Reading shear and moment diagrams
A beam is a structural member that resists bending. When a load acts on the beam, it creates internal forces: shear (cutting/sliding force perpendicular to the beam axis) and moment (bending force). Shear and moment diagrams show how these forces vary along the length of the beam.
A cantilever beam is fixed at one end and free at the other. A simply-supported beam is supported at two ends. An overhanging beam extends past its supports. Each configuration produces a different distribution of shear and moment. Understanding the diagram tells you where the beam is most likely to crack and how much material you need at each point.
Design implications from diagram analysis
The moment diagram reveals the critical stress points. The peak moment often indicates where the beam needs reinforcement. If you are designing a steel beam, you place more material (a taller cross-section) where moment is highest. If you are designing concrete with rebar, you place more rebar in the tension zone at the point of maximum moment.
Shear is less obvious but equally important. High shear near supports requires adequate shear reinforcement or a robust cross-section. A short, heavily loaded beam might fail in shear before it fails in bending. The complete diagram guides the engineer to size every part of the beam appropriately.