United States Department of Transportation
i
Field Testing and Long-Term Monitoring of Selected High-Mast Lighting Towers: Data Management Plan
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2020-03-31
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Abstract:Four high-mast lighting towers (HMLTs) were instrumented with sensors to monitor weather and structural response to wind-induced vibrations. The four HMLTs were in different locales within the state of Wyoming, each site being selected specifically due to a history of failed HMLTs at those locations, or nearby. Several HMLTs have failed in recent years, some catastrophically, within Wyoming from fatigue crack growth at the base plate-to-tube wall welds. Hence the motivation for the study. Amateur video and some limited data from previous research both supported the possibility that large-amplitude mode I vibration events could be causing the premature fatigue failures. In some cases it was surmised that ice accumulation on an HMLT could be contributing to changes in the aerodynamic response to varying wind events. The research team remotely monitored the four HMLTs with wind-based and stress-based triggers recording data of ambient weather conditions and the aerodynamic response of the HMLTs. The monitoring was carried out continuously for over two years. The instrumentation included an ice sensor capable of detecting the presence of ice, wind speed, wind direction, temperature, and strain. This way, the research team would be able to determine what the structural response to the large-amplitude events would be and if the build-up of ice could be correlated to its occurrence. Three large-amplitude events were recorded during the two years of field monitoring. Extreme stress ranges were observed during all three events, but particularly in the longest-lasting of the three, reaching peak stresses of up to 40 ksi (ranges of up to 78 ksi) and lasting tens of minutes, effectively consuming between 40 percent and 70 percent of the fatigue life in a single occurrence. The extreme events were found to be relatively rare and unpredictable in terms of when they might transpire.
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