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Frequently Asked Questions (FAQ)
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Yes, you can activate this in the "Details" dialog box of TIMBER Pro (manual p. 39).
This reduced stiffness is considered according to the equivalent member method in the buckling analysis.
Presumably, the "Stress point design also for rectangular and circular cross-sections" option in Details is activated.
Since the stress point design is not allowed for tapered members, this function must be deactivated, see the image.
If this option is to be considered despite the existing tapered cross-sections, the tapered members have to be designed in a separate design case.
If this error message is displayed, the cross-section is obviously not sufficient as there is no remaining cross-section after the specified fire resistance duration. You can check this very easily by reducing the fire resistance duration in the detail settings until the design is still possible.In the result of the fire protection design, you can see very well in the graphic how much residual cross-section is still available after the specified fire duration.
The optimization of cross-sections in RF‑/TIMBER Pro is based exclusively on the ultimate limit state (ULS), not the serviceability limit state (SLS), see the image from the RF‑TIMBER Pro manual.
More information about the cross-section optimization can be found in the RF-TIMBER Pro manual on pages 76-78 (also available with the F1 key in the add-on module).
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.
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.
- Building Information Modeling (BIM)
An extensive collection of interfaces allows for data exchange with other programs.
AnswerTapered 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):
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
- Span length: 8 m
- Beam height right: 80 cm
- Beam height left: 26 cm
- Roof inclination: 3.9°
The LVL design is carried out with the add-on modules for timber design.
The following steps are necessary for the design:
- Select a material of the LVL category (Image 01) - if the desired manufacturer is not available in the material library, you can create a user-defined material (see FAQ 002656). By selecting the material, you define the stress of the material. In the case of LVL, the load-bearing capacities for a plate stress (Image 02) are significantly different than for a wall stress (Image 03). If performing the design with the RF‑/TIMBER Pro add-on module, the wall stress is usually available. In the case of the plate stress, it is often reasonable to use the RF‑LAMINATE add-on module.
- In the RF‑/TIMBER Pro design module, the "Factor Category" in Window 1.2 (Image 04) is used for LVL.
- For the National Annex parameters, you can make adjustments for the LVL design in two tabs "Other Settings," if necessary. For example, this may be the case of shear or the manufacturer's specifications for increasing strengths (Image 05 and Image 06 (BauBuche)).
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.
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Wind Simulation & Wind Load Generation
With the stand -alone program RWIND Simulation, you can simulate wind flows around simple or complex structures 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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