Dear friends,
I have calculated the presented below frame in Abaqus and by means direct stiffness matrix method.In Abaqus I have used beam element B23.

For direct stifnessmatrix method I have used the following element stiffness matrix:

As I remember this element stiffness matrix is Euler-Bernoulli beam. The beam element B23 in abaqus is also Euler-Bernoulli beam.

If I calculate my frame as it presented by means of both methods the deviation of results (displacement) is maximum 0,01%.
But if I change the x-coordinate at node 10 from 90 to 93 mm, the deviation of results incresed to almost 8%. It depends on which node I want to compare. By means of changing x-coordinate I want to model a geometrical imperfection.
In direct stiffness matrix method I use the Newton-Raphson method to calculate displacements.

Maybe some one could shortly explain why in the first case the difference is so small and in the second one so big?

Many thanks in advance!

Abaqus ​​​​​​​