Both the determination of natural vibrations and the response spectrum analysis are always performed on a linear system. If nonlinearities exist in the system, they are linearized and thus not taken into account. They are caused by, for example, tension members, nonlinear supports, or nonlinear hinges. This article shows how you can handle them in a dynamic analysis.
To be able to evaluate the influence of local stability phenomena of slender structural components, RFEM 6 and RSTAB 9 provide you with the option of performing a linear critical load analysis on the cross-section level. The following article explains the basics of the calculation and the result interpretation.
The design of cold-formed steel members according to the AISI S100-16 is now available in RFEM 6. Design can be accessed by selecting “AISC 360” as the standard in the Steel Design add-on. “AISI S100” is then automatically selected for the cold-formed design (Image 01).
Modal analysis is the starting point for the dynamic analysis of structural systems. You can use it to determine natural vibration values such as natural frequencies, mode shapes, modal masses, and effective modal mass factors. This outcome can be used for vibration design, and it can be used for further dynamic analyses (for example, loading by a response spectrum).
The advantage of the RFEM 6 Steel Joints add-on is that you can analyze steel connections using an FE model for which the modeling runs fully automatically in the background. The input of the steel joint components that control the modeling can be done by defining the components manually, or by using the available templates in the library. The latter method is included in a previous Knowledge Base article titled “Defining Steel Joint Components Using the Library". The definition of parameters for the design of steel joints is the topic of the Knowledge Base article “Designing Steel Joints in RFEM 6".
The stability checks for the equivalent member design according to EN 1993-1-1, AISC 360, CSA S16, and other international standards require consideration of the design length (that is, the effective length of the members). In RFEM 6, it is possible to determine the effective length manually by assigning nodal supports and effective length factors or, on the other hand, by importing it from the stability analysis. Both options will be demonstrated in this article by determining the effective length of the framed column in Image 1.
Very small torsional moments in the members to be designed often prevent certain design formats. In order to neglect them and still perform the designs, you can define a limit value in RF‑/STEEL EC3 from which torsional shear stresses are taken into account.
The RF‑/STEEL EC3 add-on module automatically transfers the buckling line to be used for the flexural buckling analysis for a cross-section from the cross-section properties. The assignment of the buckling line can be adjusted manually in the module input for general cross-sections in particular, as well as for special cases.
When optimizing cross-sections in the add-on modules, you can also select arbitrarily defined cross-section favorites lists - in addition to the cross-sections from the same cross-section series as the original cross-section.
RF-/DYNAM Pro - Equivalent Loads allows you to determine the loads due to equivalent seismic loads according to the multi‑modal response spectrum method. In the example shown here, this was done for a multi‑mass oscillator.
This technical article deals with the design of structural components and cross-sections of a welded truss girder in the ultimate limit state. Furthermore, the deformation analysis in the serviceability limit state is described.
Designing rigid end plate connections is difficult for four-row connection geometries and multi-axis bending stresses, because there are no official design methods.
The elastic deformations of a structural component due to a load are based on Hooke's law, which describes a linear stress-strain relation. They are reversible: After the relief, the component returns to its original shape. However, plastic deformations lead to irreversible deformations. The plastic strains are usually considerably larger than the elastic deformations. For plastic stresses of ductile materials such as steel, yielding effects occur where the increase in deformation is accompanied by hardening. They lead to permanent deformations - and in extreme cases to the destruction of the structural component.
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.
This technical article analyzes the effects of the connection stiffness on the determination of internal forces, as well as the design of connections using the example of a two-story, double-spanned steel frame.
Both the determination of natural vibrations and the response spectrum analysis are always performed on a linear system. If nonlinearities exist in the system, they are linearized and thus not taken into account. Straight tension members are very often used in practice. This article will show how you can display them approximately correctly in a dynamic analysis.
In this technical article, a hinged column with a centrally acting axial force and a line load acting on the strong axis will be designed by means of the RF-/STEEL EC3 add-on module according to EN 1993-1-1.
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").
This example will show what you should consider when you perform column design for bending and compression with regard to the internal forces from load combinations and result combinations.
The fire resistance design can be performed according to EN 1993-1-2 in RF-/STEEL EC3. The design is carried out according to the simplified calculation method for the ultimate limit state. Claddings with different physical properties can be selected as fire protection measures. You can select the standard temperature-time curve, the external fire curve, and the hydrocarbon curve to determine the gas temperature.
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.
DIN EN 1998-1 with the National Annex DIN EN 1998-1/NA specifies how to determine seismic loads. The standard applies to structural engineering in seismic areas.
The critical factor for lateral-torsional buckling or the critical buckling moment of a single-span beam will be compared according to different stability analysis methods.
For crane runways with large spans, the horizontal load from skewing is often relevant for the design. This article describes the origin of these forces and the correct input in CRANEWAY. The practical implementation and the theoretical background are discussed.
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.
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.
In SHAPE-THIN, the calculation of stiffened buckling panels can be performed according to Section 4.5 of EN 1993-1-5. For stiffened buckling panels, the effective surfaces due to local buckling of the single panels in the plate and in the stiffeners, as well as the effective surfaces from the entire panel buckling of the stiffened entire panel, have to be considered.
This example is described in technical literature [1] as Example 9.5 and in [2] as Example 8.5. A lateral-torsional buckling analysis must be performed for a principal beam. This beam is a uniform structural member. Therefore, the stability analysis can be carried out according to Clause 6.3.3 of DIN EN 1993‑1‑1. Due to the uniaxial bending, it would also be possible to perform the design using the General Method according to Clause 6.3.4. Additionally, the determination of the critical load factor is validated with an idealized member model in line with the method mentioned above, using an FEM model.
This example is described in technical literature [1] as Example 9.5 and in [2] as Example 8.5. A lateral-torsional buckling analysis must be performed for a principal beam. This beam is a uniform structural member. Therefore, the stability analysis can be carried out according to Clause 6.3.3 of DIN EN 1993-1-1. Due to the uniaxial bending, it would also be possible to perform the design using the General Method according to Clause 6.3.4. Additionally, the determination of the moment Mcr is validated with an idealized member model in line with the method mentioned above, using an FEM model.