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• ### How can I set the deformation coefficient kdef in the program?

The setting for the deformation coefficient kdef can already be made in the model data. There, you can specify the deformation coefficient manually or select it based on the service class.

The deformationfactor k def is considered in the load combinations for serviceability in the program (similar to DIN EN 1995-1-1, 2.2.3).

For the design of mixed structures made of timber materials, see FAQ 4325 .

• ### A rigid member should only be able to absorb tensile forces or only compressive forces. What are the options for considering these nonlinearities in the calculation?

There are two options for defining the failure:

1. Assignment of member nonlinearity
For the member types "Beam" and "Rigid", you can define a member nonlinearity for each member. You can find the corresponding option in the "Settings" tab (see Figure 01).

2. Assignment of nonlinear member hinges
Alternatively, you can define a member end hinge with failure criterion for the member. For the desired degree of freedom, you can assign the hinge condition with nonlinearity accordingly (see Figure 02).
• ### In a 3D model consisting of three identical floors, I applied a unit load of 1 kN/m² to the top slab to determine the spring stiffness of the supports for 2D modeling of the slabs from normal forces and deformations of the columns. Despite the deactivation of the self-weight of the structure, there is a redistribution of the column normal forces by storey. Is it possible to deactivate this effect?

This effect is most likely caused by the bending, torsional and shear stiffness of the slabs and can be avoided by modifying the stiffnesses mentioned.

To modify stiffnesses, go to the "Modify Stiffness" tab in the "Edit Surface" dialog box, see Figure.

• ### For the direction of internal forces, I have four options under the "Grouped" selection box to smooth the internal forces. Which grouping should I choose here?

The determination of internal forces "Grouped" is divided into four subcommands.

1. u with my , mxy , vy , ny , nxy
2. v with mx , mxy , vx , nx , nxy
3. u with mx , mxy , vx , nx , nxy
4. v with my , mxy , vy , ny , nxy

The effect of these commands is explained in a simple example.

Structure:

• Plate as a wall-like beam
• Wingspan 9 m
• Beam height 1.5 m
• Concentrated load 20 kN in the center of the span
• FE mesh size 10 cm
Figure 1 shows the maximum and minimum internal forces at the load application point unsmoothed. Obviously, these internal forces are singular results. You can find detailed information about singularities in technical article 001503 .

In order to completely include at least two FE elements per side of the load introduction through the smoothing area, a smoothing area of 50/50 cm is defined (Figure 2).

The following table shows the change of smoothing separately for each grouping. Only the drawn upper area of the load application is considered. The grouping 0 stands for the unsmoothed internal forces.

01234
nx74.9 kN/m74.9 kN/m47.2 kN/m51.8 kN/m74.9 kN/m
ny109.0 kN/m26.5 kN/m109.0 kN/m109.0 kN/m5.8 kN/m
nxy75.1 kN/m30.7 kN/m15.8 kN/m30.7 kN/m15.8 kN/m

The table shows that a combination of grouping 1 and 2 as well as 3 and 4 is always reasonable in relation to the axial forces.

Figure 3 shows the smoothed internal forces for groups 1/2 and 3/4 together.

The following values are used for the combinations:

1/23/41/2 and 3/4
nx47.2 kN/m51.8 kN/m47.1 kN/m
ny26.5 kN/m5.8 kN/m5.3 kN/m
nxy12.9 kN/m12.9 kN/m12.9 kN/m

As already mentioned, the combinations 1/2 and 3/4 use the minimum average internal forces of the respective grouping. The shear force nxy is calculated from the forces in the normal direction and is therefore already displayed as "smeared shear force" for the combination 1/2 and 3/4.

Conclusion

For a material with pronounced stiffness and strength directions, such as reinforced concrete or cross-laminated timber, the orientation of the strengths is relevant for the selection of the correct grouping. In the combination of group 1/2, the internal forces are smoothed in the longitudinal direction of the structural component, in group 3/4 in the transverse direction. If the structural component is oriented in the longitudinal direction as shown in Figure 4, the smoothing in the longitudinal direction is therefore recommended. However, the type of load application and the governing design are also important here. All groupings can be used for an isotropic material as well as for a governing shear force design.
• ### Windows Defender does not allow me to install RX‑TIMBER. Is it possible to get around this?

The protection can be disabled for the duration of the installation in Windows Security → App & browser control → Reputation-based protection → Check apps and files. After deactivating this check, RX‑TIMBER can be installed now. Then, we recommend to switch on the protection again.
• ### How can I perform a stability analysis for a tapered member?

Tapered members must not be designed according to the simplified equivalent member method!

For steel structures, the design can be performed by considering the warping torsion or using the General Method. These methods are described in this technical article.

For timber structures, the design can also be performed by considering the warping torsion. The method for timber structures is explained in detail in thiswebinar.

According to the equivalent member method, the design can be performed if the provisions of the explanations for DIN 1052, Section E8.4.2 (3) for variable cross-sections are met. In various sources of technical literature, this method is adopted for Eurocode 5. An example of this can be found in the document on brettschichtholz.de, page 64 ff.

In the RX‑TIMBER program, the design of tapered members is performed according to the equivalent member method. This is briefly explained on a simple example.

Structural System (Figure 01):

• Span length: 8 m
• Beam height right: 80 cm
• Beam height left: 26 cm
• Roof inclination: 3.9°
No stiffening is defined. The lateral-torsional stability becomes governing with 99% (Figure 02) at the x‑location 1.598 m. The cross-section height is 36.8 cm. However, the slenderness ratio is based on the equivalent cross-section height of 60.9 cm (Figure 03).

The equivalent cross-section height results at the x-location 5.2 m about 0.65 × 8 m = 5.2 m.

If the stiffening is in the middle of the span, for example, the equivalent height for the x‑location changes to 45.3 cm.

Since the stiffening is usually applied over the member length, the height must be calculated according to a special algorithm. The supports are always applied as fixed points and the equivalent heights are calculated, based on the x-locations of the designs.

For the example, the following results: x0.65 = 0.32 x 4 m + 1.598 m = 2.878 m
• ### After opening a duopitch roof beam from RX‑TIMBER in RFEM/RSTAB, it is displayed with a gap in the apex zone. Does this affect the calculation?

The cross-sections of members are always related to the centroidal axis in RFEM/RSTAB. The rendering is adjusted accordingly. This has no influence on the calculation.

• ### Which add-on modules and programs do I need for laminate and sandwich structures as well as cross-laminated timber (CLT)?

RFEM allows you to perform structural analysis and design of laminate and sandwich structures. The same applies to cross-laminated timber. Stress and deflection anaylsis of laminate and sandwich surfaces is performed according to the laminate theory, taking into account the shear coupling.

#### Available Programs and Add-on Modules

• RFEM is the main program where structures, materials, and actions are defined. Planar and spatial plate, slab, shell, and member structures are possible.
• RF-LAMINATE is required for the stress and deflection analysis of laminate surfaces. It is possible to specify user-defined layer structures.

#### Add-on Module for Timber Structures

• RF-TIMBER Pro performs structural analysis and design according to Eurocode 5, for example, for further supporting elements of the structure.

There are also other add-on modules available for other structures, such as steel or concrete structures.

#### Data Exchange and BIM

Various interfaces allow for efficient work in exchange with other project participants. In this way, you can also cooperate smoothly in BIM processes.

#### Dynamic Analysis

If it is necessary to perform seismic analysis or vibration designs, the RF‑/DYNAM Pro add-on modules provide special tools for determining natural frequencies and mode shapes, an analysis of forced vibrations, a generation of equivalent loads, or for a nonlinear time history analysis.

If you have any question about the Dlubal Software programs, please do not hesitate to contact our sales department.

• ### How do I display the nodal displacements graphically?

To display the nodal displacements graphically, the setting "Nodal Displacement" in the Display Tab under Results - Deformations - Members - Nodal Displacements must be activated.

Under the Results tab, turn on Global Deformations. Then the nodes can then be highlighted and isolated by using the "Views By Selected Objects" for a better view of the nodes and displacements.

• ### Are silos/tanks possible to export from RFEM into Revit?

Yes, this is possible. Silos/tanks are usually made up of one curved 2D surface. This 2D surface needs to be split into two separate 2D surfaces for the cylinder to be exported into Revit. If it is only made up of one surface, then only half of the cylinder will be exported.

To do this, create a cylinder with one single surface. Then draw a line exactly adjacent to the original line that was create perpendicular to the top and bottom of the cylinder.

Next, delete the surface and recreate two surfaces using the quadrangle tool.

This process is also demonstrated in the attached video.

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#### First Steps

We provide hints and tips to help you get started with the main programs RFEM and RSTAB.

#### 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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