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Frequently Asked Questions (FAQ)
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As soon as at least one member with a circular cross-section is selected for design, A s, top and A s, bottom are no longer displayed.
In this case, it is recommended to create your own design case for the circular cross-sections (in the menu option "File" -> "New Case") so that they are specially designed.
The circular cross-sections should not be selected in the design of the other cross-sections so that A s, top, and s, can be selected from the result navigator at the bottom .
AnswerIn most cases, these new elements only have to be added in the relevant add-on module. In Figure 1, you can see that the tick for "all" is not set and therefore new elements have to be added manually.
AnswerThis is because the effective lengths or buckling lengths of bars and staff sets differ. While the actual length of the bars is used for the proof of stability, for bar sets it is the length of the combined bars.exampleThe frame shown in the picture (see picture 1) consists of a bar divided into 4 bars of equal length. In addition, a set of rods is created for the 4 rods. The proof of stability is carried out for both cases according to the substitute rod method.When dimensioning the bars, the length is calculated to be 1.00 m. In contrast, the rod set is 4.00 m long (see Figure 2). Of course, the difference in lengths has an effect on the stability rating, which means that the workloads also differ (see Figure 3)It is also not recommended to calculate all bars and sets of bars in a design case, as this leads to falsified results.
AnswerThe method according to EC 3 can only be used for the temperature curves from EN 1990-1-2. In addition, with the simplified calculation of the steel temperature in the EC 3-1-2, it is only possible to take into account increasing temperature profiles; a drop in the temperature is not available in this simplified calculation. However, it is also possible to use direct steel temperatures in the program (see Figure 1).
AnswerThe deduction of the superelevation in the usability test is actually not regulated in steel construction. However, in response to multiple customer requests, we have adopted this in accordance with the wood or concrete additional modules. According to the standard specification, however, this value should only be taken into account in the quasi-permanent design combination.This does not apply to the characteristic and frequent design situation. As soon as the design situation in the add-on module is adjusted accordingly (see picture), the applied camber is also subtracted from the resulting deformation.
AnswerIf you want to use a custom material in the design modules, you must make sure that it has the same properties as a standard-specific material.Example: You want to dimension a custom material in RF / concrete according to EN 1992-1-1. To create the material proceed as follows: In the material library, select a material of the EN 1992-1-1 series and select "Create new material ...". Here you can change all given values. All these values are required for a design in the add-on module.
The proof of stability for tensile structures can be converted into a pure stress analysis, if the theory is considered to be 2-fold and the imperfection required by the standard has been applied to the system.
With the help of the modules RF-STABIL and RF-IMP imperfection (resp. a preformed FE mesh). The type of imperfection depends heavily on the component and the standard used. For bars, which were modeled as a tensile structure, the values from DIN EN 1993-1-1: 2005 5.3 can be used. For flat surfaces, for example, the values from DIN EN 1993-1-5: 2006 Appendix C can be used. For trays, the problem is much more complex and there are different approaches. From a generation of imperfections I would advise against this and perform the buckle proof by means of MNA / LBA concept according to DIN EN 1993-1-6, which does not require an approach of imperfection.
If, for example, the surface model of a steel girder is to be detected, you can proceed as follows, for example:
First A burden me comparatively (compared to. other internal forces in the load case) select high normal forces, in most cases the self-weight load case or a load case combination with the corresponding own weight is suitable. It may be necessary to provide each load combination with an individual imperfection.
2. Calculate load combination according to 1-order theory and use as the basis for RF-STABIL
3. Using RF-STABILITY to find the first eigenstate of a global failure
4. Using RF-IMP, use the calculated eigenmode as the basis for an imperfection. In this case, for example, 1/300 of the carrier length can be used as the amplitude.
5. Create a load case combination that uses the generated imperfection as a basis and is calculated according to 2-order theory.
6. Perform a proof of tension on the basis of this load case combination, which at the same time is also proof of stability of the structure.
The module provides options for the reinforcement that you have to consider for the shear force check. For the shear force resistance V Rd, c , the provided longitudinal reinforcement has an influence. The options allow you to specify the longitudinal Reinforcement to be used for the shear force design. The shear force design can be performed while applying the following reinforcement:
- Calculated required reinforcement
- Maximum value from required or provided reinforcement
- Automatically increase the longitudinal reinforcement so that shear reinforcement is avoided
For example, if the second option is selected and a shear reinforcement can be avoided with the basic reinforcement, the basic reinforcement is selected and output as required.
For the stability design of compression elements, you need the combination of RF-CONCRETE Members and RF-CONCRETE NL. The reason is the following:
First, the internal forces of the individual load combinations (second-order analysis + imperfection) are subjected to the linear-elastic calculation. For this, you basically only need RFEM.
Then, the cross-section design is performed in RF-CONCRETE Members with these internal forces determined linearly-elastically, and the required bending reinforcement is determined from these internal forces.
This bending reinforcement is then compared with the user-defined entries concerning the existing basic reinforcement or the minimum reinforcement and based on this, the reinforcement concept is generated (dialog box "3.1 Existing Longitudinal Reinforcement" of the module).
This existing longitudinal reinforcement is then used for the nonlinear design.
According to Section 5.8.6 (1), geometric nonlinearities must be taken into account according to the second-order analysis. However, the general rules for nonlinear methods according to 5.7 also apply.
In Sec. 5.7(1), "an adequate non-linear behaviour for materials is assumed." According to 5.7(4)P, the use of material characteristics which represent the stiffness in a realistic way but take account of the uncertainties of failure shall be used when using non-linear analysis.
This requires the RF-CONCRETE NL add-on module. Thus, the geometric and material nonlinearities are considered and the requirements of EC 2 regarding the ultimate limit state design are fulfilled.
Similarly, this method is also available in RSTAB in the CONCRETE add-on module.
Even simple structures such as continuous beams or 2D frames can be quickly and effectively modeled, calculated and designed according to various standards in RFEM and RSTAB. For such models, several model generators are particularly recommended (see figures).
After entering the cross-section parameters, loads and geometry details, the model generator automatically creates a model including load cases (see video file).
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