Damage Detection of Bridge Structures Using Modal Flexibility under Temperature Variations

Changes in the measured structural responses, such as deflections and modal properties, induced by damage could be significantly smaller than those by environmental effects such as temperature and temperature gradients. To make the structural health monitoring more reliable and applicable to real structures, it is highly desirable to develop a methodology to distinguish the changes due to the structural damage from those by the environmental variations. In this study, a novel method to extract the damageinduced deflection under temperature variations is presented using the outlier analysis on the correlation of deflection components obtained using the modal flexibility matrix. The main idea is that temperature change in a bridge would produce global increase or decrease in deflections over the whole bridge. On the other hand, structural damages may cause local variations in deflections near the damage locations. Hence, the correlation analysis between the deflection measurements may show high abnormality near the damage locations. The proposed procedure may be summarized: (1) identification of the modal flexibility matrix from acceleration measurements, (2) calculation of the positive-bending-Inspection-load deflection using the modal flexibility for each damage and temperature case, (3) construction of the outlier-threshold for the correlation of the intact deflection at different locations, and (4) damage detection using the outlier analysis on the correlation of the deflection for damage cases. To verify the applicability of the proposed method, a series of laboratory tests were carried out on a bridge model with a steel box-girder. Nineteen experiments were carried out for the first 2 days under daily temperature variations to construct the correlation data for the intact deflection, and 51 experiments were performed for two damage scenarios for the next 12 days. It has been found that the damage existence and location were detected successfully for a case with relatively small damage under the temperature variations.