This paper presents the shaking table test results of a scaled steel gable frame subjected to earthquake ground motions of different intensities. The strain mode shape (SMS) calculated from dynamic strain gage data is used as the primary indicator to identify damaged locations of the structure due to inelastic deformation. Observations show the change of SMS to be the greatest around the damaged area. Also observed is the “recovering SMS” during an inelastic time history response. Methodology used in this analysis may help engineers foster the idea of structural diagnosis through vibration monitoring.