Evaluating damage extent of fractured beams in steel moment-resisting frames using dynamic strain responses

Delays in the postearthquake safety estimations of important buildings significantly increase unnecessary disorder in economic and social recovery following devastating earthquakes. Providing promptness and objectivity in evaluation procedures, damage detection through a structural health monitoring system using sensors attracts attention from building owners and other stakeholders. Nonetheless, local damage on individual structural elements is not easily identifiable, as such damage weakly relates to the global vibrational characteristics of buildings. The primary objectives of this research are to present and verify a method that quantifies the amount of local damage (i.e.,fractures near beam-column connections) for the health monitoring of steel moment-resisting frames that have undergone a strong earthquake ground motion. In this paper, a novel damage index based on the monitoring of dynamic strain responses of steel beams under ambient vibration before and after earthquakes is firstly presented. Then, the relation between the amount of local damage and the presented damage index is derived numerically with a parametric study using a nine-story steel moment-resisting frame model. Finally, the effectiveness of the damage index and an associated wireless strain-sensing system are examined with a series of vibration tests using a five-story steel frame test bed. Copyright (c) 2014 John Wiley & Sons, Ltd.