Dynamic response of bridge piers to ice forces

Abstract

An analysis of the dynamic response of bridge piers to measured ice loads is presented. The dynamic structural properties of piers and piles are described and the idealization of these structures for purposes of analysis is discussed. The characteristics of ice force histories recorded at a bridge pier in a large river in central Alberta are illustrated and the dynamic response of bridge piers to typical ice force events is determined. The results of this analysis are presented in the form of response spectra, which enable a rapid appraisal of the magnification, or reduction, in response that can result from dynamic effects. The analysis confirms that bridge piers, including massive ones, will fully respond to peak ice forces. Furthermore it shows that, depending on the natural frequency and damping of the pier and foundation, the dynamic response can exceed the static response to the peak ice force.

Hydraulic effects of ice breakup on bridges

“…Physical evidence, such as ice scars, can provide some indirect (but not too reliable) information on high stages that may have been attained during past breakup and ice-jam events. Montgomery et al (1980) noted that a breakup ice jam is usually a cohesionless accumulation of ice cover fragments that transfers ice loads to a bridge pier as a granular mass lightly confined by buoyancy. For a wide pier relative to accumulation thickness, the pressure imposed on the pier could be determined by multiplying the confining normal stress by the passive pressure coefficient, which depends on the internal friction angle of the ice accumulation.…”

“…Guidelines for determining ice forces and other ice effects on bridges can also be found in Gerard (1983), Neill (1981, and CSA (2000). Montgomery et al (1980) identified two categories of ice loading, namely static loads generated by the thermal expansion or contraction of an ice cover and by dynamic ice loads that develop when moving ice strikes a pier during ice breakup and movement. They stated that the geometry of the pier, the strength of the ice, and the size of the floe influence the dynamic forces applied by ice striking a pier.…”

Recent Advances in Ice Mechanics in Canada

“…This has been examined in the case of offshore structures (Reddy et al, 1979) and bridge piers These studies have been concerned with many aspects of the (Montgomery et al, 1980). interaction problems including loading rate effects, aspect ratio effects, peak and average pressures, failure modes in the ice, etc.…”

Ice-Induced Dynamic Behaviour of Structures

“…The change from one interaction mode to the other was found to be dependent on the driving velocity of the ice. Some other full scale trials on bridge piers in Alberta were conducted by Montgomery, Gerard and Lipsett (11). Tests on the Hondo bridge pier ( 6 ) exhibit frequencies between 10 and 15 Hz for crushing failure and between 0.5 and 2.0 Hz when the ice was failing in bending.…”