Browsing by Subject "Timber bridges"

Now showing 1 - 4 of 4
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    Development of Flexural Vibration Inspection Techniques to Rapidly Assess the Structural Health of Rural Bridge Systems
    (University of Minnesota Center for Transportation Studies, 2008-09) Brashaw, Brian K.; Vatalaro, Robert; Wang, Xiping; Sarvela, Kevin; Wacker, James P.
    Approximately 4,000 vehicle bridges in the State of Minnesota contain structural timber members. Recent research at the University of Minnesota Duluth Natural Resources Research Institute (UMD NRRI) has been conducted on vibration testing of timber bridges as a means of developing rapid in-place testing techniques for assessing the structural health of bridges. The technique involves measuring the frequency characteristics of the bridge superstructure under forced flexural vibration. The peak frequency of vibration was measured and compared to a set of load testing data for each of 9 bridges. Each bridge was also inspected using commercially available advanced inspection equipment to identify any major structural problems with individual bridge components such as timber pilings, pile caps, and girders. Two bridges were identified that needed immediate maintenance attention. The relationship between the load deflection data and the vibration characteristics showed a useful relationship and the results indicate that forced-vibration methods have potential for quickly assessing timber bridge superstructure stiffness. However, improvements must be made to the measurement system to correctly identify the 1st bending mode frequency of the field bridges. This global vibration technique has potential benefits for routine inspections and long-term health monitoring of timber bridge superstructures.
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    Modeling Issues Associated with Sensor Technologies for the Nondestructive Evaluation of Timber Bridges
    (Center for Transportation Studies, University of Minnesota, 2007-08) Stech, Harlan
    This report documents progress made regarding the development and validation of a class of models examining the reliability of nondestructive vibrational inspection tests of single-spanned bridges. Two important problems were identified for special consideration. The first concerned the development of a mathematical formulation of the nonlinear boundary conditions needed to accurately model the end support structures of single-span (stringerbased) timber spans. A computational algorithm for the numerical approximations of such systems was derived, implemented and tested with the commonly available Mathematica software package. The second focal problem involved the modeling and analysis of a newly-proposed vibrational testing method. The method seeks to predict bridge strength from vibrational data, and (most importantly) without the need to estimate overall bridge mass. Models developed in this project have provided the first steps towards developing a mathematical understanding of these issues, as well as the creation of a new bridge testing protocol involving the measurement of bridge vibrational responses to forced vibrations both with and without controlled loading. This work has contributed to the development and application of new motion detection sensor technologies addressing the problem of monitoring and estimating bridge integrity.
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    Relationship Between Timber Bridge Characteristics and Asphalt Pavement Wear Surface Performance
    (Minnesota Department of Transportation, 1997-06) Larson, Timothy D.; Seavey, Robert; Lange, Douglas A.
    Asphalt wear surfaces cover 1,378 of Minnesota's timber bridges. This study assessed the magnitude of premature asphalt deterioration on timber bridges; identified the primary mechanisms responsible for wear surface deterioration; and suggested methods for improving asphalt pavement performance on timber bridges. Research methods included surveys, meetings with several county engineers and tours of their timber bridges, interviews with both asphalt and timber bridge industry professionals, and literature reviews. The study revealed that approximately 50 percent of counties experience some problems with premature reduced serviceability of the asphalt pavement wear surfaces that cover their timber bridges. Possible pavement failure mechanisms include low-temperature cracking, reflective cracking from deck fault lines found at deck panel joint lines and deck lamination separations, asphalt fatigue fracturing, and asphalt de-bonding due to oil preservatives interference. The report presents the following proposed solutions for controlling timber bridge asphalt pavement cracking: asphalt pavement saw & seal, asphalt pavement fabric or material underlay, removal of extruded oil-type preservative before surfacing, conditioning of bridge timbers to the expected equilibrium moisture content before bridge installation, and tightening of timber decks through maintenance practices.
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    Relationship Between Timber Bridge Characteristics and Asphalt Pavement Wear Surface Performance: Summary
    (Minnesota Department of Transportation, 1997-06) Lange, Douglas A.; Larson, Timothy D.; Seavey, Robert
    This summary offers an overview of on a research study that assessed the magnitude of premature asphalt deterioration on timber bridges; identified the primary mechanisms responsible for wear surface deterioration; and suggested methods for improving asphalt pavement performance on timber bridges. The study revealed that approximately 50 percent of counties experience some problems with premature reduced serviceability of the asphalt pavement wear surfaces that cover their timber bridges. The summary looks at possible pavement failure mechanisms and presents the following proposed solutions for controlling timber bridge asphalt pavement cracking: asphalt pavement saw & seal, asphalt pavement fabric or material underlay, removal of extruded oil-type preservative before surfacing, conditioning of bridge timbers to the expected equilibrium moisture content before bridge installation, and tightening of timber decks through maintenance practices.