This study presents an approach for identifying both the location and severity of damage in a structure at detailed level based on the perturbation method for structural dynamic systems where measured modal data can be directly adopted in damage identification.Damage indicators are properly chosen to reflect both the location and severity of damage in bracing elements or at beam-column joints.Basic equations are developed and iterative computational procedure is proposed to solve for the damage indicators.Results for the ASCE benchmark problem show that the severity of structural damage can be identified at specific locations using only limited information on measured modal data.which makes it useful for rapid and on-line structural damage assessment and health monitoring.