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Frequently Asked Questions (FAQ)
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AnswerIn RFEM, the easiest way is to use the Plane Surface → Annulus feature. This allows you to model the reinforcement rings very quickly and easily. Then you can extrude the inner line into a surface, the chimney is already generated. Now, the existing annular surface is copied upwards and the corresponding stiffeners are modeled. You can use the Rotate command to distribute the stiffeners over the chimney perimeter.
AnswerFire resistance design is not implemented in the RF‑LAMINATE add-on module by default.However, you can calculate the charring rates yourself and consider them accordingly in the module. In the following example, this is explained on a simple plate.Structural system (Figure&nbso;01):
Factors Fire Resistance:
- Span 5 m
- Plate width 2 m
- LC1 (permanent) 1 kN/m² plus dead load
- LC2 (medium) 2.5 kN/m²
- 3 layers
- S1 35 mm C24
- S2 20 mm C24
- S3 35 mm C24
Residual thickness of layer 3 = 35-26.5 = 8.5mm> 3mm => thickness may be applied. (Photo 2)Due to the changed layer thicknesses, a new stiffness matrix results, which is applied in RFEM for the Extraordinary Combinations with characteristic stiffness values. Design values are calculated for the ultimate limit state (Figure 3).
- Burning rate ß0 = 0.65mm/min
- Pyrolysis zone k0 d0 = 7 mm
- Burning time t = 30min
- Effective thickness def = t ß0 + k0 d0 = 30min x 0.65mm/min + 7mm = 26.5mm
AnswerThe 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.
In principle, it is also possible to perform detailed analysis in RF‑LAMINATE. In the case of a very high shear distortion, for example, it can be reasonable to use orthotropic solids for modeling. The video shows a simple modeling and result evaluation of a layer structure by using solids.
A criterion, as of when is the modeling using solids useful, is the shear correction factor. Further information and other criteria can be found in the following FAQ:
AnswerThe easiest way to consider this is to use the RF‑/JOINTS Timber - Steel to Timber add-on module. For this purpose, the module decomposes the original connection, and creates a new structural system that considers the flexibility accordingly. In this case, the ultimate limit state, the serviceability limit state, and the accidental design situation are considered separately.
AnswerThis is not possible directly in RFEM, but the RF‑/STEEL EC3 add-on module allows you to create a list of steel parts. In Details of the add-on module, you can specify whether the parts list should apply to all members or only for members to be designed. Then, you can simply carry out the calculation and the parts list will be displayed. It is also possible to export the parts list to Excel and further edit it.
AnswerIn order to display the loads correctly, it is necessary to make some adjustments. In the case of an incrementally applied load, the boundary of the area load plane may only be defined in sections (by load increment). Otherwise, the load is distributed linearly over the entire area load plane.
The result display of intermediate values is generally linked to the member division property. Also, member loads defined in sections in RFEM generate further intermediate results. For example, if a member load defined in sections is distributed from the member start to the member end, the intermediate results are obtained at the member end nodes.
In the Dlubal programs, all values are stored internally based on SI units. When a user changes the units in the program to metric or imperial, SI units are still used internally and only the value displayed in the interface is modified. Therefore, all values set in the time diagram function also default to SI units unless the user clarifies an alternative unit.Let's look at a simple example shown in Figure 1 where the parameter x = 1 ft has been set in RFEM.In RF-DYNAM PRO - Forced Vibrations, the time diagram function is defined as k(t) = 1*x where 1 is the multiplier (1/ft) to convert x to a dimensionless value. You can see in Figure 2, because all values default to SI units, the Multiplier column produces values of 0.305 instead of the correct value of 1.000.In order to correct the issue, the user only needs to specify the units of the multiplier as (1/ft) in the function equation. This can be done with the formula modification k(t) = 1/1[ft]*x as shown in Figure 3. Notice the Multiplier column now shows the correct values of 1.000.In summary, when using units in the program other than SI units, coefficients or multipliers in the time diagram function should be accompanied with alternative units defined in brackets.
AnswerThe Poisson's ratio is set under the material by using the Edit Material dialog box.
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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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