Measures taken to mitigate the effects of fatigue on critical railway bridges at Canadian National

Abstract

Since conducting fatigue life studies over 25 years ago of several major railroad bridges, management at Canadian National (CN) has taken constructive steps to introduce measures to mitigate the effects of fatigue distress and ensure the safety of operations over its many aging steel bridge structures despite increasing stress from the introduction of heavier and more efficient use of rolling stock, greater volumes of tonnage, and higher operating speeds. Besides developing an in-house strain gauge testing program and specific inspection practices over the last 16 years, acoustic emission monitoring was utilized on a considerable number of bridges and continues to be an effective, reliable method of crack detection and monitoring of critical fatigue prone details. Recent investigation of developments in ultrasonic impact treatment (UIT) has prompted the use of this promising technology on fatigue susceptible welded details on CN bridge structures. UIT was first applied to one of CN's larger bridges in 2001 with the expectation that this treatment would considerably extend its fatigue life expectations. This paper reviews fatigue related issues afflicting CN steel bridge structures and measures taken over the past 20 years to address effectively these concerns and ensure the continued safe movement of trains across the network.