Stability

Définitiona) Partial constraints

A structure or one of its members may have fewer reactive forces than equations of equilibrium thar must be satisfied.

Exemple

Définitionb) Improper constraints

Improper constraining by the supports causing instability although there may be as many unknown forces as there are equations of equilibrium.

This can occur if:

  • All the supports reactions are concurrent at a point.

  • The reactive forces are all parallel

Remarque

If the structure in unstable, it does not matter if it is statically determinate or indeterminate. In all cases such types of structutres must be avoided in practice.