Frozen ground is significantly stiffer than unfrozen ground. For bridges supported on deep foundations, significant changes in the pier boundary conditions are expected due to seasonal freezing of the ground in winter months. Consequently, the stiffness, seismic demand and displacement capacities of the critical bridge elements are appreciably altered in cold temperatures, making the bridges vulnerable to brittle failure under seismic loading. To ensure ductile performance of bridges when subjected to a design-level earthquake in warm and cold conditions, additional design steps and suitable detailing will be necessary. Currently, there are no design guidelines for including the effects of frozen ground in seismic analysis and design of bridges. Recent research in Iowa and Alaska has demonstrated the significance of frozen ground effects on seismic response of bridges and validate the need for including temperature effects in seismic design guidelines. A significant finding of this research is that thermal effects will be pronounced even at temperatures just below freezing with a frozen soil depth of 3 inches, suggesting the need to account of the seasonal temperature effects in much of the United States including the West Coast. Literature Search Summary: AASHTO LRFD Bridge Design Specifications, 2004, 3rd Edition, Washington D.C. Crowther, S.G., "Analysis of Laterally Loaded Piles Embedded in Layered Frozen Soil," 1990, ASCE Journal of Geotechnical Engineering; 116(7), pp 1137-54. Neukirchner, R.J., "Analysis of Laterally Loaded Piles in Permafrost," ASCE Journal of Geotechnical Engineering; 113(1), pp 15-29. Neukirchner, R.J. and Nixon, J.F., "Behavior of Laterally Loaded Piles in Permafrost," ASCE Journal of Geotechnical Engineering; 113(1), pp 1-14. Nixon, J.F., "Laterally Loaded Piles in Permafrost," 1984, Canadian Geotechnical Journal; 21:431-438. Rowley, R.K., Watson, G.H., and Ladanyi, B., "Predictions of Pile Performance in Permafrost under Lateral Load," 1975, Canadian Geotechnical Journal; (12), pp 510-523. Sritharan, S., White, D., and Suleiman, M.T., "Bridge Column Foundation-Soil Structure Interaction under Earthquake Loads in Frozen Conditions," 2004, 13th World Conference on Earthquake Engineering, Vancouver, B.C., Canada, August 1-6. Sritharan, S., Suleiman, M. T. and White, D., "Effects of seasonal freezing on Bridge Column-Foundation-Soil Interaction and their Implications," submitted in 2005 to Earthquake Spectra. Suleiman, M.T., Sritharan, S., and White, D., "Cyclic Lateral Load Response of Bridge Column-Foundation-Soil Systems in Freezing Conditions," submitted in 2005 to the ASCE Journal of Structural Engineering. Z. Yang, et. al. "Strong-Motion Instrumentation and Structural Health Monitoring of the Port Access Bridge, Anchorage, Alaska". Proceedings of 2005 Joint ASME/ASCE/SES Conference on Mechanics and Materials (McMat), Baton Rouge, LA, June 1-3 2005.

1. Quantify the effects of different frozen soil conditions on the behavior of bridges supported on deep foundations. 2. Provide design guidelines for including the effects of frozen soil conditions in bridge seismic analysis including modeling, analyzing, and detailing bridge structures. Provide these guidelines in a format compatible with current AASHTO specifications for inclusion in the bridge design code.

The current bridge seismic design philosophy relies on developing inelastic response of bridges under design-level earthquake by ensuring adequate inelastic displacement capacity for critical substructure elements. These details may include the formation of plastic hinges in cast-in-drilled-hole (drilled shafts) columns and pile extensions above and below the ground surface. The distance between these hinge locations is often used to determine the maximum shear associated with the formation of the plastic hinges as well as the ultimate displacement capacity of the system. In frozen ground, the formation of the plastic hinge will be closer to the ground surface than it would be in the unfrozen ground condition. Consequently, the shear demand will likely increase in both the column and drilled shaft and the ultimate displacement capacity will likely decrease in the frozen ground condition. Although the effects of frozen ground on seismic response of bridges are not addressed in the current design codes, the Alaska DOT&PF is using an approximate method to include frozen ground effects in bridge models. However, the accuracy of this approximate method has never been examined so the method remains unverified. Research at Iowa State University has identified the significance of frozen ground effects on seismic bridge performance. Unrelated research performed by the University of Alaska at Anchorage has produced measurable results of the frozen ground effects on a large highway bridge in Anchorage, Alaska. The results of these unrelated research projects demonstrate the need for including the effects of frozen ground in the seismic design of highway bridges in various seismic regions of the country. This project is expected to develop a method for modeling the effects of frozen soil on seismic behavior of bridges and provide adequate validation. The method is expected to include two different models at the minimum: a simplified model with appropriate boundary conditions and a detailed model involving nonlinear P-Y springs as used in laterally loaded pile analysis. Furthermore, the project should provide structural detailing recommendations that recognize the variable location of the plastic hinge zone, and other design guidelines that can be readily incorporated in the AASHTO LRFD Bridge Design Specifications.