Fine Temperature Effect Analysis–Based Time-Varying Dynamic Properties Evaluation of Long-Span Suspension Bridges in Natural Environments

Abstract

Structural modal parameters are greatly sensitive to ambient temperatures. Therefore, false identification of damages may arise in vibration-based health monitoring. In this paper, the dynamic properties of long-span suspension bridges are described according to fine temperature effect analysis and thermoeigenvalue theory. Heat transfer between a structure and the surroundings is related to solar radiation, wind speed, atmospheric environment, and thermal properties of the water surface. Temperature variations in cables and nonuniform surface transfer coefficients for the pylon were obtained through multiscale modeling and the computational fluid dynamics (CFD) method, respectively. Then, natural frequencies of the fine model were compared with those from the three-dimensional (3D) beam–shell element model and measurement data from other bridges. Finally, on the basis of the fine temperature distribution, the effect of temperature variations, temperature gradient, material properties, and pavement on the structural dynamic properties were quantified and compared for different seasons. Consistent with other research on various types of bridges, an overall decrease in modal frequency was observed with increasing temperature; however, for long-span suspension bridges, the time-varying dynamic properties were mainly caused by a thermal stress stiffening effect. Furthermore, removal of asphalt pavement caused higher average temperatures of the girder, which resulted in lower natural frequencies. The novelty of this work relates to the accurate description of the temperature field and the refined mechanical representation of time-varying thermodynamic properties for cable-suspended structures.