Line releases are special objects in RFEM 6 that allow structural decoupling of objects connected to a line. They are mostly used to decouple two surfaces that are not rigidly connected or transferring only compressive forces at the common boundary line. By defining a line release, a new line is generated at the same place which transfers only the locked degrees of freedom. This article will show the definition of line releases in a practical example.
In RFEM 6 it is possible to define multilayer surface structures with the help of the “Multilayer Surfaces” add-on. Hence, if you have activated the add-on in the model’s Base Data, it is possible to define layer structures of any material model. You can also combine material models of, for example, isotropic and orthotropic materials.
This article describes how a flat slab of a residential building is modeled in RFEM 6 and designed according to Eurocode 2. The plate is 24 cm thick and is supported by 45/45/300 cm columns at distances of 6.75 m in both the X and Y directions (Image 1). The columns are modeled as elastic nodal supports by determining the spring stiffness based on the boundary conditions (Image 2). C35/45 concrete and B 500 S (A) reinforcing steel are selected as the materials for the design.
RFEM 6 includes the Form-Finding add-on to determine the equilibrium shapes of surface models subjected to tension and members subjected to axial forces. Activate this add-on in the model's Base Data and use it to find the geometric position in which the prestress of lightweight structures is in equilibrium with the existing boundary conditions.
If you want to consider guide objects in the overall view (F8 key or double-click on the mouse wheel) or, for example, in a particular direction of the views, you can enable this option in the settings of the particular guide objects (guidelines, background layers, line grids).
A member's boundary conditions decisively influence the elastic critical moment for lateral-torsional buckling Mcr. The program uses a planar model with four degrees of freedom for its determination. The corresponding coefficients kz and kw can be defined individually for standard-compliant cross-sections. This allows you to describe the degrees of freedom available at both member ends due to the support conditions.
Designing vertical insulating glass requires assigning different loads on the individual layers of the entire glass unit. This occurs, for example, with simultaneous actions from wind loads and fall protection.
To work even more efficiently, RF‑GLASS allows you to create and save different, user‑defined layer structures that can be reimported later or loaded in another project.
The additional loads from self‑weight are usually composed of several layers; for example, classic floor and ceiling layers in buildings, or road coatings for bridge constructions. When defining load definitions in RFEM and RSTAB, you can use the multi-layer load to define the individual layers with thickness and specific weight.
For designing glass in the RF‑GLASS add‑on module, you can use one of two calculation methods: a 2D or a 3D calculation. The main difference between these design options is the automatic modeling of the layers in a temporary model. In a 2D calculation, each layer is generated as a surface element (plate theory); in a 3D calculation, it is generated as a solid. Depending on the selected layer composition, you can either select an option or find it preselected by the program.
For solids, there is another option for the FE mesh setting. You can arrange a layered FE mesh in addition to a holistic FE mesh refinement. For this option, you can perform a defined division of the solid with finite elements between two parallel surfaces. This option is particularly suitable for very large solid geometries with a low height.
You can use the "Free Circular Load" option in RFEM to apply a partial uplift force to a cone‑shaped floor slab. It can be defined as linearly variable. The definition of center C and the outer boundary R can be specified easily, using the select function.
When calculating foundations according to EC 7 or EC 2, different foundation types or sizes are usually used in one object. However, boundary conditions like the soil parameters, the materials for foundations, concrete covers, and the load combinations selected for design remain the same for all foundations, as a rule.
DXF layers of ground plans cannot be used directly in FEA programs because only the outer contours of the elements (walls, ceilings, and so on) are available in the drawing. The FEM programs require system axes, but only the outer contours of the elements (walls, ceilings, and so on) are available in the DXF drawing.
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 RFEM, surfaces are automatically connected if they have common boundary lines. If the definition line of a surface is lying in another surface, the line is automatically integrated into the surface, provided that it is a planar surface. For quadrangle surfaces, however, automatic object detection would be relatively time-consuming. For this reason, the corresponding function is deactivated. The integrated objects must be specified manually.
The "Mapped Mesh Preferred" option has an influence on the mesh generation of surfaces with curved and folded outlines. The program tries to align the FE mesh with the boundary lines of the surfaces.
Before creating a structural model, every user gives thought to the boundary parameters of the system and how best to represent the model. Special attention should be paid to the orientation of the global coordinate system. In engineering, the global Z‑axis is usually oriented downwards (in the direction of the dead load), while it tends to be upwards in architecture. These differences can often lead to complications during modeling; for example, when you replace global models or DXF layers.
When using the RF‑GLASS add‑on module, you can define just the geometry in the main program, as well as the load situation of the structural component to be designed. The respective support conditions and all further design-relevant definitions (for example, the layer structure and support conditions), can be further specified in RF‑GLASS.
If the geometry of a surface for which you must remove some of the existing boundary lines changes subsequently, you do not need to redefine the surface.
To better distinguish between the different layer compositions (for example, for walls and ceilings), you can assign user‑defined colors and textures to each composition.
In RFEM and RSTAB, you can use many interfaces to simplify the modeling of your structure. From background layers, to the import of IFC objects that can be converted into members or surfaces, to the import of the entire structural system from Revit or Tekla. Regardless of the performance of the selected interface, further utilization also depends on the accuracy of the imported data.
Different glass types and layer structures are available for glass structures used for different purposes. The following types are usually used: float glass, partly tempered glass, and toughened safety glass.
RFEM and RSTAB offer different options to model bored piles. One option is to display bored piles as single-valued supports or hinged columns. Another option is realistic modeling while taking the soil into account by means of applying a member elastic foundation. The two following examples will describe it in detail. However, pile base resistance, skin friction, and soil layers are not considered in this technical article.
Cable and tensile membrane structures are regarded as very slender and aesthetic building structures. The partly very complex double-curved shapes can be found using suitable form-finding algorithms. One possible solution is to search for the form via the equilibrium between the surface stress (provided prestress and an additional load such as self-weight, pressure, and so on) and the given boundary conditions.
The boundary conditions of a plate support can be entered quickly as singular and line supports in the FEA software. However, if the flexibility of the supports is not considered when modeling the structure, it is often necessary to take a closer look at the support definitions during the design using stresses or the determination of the required reinforcement, at the latest.
For the serviceability limit state design according to Section 6.6 of Eurocode EN 1997‑1, settlement has to be calculated for spread foundations. RF-/FOUNDATION Pro allows you to perform the settlement calculation for a single foundation. For this, you can chose between an elastic and a solid foundation. By defining a soil profile, it is possible to consider several soil layers under the foundation base. The results of the settlement, foundation tilting, and vertical soil contact stress distribution are displayed graphically and in tables to provide a quick and clear overview of the calculation performed. In addition to the design of the foundation settlement in RF-/FOUNDATION Pro, the structural analysis determines the representative spring constants for the support and can be exported to the structural model of RFEM or RSTAB.
In RFEM and RSTAB, you can import background layers from a DXF file. If the main nodes of the model have already been set, it can be useful to deactivate the snap mode of the background layer.