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Frequently Asked Questions (FAQ)
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AnswerThe sets of members to be designed in the add-on module must be based on the same or uniformly running cross-section.A special feature is a set of members consisting of ribs. This results in an identical cross-section only if the integration width of the rib is selected to be the same. Thus, there must be a uniform rib type for the entire set of members.Tapered sets of members are only designed if the entire set of members is linear
Has cross-sectional shape.
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.
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).
This message appears if both cross-sections of the taper have a different number of stress points.
The stresses in STEEL are determined with the second moments of area and the distances to the stress points. Now, if the taper's start and end cross-section have different numbers and locations of stress points, the program cannot interpolate the intermediate values. In the rendering mode, no taper is often displayed but only the two cross-sections at the start and end. You can see a "break" in the middle of the member.
You can look at the stress points of a cross-section in its details. With a click on the button [Details of Stress Points] you can open a table showing the exact values for the stress points (number, location, and so on).
To solve the problem, you have to create the same number of stress points. You can do it, for example, by creating a cross-section at the end of the taper as a copy of the start cross-section and adjusting the height. However, the original form must be preserved. Therefore, it might be necessary to also model a very small strengthening.
You can also create the tapered cross-sections with the sections of the RSTAB library: For this purpose, there are the "Strengthened I-Section with Lower T-Section" among the welded cross-sections.
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