Sign Convention:

As the calculations are algebraic the sign conventions must be properly followed to get the correct results. Here a sagging bending moment M_u (producing tension below the axis UU and compression above it) is considered positive. Same, a bending moment M_v producing tension to the left of the axis VV and compression on the right of it is considered positive under this convention, M_u and M_v are both positive if M lies within the first quadrant. For M lying within the second quadrant, M_u will be positive and M_v will be negative and so on for the other quadrants.

As regards the signs of u and v, the usual convention (that is above axis u-u, v is positive and right of axis vv, u is positive) is followed. Finally for the resultant stress, f, the positive sign will mean a compressive stress and a negative sign will mean a tensile stress.