In-operation performance evaluation of damped light poles using fatigue life estimations

Abstract

This study demonstrates the practical application of vibration-based monitoring for the health evaluation of slender structures. The subject structures are the light poles installed on the Confederation Bridge in eastern Canada. The unique nature of this 12.9 km bridge and its location in the Northumberland Strait provides an opportunity to study light pole vibrations in harsh environmental conditions. In a previous study, a prototype impact damper using two lead balls within a pipe cylinder added to the top of the pole was developed to attenuate the large amplitude first-mode vibrations. In this current study, an extended full-scale vibration monitoring program of two bridge light poles under actual wind loading conditions is carried out over a period of several months to evaluate the in-operation performance of the custom prototype pole-top impact damper. An analysis method for calculating the cumulative fatigue damage (cFD) from vibration data and for estimating the remaining fatigue service life of in-operation bridge light poles is presented. With these methods, it is found that the pole-top impact dampers increase the remaining fatigue service life of the original Confederation bridge light poles by approximately 2.5 years. From fatigue modeling, it is also found that if the dampers had originally been installed with the light poles during construction in 1997, the cumulative fatigue damage could have been reduced by an average of 25% with a projected service life increase of 48%, which represents an additional 12 years of service above the actual estimated service life of 25 years.