- More than 45,000 users in 95 countries
- One software package for all application areas
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- Flexible modular concept, extensible according to your needs
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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. This article will show how you can display them approximately correctly in a dynamic analysis.
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.
DIN EN 1998-1 with the National Annex DIN EN 1998-1/NA specifies how to determine seismic loads. The standard applies to structural engineering in seismic areas.
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 a multi-modal response spectrum analysis, it is important to determine a sufficient number of eigenvalues of the structure and to consider their dynamic responses. Regulations such as EN 1998-1  and other international standards require to activate 90 % of the structural mass. This means: to determine as many eigenvalues that the sum of the effective modal mass factor is greater 0.9.
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