A force that lies on the axis of member, which produces either compression or tension, is the axial force. Axial force and torsion bending diagrams are easy to derive.
However, Positive Sign Conventions is taken for Tension axial force on the section, and negative of Compression axial force.
A shearing force having an upward direction to the left hand side of the section is positive, or downward force to the right side of the section is negative. The reverse is negative.
Shear diagram is a graphic representation of the shear at every point along the length of a member.
Clockwise moment to the left is positive, or counter clockwise moment to the right of the section is positive. The reverse is negative. Also, you may think that a positive moment will cause compression of the upper layer of the beam and negative moments will cause tension in the upper layer of the beam.
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