In statics and structural mechanics, a structure is statically indeterminate when the static equilibrium equations – force and moment equilibrium conditions – are insufficient for determining the internal forces and reactions on that structure.

How do you determine if a structure is statically determinate or indeterminate?

A statically determinate structure is one that is stable and all unknown reactive forces can be determined from the equations of equilibrium alone. A statically indeterminate structure is one that is stable but contains more unknown forces than available equations of equilibrium.

When can you say that a frame is statically indeterminate?

If a portal frame has more than three reactions it is statically indeterminate, the degree of indeterminacy or redundancy being equal to the number of redundant or extra reactions to be determined.