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- One software package for all application areas
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- Proven software used in many well-known projects
Why Dlubal Software?
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.
Both the determination of natural vibrations and the response spectrum analysis are always performed on a linear system. If nonlinearities exist in the system, they are linearized and thus not taken into account. Straight tension members are very often used in practice. How this can be approximated correctly in a dynamic analysis will be shown in this article.
In order to consider inaccuracies regarding the position of masses in a response spectrum analysis, the standard EN 1998-1 specifies rules which have to be applied in both the simplified and multi-modal response spectrum analysis. These rules describe the following general procedure: The story mass must be shifted by a certain eccentricity, which results in a torsional moment.
When introducing and transferring horizontal loads such as wind or seismic loads, there are increasing difficulties in 3D models. To avoid such issues, some standards (for example ASCE 7, NBC) require the simplification of the model by using diaphragms that distribute the horizontal loads to structural components transferring loads, but cannot transfer bending themselves (called "Diaphragm").
As gravity loads act on a structure, lateral displacement occurs. In turn, a secondary overturning moment is generated as the gravity load continues to act on the elements in the laterally displaced position. This effect is also known as "P-Delta (Δ)." Sect. 220.127.116.11 of the ASCE 7-16 Standard and the NBC 2015 Commentary specify when P-Delta effects should be considered during a modal response spectrum analysis.
There can be numerous nonlinearities in a structural system. In order to model them realistically in a dynamic analysis, the RF-DYNAM Pro - Nonlinear Time Histoey add-on module was developed. To explain how the add-on module works, the procedure is described below with an example.
The story drift of a building provides valuable information about its structural behavior under seismic loads.
Consideration of P-Delta Effects (Second-Order Analysis) in the Response Spectrum Analysis According to ASCE 7-16RFEM offers the option to perform a response spectrum analysis according to ASCE 7-16. This standard describes the determination of seismic loads for the US-American market. It might happen that the so-called P-Delta effect has to be considered due to the stiffness of the entire structure to be able to calculate the internal forces and carry out the design.
In RF-/DYNAM Pro - Equivalent Loads, the equivalent seismic loads can be calculated according to different standards. By calculating the equivalent loads for each eigenvalue, it is not directly possible to obtain the transversal shear for each story to perform an analysis afterwards. The following example describes the option to calculate the transversal shear quickly and efficiently.
In RF-/DYNAM Pro - Equivalent Loads, a signed result option in accordance to the dominant eigenmode is available since version X.06.3039. For the modal combination of results corresponding to the single eigenvalues a quadratic combination rule has to be used. In RFEM and RSTAB, the SRSS and the CQC rule are available. It is only allowed to combine results not loads directly. The reason are the mode shapes which are arbitrarly scaled and signed.
The Time Course Monitor displays results of a time history analysis from RF‑/DYNAM Pro - Forced Vibrations. The graphic can be adjusted in the settings. This can be reached via the right click in the context menu. For example you can activate or deactivate the grid in the graphic. Those changes are overtaken into the printout report when you print the graphic.
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