Nodal releases are special objects in RFEM 6 that allow structural decoupling of objects connected to a node. The release is controlled by the release type conditions, which may also have nonlinear properties. This article will show the definition of nodal releases in a practical example.
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.
This article will show you how to properly consider the connection between surfaces that touch each other on one line with the help of line hinges in RFEM 6.
Generally, overlapping members in the model are not desired. To prevent RFEM from deleting an already defined member if another member is placed upon it, select "Allow Double Members" on the "Edit" menu.
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.
The architectural requirements for guardrails are still very high, and railings usually require a high degree of transparency. Glass railings, which do not require a visible support frame, offer a possible solution.
Pay particular attention to the connection points of members and surfaces when you deal with mixed systems, because not all internal forces can always be transferred without difficulty at the coupling location.
When you perform the subsequent modeling of a beam under an existing floor, the first issues that arise are which forces should be transferred between the downstand beam and the floor, and whether a composite effect is the goal. In this case, the floor should rest on the downstand beam without a composite.
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.
Due to the special properties of glass, you also have to pay close attention to the details when modeling in an FE model. Glass has a very high compressive strength and is, therefore, generally only designed for its tensile stresses. One particular disadvantage of the material is its brittleness. Stress peaks that occur in the calculation must, therefore, not be readily neglected.
When modeling a reinforced concrete rib with a masonry wall above, there is the risk that the rib is underdesigned if the structural behavior of the masonry is not correctly considered and the connection between the masonry wall and downstand beam is not modeled sufficiently accurately. This article deals with this issue and shows the possible modeling options of such a structure. In this example, the reinforcement is determined only from the internal forces and without secondary minimum reinforcement.
Modeling planar structural components such as glass panes is generally possible only in RFEM. If it is necessary to define the stiffening effect of a pane in a particular case, it can also be simulated in RSTAB.
The calculation of structures based on digital twins is becoming an everyday task in the engineering office. If a digital building model already exists, you want to continue to use the information contained in it as seamlessly as possible. This places far-reaching demands on modeling and interfaces for BIM-compatible structural analysis software.
When introducing and transferring horizontal loads such as wind or seismic loads, increasing difficulties arise in 3D models. To avoid such issues, some standards (for example, ASCE 7, NBC) require the simplification of the model using diaphragms that distribute the horizontal loads to structural components transferring loads, but cannot transfer bending themselves (called "Diaphragm").
With RF-FOUNDATION Pro, it is possible to determine the settlements of single foundations and resulting spring stiffnesses of the nodal supports. These spring stiffnesses can be exported into the RFEM model and used for further analyses.
When designing steel columns or steel beams, it is usually necessary to carry out cross-section design and stability analysis. While the cross-section design can usually be performed without giving further details, the stability analysis requires further user-defined entries. To a certain extent, the member is cut out of the structure; therefore, the support conditions have to be specified. This is particularly important when determining the ideal elastic critical moment Mcr. Furthermore, it is necessary to define the correct effective lengths Lcr. These are required for the internal calculation of slenderness ratios.
There are several options for calculating a semi-rigid composite beam. They differ primarily in the type of modeling. Whereas the Gamma method ensures simple modeling, additional efforts are required when using other methods (for example, shear analogy) for the modeling which are, however, offset by the much more flexible application compared to the Gamma method.
There are different options to model composite cross‑sections in RFEM. In the following example, three different modeling options for a composite cross‑section, consisting of a rolled steel section HEA 300 and a rectangular cross‑section made of concrete w/l = 100/30 cm, will be displayed and explained.
In the case of plate structures, it is always necessary to consider realistic definition support conditions. Depending on the way of defining the flexibility of the supports, clear differences may occur in the results.
If a bending load of a brittle beam element (an unreinforced concrete beam) is increased by means of the bending capacity, the structure responds by breaking the cross-section and the member is separated into two segments. At the time of the failure, the broken part suddenly loses its potential to transfer the bending moment. Due to the segmentation, the critical part also fails to transfer the other force types, such as axial forces.
Heat loss due to external components without thermal decoupling of the internal components is enormous. For this reason, external structural components are thermally separated from the building envelope using a special built-in component. For the connection of a balcony slab with a reinforced concrete floor, Schöck Isokorb® or HALFEN HIT Insulated Connection can be used, for example. For the design of such built-in components, the respective technical approval must be taken into account. The following article shows an example of considering Schöck Isokorb® in the FEM calculation.
Platforms can be connected directly to leg members using the new "Leg Member Axis" option. Thus, it is no longer necessary to define the platform width or coupling member.
The vibration design of cross‑laminated timber plates often governs for wide-span ceilings. The advantage of the lighter material of timber over concrete turns into a disadvantage as the high mass material is advantageous for a low natural frequency.
In order to represent the stiffness of the entire structure correctly, you can consider shear coupling between the ceiling and the downstand beam using the line release. This way, you can define a spring constant, thus avoiding the replacement system by using coupling members. The spring constant results from the shift modulus of the fastener, which can be determined according to EN 1995-1-1 or ANSI/AWC NDS, for example.
Modern buildings are designed with spaces tailored to personal desires and dreams, expressing individual lifestyles. These requirements often include ceilings - whether in houses, office buildings, or public buildings - that have an enormous span and no support, allowing optimal use of the space below. However, this requires a very high stability level for load‑bearing capacity and serviceability reasons. By extending the size of beam or plate cross-sections, you can increase the stability, but the cost effectiveness decreases because of the additional consumption of material. One common solution for these large spans is to use timber or steel downstand beams.
The increasing use of the BIM method in planning buildings also opens up new possibilities for structural engineers. Once a comprehensive 3D model of a building has been created, you want to continue using it for the structural analysis and gain the maximum benefit from it. However, there are also some new challenges for the structural engineer and the software used, which are described in this article.
In order to display the internal forces of rigid members, it is necessary to select the corresponding option under ‘Results’ → ‘Members’ → ‘Results on Couplings’ in the Display navigator.