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Frequently Asked Questions (FAQ)
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AnswerIf the holes are subject to a regular grid, they may be defined by the composite cross sections (Figure 1).Otherwise it is still possible to reduce the cross section in the properties as a whole (Fig. 2).Thus, a flat reduction of the stiffness of the cross section is made. Unfortunately, it is not possible to distinguish between reductions in the compression and tension of the cross section.
AnswerFE-BEUL offers in the details the choice between a rigid and deformable support stiffness for determining the reduction factor for shear bumps (see Figure 1).
AnswerThe modulus of elasticity of the material is reduced for the proofs according to EC 3, but not for the internal forces, since this is not intended according to the method of DIN EN 1993-1-2. It is always assumed that the structure is cold. In the calculation of the internal forces, one has to take into account only the internal constraint of temperature stress, if this is present.
AnswerIn Window 1.12 'Parameters - Members' and Window 1.13 'Parameters - Sets of Members', you can define the cross-sectional areas for tension designs according to EN 1993‑1‑1 (see figure).
I have modified cross-section properties or reduced stiffnesses of a members in RFEM/RSTAB. After a new calculation, the deformation of the structural system has adjusted itself to the new cross-section properties. However, this change is not taken into account when performing design in add-on modules.
In principle, the modified cross-section properties are not transferred into add-on modules, such as RF‑/STEEL or RF‑/STEEL EC3. They are only used for the calculation of internal forces.
In the add-on modules, stresses are calculated using the real cross-section dimensions, which cannot be modified. This would be difficult to implement as many designs require the element width or height and due to the modification, it is not known which parameter has been reduced exactly. This is important for the c/t-designs in RF‑/STEEL EC3, for example.
By default, load combinations are calculated according to the second-order analysis, load cases according to the linear static analysis. It is possible that the stiffness is reduced by a standard-dependent partial safety factor in the calculation according to the second-order analysis, which has the corresponding effect on deformations.
In order to obtain the same results in the load case and in the load combination, it is necessary for this case to regulate the consideration of stiffness factors in a uniform manner (see figure).
The problem of the generated load combinations is the variety of mathematical possibilities. The most important mechanisms for the effective reduction include:
- Reducing the number of load cases
- Restricting actions by alternative or grouped exclusion criteria (for example, wind in y does not act with wind in x or wind in +x does not act with wind in -x) (see Figure 01)
- Assigning imperfections to load cases (for example, imperfection +x never with wind -x or imperfection +x never with wind +y)
In this way, the generated load combinations can be significantly reduced in most cases.
Another important possibility is to use load or result combinations. In the case a purely linear structure, it is possible to use result combinations. Thus, only the load cases included in the result combination are calculated. All combinations can then be carried out with the results of these load cases.
The last possibility is to use the integrated automated reduction of load cases (see Figure 02). The relatively extensive features are described in the articles that you can access under Links below.
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