A substantial body of structural health monitoring (SHM) research has been carried out in the context of structural dynamics. In this context, it is natural to make use of features for damage identification, which arise in the normal course of structural dynamic testing. The accepted standard for a dynamic test is a
modal analysis
, which derives a description of the dynamics in terms of natural frequencies, damping ratios, and modeshapes. This article discusses how such features can be used to extract a damage diagnosis. From a modal test, it is possible to extract the physical matrices that enter the structural equations of motion: mass, damping, and stiffness matrices. This article also describes damage identification strategies based on these matrices.