Flexibility method

Summary

The flexibility method, also called the force method, analyses a statically indeterminate structure by taking some redundant forces as unknowns. Removing the redundant supports or members leaves a statically determinate structure; the redundant forces are then fixed by requiring that the removed constraints are respected. These compatibility conditions form a linear system whose matrix is the flexibility matrix. It is the counterpart of the direct stiffness method, which takes displacements as unknowns.