an initial condition is imported where the tension members are not available. The equivalent loads are therefore based on the same structure as the structure for the calculation of internal forces and deformations.
In the response spectrum analysis or the time history analysis with the add-on module RF-/DYNAM Pro Forced Vibrations the modified stiffness of the Natural Vibration Cases (NVCs) is also used for the calculation of further results. The overall linear analysis with consideration of initial conditions is performed within the module RF-/DYNAM Pro.
AnswerNo, the calculation is always linear. All nonlinarities (for example failure at tension, nonlinear material, etc.) are ignored. Cables or tension members can be replaced by the "Truss" member type, for example.
Yes, they are considered in the eigenvalue analysis (Natural Vibrations module) and in the time history analysis (Forced Vibrations module) as well as in the response spectrum analysis (Forced Vibrations and Equivalent Loads modules).
It can be determined as many eigenvalues as there are degrees of freedom in the structure to which a mass is assigned. In order to determine the number of degrees of freedom, the number of nodal points of FE nodes must be multiplied by the active mass directions. The masses in fixed supports are not considered for this as they cannot freely oscillate.
If the 'Divison for straight members' (RFEM) / 'internal member division' (RSTAB) is not activated, it may happen, for example in the case of single-span beams, that the masses only exist in the supports and thus no eigenvalue can be determined. In such cases, activate the member division as shown in the figures.
Since the Lanczos solver in RF-DYNAM Pro cannot determine all existing eigenvalues, the 'root of the characteristic polynomial' solving method can also provide remedy.
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