Determinacy
Définition :
The structure is statically determinate when all forces in a structure can be determined strictly from equilibrium equations.
The structure is statically indeterminate when structures having more unknown forces than available equilibrium equations.
We have:

Where:
r: is the number of force and moment reaction components
n: is the number of parts
The additional number of equations required for the solution refers to the degree of indeterminacy.
For truss, we have:
