General thin-walled cross-sections often have asymmetrical geometries. The principal axes of such sections are then not parallel to the horizontally and vertically aligned axes Y and Z. When determining the cross-section properties, the angle α between the center-of-gravity axis y and the principal axis u is determined in addition to the principal axis-related moments of inertia.
You can color the surfaces in the direction of the local z‑axis using the indicated option in the Display Navigator. By default, the side lying in the negative z-direction is colored red and the side lying in the positive z-direction is colored blue.
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.
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.
In the "Material Model - Isotropic Nonlinear Elastic" window, you can select the yield laws according to the von Mises, Tresca, Drucker-Prager, and Mohr-Coulomb yield rules. This makes it possible to describe the elasto-plastic material behavior. The yield function depends on the principal stresses or the invariants of a stress tensor. The criteria apply to 2D and 3D material models.
Designing rigid end plate connections is difficult for four-row connection geometries and multi-axis bending stresses, because there are no official design methods.
In the existing standard, there were no regulations for the distribution of snow loads for elevated solar thermal and photovoltaic systems on roofs. Only distribution of the loads was advised. It was only with the National Annex DIN EN 1991-1-3/NA: 2019-04 that specific regulations were made for this.
Slender bending beams that have a large h/w ratio and are loaded parallel to the minor axis tend to have stability issues. This is due to the deflection of the compression chord.
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.
In this technical article, a hinged column with a centrally acting axial force and a linear load that acts on the major axis are designed according to EN 1993-1-1 with the aid of the RF-/STEEL EC3 add-on module. The column head and column base are assumed as a lateral and torsional restraint. The column is not held against rotation between the supports. The cross-section of the column is an HEB 360 from S235.
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.
One of my earlier articles described the Isotropic Nonlinear Elastic material model. However, many materials do not have purely symmetrical nonlinear material behavior. In this regard, the yield laws according to von Mises, Drucker-Prager and Mohr-Coulomb mentioned in this previous article are also limited to the yield surface in the principal stress space.
Buildings must be designed and dimensioned in the way that both vertical and horizontal loads are conducted safely and without large deformations in the building. Examples of horizontal loads are wind, unintentional inclination, earthquake, and a blast.
You can now use axial expansion joints in RF‑PIPING. These are applied to absorb movements of extension and compression in the axis direction due to the thermal expansions of the piping.
Click the [Details] button in RF-GLASS to select the results to be displayed. In order to get a better overview for the result evaluation, you can select the individual stress graphics (principal stresses, stresses oriented to axes, shear stresses) as well as various result windows. This way, you can show only the results you require.
Nodal supports are usually defined with regard to the global axis system. However, it is sometimes necessary to rotate the nodal support. For example, for a floor slab with a pile foundation. For geological reasons, the piles do not rest in the ground vertically, but in an inclined position. Each end point of the piles has a nodal support that can only absorb forces along the pile foundation direction. Therefore, rotating the nodal support is required. Various options for this are described in previous posts.
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.
In RF-STEEL Surfaces, it is possible to display the stresses relevant for the design of welds, for example, according to EN 1993‑1‑8, Figure 4.5. When evaluating the stress components, the local xyz-axis system of the surfaces must be considered.
In order to facilitate the selection of the corresponding line release, the axis system of the line release appears when selecting a line release. In the case of a line hinge, the orientation is often different; therefore, the representation has been improved in the pre‑selection for line hinges.
When modeling arc-shaped members, the problem shown in the figure may occur. It seems as if the member cross‑section is twisted or the load applied on the local z‑axis changes direction. How does this come about?
If you consider rotating the structure shown in the figure around the global Y‑axis, this might be not straightforward. In order to achieve better handling, the axis is always locked in the direction of your view. In the case of very high structures, it may be helpful to rotate the view about 90 degrees in the viewing direction.
A new direction for temperature load is available in RFEM. Now, it is also possible to apply temperature loads with radial load distribution on a structure. The load is defined using an outer and an inner node, and an axis around which the radial load is applied.
When calculating the surface reinforcement in RF-CONCRETE Surfaces, the result values for both surface sides +/- z are available. If you are unsure which side of a surface is the positive or the negative z side, you can hide the local coordinate system of each surface in the RFEM Project Navigator - Display under "Model" → "Surfaces" → "Surface Axis Systems x,y,z". In the case of complex structures, this can quickly become confusing. Displaying multiple axis systems makes it difficult to recognize the incorrect direction of a surface, for example (see the figure on the top).
It is often necessary to adjust the FE mesh of surface elements to the geometric structure. RFEM provides various options for this. For example, the FE axis can be rotated around a point, aligned in the direction of a point, or oriented to a user-defined coordinate system. Another option is the direction parallel to a line, and in this case in particular, it is possible to enter or select several lines.
In RFEM and RSTAB, you can now rotate nodal loads or apply them on member axes. Thus, inclined members can also be loaded with nodal loads perpendicularly or along the member axis.