Axial Force

An axial force is a force that acts along the longitudinal axis (centerline) of a structural member.

In an ideal truss, each member carries only axial force, meaning the force acts along the member itself. There are two possible types:

Tension — the member is being pulled apart.

Compression — the member is being pushed together.

So, in static analysis, when you calculate the force in a truss member, the result is generally:

\[ F \gt 0 \rightarrow Tension\ Force\]

\[F \lt 0 \rightarrow Compression Force\]

The direction of the member itself determines the direction of its axial force