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Frequently Asked Questions (FAQ)
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After the calculation, you can switch to the result window "2.4 Required Reinforcement by x‑Location" in the RF‑CONCRETE Members (RFEM) or CONCRETE (RSTAB) add-on module.
Here, you can select a certain result row for a particular design and x-location (upper table in Window 2.4). Then, you can evaluate the intermediate results in the lower table in Window 2.4. This covers the "Neutral Axis Depth x", for example. The location of the neutral axis for the selected design location is displayed in the graphic on the right of Window 2.4 .
Furthermore, you can display the distribution of the neutral axis depth along the member length graphically in the model or in "Result Diagrams on Member."
For the calculation, the program creates a solid mesh between the model and the outer sides of the wind tunnel. In this case, the solid mesh does not connect directly to the model geometry, but to a separate model wrapping mesh placed around the model geometry. This model wrapping mesh has a certain distance to the exact model geometry, depending on the model mesh setting (Simplified Model - Shrink-Wrapping-Mesh). Similar to the surrounding model wrapping mesh, the exact model geometry itself is also represented from a wrapping mesh, but on the exact model shape.
Figure 01 - Mesh Types
With the OpenFOAM calculation, a print result is obtained on each solid element. These values are extrapolated to the respective edge nodes at the transition to the model. To determine the final surface pressures on the model geometry, the pressures at the edge nodes of the solid mesh are transformed into the exact model mesh wrapping in a further step. In the event that the triangular meshing of the exact model mesh geometry is too rough, the last transformation process initiates a partial refinement of the exact model mesh wrapping.
Figure 02 - Difference Between Wrapping Mesh Geometry and Exact Model Geometry
Yes, it is because the CONCRETE module of RSTAB 8 also includes the nonlinear reinforced concrete design. Thus, you can activate the 'Nonlinear Analysis (State II)' in the 'Ultimate Limit State' tab.
In the detail settings for the nonlinear design, you can select the 'General Design Method for Members in Axial Compression acc. to Second Order Theory'.
It is important that you define the imperfections in RSTAB and apply load curves (CO) according to the second-order analysis for the design, no result combinations (RC)!
Note on RFEM 5:
In RFEM 5, the same procedure is possible in RF-CONCRETE Members. However, the add-on module RF-CONCRETE NL in RFEM is required for the non-linear reinforced concrete design.
AnswerSection 6.1.5 (4) of Eurocode 5 requires to apply the smaller transversal compression coefficient of kc,90 for the concentrated loads that are close to the support.As an option, it is possible to deactivate the support pressure design in the RX‑TIMBER program and set the corresponding transversal compression stiffening.If the entered concentrated load is not relevant for design, there is the additional option to assign the user-defined transversal compression factor (Figure 03).
AnswerEspecially in the case of the "Column web, Compression Force, Bottom" design, a specified web stiffener is only applied to the design if it is actually required, or if the design cannot be performed without the web stiffener. In the latter case, the comment "Web stiffener required" appears in the last column of the result table.It is also important to note whether a continuous or a partial rib is applied.In the case of the partial rib, the compressive force is divided into a web and a rib and designed in this way.If a continuous rib is used, the column web is first fully loaded and the excess load is applied to the rib. In the case of T-joints and cross joints, this approach prevents the rib from being overloaded.
AnswerNo, they are not included by default. The wind load generation using surface loads always determines the wind load that is orthogonal to the spanned surface.For the attached example, however, Figure 02 shows that the loading in the wind load surface amounting 0.5 kN/m² is relatively easy to convert.It is also possible to generate the wind load for any building geometry with the new stand-alone program RWIND Simulation. This provides you with the possibilities for wind simulations and generating wind loads.In conjunction with the structural FEA software RFEM or the structural frame analysis software RSTAB.InputThe direct import of models from RFEM or RSTAB allows you to define the relevant parameters for the analyzed wind directions with the height-dependent wind profiles, based on the wind standard. This results in the corresponding load cases with globally defined parameters.Without RFEM or RSTAB, RWIND Simulation can also be run manually. Furthermore, you can import the data from the STL vector graphics.It is also possible to import terrain and buildings of the environment into the simulation from the STL files.By exchanging the data between RFEM or RSTAB and RWIND Simulation, you can easily use the results of the wind analysis as load cases in your usual RFEM or RSTAB work environment.Features of RWIND Simulation3D incompressible wind flow analysis with OpenFoam solversDirect model import from RFEM/RSTAB or STL filesSimple model changes using drag & drop and graphical adjustment assistanceAutomatic corrections of the model topology with shrink wrap networksOption to add objects from the environment (buildings, terrain, ...)Height-dependent velocity profiles according to the standardK-epsilon and K-omega turbulence modelsAutomatic mesh generating adjusted to the selected depth of detailParallel calculation with optimal utilization of the capacity of multicore computersResults within a few minutes for low-resolution simulations (up to 1 million cells)Results within a few hours for simulations with the medium/high resolution (1‑10 million cells)Graphically display of results on the Clipper/Slicer planes (scalar and vector fields)Graphical display of streamlines and streamline animation
For the stability design of compression elements, you need the combination of RF‑CONCRETE Members and RF‑CONCRETE NL. The reason is the following:
First, the internal forces of the individual load combinations (second-order analysis + imperfection) are subjected to the linear-elastic calculation. For this, you basically only need RFEM.
Then, the cross-section design is performed in RF-CONCRETE Members with these internal forces determined linearly-elastically, and the required bending reinforcement is determined from these internal forces.
This bending reinforcement is then compared with the user-defined entries concerning the existing basic reinforcement or the minimum reinforcement and based on this, the reinforcement concept is generated (dialog box "3.1 Existing Longitudinal Reinforcement" of the module).
This existing longitudinal reinforcement is then used for the nonlinear design.
According to Section 5.8.6 (1), geometric nonlinearities must be taken into account according to the second-order analysis. However, the general rules for nonlinear methods according to 5.7 also apply.
In Sec. 5.7(1), "an adequate non-linear behaviour for materials is assumed." According to 5.7(4)P, the use of material characteristics which represent the stiffness in a realistic way but take account of the uncertainties of failure shall be used when using non-linear analysis.
This requires the RF-CONCRETE NL add-on module. Thus, the geometric and material nonlinearities are considered and the requirements of EC 2 regarding the ultimate limit state design are fulfilled.
Similarly, this method is also available in RSTAB in the CONCRETE add-on module.
No, you do not have to worry. If the value of alpha*crit (the critical buckling value without torsional stiffness) is displayed in red and thus amounts to "0," there is no reduction of the imperfection factor (European lateral-torsional buckling line). The basic value for the imperfection factor is used.
The filter functions in the "Details" dialog box, "Stability" tab, should allow you to neglect small moments or compression forces, and thus, for example, to perform a buckling analysis for asymmetric cross-sections without taking into account the interaction "bending and compression." Otherwise, a warning would appear saying that no stability analysis is possible.
The limits are applied and set at the user's discretion and usually agreed with a tester. Dlubal Software cannot provide a general recommendation. However, it can be reasonable for very slender components to reduce the limit value to 0%.
In the case of a hole bearing, the forces are only transferred by compression. Tensile forces do not occur. These effects could be modeled as follows (for an example, see the figure):
1. Create an opening in a surface.
2. Create a beam member with the nonlinearity failure under tension and apply it in the opening. It is important to use a beam member and no compression member (a compression member is a truss member, which would make the structural system kinematic).
3. Rotate the member in the opening and copy it several times.
Instead of the member, you could also fill in the opening by a surface with the stiffness membrane without tension. When using this surface stiffness, the following happens:
The calculation is performed in several iterations. After the first iteration, it is checked, in which surface element for the main membrane stress the tension occurs. These elements will fail in the next iteration (to be more precise, the stiffness is greatly reduced).
Both modeling variants should give you roughly the same results.
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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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