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Frequently Asked Questions (FAQ)
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In order to consider the failure of certain members when using RF‑/DYNAM Pro - Equivalent Loads, proceed as follows:
1) Deactivating the corresponding members for the eigenvalue determination within the corresponding load case, see Image 01 (add-on module, tab Natural Vibration Cases, Calculation Parameters) and Image 02 (main program, Calculation Parameters, Deactivate and select).
2) Determination of dynamic load cases from RF‑/DYNAM Pro by using
You have probably defined a shear panel and a rotational restraint for your design case in the RF-/STEEL EC 3 add-on module, but have not yet defined all specifications for the rotational restraint.
If you scroll down, you can see that the "Spacing of beams" is still defined as 0 m for the rotational restraint and must be adjusted.
In principle, the program always tries to perform a plastic design for cross-section classes 1 and 2. However, if torsion is additionally contained, the design can only be performed elastically. This is due to the interaction conditions according to EN 1993-1-1 clause 6.2.9, which do not include any torsional component.
For this reason, the "Cross-Section Design and Torsion" setting is available in the details of the add-on module. By adjusting the limit shear stress for the cross-section designs, you can also neglect the torsion under your own responsibility.
AnswerThere are two options for defining the failure:
- Assignment of member nonlinearity
For the member types "Beam" and "Rigid", you can define a member nonlinearity for each member. You can find the corresponding option in the "Settings" tab (see Figure 01).
- Assignment of nonlinear member hinges
Alternatively, you can define a member end hinge with failure criterion for the member. For the desired degree of freedom, you can assign the hinge condition with nonlinearity accordingly (see Figure 02).
- Assignment of member nonlinearity
In a 3D model consisting of three identical floors, I applied a unit load of 1 kN/m² to the top slab to determine the spring stiffness of the supports for 2D modeling of the slabs from normal forces and deformations of the columns. Despite the deactivation of the self-weight of the structure, there is a redistribution of the column normal forces by storey. Is it possible to deactivate this effect?
This effect is most likely caused by the bending, torsional and shear stiffness of the slabs and can be avoided by modifying the stiffnesses mentioned.
To modify stiffnesses, go to the "Modify Stiffness" tab in the "Edit Surface" dialog box, see Figure.
For the structural analysis software RFEM, the special add-on modules RF-FORM-FINDING and RF-CUTTING-PATTERN are available to edit and calculate membrane and textile structures.
The supporting/substructures can be modeled with RFEM or imported and refined using various interfaces to various CAD solutions.
The calculation is performed according to the large deformation analysis. Furthermore, you can use the RF‑FORM‑FINDING add-on module to perform form-finding of the cable system before the calculation.
- RFEM is the main program where structures, materials, and actions are defined. Planar and spatial plate, slab, shell, and member structures are possible.
- RF-FORM-FINDING searches for the shape of member and surface models subjected to tension or compression.
- RF-CUTTING-PATTERN determines cutting patterns for membrane structures.
More programs and add-on modules
- RWIND Simulation allows for simulations in the digital wind tunnel for complex structures. The generated wind loads can be imported into RFEM.
Data Exchange and BIM
Various interfaces allow for efficient work in exchange with other project participants. In this way, you can also cooperate smoothly in BIM processes.
If it is necessary to perform seismic analysis or vibration designs, the RF‑/DYNAM Pro add-on modules provide special tools for determining natural frequencies and mode shapes, 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.
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°
In this case, the following options are available:
1) Corresponding division of the beam (right-click Member → Divide Member) and set the parameterization in the way that there is only one central hole for one of the beams, see Figure 01.
2) Generating surfaces from the member (right-click Member → Generate Surfaces from Member), inserting a circular opening, defining a result beam, see Figure 02.
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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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