Modelling the response of cyclically loaded bridge columns embedded in warm and seasonally frozen soils

Several significant seismic events have occurred in winter months in areas that experience seasonal freezing. In a recent study, cyclic lateral load testing of identical full-scale column-foundation systems was conducted in summer and winter months, showing that freezing temperatures and a thin layer of frozen soil can significantly influence the soil-foundation-structure interaction (SFSI) and thus the lateral load response of bridge columns supported by deep foundations. The primary cause of this phenomenon has been demonstrated to be the drastic changes in the properties of soil due to seasonal freezing. Using material properties from the two tests, numerical models were developed to study the monotonic and cyclic responses of the test units that were influenced by structural and soil nonlinearity. Validation using a range of recorded responses indicated that the proposed models were able to satisfactorily capture the characteristics of test units at both warm and freezing conditions. Analysis results and their comparisons with experimental data showing the significant differences in the displacement, effective stiffness, maximum moment, shear demand and length of plastic region between the warm and frozen conditions are presented in the paper. Freezing temperatures enlarged the maximum shear demands and shifted the location of the plastic region, both of which could have significant ramifications for performance of the system if only the non-frozen condition is used in the design.