Ice Forces on Inclined Bridge Piers

The American Association of State and Highway Transportation Officials (AASHTO) and the Canadian Standards Association (CSA) codes provide design guidelines for determination of ice loads due to ice crushing and ice bending failures. Both organizations' bridge codes are based upon in-situ field measurements on two bridges in Alberta, Canada. Design formulas provided by both organizations (AASTHO and CSA) rely only on the effective crushing strength of ice to determine ice loading due to crushing failures and ice bending failures. Equations provided for bending failures rely on an assumed linear relationship between effective ice crushing strength and ice bending strength. Ice bending strength is apparently assumed to be 0.84 times the effective crushing strength using these codes. Recent in-situ testing of fresh water river ice on the North Slope of Alaska indicates that the ice bending strength is closer to 0.5 times the effective ice crushing strength for this location. Additionally, numerous studies have identified that ice crushing strength is highly dependent upon temperature, while ice bending strength remains relatively constant through changing temperatures. Results of the in-situ bending tests and other associated research indicate that calculations to determine ice forces due to bending failure should consider ice flexural or tensile strength rather than a direct correlation to effective ice crushing strengthen. This paper will present the testing methods and procedures, results and conclusions of flexural and compressive ice testing performed on river ice on the North Slope of Alaska. Comparisons between AASHTO and CSA predicted and actual bending strength will be made. An alternative calculation method determining the ice sheet bending strength will be presented. The authors recommend that the presented, alternative methods be adopted within the CSA and AASHTO codes to better predict ice loads associated with ice bending behavior.