ABSTRACT
Vibration-based structural health monitoring (SHM) utilizes variation of modal parameters as indicators to assess structural conditions. However, it was widely recognized by many researches that bridges’ modal parameters can suffer a considerable variation with the normal change of such environmental or operational factors as temperature, wind and traffic loadings, which would lead to an unsuccessful structural evaluation. So it is quite necessary to investigate the correlations between these environmental or operational factors and structural modal parameters to “normalize” the environmental/operational condition. Based on the 5-year long-term monitoring data recorded by the Structural Health Monitoring Systems (SHMS) of Donghai Bridge (DHB) and Shanghai Yangtze River Bridge (SYRB), both of which are long-span cable-stayed bridges (CSB) with center spans longer than 400m in Shanghai, China, this paper studied the modal frequencies’ variation during the bridges’ operational stage, as affected by temperature and traffics. The spectral analysis showed that the variation of modal frequencies possessed some long-period components such as 1 year, 1 week, 1 day, 12 hours and so on. Focused on the first vertical bending mode and the first lateral bending mode of DHB, this paper inferred the reasons for periodic characteristics of modal frequencies’ variation, and compared the relative importance of temperature and traffics on each dominating cycle by the regression analysis. In addition, traffic loading monitoring method was also investigated. The incorporation of video monitoring technology into SHMS was recommended to bridge the gap between traffic load monitoring and structural response monitoring. Taking full advantage of the complementary capabilities found in video camera, inductive loop and Weigh-In-Motion (WIM) system, a comprehensive solution for traffic monitoring can provide sufficient and accurate information. The study herein can advance the understanding on the bridge’s behavior and benefit the monitoring and maintenance of long-span bridges.
