The AISC 360-16 steel standard requires stability consideration for a structure as a whole and each of its elements. Various methods for this are available, including direct consideration in the analysis, the effective length method, and the direct analysis method. This article will highlight the important requirements from Ch. C [1] and the direct analysis method to be incorporated in a structural steel model along with the application in RFEM 6.
In RFEM 6 it is possible to save selected objects (as well as whole structures) as blocks and reuse them in other models. Three types of blocks can be distinguished: non-parameterized, parameterized, and dynamic blocks (via JavaScript). This article will focus on the first block type (non-parameterized).
Inserting holes in surfaces is very easy due to the large selection of tools. In order to insert holes or drilling in solids, it is necessary to keep in mind that an opening at the beginning and the end of a continuous hole must be created, as well as a surface that separates the hole from the solids.
In timber design, beams are often built from several timber elements. The individual elements can be connected with glue, nails, bolts, or dowels. A glued connection is to be assumed as rigid. In the case of dowel‑type fasteners, the joint is compliant (slip joint), and the cross‑section properties of the connected elements cannot be fully applied.
RFEM 5 allows you to use many different member nonlinearities for designing a model. In the following text, we look at an example of the use of the "slippage" member nonlinearity. The example is a simplified model of a concrete manhole with a square plan view.
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.
When connecting tension-loaded components with bolted connections, the cross-section reduction due to the bolt holes must be taken into account in the ultimate limit state design. This article describes how the design of the tension resistance according to DIN EN 1993‑1‑1 can be performed with the net cross-section area of the tension member in the RF‑/STEEL EC3 add-on module.
Table 3.1 of EN 1993‑1‑8:2010‑12 defines the nominal values of the yield strength and the ultimate limit strength of bolts. The bolt classes given here are 4.6, 4.8, 5.6, 5.8, 6.8, 8.8, 10.9. The note for this table states that the National Annex may exclude certain bolt classes. For the NA of Germany, these are the bolt classes 4.8, 5.8, and 6.8.
In cross‑sections created in SHAPE‑THIN, the openings, such as bolt holes, can be modeled by using the elements with zero thickness. The program provides two options for calculating shear stresses in the area of such null elements.
The simplest way to model a bolt connection in RFEM 5 is to define a node in the center of a hole, then connect it by means of internal members to the surface.
This technical article deals with the stability analysis of a roof purlin, which is connected without stiffeners by means of a bolt connection on the lower flange to have a minimum manufacturing effort.
The definition of the non-linear contact problem plays an important role for more detailed investigations of shear/hole bearing connections or their immediate environment. This article uses a solid model to search for comparable and simplified surface models.
RFEM offers the following options to design a pinned end plate connection. First, there is the option in RF-JOINTS Steel - Pinned to enter the corresponding parameters quickly and easily to receive a documented analysis, including graphics. It is also possible to model such a connection individually in RFEM and then to evaluate or manually design the results. In the following example, the particularities of this modeling will be explained and the shear forces of the bolts will be compared to the corresponding results from RF-JOINTS Steel - Pinned.
When modeling surface models, such as a frame joint or similar structures, there is always the question of how to model a prestressed bolt connection. In this case, it is always necessary to find a compromise between the practicable and detailed solution. The following article describes the modeling procedure of such a connection, based on the joint diagram calculation method.
In this example, the design resistance of an end plate according to EN 1993-1-8 [1] is to be determined; the other components are not described here. To check the results, the dimensions of the connection IH 3.1 B 30 24 of Typified Connections [2] were used. S 235 material and bolts with strength 10.9 are used.
SHAPE-THIN allows you to calculate section properties and stresses of any cross-sections. If a flange or a web is weakened by bolt holes, you can consider this by using null elements. The stresses are subsequently recalculated with the reduced cross-section values. In this case, it is necessary to pay a special attention to shear stresses. By default, these are set to zero in the area of the null elements. When recalculating shear stresses with the reduced cross-section values and without further adaptation, it turns out that the integral of the shear stresses is no longer equal to the applied shear force. The following example shows in detail how to calculate the shear stress.
When designing bending-resistant connections from I-beams, the connection is dissolved into the individual parts. For these basic components of a joint, there are separate formula calculators for load-bearing capacity and stiffness. In RFEM and RSTAB, frame joints can be designed using the RF-/FRAME-JOINT Pro add-on module.
Sometimes, a model in the graphic window is displayed without filling the entire window, or with overly large margins after clicking the [Show Whole Model] button. To set the size of the graphic margins, click "Options" → "Display Margins and Stretch Factors". The value specifies the percentage of the margin relative to the graphic window size.
Downstand beams or T-beams are often used in reinforced concrete structures. In contrast to the previous representation and calculation options where, for example, a downstand beam was considered as a fixed support and the determined support reaction was applied to a separate member structure using a T-beam section, the ultimate structural FEA software like RFEM allow you to consider the structure as a whole and thus achieve a more precise analysis.
In RF-JOINTS Timber – Steel to Timber, you can consider the possible minimum slippage of bolts in the case of guide pins. In RFEM, this slippage is taken into account using the flexibility in member end releases.
In RF-/JOINTS Timber – Steel to Timber, you can select a circular connection type for the dowel, bolt, nail, and screw joint categories. For this connection type, the minimum radius is set in compliance with the recommendations of the STEP-1 report of the German Information Service Timber.