Modal dynamic analysis for finite element models (FEMs) that include Lagrange multipliers may generate incorrect stress and reaction forces. Computer systems and computer-implemented methods are provided for modifying the modal analysis to correctly generate stress and reaction forces. The systems and methods perform the modal analysis by employing a FEM and modeling stress and reaction forces of the FEM using Lagrange multipliers. The systems and methods calculate a correction term that comprises corrected values of the Lagrange multipliers. The methods and systems modify (and improve) the modal analysis by using the correction term to correct the Lagrange multipliers of the FEM, which enables the modal analysis to generate correct stress and reaction forces.