When RISA-3D solves a model, it looks for degrees of freedom that have zero or “very little” stiffness. Since all degrees of freedom must have some stiffness, RISA-3D will lock these degrees of freedom so that it can finish the model solution. When the model solution is finished, a window will “pop up” and report all the locks that RISA-3D had to apply to solve the model. Sometimes these locks are trivial (such as the case where a member can spin about it’s own axis, caused by AllPin’s at both ends), and sometimes these are quite serious. The locked degrees of freedom should always be studied to determine if the original model was unstable. It’s a good habit to always resolve any locked degrees of freedom by modifying your Member End-Releases or Nodal Boundary Conditions.