The following article describes design using the equivalent member method according to  Section 6.3.2, performed on the example of 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 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).
This example presents a flexural buckling analysis of a quadrilateral cross-laminated timber wall with two door openings (see Figure 1). In this case, the governing case is the wall section between the doors.
This article explains how to determine loads on the basis of the internal force situations defined in the RF-/STEEL Warping Torsion extension of the RF-/STEEL EC3 add-on module. Since this new program allows you to also analyze extracted chain-like beam structures in addition to entire chain-like beam structures, it is necessary to determine the loads of the partial structure separately. For this, a special transformation function has been developed, which determines new loads of all partial structures (depending on the internal forces calculated in RFEM/RSTAB) according to each load situation for geometrically nonlinear warping torsion analysis with seven degrees of freedom.
In addition to linear buckling analysis, RFEM also allows for nonlinear buckling analysis using the Finite Element Method. Geometrically and materially nonlinear analysis with imperfections included (GMNIA) represents the ‘real’ structural behaviour. Imperfections can be generated using the add‑on modules RF‑STABILITY and RF‑IMP. Nonlinear material behaviour can be considered by using the ‘Isotropic Plastic 2D’ material model (requires RF‑MAT NL).
For the serviceability limit state design according to Section 6.6 of Eurocode EN 1997-1, settlement has to be calculated for spread foundations. RF-/FOUNDATION Pro allows you to perform the settlement calculation for a single foundation. For this, you can select between elastic or solid foundation. By defining a soil profile, it is possible to consider several soil layers under the foundation base. The results of the settlement, foundation tilting, and vertical soil contact stress distribution are displayed graphically and in tables to provide a quick and clear overview of the calculation performed. In addition to the design of the foundation settlement in RF-/FOUNDATION Pro, the structural analysis determines the representative spring constants for the support and can be exported to the structural model of RFEM or RSTAB.
The total settlement s tot on soil caused by structural loads consists of the components of the immediate settlement s0, consolidation settlement s1, and the time-dependent creep settlement s2.
stot = s0 + s1 + s2 = s + s2
According to DIN 4019 , the method described below includes a specific setting “s” consisting of both settlement components – the settlement caused by consolidation and the settlement caused by creep (secondary settlement). Figure 1 shows the time-dependent settlement components graphically. In this case, the time t0 represents the period until complete consolidation occurs.
As mentioned in Part 1 of the article, the current standard for glass structures DIN 18008-3 requires point-supported fittings for glass components created using FEM in order to design the sufficient load-bearing capacity. The rules are described in Annex B of the standard .
Background of Design
To perform the design, it is necessary to create the relevant analytical model and verify it with regard to the standard or the general technical approval of the individual products.
Verification of Analytical Model
First, the quality of results on a drilling hole has to be checked. For this, it is important to define the FE mesh settings or to refine the FE mesh in the drilling area in such a way that the results correspond with the required values specified in DIN 18008.
The base structure is a rectangular plate with drilling:
a = 300 mm
b = 600 mm
t = 10 mm
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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.
Advantages of Representation Using Rib Member Type in RFEM
Rigidity or flexibility of a downstand beam is considered. Thus, its influence on the distribution of internal forces and the deformation can be represented.