I wrote a UEL (User Element in Abaqus) for one element and compared to a reference UEL which used standard FEM, where the results agreed satisfactorily, except the reaction force. The stress, strain, strain energy all were pretty accurate.
I am unable to understand this, how the reaction force is calculated?
I am simply restraining the element in the bottom (two nodes) and applying displacement (incrementally) at the top (two nodes).
As far as I know, the stiffness matrix is used to calculate reaction forces in these cases, the stiffness values are quite similar in my UEL and the FEM UEL. Also if this was the case, the other parameters wouldn't have had the same values.
Would be grateful if anybody could help me figure this out.