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Frequently Asked Questions (FAQ)
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AnswerAfter running a calculation, you can view the member internal forces under Table 4.6 Members - Internal Forces. The tools at the top of the table include a filter function. Under the detail setting for the filter, you can turn on/off the internal force values for the start of members, internal points, or end of members. For connection design, the start of members and end of members will be most of interest. This information can additionally be exported to Microsoft Excel with the direct link in the table options.For additional information on the filter options, refer to the RFEM Online Manual 11.5.5. Filter Functions.
In the calculation parameters of the load combinations, the calculation type according to the second-order analysis is preset by default. For example, the calculation is performed according to EN 1995‑1‑1, 2.2.2(1)P, using the design values of the stiffness property of the structural component, that is, the stiffnesses divided by the partial safety factor. For this reason, this stiffness modification is activated by default (see Image 01). For the load combinations in the serviceability limit state, there should be no reduction of the stiffness, of course.
Manual Creation of Load Combinations
If you create the load combinations manually, the load combination cannot "know" which limit state is involved. In this case, it is necessary to make the setting manually (see Image 02). This setting must also be deactivated manually when switching to the geometrically linear analysis.
Automatic Generation of Load Combinations
If the load combinations are generated automatically by the program (see Image 03), the stiffness reduction is automatically deactivated for the SLS combinations specific to timber structures. For the ULS combinations, the reduction depending on the method of analysis is considered (second-order analysis and higher) or not (geometrically linear analysis). However, this requires the definition of the calculation type in the combination expressions (see Image 04). Changing the calculation type in the calculation parameters of the CO has no impact on the stiffness.
AnswerThis program is not an add-on module. The RX-TIMBER programs work independently. You can search for them, for example, via the Windows search or via the Windows START button → Dlubal → RX-TIMBER. Then, Project Manager starts. You can open one of the previous projects or create a new one by using the selected program.By default, the program is installed in C:\Program Files\Dlubal\RX‑TIMBER 2.24\ and can be started using the PRM64.exe file.
AnswerThese increments result from the creep components in a quasi-permanent combination. You can find the overview of which combinations are to be analyzed in the serviceability limit state according to DIN EN 1995‑1‑1 here or in the links of the FAQ.The creep components are then simply added to the characteristic deformation, for example with 0.8 × dead load. This results in the factor 1.8 (see also Section 2.2.3 in EN 1995‑1‑1).In this specific case, the following coefficients must be applied for the quasi-permanent design situation:Gk ⋅ (1 + 0.8) + Qk ⋅ (1 + 0.6 ⋅ 0.8) = Gk ⋅ 1.8 + Qk ⋅ 1.48
The effective length can be adjusted in Window 1.5 of the add-on module, depending on the type of bending moment in the "Define Lcr" line.
In the graphic, this is not possible for clarity reasons. However, the RF‑LAMINATE add-on module allows you to also display the stresses in all points. This is deactivated by default because it quickly produces a huge amount of data for large structures.
If you also filter by the stress component that interests you, the results in the table becomes quickly clear, and you can easily evaluate the distribution of stresses at a point using the layers there.
AnswerBoth DLT and NLT are considered to behave more like single-axis beam elements stressed primarily in bending. Although realistically there is a small amount of stiffness perpendicular to the span direction, this is neglected in beam design. This is in contrast to cross-laminated timber (CLT) which includes two-way stiffness in both the directions parallel and perpendicular to the span direction. Therefore, RF-LAMINATE is not the suitable add-on module to NLT or DLT design but rather used for CLT design.The best approach in RFEM is to model a standard stiffness surface with modified orthotropic elastic 2D material properties. For the material model details, the modulus of elasticity in the local y-axis direction (Ey) should be set to a very small number (i.e. 0.001). The shear modulus in the local yz-plane (Gyz) should also be set to this small value. This will replicate little to no stiffness in the direction perpendicular to the DLT or NLT span direction.The surface can then be applied in the RFEM model for the full analysis. Note, design is not possible for these elements directly in RFEM. Internal forces, stresses, deflections, etc. from the RFEM analysis can be exported to alternative programs (i.e. Excel) for further design according to the various standards.
The reason there is a difference in results between superimposing LCs in COs vs. RCs is because when you apply the loads at once in a CO you will receive a different load distribution throughout the entire structure compared to the RC where the results are what are being added together. This is based on FEA where adding all of the loading together is different compared to solving the LCs each individually and adding the results together. Can be compared to a different order of operations to put it simply. You can see the comparison in the two figures below. Figure 1 is the load cases added up in CO1 and figure 2 has the LCs added together in RC1.
AnswerSolutions are available for RFEM, RSTAB, and RX‑TIMBER as an independent stand-alone program.
RFEM provides you with the most extensive options; in addition to the general structural elements in timber construction, you can also use the RF‑LAMINATE add-on module to process laminates or cross-laminated timber elements. Furthermore, it is possible to design curved beams, and for the JOINTS Timber - Steel to Timber add-on module, it is possible to design semi-rigid fasteners with RFEM.
With RF‑/TIMBER Pro, you can perform a stress or stability analysis for members according to the equivalent member method or the second-order analysis in RFEM or RSTAB. Furthermore, you can use it to demonstrate the serviceability limit state and fire resistance. Cross-sections can be optimized automatically.
The individual RX‑TIMBER stand-alone programs allow you to design glued-laminated timber beams, continuous beams, timber columns, coupled purlins and continuous beams, three-hinged frames with finger-jointed frame joints, stiffening bracings, or monopitch and duopitch roofs.
Main Programs RFEM or RSTABThe main programs RFEM or RSTAB are used to define structures, materials, and actions.
- RF-/TIMBER Pro (with fire resistance) according to EN 1995‑1‑1 (Eurocode 5) and SIA 265 (Swiss standard)
- RF-/TIMBER AWC (with fire resistance) according to ANSI/AWC NDS‑2018 (US standards)
- RF-/TIMBER CSA according to CSA O86‑14 (Canadian standard)
- RF-/TIMBER NBR according to NBR 7190:1997 (Brazilian standard)
- RF-/TIMBER SANS according to SANS 10163‑1:2003 and SANS 10163‑2:2001 (South African standards)
- RF-LAMINATE (RFEM only)
Stress and deflection analysis of laminate surfaces (for example, cross-laminated timber panels)
- RF-/JOINTS Timber - Steel to Timber
for indirect connections with steel plates and steel dowels
- RF-/JOINTS Timber - Timber to Timber
for direct connection of members with slant screws
analyzes the load-bearing capacity of members, member ends, nodes, nodal supports, and surfaces by means of a defined ultimate load capacity.
- RWIND Simulation
Complex analysis of any structures in the digital wind tunnel with the transfer of load cases to RFEM or RSTAB for further processing
Dynamic AnalysisIf it is necessary to perform seismic analysis or vibration designs of a building, the RF‑/DYNAM Pro add-on modules provide special tools for determining natural frequencies and mode shapes, for 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.
- Building Information Modeling (BIM)
An extensive collection of interfaces allows for data exchange with other programs.
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 .
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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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