, Program Director, UMD-NRRI
This project supplemented and continued a FY 05/06 UMD NATSRL project, Development of Flexural Vibration Inspection Techniques to Rapidly Assess the Structural Health of Rural Bridge Systems, by expanding the bridge types studied to include dowel laminated bridges and by designing and fabricating an automated testing system. In this project, the UMD Natural Resources Research Institute and research partners worked to refine rapid in-place testing techniques for assessing the structural health of timber bridges, as it was 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. In contrast to typical bridge inspections that evaluate individual components, this system tested the entire bridge as a unit using forced vibration. These techniques were used to determine the natural frequency of the entire bridge; this frequency converted to an equivalent measure of bridge system stiffness, enabling an assessment of bridge integrity. In the course of their work, the researchers found that over 1,200 timber bridges in Minnesota employ a dowel-laminated design that had not been previously evaluated using the vibration techniques. These bridges offered new challenges to vibration techniques because they were considered more of a plate structure than a beam structure, with structural members in both the span and cross-span direction. To further understand this style of bridge, researchers completed testing of this bridge style in cooperation with a manufacturer of dowel-laminated bridges. 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.