In Plaxis 2D2010.01, there is a bug with the use of rotational springs. The bending moments in the rotational springs are reset at the beginning of each phase. Despite that the bending moment is correct after the calculated phase, the resulting stiffness is too low. The calculation results in higher deformations than expected, and a possible wrong stress distribution in the model due to the incorrect stiffness.
At this moment there is no standard work around available. Users who want to use rotational springs are requested to contact our support department.
This has been fixed since PLAXIS 2D 2011.00