Development of Flexural Vibration Inspection Techniques to Rapidly Assess the Structural Health of Rural Bridge Systems: Phase II


Brian Brashaw, Robert Vatalaro, Xiping Wang, Matthew Verreaux, Kevin Sarvela

December 2009

Report no. MnDOT 2009-40

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 of maintenance.

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