Windbreak structures are special types of fabric structures which protect the environment from harmful chemical particles, abate wind erosion, and help to maintain valuable sources. RFEM and RWIND are used for wind-structure analysis as one-way fluid-structure interaction (FSI).
This article demonstrates how to structural design windbreak structures using RFEM and RWIND.
The RF-STABILITY add-on module determines any critical load factors, effective lengths, and eigenvectors of RFEM models. Stability analyses can be carried out by various eigenvalue methods, the advantages of which depend on the structural system as well as computer configurations.
When analyzing structural elements susceptible to buckling by using the modules RF‑STABILITY (for RFEM) or RSBUCK (for RSTAB), it might be necessary to activate the internal division of members.
The function, which is also known as shifting, allows you to calculate critical load factors beyond a user‑defined initial value. Determination of the critical load factors is usually done from the smallest to the greatest critical load factor.
A calculation break‑off due to an unstable system can have different reasons. On one hand, it can indicate a "real" instability due to overloading of the system; on the other hand, the error message can result from inaccuracies in the model.
If a member is supported laterally to prevent buckling due to a compressive axial force, it must be ensured that the lateral support is actually able to prevent buckling. Therefore, the aim of this article is to determine the ideal spring stiffness of a lateral support using the Winter model.
The previous article, titled Lateral-Torsional Buckling in Timber Construction | Examples 1, explains the practical application for determining the critical bending moment Mcrit or the critical bending stress σcrit for a bending beam's lateral buckling using simple examples. In this article, the critical bending moment is determined by considering an elastic foundation resulting from a stiffening bracing.
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.
The article titled Lateral-Torsional Buckling in Timber Construction | Theory explains the theoretical background for the analytical determination of the critical bending moment Mcrit or the critical bending stress σcrit for the lateral buckling of a bending beam. This article uses examples to verify the analytical solution with the result from the eigenvalue analysis.
With the RF-STABILITY and RSBUCK add-on modules for RFEM and RSTAB, it is possible to perform eigenvalue analyses for member structures in order to determine the effective length factors. The effective length coefficients can then be used for the stability design.
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.
Shell buckling is considered to be the most recent and least explored stability issue of structural engineering. This is due less to a lack of research activities than to the complexity of the theory. With the introduction and further development of the finite element method in structural engineering practice, some engineers no longer have to deal with the complicated theory of shell buckling. Evidence of the problems and errors to which this gives rise is very well summarized in [1].
Buckling analysis according to the effective width method or the reduced stress method is based on the determination of the system critical load, hereinafter called LBA (linear buckling analysis). This article explains the analytical calculation of the critical load factor as well as utilization of the finite element method (FEM).
Critical load factors and the corresponding mode shapes of any structure can be determined efficiently in RFEM and RSTAB, using the RF-STABILITY or RSBUCK add-on module (linear eigenvalue solver or nonlinear analysis).
As an alternative to the equivalent member method, this article describes the possibility to determine the internal forces of a wall at risk of buckling according to the second-order analysis, taking imperfections into account, and to subsequently perform the cross-section design for bending and compression.
The following article describes a design using the equivalent member method according to [1] Section 6.3.2, performed on an example of a cross-laminated timber wall susceptible to buckling described in Part 1 of this article series. The buckling analysis will be performed as a compressive stress analysis with reduced compressive strength. For this, the instability factor kc is determined, which depends primarily on the component slenderness and the support type.
Basically, you can design the structural components made of cross-laminated timber in the RF-LAMINATE add-on module. Since the design is a pure elastic stress analysis, it is necessary to additionally consider the stability issues (flexural buckling and lateral-torsional buckling).
The RF‑STABILITY and RSBUCK add‑on modules for RFEM and RSTAB allow you to perform eigenvalue analysis for frame structures in order to determine critical load factors, including the buckling modes. Several buckling modes can be determined. They provide information about the model areas bearing stability risks.
This post verifies the determined mode shapes or critical load factors of the previous beam structures using an FE model in RFEM (surface elements) and RF‑STABILITY.
The previous post on this topic describes instabilities that may occur when using tension members. The example shown refers primarily to wall stiffening. Now, instability error messages can also refer to nodes within the range of supports. Truss girders and support trusses are especially susceptible to this. What causes the instability here?