For a timber connection as shown in Figure 01, you can take into account the torsional spring rigidity (spring stiffness for rotation) of the connections. You can determine it by means of the slip modulus of the fastener and the polar moment of inertia of the connection.
In RFEM, orthotropic plastic analyses using the Tsai‑Wu plasticity criterion have been possible for quite some time now. The hardening modulus Ep,x or Ep,y can be used to consider the hardening of the material during the iterative calculation.
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.
Strain hardening is the material ability to reach a higher stiffness by redistributing (stretching) microcrystals in the crystal lattice of the structure. A distinction is made between the material isotropic hardening as scalar quantities or tensorial kinematic hardening.
A previous article presented different variants of surface elastic foundations in addition to the traditional subgrade reaction modulus method. The following article describes another method for surface foundation. This method considers the adjacent ground areas by means of a foundation overlap. In this case, foundation parameters refer to the continuing works by Pasternak and Barwaschow.
A foundation is usually created in RFEM using the subgrade reaction modulus method. The reason for this is the relatively easy and straightforward manageability. Also, no iterative calculations are necessary and the computing time is relatively short. The subgrade reaction means that, for example, a foundation plate is loaded flat elastically.
During the form-finding process, the slip modulus of a substructure is also taken into account when searching for the equilibrium state. You can also consider large deflections of supporting trusses or pure bending deformation of the edge beams when determining the membrane shape.
In order to represent the stiffness of the entire structure correctly, you can consider shear coupling between the ceiling and the downstand beam using the line release. This way, you can define a spring constant, thus avoiding the replacement system by using coupling members. The spring constant results from the shift modulus of the fastener, which can be determined according to EN 1995-1-1 or ANSI/AWC NDS, for example.