Dear Michele,
I have doubts that small differences in blade-root loads can cause the large of differences in the yaw-bearing loads that you are showing. The yaw-bearing loads are also influenced by tower deflection; does your model account for that?
Please see my May 3, 2012 post in the topic found here for a basic description of how FAST calculates the blade root moments (including bending and pitching): Root moment of blades verification from mode shape function. Your appraoch sounds similar to what FAST does, although I notice a few subtle differences:
*FAST also includes the aerodynamic moment (Cm) in the calculation
*FAST uses all inertial loads (centrifugal, coriolis, gyroscopic, etc.), not just “centrifugal” loads
*In FAST, the position vectors follow the blade as it deflects
Best regards,