For the calculation of stiffness and the diagrams for deflection and tilting angle, two points have to be defined. The software averages the deflections around the circumference for these points and the result is used to calculate a stiffness value if a series calculation is active.
If the check box "calculate stiffness" is set for a surface load all surface nodes of this face are connected to a central node by averaging and a stiffness matrix for this central node is calculated based on a static condensation of the model. The main diagonals of the compliance matrix (inverse of the stiffness matrix) are then use to set the stiffness values cxx, cyy, czz, crx, crz.
