Current timber bridge inspection procedures used in Minnesota and across the United States are mostly limited to
visual inspection of the wood components. Use of advanced techniques like stress wave timing, moisture meters,
resistance drills will significantly improve the reliability of the inspections but these inspection techniques are time
consuming. The objective of this project was to conduct vibration testing of dowel laminated timber bridge
systems to better understand the potential for using vibration testing to assess the structural health and condition of
bridges in Minnesota. A second key objective was to improve and automate the vibration testing system that is
currently being used. This research showed that the forced vibration system developed is an effective tool for
conducting forced vibration tests of timber bridges and that there is a noted increase in frequency during each
successive stage of construction. A reliable means for assessing the peak frequencies and an identification of the
mode still needs to be developed for this system to use the vibration response to predict the EI product for use in
load ratings. Each bridge has a unique set of vibration characteristics that were identified using the automated
system. These characteristics showed peaks in amplitude as the frequency of the vibration was increased from 0 -
35 Hz during testing. It is believed that monitoring of the characteristic vibration response for each bridge would
be a means of identifying changes in structural health over time due to wood decay, accidents, vandalism, or lack
Brashaw, Brian K.; Vatalaro, Robert J.; Wang, Xiping; Verreaux, Matthew; Sarvela, Kevin.
Development of Flexural Vibration Inspection Techniques to Rapidly Assess the Structural Health of Rural Bridge Systems: Phase II.
Minnesota Department of Transportation.
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