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Frequently Asked Questions (FAQ)
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AnswerThe reason is that there is no stability analysis for unsymmetrical, open cross-sections according to EN 1999-1-1 when the compressive normal forces and the bending moments are effective.You can neglect the bending moments in Details in the Stability tab by selecting a filter. Then, the flexural buckling design is performed without moments. However, this is under your own responsibility. An alternative is to use a stability check according to the second-order analysis, which would be possible by means of the RF-/FE-LTB add-on module.
AnswerIn the 'c/t-Parts and Effective Cross-Section' tab of the 'Calculation Parameters' dialog box, you can define settings for the automatic creation of c/t-Parts.
It is also possible to specify an angle from which a support should be created between two elements. In case that the angle for connection of elements is smaller, they are considered as an interconnected c/t-Part. Stiffeners (longitudinal ribs, slopes (lips), or bulges, etc.) are not recognized by the program during the automatic generation of the c/t-Parts. The c/t-Parts have to be adjusted manually. The changes can be made in Table '1.7 Cross-Section Parts for Classification' or in the 'Edit c/t-Part' dialog box.
The check box with the reference to Element is 'significant' controls whether a curved element is considered as a c/t-Part. If the length of the arc is larger than the diameter entered here, it cannot be neglected.
A corresponding error message appears before the calculation.
The option Element ist 'straight' refers to curved elements. Arcs are normally excluded from the determination of the effective widths because the standards do not provide clear specifications. A curved element is assumed to be straight if the ratio of connecting line (start/end node) to element length is higher than the specified value.
If you need to define different types of lateral intermediate supports, you need to divide the specific member. After that, you can create a set of member and with that done, you can easily define different types of intermediate supports along this set of member, or you can use different nodal supports in the nodes of the set of member.
AnswerThis kind of result may occur if the limit internal forces of the cross-section can not be determined. In most cases, the problem consist in a wrongly defined cross-section or in the selection of an unsupported cross-section. Please check if you have selected a cross-section allowable for the aluminum structure in the add-on module. These include rolled cross-sections and parametric thin-walled cross-sections.The cross-section HK 120/40/5/5/5/5 shown in Figure 01 is not an allowable cross-section because it has been selected from the range of solid cross-sections (concrete components).
In this case, you have to change the cross-section to TO 120/40/5/5/5/5.When designing in the RF-/ALUMINUM, please note that it is necessary to select a material which also involves thicknesses used for the cross-sections. A material that is only allowed up to t=3 mm can not be used for a cross-section with t=5 mm.
AnswerYou can usually set the standard and the National Annex in the top right corner of an add‑on module (see Figure 01). In most cases, it is also possible to display the factors of the National Annex and edit them, if necessary (see Figure 02).
For members (RSTAB) or members, surfaces, and solids (RFEM), you can display the material weight W. Simply select the entire structure or a part thereof and right-click to open the shortcut menu. Here you will find the entry "Center of Gravity and Info ...".However, the nodal masses are not apparent from this.To generate nodal masses, you can use the RF-/DYNAM Pro Natural Vibrations add-on module. In this case, you it is possible to create a natural vibration case where the mass acts e.g. only in the Z direction. After having calculated the natural mode case, the "nodal masses" are available in the results tables of RF-/DYNAM Pro.In RF-/DYNAM Pro, you can optionally convert the nodal loads into masses by applying the force components of the respective load case to the natural case calculation.
The cross-section class is defined according to EN 1993-1-1 and EN 1999-1-1 by the maximum width/width ratio c/t or b/t of the cross-section parts subjected to compression. EN 1993-1-1 or EN 1999-1-1 only list different straight c/t or b/t parts. Therefore, a classification and a determination of the effective widths is not carried out for curved c/t or b/t sections.
AnswerBy default, the compute core of the cross-section program SHAPE-THIN is used in the RF-/ALUMINUM add-on module to determine the stresses of the effective cross-section in an iterative procedure. This method is precise because all vertices and edges of the cross-section are considered, but can be very time-consuming for complex sections.Alternatively, it is possible to determine the effective cross-section by means of a simplified analytical method (see Figure 01) that runs much faster. Using that approach, corners, roundings, etc. are neglected and subsequently compensated by a factor. No iterative calculation is performed. Therefore, the effective cross-section values may be higher than with the SHAPE-THIN calculation.In such a case, it is recommended to carry out the calculation with the analytical method and then to design only the governing structural component with the governing load combination by means of the SHAPE-THIN solution.
Unfortunately not. Intermediate supports and nodal supports have to be set manually. The default configuration for effective lengths is 1,0*member length and for set of members, one nodal support with definition u_y' and phi_x' is defined on each side of the set of member.To speed up the process of defining nodal supports, you can pick more nodes in one step by using the highlighted function in the attached picture.
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