Eccentricities

To assign an eccentricity to one or more elements, select the relevant bar(s) and click on . The following dialogue appears:

This dialog can contain padlocks depending on the properties of the elements you have selected. Read all about the padlocks in this article.

• Tab page « Eccentricity »
  • You can define a different eccentricity for the two local axes (y’ and z’) of the bar. These are the available options:
    • Either you align the beams (columns) with one of the edges of the plate (wall).
      This will be done automatically, if you draw the beams with the use the button . But there is one condition: the beams need to be drawn inside or along the circumference of the plate. If you, then, modify the thickness of the plate, the eccentricity of the beams will be modified automatically.
    • Either you set a custom eccentricity. The eccentricity here is the distance between the neutral fibers of the beam or the plate.
  • Remove all eccentricities with .
  • It is possible to define a different eccentricity at the starting point and at the ending point of the bar (might be useful for beams of various heights). Read more on how to link eccentricities to a physical group in this article.
• Tab pages « Connection to plate/system axis » and « Connection to beam »
  Here you define how the connection between the beam and the plate should be behave. Thus which boundary conditions should be assigned to the ends of the rigid links.

• Tab page « Physical« 
  Diamonds offers the possibility to define physical eccentricities (this is only important for the BIM-link with modelling software such as Tekla Structures).

Sense and nonsense about eccentricities

Eccentricities are added to the analysis model (= Diamonds model) so that the model describes the actual behaviour of the structure as accurately as possible. The purpose of eccentricities is NOT to give the calculation model the same appearance as the architectural model.

The table below tries to explain when eccentricities are necessary and when not.

	Eccentricities shouldn’t be used to make the solid representation look like the structure in real life. Remove the eccentricities.
	The grey secundairy beams are continuous. They run on top of the frames, from one side of the building to the other side. If no eccentricities would be used on the grey beams, the different segments wouldn’t work as continuous. So eccentricities are required in this model.
	Eccentricities shouldn’t be used to model a grid of principal and secundairy beams. Although using eccentricities will lead to correct results in this case, this is a complex modelling. You’ll obtain the same results without eccentricities.
	Eccentricities are used to model the correct beam-plate interaction. This beam is cast in the plate. They work together as a T-section. If no eccentricities were used, the stiffness would be underestimated and the internal forces in these elements would not be representative for the reality.
	Two plates on a different level (Y-coordinate) are connected to each other by a beam. The difference in Y-coordinates is significant, so you can’t ignore it. This is something that requires eccentricities. However, the dialogue doesn’t contain options to set a plate eccentric in relation to anther plate. It is designed to give bars an eccentricity in relation to a plate. This is modelled using rigid links . More info in the article about the beam-plate interaction.