What is the sign convention

The bending moment is drawn on the tensile side of the member

• If the upper side (z’ > 0 or y’ > 0) is subjected to tension, the bending moment is positive.
• If the lower side (z’ < 0 or y’ < 0) is subjected to tension, the bending moment is negative.

The sign of the shear force depends on the variation of the corresponding moment.

• Ascending curve for the bending moment → shear force is negative
• Descending curve for the bending moment → shear force is positive

The sign of the reactions depends on its direction:

• If the reaction goes in the same direction as the global coordinate system, the sign is positive.
• If the reaction goes in the opposite direction of the global coordinate system, the sign is negative.