For members or member sets with the activated design properties, there is an additional Design Supports & Deflection tab in the editing dialog box. Define the boundary conditions for the design of "compression perpendicular to the grain" as well as for the serviceability limit state design.
Design Support
Basically, the design supports have two functions:
- Definition of the boundary conditions for the design of "compression perpendicular to grain"
- Segmentation of a member or a member set for a deflection analysis
In order to perform the design of "compression perpendicular to grain" on the support, it is necessary to define a design support. Select a design support type from the list or create a new one using the
button. Click the
button to edit the selected design support type. The
button allows you to graphically select an existing design support from the model.
The definition of a design support can be defined at all intermediate nodes of the object by using a table. Both nodes of the "Node on Member" type and standard nodes between the members of a member set are recognized.
The input dialog boxes differ, depending on the selected design standard. If a material of the "Timber" category is assigned to a member or a member set, "Timber" is automatically preset as the design support type.
You can use the Active option to control whether there is a design support in the respective direction (z-axis or y-axis). If a member is rotated 90°, for example, you can deactivate the "support in z-axis" and activate it in the y-axis.
If you do not want to perform the design of "compression perpendicular to grain", but use the design support to segment the member or member set for a deflection analysis, you can deactivate the Direct Support option. This means that no entries regarding the support geometry and position are required and the support is only used for the segmentation of the deformation analysis. As an alternative, you can use the "General" design support type in order to avoid performing the design of "compression perpendicular to grain".
The support length always refers to a real beam and, based on the structural system or the node, it is shown half in the positive x-direction of the member and half in the negative x-direction.
The Support from edge option allows for the program to automatically detect whether a design support receives compressive or tensile forces. Accordingly, the design of "compression perpendicular to grain" is only performed in the case of compressive forces.
If a design support acts on an intermediate support, the "Inner support" function must be activated. Depending on the selected design standard, this is included in the determination of the effective bearing area.
The Shear force reduction option allows you to perform shear force design on the support with the governing shear force. The shear force is taken into account in the design at a certain distance from the support edge. The distance depends on the selected standard. This assumes that the force acts on the opposite side of the support; that is, usually on the top side of the beam.
If the transversal compression stresses are too great, they can also be absorbed by stiffening elements (for standard EN 1995‑1‑1 only). In this case, it is necessary to define fully threaded screws. Find more information here.
If you do not want to perform the design of support pressure in the fire situation, deactivate the Active for fire design function.
As already mentioned, a design support is also used to segment a member or a member set for a deflection analysis. If you do not want to consider the design support for the segmentation, deactivate the Active for deflection design option.
Deflection Analysis
Use Check direction to specify which deflection values are to be checked in the design. You can select the local axes y and z, as well as the resulting deflection, in the list.
By selecting the Displacement Reference, you can influence the deflection values to be checked for the design. If an undeformed system is selected as the reference, the local deformation values uy and uz are taken directly from the results and the deformations refer to the initial system. With regard to the deformed segment ends (connecting line between the start and end nodes of the deformed system), the deflection values for the design check are reduced by the deformation values of the start or end nodes in order to be able to check the local deflections.
By defining the design support in the corresponding direction at the member start, member end, and intermediate nodes, the program automatically recognizes the segments and segment lengths to which the allowable deformation is related. It automatically detects whether it is a beam or a cantilever by using the defined design supports. The manual assignment, as in the previous versions (RFEM 5), is no longer necessary.
In the image below, no design support was defined at Intermediate Node 50. As a result, the program only recognizes one segment and the reference length corresponds to the member or member set length.
If the design support is defined at an intermediate node, two segments are recognized and the reference length is adjusted accordingly.
If no deformation analysis should be performed for the segment, it can be deactivated using the respective checkbox:
The User-Defined Lengths option allows you to modify the reference lengths in the table. The corresponding segment length is always used by default. If the reference length deviates from the segment length (for example, in the case of curved members), it can be adjusted.
Activate the Precamber checkbox in order to consider it for the design and thus reduce the deflection value. The precamber is always applied as a single-wave shape on the entire member or member set. Enter the precamber z as a positive value if it is opposite to the local member axis z. To design the resulting direction, the precamber components are converted into the resulting direction. In the case of design according to EN 1995‑1‑1, the precamber is only taken into account for quasi-permanent design situations.