Compression or tension-only line elements

Compression/tension-only members in practice #

Generally, the application of tension-only elements can be useful in case of tension-only bracing systems, if the applied bracing members comprise of such elements which can only resist tensile forces (e.g. angle profiles, cables or rods etc.)

Compression-only elements can be useful in case of such elements, which can only resist compression forces, such as brick etc.

Properties #

Nonlinear behaviour for a line element is available only for truss elements. 

As compression only or tension-only behaviour is a nonlinear property therefore it will be taken into account during nonlinear or dynamic analysis. 

In the case of linear static, vibration or buckling analysis the truss elements will be taken into account with their initial elastic stiffness, any nonlinear property will be ignored.

Modeling #

There are two options to set nonlinear behaviour in case of a line element:

  • Set nonlinear behaviour in the member definition dialogue box

As already mentioned, nonlinear parameters are available only in case of truss elements. For this reason, user has to set the line element as a truss. This can be done by choosing the following icon from the icon ribbon, located on the upper side of the display.

After that, the type of element can be set to truss and nonlinear parameters will be available. It is possible to specify if the truss has only compression or tensile stiffness. Moreover, the resistance can be also entered.

  • Define nonlinear materials for the element

In this case, nonlinear behaviour will be handled by means of the applied material.

Firstly, the nonlinear properties of the material have to be set. It can be done by choosing the below-displayed icon, from the upper icon ribbon.

It is an option to modify an existing material model, or to define a new one. In order to set the required behaviour, nonlinear properties have to be activated.  NL elastic/Strain energy-based or Plastic / Bresler-Pister material /yield criterion can be chosen for this purpose. Von Mises criterion is not appropriate for this purpose, because in this case, only symmetric stress-strain behaviour is available (σyc= σyT).

In case of tension-only behaviour, it is necessary to apply a negligibly small value for compressive yield strength (σyc) and vice versa. In case of compression-only behaviour it required to set a negligibly small value for tensile yield strength (σyT) in order to avoid numerical and stability problems.

The following table summarizes the application conditions for different material types.