Effects of environmental and operational actions on the modal frequency variations of a sea-crossing bridge: A periodicity perspective

Abstract

Abstract The modal frequency variations of bridges associated with environmental and operational actions are among the primary research topics in structural health monitoring (SHM). Based on the periodic variations of the monitoring data obtained over 6 years for the Donghai Bridge (DHB), we investigated the effects of environmental and operational factors on the modal frequency variations and identified the main periods and influencing factors of the DHB frequency changes. Partial correlation coefficients and cyclic averaging were applied to compare the contributions of various actions to the frequency changes, and the underlying mechanisms of the frequency changes were preliminarily studied. The modal frequencies of the DHB were found to vary with periods such as 1 year, 1 week, 1 day, and 12.42 h in a manner corresponding to inherent variation cycles of structural temperature, traffic loading, wind loading, and sea level. Structural temperature and traffic loading were the primary factors influencing the DHB frequency changes, and their relative degrees of impact on the frequency changes were different for different cycles. All modal frequencies of the DHB decreased with increasing temperature due to variation in the temperature-dependent elastic moduli of the structural materials. However, as traffic loading increased, the fundamental frequencies of the vertical bending, lateral bending, and torsional modes of the girder decreased, while some higher-order frequencies increased. The influence of traffic on the modal frequencies could be qualitatively explained by employing an equivalent spring–mass model of the traffic flow on the bridge. The results of this study will deepen the understanding of the frequency changes occurring in bridges during operation and can serve as a reference for vibration-based SHM.