Before revision: Description A rectangular box can be distorted with a small load (left), but adding a diagonal member to form a triangular truss results in a more rigid structure (right) A framework box is not inherently rigid as it will distort from being square under relatively light loads; however, adding one or more diagonal element(s) that take either tension or compression triangulates the structure and makes it rigid, because the box cannot deviate from right angles without also altering the diagonals.
After revision: Description A rectangular box can be distorted with a small load (left), but adding a diagonal member to form a triangular truss results in a more rigid structure (right) A simple framework box with four discrete members is not inherently rigid as it will distort from being square under relatively light loads; however, adding one or more diagonal element(s) that take either tension or compression triangulates the structure and makes it rigid, because the box cannot deviate from right angles without also altering the diagonals.