What is the difference between a beam and a column?

Beam and Column

In structural engineering we give names to different structural members based on their behavior under applied load.

For example:

Say you have a rod of length 3 m made out of steel and a load P to support.

1. You decide to hang the rod from ceiling and hook the load to the other end of the rod. The load in this case is being transferred primarily by tension and thus we call it a Tie.
2. In the second case the rod is kept vertically on the floor and the load is placed on top of it. Now the load is being transferred by compression and thus we call it a Column.
3. In the third case we keep the rod on two supports and then place load on top of it. This time the primary mode of load transfer is by bending and thus we call it a Beam.
4. In the fourth case we keep the rod vertical and apply load horizontally to it. This time the primary mode of load transfer is also by bending and thus we call it a Beam.

It is important to notice here that in all the above four cases nothing physically got changed with the rod in term of its material properties,cross-section or length. The only thing that changed was the way in which the load was being transferred by it.

Conclusion

What we call a structural member depends less on what it is made of and more on how it carries load.

In all the cases discussed, the rod remains exactly the same.
Same material.
Same length.
Same cross-section.

Yet, it behaves as a tie, a column, or a beam.

The change happens only because the mode of load transfer changes—tension, compression, or bending.

This highlights a fundamental idea in structural engineering:
structural behavior defines the member, not geometry alone.

Once this idea is clear, many design concepts become intuitive.
Why columns buckle.
Why beams crack in tension.
Why ties need ductility.

Understanding members through their load path and stress behavior is the first step toward first-principle structural design—the core of how engineers think in practice.