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Frequently Asked Questions (FAQ)
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It is necessary to consider the effect of the stress concentration at the notch for the ultimate limit state design. According to EN 1995‑1‑1, 6.5.1, this is ensured by the reduction factor kv. The calculation of kv is defined in EN 1995‑1‑1 in the equations 6.61 to 6.63. Further specifications for the reduction factor can also be found in the national annexes.
In our example, the reduction factor kv is determined as expected.
In the other structural system, the reduction factor kv is determined as 1.222.
In the example, this is because the fact that a supporting moment is created in the static system and the load on the supports.
Therefore, the effect of the stress concentration may be neglected at this point, according to EN 1995‑1‑1, 6.5.1 (2). "The effect of the stress concentrations may be disregarded in the following cases: [...] bending with compressive stresses at the notch, see Figure 6.10b."
In our example, the reduction factor can even exceed 1.0 according to the specifications in DIN EN 1995‑1‑1/NA Formula (NA.60).
AnswerThe RF-TIMBER AWC module does not optimize cross-sections for the Serviceability Limit State or the Fire Resistance design. Optimization is only calculated for the Ultimate Limit State design.Users must manually adjust the cross-section in RFEM or within the add-on module and can export the cross-section back into RFEM. In either scenario, the model must be rerun in order to calculate the correct internal forces with the adjusted member size.
AnswerIncreasing the crack factor kcr still has to be done manually because the program does not know where is the grain plane defined. To do this, divide the member accordingly by 1.5 m from the grain plain, so that the affected areas can be designed as a separate member (see Figure 01).Two design cases are now required (File → New Case ...). In Case 1, the members within the 1.5 m are selected for the design. In Case 2, it is necessary to select the members where the 30% should be considered. In Case 2, the kcr value is then adjusted manually in the National Annex settings. Thus, the kcr of 0.65 results for C24, which is entered as shown in Figure 02. In this way, the design is performed with the increased kcr value.
Basically, all cross-sections of the massive and hybrid cross-section groups can be designed in the RF‑/TIMBER Pro add-on module. In Figure 01, they are displayed on the right.
In the case of more complex asymmetric cross-section shapes, a user-defined adjustment of the allowable angle of principal axes may be necessary in the add-on module (see Figure 02).
Yes, it is possible.First, RF‑STABILITY (or RSBUCK in RSTAB 8) can be used to determine the effective lengths for a structural system and certain loading.They can then be imported in the "Effective Lengths" dialog box in RF‑/TIMBER Pro.
In the main program RFEM/RSTAB, it is first necessary to rotate the member about 90° so that the lamellas of the glued-laminated beam are lying edgewise, see Figure 01.
In order to also consider the on-edge position of the beam for the design in the RF‑/TIMBER Pro add-on module, increase the resistance for edgewise bending under National Annex Settins in the "Other Settings 2/2" tab, see Figure 02.
The setting in Figure 01 only controls the effect on the design side. After activating this function, the buckling designs in the "Effective Lengths" window are deactivated. Thus, the lateral-torsional buckling analysis is only performed.
In order to calculate with the design values of stiffnesses, it is necessary to reduce them by the partial safety factor according to . For this, select the highlighted option in the calculation parameters (see Figure 02).
If using the automatic combinations for the standard EN 1990 + EN 1995, this setting is automatically activated in the combinations for ULS according to the second-order analysis. In the case of the combinations for SLS and the combinations generated according to the linear static analysis, this option is automatically deactivated. However, the combinations are only assigned automatically by using the method of analysis in the "Combination Expressions" tab (see Figure 03).
If you want to calculate the component stiffnesses with the 5% quantile value of the stiffness parameters divided by the partial safety factor, you have to additionally activate the "Modify stiffnesses" option in the calculation parameters and modify the stiffnesses manually.
AnswerFor many users, the very realistic display of a building in construction programs arouses the wish to carry out the structural analysis of the building with the same complex spatial model.Again and again, the design of log cabins is approached to us. Unfortunately, this attractive construction method is relatively complex for three-dimensional analysis. In dimensioning, there are some critical questions that cannot be answered.
Furthermore, log houses are common for the houses with the maximum of 2 full floors because of their high placement of more than 15 cm per story. Thus, the occurring forces are within a manageable framework and can be determined sufficiently precisely with the methods of the structural analysis for members in 2D structures. In RFEM/RSTAB, there is an option to define round members in a tapered way for this purpose. Thus, the definition of 2D equivalent systems can be done much faster in RFEM/RSTAB.There is some information in the given literature source.
- Which sorting class is the timber subject to? In a log house, unsorted damp wood is often used.
- How is the contact between the timber types controlled? Diamond notch, connection with moving timbers, and so on?
- Have mullions been installed? Which type of timber and how are they supported horizontally?
- Which dimensions does the timber have? In a log structure, a grown trunk can often be integrated. These trunks do not have uniform dimensions as the nature cannot be put into a grid.
- How is it possible to consider the contact between two timber layers?
AnswerIn general, all result combinations can be designed with the RF‑/TIMBER Pro program. However, there is the special feature in timber construction, that the governing load combination is not the combination with the largest internal forces due to the load duration class (LDC).In the case of the result combinations, it is necessary to distinguish between 4 basic types of combinations.
In this respect, there is a special feature of the combination from the RF‑/DYNAM Pro add‑on module. In this case, the results are constantly superimposed and additionally squared. However, these combinations are then comparable with the third combination mentioned above.Results used in TIMBER Pro for each result combination.
- Permanent and additive (+/-) superposition of all actions.
- Actions different in permanent or variable, but additive (+/-) superposition.
- All actions permanent, but superimposed with 'or'.
- All actions variable, but superimposed with 'or'.
- The maximum moment in the attached file is used. The "Short" LDC is correctly taken into account.
- In a simple example, the moment is correctly taken into account. However, a support moment on the continuous beam can be taken into account incorrectly. The LDC in RC2 is considered as "permanent" by default. Therefore, the design becomes very unefficient and must be changed in this case (see Figure 02). However, "permanent" might be correct for the continuous beam mentioned above.
- In the case of RC3 and RC4, there is a pure result evaluation, which is possible in all design modules.
AnswerWhen selecting the standard SIA 265, RF‑/TIMBER Pro can only use the materials for the members to be designed that are also allowed in the standard. You can easily find the valid materials in the material library by using the filter of the standard.
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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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