Seismic performance evaluation of existing light poles on elevated highway bridges

Abstract

Damages on light poles and utility poles mounted on elevated highway or railway bridges were observed in the past several large earthquakes. They were mostly due to excessive pole deformation, bending failure caused by yielding, buckling of the pole and falling of the mast. The damages did not only affect functionalities but also impeded the traffic and further complicated post-earthquake recovery of affected area. While seismic resistance of elevated highway bridges has been evaluated and upgraded in the seismic codes, most light and utility poles were designed for wind loading and not for earthquake, so their seismic performances were rarely evaluated. In this research, seismic performance of a typical light pole mounted on elevated highway bridges is investigated. The study includes experimental modal analysis of existing light pole, finite element simulation, and case study of the light pole on existing elevated highway bridge. The results of finite element simulations show that response amplification occurs when the bridge’s natural frequency is within a close range of the light pole’s fundamental frequency. Due to inherently low structural damping, the light pole experiences large amplification at the resonance, and this leads to bending failure when the maximum stress exceeds the yield stress limit.