Hi Jason,
I observer the following output parameters in the FAST manual (Table 42). The tower side-to-side shear force is not in the same direction as the side-to-side bending moment (along yt axis)?
TwrBsFyt, Tower base side-to-side shear force, Directed along the yt-axis, (kN)
TwrBsMxt, Tower base roll (or side-to-side) moment (i.e., the moment caused by side-to-side forces), About the xt-axis, (kN·m)
Regards,
Xiao