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Frequently Asked Questions (FAQ)
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AnswerThe reason for this error message is the wrong title of the excel-sheet. The sheet with the acceleration data should be named "Acceleration Data" so that the module knows in which sheet the data is contained.
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.
AnswerYes the possibility exists. In many standards we have implemented this possibility. Here you can select the option "Other" as subsoil class and thus adapt some parameters according to your wishes.The following annexes to EN 1998-1 have this option: CEN, NBN, CSN, DIN, UNI, NP, STN, CYS, BS, NS and NF.
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.
AnswerThere are two options to choose from: an automatic time step selection and a manual one. Especially for a structure with nonlinearities, it is always recommended to manually select the time step and perform a time step convergence study that compares the computation time and accuracy.The time step to choose depends on many factors, including the excitation frequency, the frequency and size of the structure, and the degree of non-linearity. So no general statement about the size of the time step can be made.For detailed information on this and many other topics, see the <a href="https://www.dlubal.com/-media/3BEF143083FA4DC3A9463B0E4166CCF0.ashx" target="_blank"> manual </a> of the additional module RF- / DYNAM Pro.
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)
The RF-/DYNAM Pro - Equivalent Loads add-on module analyzes structural equivalent loads and export them into load cases. Further analysis is performed in RFEM or RSTAB then. Result combinations are created.
The RF-/DYNAM Pro - Forced Vibrations add-on module provides the multi-point response spectrum analysis. It means that buildings on different supports can excite different situations. Only the final result combination is created here, so you receive no equivalent load and the traceability is more difficult.
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).
The complete quadratic combination (Complete Quadratic Combination, CQC) is used if in the analysis of spacial models with mixed torsional / translational eigenvectors there are adjacent mode shapes, whose periods differ by less than 10 %. If this is not the case, the quadratic combination (SRSS) is used.
More information can be found in the literature mentioned below.
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