#### Further Information

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• ### Why is an opening not taken into account when determining the punching load due to shear forces in the critical perimeter?

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FAQ 004352 EN-US

When determining the punching load from shear forces in the critical perimeter, a continuous perimeter is applied.

If an intermittent perimeter was to be used when determining the punching load, the load component (along the intermittent length) might not be considered. This would be the case, for example, if you have only defined the opening in RF‑PUNCH Pro, but not in the RFEM model. In the RFEM model, the shear force would be generated by using the continuous cross-section. If the component were neglected, there would be too small punching load determined.

Therefore, the intermittent control perimeter is always applied in RF‑PUNCH Pro when determining the punching load from the shear forces within the critical perimeter.

During the design (on the resistance side), the opening is considered again and the perimeter section is reduced accordingly.

• ### Is it possible to perform automatic live load reduction in RFEM or RSTAB per the ASCE, IBC, or NBCC?

Live load reduction is not considered automatically in RFEM. RFEM and RSTAB are general FEA and framework programs. The program does not understand what is a floor element vs wall element. Only a general plate element is defined. It is not possible for the program to determine the area of a floor for live load reduction.

A user must manually consider the reduction by modifying the live load magnitude directly in the load application.

• ### After dividing a column with intermediate nodes, the results in the RF‑/CONCRETE Columns add-on module are different from those before the division. What is the reason?

The reason for the different results is probably the settings of effective lengths for the stability analysis. According to the default setting, these are determined automatically in the RF‑/CONCRETE Columns add-on module. However, this method does not work for divided members, and thus no stability analysis is performed (a corresponding warning message appears).

If you have entered the effective lengths manually, this only applies to a single member. In order to perform a correct stability analysis of the column as an entire structural component, it is necessary to define it as a set of members.

• ### Where can I set the Poisson's ratio?

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FAQ 004341 EN-US

The Poisson's ratio is set under the material by using the Edit Material dialog box.
• ### When displaying the result diagrams on a member (the "rib" type), there is the option to display the internal force VL. What is this value and how is it calculated?

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FAQ 004340 EN-US

The force VL is the longitudinal shear force between the top surface and the member. It is calculated as an integrated shear flow between the plate and the member at a particular point on the member.

For the simplified example provided here, the resulting cross-section values for the integration width of 10 cm are as follows:

• $I_y=\frac{b\times h^3}{12}=\frac{10 cm\times20 cm^3}{12}=6,666.67 cm^4$
• $S_y=h_1\times b\times((h-e_z)-\frac{h_2}2)=10 cm\times10 cm\times((20 cm-10 cm)-\frac{10 cm}2)=500 cm^3$
• $\tau=V_L=\frac{V_z\times S_y}{I_y\times b}=\frac{5.53 kN\times500 cm^3}{6,666.67 cm^4}=0.415 kN/cm=41.5 kN/m$
The integration width has been set to the total of 10 cm.

Values:
• Iy second moment of area
• Sy statical moment
• h1 height of the upper cross-section part
• h2 height of the lower cross-section part
• ez centroidal distance
• h total height
The values can be adjusted for a T-beam.
• ### In RF-FOUNDATION Pro, I receive error message No. 30195. What can I do?

The error message indicates that no option was found to define the required reinforcement for the mats and rebars selected from you.
After clicking OK, you will automatically be redirected to Window 1.3. Here, please select additional mats and/or rebars and then perform the design again.
• ### Does it make a difference if I model a floor-level downstand beam as a ‘Rib’ or as a ‘Result Beam’?

Yes, it makes because this affects the stiffness of the entire system.

When entering a level-floor downstand beam as a ‘Rib’, you will add the stiffness of the defined rectangular cross-section to the area of the line.

For the result beam, however, you have only to define the integration width. The entered rectangular cross-section does not influence the stiffness of the entire system but is only applied as a design cross-section in the add-on modules (e.g. RF-CONCRETE Members).

• ### In RF-CONCRETE Surfaces, I get non-designable situations with a note saying that the shear resistance cannot be checked (cross-section entirely cracked). What is the reason for this message?

A non-designable situation like this is displayed if the shear resistance without shear reinforcement VRd,c is arithmetically smaller than zero.

A VRd,c value of less than zero is caused by large tensile axial forces. In this context, the cross-section is completely under tension or completely cracked, and no shear force resistance can be created.

For coated cross-sections with planned shear reinforcement, the following situation results:
In RF-CONCRETE Surfaces, if VRd,c < 0, no further shear check is performed, and message 13) is displayed. This approach is conservative.

In this context, there was a request (194) for the interpretation of the standard, which allows the truss model to be used even with a completely cracked cross-section.

If a shear reinforcement is designed as planned, the message about the non-designable situation in the program can be ignored. In this case, it should be ensured that VEd is smaller than VRd,max and VRd,s.
• ### Is it possible to connect a rib member to two surfaces with different thicknesses? And where can I check the cross-section properties of this composite cross-section? In RFEM, I can only see the eccentric rectangular profile and its cross-section properties.

You can connect a rib member to a line on two surfaces with different thicknesses.

To determine the stiffness or internal forces, the eccentricity of the rectangular cross-section is determined using the mean value of both connected surfaces in RFEM.

For designing in RF-CONCRETE Members, the add-on module determines its cross-section, which is displayed in the input dialog box ‘1.4 Ribs’ of the add-on module.

By clicking the ‘i’ button (see Figure 02), it is possible to open an info dialog box for the generated rib cross-section, where all cross-section properties applied for the design in the module, like the position of the shear center and centroid, etc., can be viewed.

If the ‘Effective Width’ is adjusted in the ‘1.4 Ribs’ dialog box (e.g. to 0.50 m) this has influences on the cross-section applied in RF-CONCRETE Members and its cross-section properties.

However, this does not influence the stiffness or the determination of internal forces in the 3D model in RFEM.

• ### Is the Gust-effect (G or Gf) from the ASCE 7-16 Sect. 26.11 considered in RWIND Simulation?

In the ASCE 7-16, the conservative value for the Gust-factor, G, is 0.85 for rigid buildings. The engineer can calculate an alternative and more accurate value. The Gust-effect, Gf, for flexible buildings accounts for size and gust size similar to rigid buildings but also considers dynamic amplification including wind speed, natural frequency, and damping ratio.

The Gust-factor G or Gf, is considered to be 1.0 in RWIND Simulation. The structure is rigidly simulated in the numerical wind tunnel. The loads which are transferred back into RFEM are applied to the elastic structure with true stiffness considered.

To account for any value other than 1.0 for this factor, the wind load case factor can be adjusted in RFEM under the applicable load combination.

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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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