Determining shear and moment diagrams is an essential skill for any engineer. Unfortunately, it’s probably the one structural analysis skill most students struggle with most.

This is a problem. Without understanding the shear forces and bending moments developed in a structure you can’t complete a design. Shear force and bending moment diagrams tell us about the underlying state of stress in the structure. So naturally, they’re the starting point in any design process.

Another reason every graduating engineer needs to have a solid grasp of shear forces and bending moments is that they’re absolutely going to be tested in almost every graduate interview. The quickest way to tell a great CV writer from a great graduate engineer is to ask them to sketch a qualitative bending moment diagram for a given structure and load combination!

Shear and bending moment diagrams are analytical tools used in conjunction with structural analysis to help perform structural design by determining the value of shear force and bending moment at a given point of a structural element such as a beam. These diagrams can be used to easily determine the type, size, and material of a member in a structure so that a given set of loads can be supported without structural failure. Another application of shear and moment diagrams is that the deflection of a beam can be easily determined using either the moment area method or the conjugate beam method.

Shear Force – A positive internal shear force causes a clockwise rotation of the beam segment. (i.e., it pushes a left-facing cross-section upward or a right-facing cross-section downward).
Bending Moment – A positive internal moment causes compression in
the top fibers of the segment (i.e., clockwise on a
left-facing cross-section or counter-clockwise on a
right-facing cross-section).

what is a Bending Moment? A moment is a rotational force that occurs when a force is applied perpendicularly to a point at a given distance away from that point. It is calculated as the perpendicular force multiplied by the distance from the point. A Bending Moment is simply the bend that occurs in a beam due to a moment.