What does NASTRAN intend for neutral axis?

[zipzip]

Hi all!
I do not understand the definition of neutral axis assumed by NASTRAN. In fact, I studied that neutral axis lies in the plane of beam section but the figure 4-25 reported in the NASTRAN documentation (click here to see it) represents the neutral axis as a line along the entire beam. Can someone clarify my ideas?
thanks in advance

 

[stresscalcs]

Hi

I have no doubt that you have learnt about the "neutral axis" position as the property of a 2 dimensional surface (cross section).

You are looking at the Natran CBEAM element which is 3 dimensional, ie a collection of 2 dimensional surfaces strung together to make a length of the cross section, or a beam (bar). The line in the diagram represents a line through all the positions of the neutral axis from one end of the beam to the other.