Shear and moment diagrams are a statics tool that engineers create to determine the internal shear force and moments at all locations within an object. Start by locating the critical points and then sketching the shear diagram.
Critical point locations:
Start and stop of structure (extreme ends)
Concentrated forces
Concentrated moments
Start and stop of distributed loads
Internal hinges
Support locations
Points of zero shear (V = 0) — for moment diagrams only.
Important features to remember when drawing the diagram:
Concentrated forces cause an instant jump in shear.
Concentrated moments cause an instant jump in moment.
Order increases from load to shear to moment (that is, 1st order load diagram, 2nd order shear, 3rd order moment).
The slope of the moment diagram is equal to the value of shear.
If the load area is positive, the change in shear is positive. If the shear area is positive, the change in moment is positive.
