For members or member sets with activated design properties, there is an additional tab in the editing dialog box called Design Supports and Deflection. Here you can define the boundary conditions for the serviceability limit state design of the aluminum design.
You can specify the settings for the deflection analysis of surfaces in the Deflection tab of the surface editing dialog box.
Members
Design Supports
Design supports allow for segmentation of the member or member set for the deflection analysis. Design supports can be assigned to all intermediate nodes of the object using the table. Both nodes of the “Node on Member” type and standard nodes between members of a member set are recognized.
Select a design support type from the list or create a new one using the
button. Use the
button for editing the selected design support type. The
button allows for graphical selection of an existing design support from the model.
A “General” type design support can be used for the aluminum design. Additional design checks, such as for local load introduction, are currently not available for EN 1999-1-1, ADM 2020, and GB 50429. Therefore, information on support width or depth is not relevant for the aluminium design.
However, design checks against web buckling are available according to CSA S157-17, 12.3. If this is to be performed, select the “Aluminum” design support type.
Use the “Support width” n to define the length of the load introduction. The “Support depth” d, on the other hand, has no influence on the design. The “support” is therefore not a support in the true sense of the word, but rather serves to describe the geometric parameters for considering the load.
Specify the effect of the support using the “Support from edge” list. The parameters +z and -z refer to the orientation of the local z-axis of the member. For example, if the load acts on the upper edge of the member and the local z-axis shows downwards, select the “-z/z-axis” option. This assumes that the load is a compressive stress for the cross-section. In the case of the “+z/z axis” option, it would be a tensile stress, as the load then acts on the lower edge.
If there is an “end support,” select the corresponding check box and define the distance e between the support center and the beam end. If the check box is deactivated, the distance e is considered to be endless.
If a design support is not to be considered for the segmentation, deactivate the “Active for deflection design” option.
Deflection Analysis
Segments and Reference Lengths
The right section of the Design Supports and Deflection tab lists the segments that result from assigning the design supports for the respective directions of the deflection analysis. For each design location in a segment, the displayed length Lc is used as the reference length for determining the limit value. If you want to change the automatically determined reference lengths, select the “User-defined lengths” check box. You can then edit the values. However, these user-defined lengths are not adapted automatically if you subsequently change the member length in the model.
Limit Values for Beams and Cantilevers
The deflection limits for beams supported on both sides and cantilevers are managed in the Serviceability Configurations. The corresponding limit value is applied to each segment during the design, depending on the arrangement of the design supports: A segment with design supports on both sides or without design supports is assumed to be a beam segment type, while a segment with a design support on one side is assumed to be a cantilever segment.
Check Direction
Use the “Check Direction” to specify which deflection result values are to be checked. The list contains the local axes y and z, the resulting deflection, and the local auxiliary axes y' and z' for selection. The segments below adjust accordingly.
Displacement Reference
You can use the options in the “Displacement reference” list to influence the deflection values to be checked for the design:
- Undeformed system: The local deformation values uy and uz are taken directly from the results.
- Deformed segment ends: The deflection values are reduced for the design by the deformation values of the start and end nodes, so that only the local deflections are checked.
Precamber
When performing design for each segment, you can take into account a "precamber" and thus reduce the value of the deflection. The precamber is applied as a single-wave shape for beam segments and as a linear distribution for cantilever segments. Enter the precamber wc,z or wc,y as a positive value if it is opposite to the local member axis z or y. To design the resulting direction, the components of the precamber are converted to the resulting direction.
Surfaces
For the ultimate limit state design of surfaces, the equivalent stresses are analyzed. The design checks are based on the material properties and surface thicknesses. On the other hand, the serviceability limit state design requires surface-specific data. You can enter this data in the Deflection tab of the ‘‘Edit Surface’’ dialog box.
Surface Type
Use the surface type to specify which deflection limits are to be applied during design. There are two options to select from in the list:
- Double-supported
- Cantilever
The limit values are stored in the Serviceability Configurations dialog box for various design situations of surfaces with support on one or both sides.
Displacement Reference
The displacement reference controls which reference model is used for the design of deformations. The list contains three options:
- Deformed user-defined reference plane: If the supports have very different displacements, you should specify an inclined reference plane for the displacement uz to be designed. Define the plane in the “User-defined reference plane” section by three points of the undeformed structural system. RFEM determines the deformation of the three definition points, sets the reference plane through these shifted points, and uses the related maximum deformation uz for the design.
- Parallel surface at the point of minimum nodal deformation: This option is recommended for flexible surface supports. The maximum deformation uz is related to a reference plane shifted parallel to the undeformed structural system, which RFEM sets through the node with the smallest displacement value uz,min.
- Undeformed system: The local deformations uz are taken directly from the results and used for the design.
Reference Length and Definition Type
The deflection limit value depends on the reference length Lz. For the definition type options “By maximum boundary line” and “By minimum boundary line” (default setting), RFEM determines the length of the longest or shortest edge from the surface geometry and sets the reference length automatically. If you want to define the reference length yourself, select the definition type “Manual” from the list and enter the value.
