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Monitoring vibrations on the Jefferson City Truss Bridge.
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2016-05-25
[PDF-2.78 MB]
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Edition:Final report, August 2015-February 2016
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Abstract:The objective of the research was to determine the frequency and cause of resonant vibrations of truss verticals on bridge A4497
over the Missouri River in Jefferson City, MO. Instrumentation to monitor the vibrations of four verticals was installed on the
bridge and monitored for 42 days. The instrumentation consisted of wireless accelerometers that monitored the accelerations on
the four verticals. Weather data available from a weather station located at the Jefferson City Airport was used to analyze the
weather conditions causing resonant vibrations of the verticals. It was found that there were eleven vibration “events” in which the
vertical members vibrated with higher than normal accelerations. The average wind speeds during the events was about 17 mph.
The wind direction during the events was from the WNW/NW during nine of the “events” and from the SE for 2 of the “events.”
It was found that the frequency of the events was 0.26 events per day during the monitoring period.
Historical weather data was analyzed to determine how frequently the resonance vibrations may be occurring, i.e., how frequently
the combined wind speed and direction matched the conditions determined through the field monitoring. Historical weather data
from 442 days was analyzed and it was found that there were 89 occurrences of the combined wind speed and direction that could
cause vibrations of the vertical members. The resulting frequency of events was determined to be 0.20 events per day.
It was concluded that the frequency of resonant vibration events is likely 0.25 events per day or less. The vibrations are caused by
average winds from the WNW/NW or SW of ~17 mph or greater, based on monitoring results. Recommendations stemming from
the research were as follows: 1) The effect of the vibration events on the durability of the members should be analyzed further to
determine if a retrofit is necessary. The data provided through the field monitoring should be used in the analysis; and 2) Other
vertical members of a similar length should be monitored to determine if they are affected by resonant vibrations.
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