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Frequently Asked Questions (FAQ)
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AnswerWith the PLATE-BUCKLING add-on module, you can only calculate rectangular buckling panels.The panel is entered via 1.1 of the add-on module. Alternatively, the panel can also be created from an existing RFEM or RSTAB file by selecting the respective c/t-part.
AnswerThe option to enter a taper on a beam can be activated in the Arrangement section of Window 1.4 Geometry. Here you can model the taper on the bottom or top side of the beam.The plate thicknesses as well as the height of the taper are defined by selecting the cross-section of the taper, since the cut rolled cross-sections are often used, for example. If user-defined plates are used, you can select a parametric T‑section. The length of the taper as well as the material are entered in the same section. The weld thicknesses for connecting the taper to the beam can be defined in the Welds section.If there is a tapered member already used as a beam (entered in the "Nodes and Members" section by specifying different cross-sections and lengths), it is not possible to model an additional taper.
AnswerThe cross-section library provides a large number of various cross-sections. For many cross-section shapes, the option of the parametric definition is also available. The video shows an easy way of how to model a conical tower. When dividing this member, the software automatically determines the new cross-sections at the division points.
AnswerFor many users, the very realistic display of a building in construction programs arouses the wish to carry out the structural analysis of the building with the same complex spatial model.Again and again, the design of log cabins is approached to us. Unfortunately, this attractive construction method is relatively complex for three-dimensional analysis. In dimensioning, there are some critical questions that cannot be answered.
Furthermore, log houses are common for the houses with the maximum of 2 full floors because of their high placement of more than 15 cm per story. Thus, the occurring forces are within a manageable framework and can be determined sufficiently precisely with the methods of the structural analysis for members in 2D structures. In RFEM/RSTAB, there is an option to define round members in a tapered way for this purpose. Thus, the definition of 2D equivalent systems can be done much faster in RFEM/RSTAB.There is some information in the given literature source.
- Which sorting class is the timber subject to? In a log house, unsorted damp wood is often used.
- How is the contact between the timber types controlled? Diamond notch, connection with moving timbers, and so on?
- Have mullions been installed? Which type of timber and how are they supported horizontally?
- Which dimensions does the timber have? In a log structure, a grown trunk can often be integrated. These trunks do not have uniform dimensions as the nature cannot be put into a grid.
- How is it possible to consider the contact between two timber layers?
The sets of members to be designed in the add-on module must be based on the same or the consistently running cross-section.
An exception is a set of members consisting of ribs. This only results in an identical cross-section if the integration width of the rib is selected to be the same. Thus, there must be a single rib type for the entire set of members.
Tapered sets of members are only designed if the entire set of members has a linear cross-section diagram.
You have probably carried out the design in RF‑/TIMBER Pro according to DIN 1052:2008 and used a cut-to-grain angle of less than 3° (see Figure 01). According to Section 10.4.1 (1) of DIN 1052, such a cut-to-grain angle does not need to be considered. If you switch the design to the current DIN EN 1995 (see Figure 02), the design will also be carried out for the angle of less than 3°.
Furthermore, the module allows you to analyze transversal tension stress in the apex etc., according to the Section 6.4.3 ff. of the Eurocode. This procedure is explained in detail in the webinar.
The reason for this warning is that tapered cross-sections cannot be designed by using the methods 6.3.3 of EN 1993‑1‑1. The RF‑/STEEL EC3 module designs such cross-sections by using General Method 6.3.4 of EN 1993‑1‑1. However, this method is only allowed for loading in the support direction, that is, without the transverse bending moment. Therefore, the warning appears.
You can perform the stability analysis as cross-section design according to the second-order theory, which is possible by using the add‑on modules RF‑/FE‑LTB or RF‑/STEEL Warping Torsion.
As an alternative, you can neglect the transverse bending in the filter options of the "Details" dialog box, the "Stability" tab, or activate the adapted method according to Naumes in the "National Annex" dialog box, which enables transverse bending.
AnswerTo use SHAPE-MASSIVE cross-sections for tapered members, two conditions must be met.1st In the General Data of the SHAPE-MASSIVE structure, the option "Stresses in stress points" must be deactivated. See Figure 01.2nd The nodes (corner points) of the cross-sections used for the taper must be arranged the same way in both cross-sections. See Figure 02.
AnswerWhen a beam with variable cross-section dimensions is divided retroactively, the dimensions for the beam start and beam end can no longer be modified easily. Due to the resulting intermediate nodes, a new cross-section would have to be calculated for every member segment. In order for you to not have to do this manually, it is recommended to delete the members. In doing so, take care to only delete the selected members and not their nodes. The new member can subsequently be modelled from beam start to beam end and connected to the intermediate nodes with the "Connect Members" tool.Summary (see Figure 1):1. Delete members (nodes must remain unchanged)2. Insert new member from beam start to beam end3. Connect member with intermediate nodesIn RSTAB, the members always have to be connected to each other in a node.This is not absolutely necessary in RFEM, because it allows a node to lie on a line without dividing the member (see Figure 2). It is therefore sufficient to modify the cross-section at the beam start and beam end. If the intermediate nodes (which members already connect to) already exist and you wish to create the tapered member retroactively in RFEM, it is recommended to deactivate the option "Auto Connect Lines/Members" (see Figure 3). Afterwards the member can be created without divisions at the intermediate nodes.
RFEM and RSTAB interpolate the variable stiffnesses along the member by higher-order polynomials. The internal determination of tapered cross-sections is done by using the taper shape (see Figure 01). If different cross-sections are defined for the member start and end, you can select the "linear" or "quadratic" taper shape. In this way, it is possible to represent the taper geometry for the determination of the interpolated cross-section properties.
In most cases, the layout of the taper is linear, that is, the member only tapers and extends regularly over the depth of the start to the end section. However, if the cross-section width and depth changes, the quadratic shape is recommended for the interpolation of the cross-section properties.
For more precise results, it can also be reasonable to divide the tapered member and create additional cross-sections.
The influence on the calculation of tapers also has the division of taper and foundation members that is controlled in the calculation parameters (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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