What are the types of beams, and what is the difference between a simple and a compound beam?

In one line

Beams are classified by their supports into simply supported, cantilever, overhanging, fixed, propped cantilever and continuous; a compound beam is two or more beams that rest on or are connected to one another.

Explained simply

A plank across a stream resting on two stones is a simply supported beam. A diving board fixed at one end and free at the other is a cantilever. A shelf bracket that sticks out past its support is overhanging.

Technically, a beam is a structural member that carries loads mainly perpendicular to its axis. Its type depends on the number and kind of supports, which decides whether reactions can be found by statics alone.

How it works

1. Simply supported: hinge at one end, roller at the other (or two simple supports).
2. Cantilever: fixed at one end, free at the other.
3. Overhanging: simply supported, with one or both ends extending beyond the supports.
4. Fixed (built-in): both ends fixed.
5. Propped cantilever: fixed at one end, propped (roller) at the other.
6. Continuous: more than two supports.
7. The first three are statically determinate (3 unknowns, 3 equations). Fixed, propped and continuous beams are indeterminate.
8. Simple beam: a single beam on its own supports. Compound beam: a combination of beams, e.g. one beam resting on another, where a reaction of one beam acts as a load on the other. Solve by drawing an FBD of each beam separately, upper beam first. (MU excludes problems with internal hinges.)

Quick example

A road bridge span resting on piers acts as a simply supported beam; a balcony slab projecting from a building is a cantilever. In a compound arrangement, a short beam CD resting on beam AB at point E passes its support reaction at E down to AB as a point load.

Common mistakes

• Calling a beam on a hinge and a roller 'fixed'.
• Solving a compound beam as one body, which hides the reaction between the beams.
• Thinking every beam can be solved by statics; indeterminate beams cannot.

How MU asks it

Asked as a 3 to 4-mark theory part: 'Explain the types of beams with sketches' or 'Differentiate between a simple and a compound beam'. Draw each beam with standard support symbols (triangle for hinge, circle for roller, hatched wall for fixed) and label it.