Experimental comparison of the dynamic performance for steel, aluminum and glass-fiber-reinforced-polymer light poles

This study is conceived as the second part of an experimental analysis and focused on the performance of tapered highway light poles under dynamic excitation. The original motivation coincides with a forensic investigation for the definition of the most plausible collapse cause for aluminum-alloy highway light poles during a wind and winter storm. The comparison of the performances is based on frequency and damping ratios corresponding to first- and second-mode vibration. Experimental testing is employed to derive the dynamic characteristics of the units; moreover, the behavior of a damping device, previously proposed for mitigation of vulnerable units, is analyzed. Previous results, derived for a limited set of cases, are extended in this study to other configurations, including different materials and geometry. Discussion on the derivation of frequency and damping in the presence of closely spaced modes, typical of these systems, is provided. In particular, the effectiveness of several methods for the identification of such quantities is carefully compared.