Influence of seasonal freezing on dynamic bridge characteristics using in-situ monitoring data

摘要

This paper uses the results of experimental and finite element analyses of the Campbell Creek Bridge in Alaska to highlight the effect of seasonal freezing on bridge dynamic response and the structural and geotechnical parameters controlling the changes in response. The experimental modal characteristics of the bridge were defined using dynamic monitoring data collected over 1 year by means of several frequency and time domain system identification techniques. Good agreement was shown across the range of techniques and clear modal characteristics were defined, suggesting a significant increase in natural frequency and change in mode shape of the bridge due to seasonal freezing effects. Elastic finite element models of the bridge, utilizing a Winkler spring approach, were able to effectively capture the experimental dynamic response, with the natural frequencies and mode shapes of the bridge in the transverse direction shown to be controlled by the changes in the stiffness of the foundation soil and the bearings. The significant shift in bridge dynamic characteristics and change in boundary conditions due to seasonal freezing demonstrates the need for seismic assessment of the bridge stock across potential temperature ranges in seismically active regions that experience seasonal freezing.