Structural Analysis & Design of Steel Structures | Dlubal Software

The input windows in RF-/STEEL EC3 distinguish between the flexural and lateral-torsional buckling analyses. In the following text, an example will show the parameters for lateral-torsional buckling.

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 M_cr. Furthermore, it is necessary to define the correct effective lengths L_cr. These are required for the internal calculation of slenderness ratios.

This article is about the stability analysis of a steel column with axial compression according to EN 1993‑1‑1, Clause 6.3.1. Additionally, a variation study is carried out aiming at steel optimization.

RF-/STEEL EC3 automatically imports the cross-sections defined in RFEM/RSTAB. It is possible to design all thin-walled cross-sections. The program automatically selects the most efficient method according to standards.

The ultimate limit state design takes into account several loads and you can select the interaction designs available in the standard.

The classification of designed cross-sections into Classes 1 to 4 is an essential part of the analysis according to Eurocode 3. This way, you can check the limitation of the design and rotational capacity by means of the local buckling of cross-section parts. RF-/STEEL EC3 determines the c/t-ratios of the cross-section parts subjected to compression stress and performs the classification automatically.

For the stability analysis, you can specify for each member or set of members whether flexural buckling occurs in the y- and/or the z-direction. You can also define additional lateral restraints in order to represent the model close to reality. The slenderness ratio and elastic critical load are determined automatically on the basis of the boundary conditions of RF-/STEEL EC3. The elastic critical moment for lateral-torsional buckling required for the lateral-torsional buckling analysis can be determined automatically or specified manually. The load application point of transverse loads, which has an influence on the torsional resistance, can also be taken into account via the setting in the details. In addition, you can take into account rotational restraints (for example trapezoidal sheeting and purlins) and shear panels (for example trapeziodal sheeting and bracing).

In modern construction, where cross-sections are increasingly slender, the serviceability limit state is an important factor in structural analysis. RF-/STEEL EC3 assigns load cases, load combinations, and result combinations to different design situations. The respective limit deformations are preset in the National Annex and can be adjusted, if necessary. In addition, it is possible to define reference lengths and precambers for the design.

When performing the design of tension, compression, bending, and shear loading, the module compares the design values of the maximum load capacity to the design values of the actions.

If the components are subjected to both bending and compression, the program performs an interaction. In RF-/STEEL EC3, you can determine the factors according to Method 1 (Annex A) or Method 2 (Annex B).

The flexural buckling design requires neither the slenderness nor the elastic critical buckling load of the governing buckling case. The module automatically calculates all required factors for the bending stress design value. RF-/STEEL EC3 determines the elastic critical moment for lateral-torsional buckling for each member on every x-location of the cross-section. If required, you only need to specify lateral intermediate supports of the individual members/sets of members, definable in one of the input windows.

If members are selected for the fire resistance design in RF-/STEEL EC3, there is another input window available where you can enter additional parameters, such as: a coating or cladding type. Global settings cover the required time of fire resistance, temperature curve, and other coefficients. The printout report lists all intermediate results and the final result of the fire resistance design. Furthermore, it is possible to print the temperature curve in the report.

The results sorted by load case, cross-section, member, set of members, or x-location are displayed in clearly arranged result windows. By selecting the corresponding table row, detailed information about the performed design is displayed.

The results include a comprehensible list of all material and cross-section properties, design internal forces, and design factors. Furthermore, it is possible to display the distribution of internal forces of each x-location in a separate graphic window.

Parts lists by members/sets of members for the individual cross-section types complete the detailed and structured display of results. To print input data and results, you can use the global printout report in RFEM/RSTAB.

For further processing of various data, it is possible to export all tables to MS Excel.