Steel connections in RFEM 6 are defined as an assembly of components. In the new Steel Joints add-on, universally applicable basic components (plates, welds, auxiliary planes) are available for entering complex connection situations. The methods with which connections can be defined are considered in two previous Knowledge Base articles: “A Novel Approach to Designing Steel Joints in RFEM 6" and “Defining Steel Joint Components Using the Library".
If members aligned in space meet in a node, the local x- or y-axes of the members do not lie in one plane, since the local z-axes are aligned in the plane of gravity.
In the RF-GLASS add-on module, 3D rendering is implemented to facilitate the definition of the support conditions. This interactive graphical visualization facilitates the input and control of line and nodal supports. However, the schematic display can also be selected, if necessary.
In the case of wall-like load-bearing behavior of the cross-laminated timber plate, special attention must be paid to the shear deformation in the plane of the pane and thus, in particular, to the displaceability of the fasteners.
You can color the surfaces in the direction of the local z‑axis using the indicated option in the Display Navigator. By default, the side lying in the negative z-direction is colored red and the side lying in the positive z-direction is colored blue.
In RFEM and RSTAB, you can now also display and check the types of members used visually, by means of colors. To do this, an option has been integrated into the Display Navigator.
In EN 1993-1-1, the General Method was introduced as a design format for stability analyses that can be applied to planar systems with arbitrary boundary conditions and variable structural height. The design checks can be performed for loading in the main load-bearing plane and simultaneous compression. The stability cases of lateral-torsional buckling and flexural buckling are analyzed from the main supporting plane; that is, about the weak component axis. Therefore, the issue often arises as to how to design, in this context, flexural buckling in the main load-bearing plane.
In RF‑/FOUNDATION Pro, the reinforcement to be placed in the foundation slab and, if necessary, the bucket links, is displayed in a 3D rendering and in the reinforcement drawings.
With the orthotropic elastic-plastic material model, you can calculate solids with plastic material properties in RFEM 5 and evaluate them according to the Tsai‑Wu failure criterion. The Tsai-Wu criterion is named for Stephen W. Tsai and Edward M. Wu, who published it in 1971 for plane stress states.
In RFEM and RSTAB, you can add a comment to model objects in the graphic. When inserting a comment, the origin of the current work plane automatically jumps temporarily to the same plane in which the comment is placed. This prevents comments from being accidentally placed very far from the object.
In RFEM 5 and RSTAB 8, you can now create a work plane by simply selecting three points. It is no longer necessary to create a user-defined coordinate system.
Friction plays an important role in practice. Without friction, the brakes of cars would be useless, objects on inclined planes would just slide away, and prestressed bolt connections would be impossible.
This example describes a definition of a planar surface by four nodes that have been imported and seem to lie in a common plane. In reality, they are not exactly in one plane due to (for example) a previous modeling error of a few millimeters. When trying to create a planar surface, the error message "Error in the surface definition! The nodes do not lie in a common plane." appears.
When modeling with finite elements, sooner or later you come up with the question of how two surfaces (2D elements) lying on top of each other can be modeled. Hence, both surfaces are often modeled in the same plane. The possible consequences of this approach, and whether there are better solutions, are described below.
RF-COM/RS-COM is a programmable interface that allows the user to expand the main programs RFEM and RSTAB with customized input macros or post‑processing programs. A tool to copy and move selected guidelines in RFEM will be developed in this article. It is also possible to copy or move the guidelines to another work plane. VBA in Excel will be used as the programming environment.
In the case of a parallel offset of the structural plane of members and surfaces and also applying an axial offset to members, for example, the function of eccentricities may be useful.
Some compound beam structures, such as stacked containers or retracted telescopic bars, transfer the forces in the connection between the components by friction. The load-bearing capacity of such a connection depends on the effective axial force perpendicular to the friction plane and on the friction coefficients between both friction surfaces. For example, the more the friction surfaces are compressed, the more horizontal shear force can be transferred by the friction surfaces (static friction).
If you want to connect members tangentially to a curved member or a curved surface in RFEM, it is necessary to define the member rotation of the connected members. In order to avoid manual determination, you can display the center point of the curved line and place a node on it. Then, you can select the "Member Rotation via Help node" option and specify the relevant help nodes. Thus, the members are rotated automatically in the defined plane (x-z in our example) and the top edge of the rotated cross-section is parallel to the tangent of the curved line.
The form-finding process in RF-FORM-FINDING displaces the corner nodes of FE elements of a membrane surface in space until the defined surface stress is in equilibrium with the boundary conditions. This displacement is independent of the element geometry. In the case of elements with four corner nodes, the free displacement may cause spatial drilling in the element plane and thus exceed the validity limits of the calculation; therefore, triangular elements are generally recommended for form‑finding systems. Triangular elements remain independent of the corner node displacement and stay within the calculation limitations.
In the following example, the stability analysis of a steel frame can be performed according to the General Method in compliance with EN 1993‑1‑1, Sect. 6.3.4 in the RF‑/STEEL EC3 add-on module. The first of my three posts shows the determination of the critical load factor for design loads required by the design concept, which reaches the elastic critical buckling load with deformations from the main framework plane.
In the latest version of RFEM, nodal constraints were implemented. Therefore, you can now connect the nodes in an ideal way. The diaphragm type represents the option to couple nodes in a plane. This option is available not only for the global coordinate system, but also for user-defined coordinate systems.
In CONCRETE and RF‑CONCRETE Members, you can open a dialog box with a 3D rendering of the existing reinforcement in Window 3.1 or 3.2. Now, you can also display different reinforcement views in several dialog boxes at the same time. The "Isometric and 3 Views" option known from RFEM is available here as well.
Surfaces can be created using the "Surface via Line Extrusion" function by extruding lines perpendicular to the active work plane. The Video (WMV) shows how to use this function.