Seasonally frozen soil effects on the dynamic behaviorof highway bridges

Frozen ground is significantly stiffer than unfrozen ground. For bridges supported on deep foundations, bridge stiffness is alsomeasurably higher in winter months. Significant changes due to seasonal freezing in bridge pier boundary conditions require additionaldetailing in order to ensure a ductile performance of the bridge during a design earthquake event. This paper reports the latestresults obtained from a project that systematically investigated the effects of seasonally frozen soil on the seismic behavior ofhighway bridges in cold regions. A bridge was chosen and was monitored to study its seismic performance and assess the impactof seasonally frozen soil on its dynamic properties. A Finite Element (FE) model was created for this bridge to analyze the impactof seasonal frost. It was found that when frost depth reaches 1.2 m, the first transverse modal frequency increases about 200%when compared with the no-frost case. The results show that seasonal frost has a significant impact on the overall dynamic behaviorof bridges supported by pile foundations in cold regions, and that these effects should be accounted for in seismic design.