Attached are a short note on the ratio of the shear deflection Vs and the deflection Vb due to pure bending. In the back calculation procedure, it is assumed that this ratio is constant and only depends on a shear coefficient and the dimensions of the beam.

But this in principle not correct. Due to moving masses, the inertia forces couple the differential equations for Vs and Vb.

Fortunately the changes in the ratio Vs/Vb are not large.