Non-Proportionality Indices and Error Constraint in Modal Analysis of Viscously Damped Linear Structures

Use of modal procedures in systems with non-proportional damping (such as structures added viscous systems) results response errors, shown this study to depend on dissimilar and often conflicting conditions for different variables stories; thus, it is not possible propose simple rules based structural or properties limit the error a global way. However, four existing indices (originally proposed measure non-proportionality) present positive correlation extreme errors all stories. Thus, limiting index value sufficient condition keep within given threshold. For practical application, values these are tabulated function can be used an acceptance criterion validity procedures.