Shear and Moment Diagrams

• Internal force diagram: An internal force diagram (e.g. shear or moment diagram) is a graph showing the magnitude and sense of an internal force as distributed along the member axis.

• Calculating change in shear between points: The change in the shear between two points on a member is equal to the sum of the transverse loads between the two points (transverse means applied perpendicular to the member axis, as with vertical loads and a horizontal beam axis).

• Calculating change in moment between two points: The change in the moment between two points on a member is equal to the area under the shear diagram between those points.

• Moment diagram slope: The slope of the moment at a point is equal to the value of the shear at that point.

• Why it's true: These relationships all arise from considering the equilibrium of a small portion of a member.

• Internal force diagrams and structural form: Shear and moment diagrams are important for understanding and design decision making regarding form and configuration.