Dear Yahya,
The difference in the loads between the blade root and local span gages (blade analysis nodes) can be explained as follows. At the root of blade 1, FAST only permits output of loads in the “b1” and “c1” systems, so, neither are rotated by the structural twist. The only difference between the “b1” system and the “c1” system is the rotation of the pitch angle of blade 1. The “Lb1” system (local blade system) available at the blade analysis nodes is rotated additionally by the structural twist (and by the deflection of the blade). With a simple vector rotation using the structural twist angle at the root, you should be able to compare the root loads in the b1 system with the near-to-the-root loads in the Lb1 system.
I hope that helps,