Effects of seasonally frozen soil on the seismic behavior of bridges

Many of the broad cold regions are located in seismic active zones. Little research has been conducted to investigate the seasonally frozen soil effects on the seismic performance of bridge structures. An analytical investigation of the seasonally frozen soil effects on the seismic behavior of a soil–pile–bridge pier system is presented. Elastic–plastic Finite Element (FE) analyses of a soil–pile model were conducted to obtain the cyclic behavior of the soil–pile system under the unfrozen and frozen soil condition. The equivalent foundation spring coefficients widely used for design practices were developed for the frozen soil condition. A simplified FE model of the soil–pile–bridge pier system was built by representing the soil–pile system with the derived equivalent foundation springs. Modal and push-over analyses were conducted to investigate the effects of seasonally frozen soil on the seismic behavior of the bridge bents. It is found that seasonally frozen soil causes significant change in the stiffness and damping ratio of the soil–pile system, and may have greatly impact the dynamic response of the bridge piers; the influence increases with decreasing pier height-span ratio or increasing overall pier stiffness. It is also found that seasonally frozen soil may impact bridge seismic behavior; the lateral displacement capacity of the pier decreases and the shear demand increases in the frozen soil condition.