For relative displacement, what confused me is that:
There are 5 points(cross sections) listed for each beam. Do we assume that the 3 displacements of the first and last point is 0?
(Since there is only linear displacement, so even when restriction is released, no end rotation shown here)
But if node displacements for the first and last point is different，how could their relative displacements be equal to each other？
Here is how the beam relative displacements are calculated. A straight line is drawn joining the displaced positions of the start and end nodes for the beam. The displacement at all intermediate section locations are reported relative to that straight line. So irrespective of the global displacement of the start and end nodes of the beam ( which you can get from the node displacement table), you are always going to see zero values for the start and end locations in the beam relative displacement detail table.
Thank you, Sye. Assuming that all 5 sections including start/end nodes are along the straight line, this line is one axis, for start/end nodes one coordinates is the same, but here 3 diplacements are totally the same and equal to 0?
If the beam has displaced in a manner such that the deformed positions of the intermediate section locations also lie on the same line joining the displaced positions of the start and end node, then you will get 0 for all the sections.