Development of Flexural Vibration Inspection Techniques to Rapidly Assess the Structural Health of Timber Bridge Systems

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1 Development of Flexural Vibration Inspection Techniques to Rapidly Assess the Structural Health of Timber Bridge Systems Brian Brashaw, Robert Vatalaro, Kevin Sarvela and Matt Verreaux University of Minnesota Duluth Xiping Wang, James Wacker and Robert Ross USDA Forest Products Laboratory

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3 Timber Bridges in US!! 41,740 timber bridges with a span of greater than 20 ft are currently in use.!! Another 42,100 are timber decks supported by steel stringers and classified as steel bridges.!! Many bridges (up to 50 years of age) are in need of repair or replacement.!! Inspection required by Federal Highway Administration and State DOT s

4 Typical Single-span Timber Bridge

5 Typical Dowel Laminated Slab Span Bridge

6 Timber Bridge Inspection Techniques!! Visual!! Hammer sounding!! Probing!! Moisture content!! Stress wave timing!! Resistance microdrilling!! Load testing

7 University of Minnesota Duluth USDA and USDA Forest Products Laboratory Publications

8 How can we develop global testing procedures for structural health monitoring of timber bridges?

9 Dynamic Response of Systems!! Deterioration of wood structures caused by any organism or overloading reduces strength and stiffness of wood components, and thus could affect the dynamic behavior of the system.

10 Initial Research Focus!! Girder/stringer style timber bridges "! Subset of steel girder bridges!! Wood decks

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13 Static Load Testing Fully loaded tri-axle gravel truck Gross weight: 46,540 lbs Rear axle: 33,680 lbs

14 Positive news!

15 Technical Issues!! Misidentify 1 st bending mode (Hz)!! Estimation of bridge mass!! Environmental variables (temp., moisture, etc) Edge stiffening effects from curb/rail systems!! Deformed pile abutment affects both static and dynamic measurements!! Decayed pile caps!! Noise interference!! Boundary conditions at supports

16 Phase II Activities!! Develop an automated testing system!! Conduct vibration testing on bridge sections during construction!! Conduct load and vibration testing of in-service spike laminated Wheeler bridges in northeastern Minnesota With a goal of further developing background information for using forced vibration as a structural health monitoring and control system.

17 Project Task 1!! Design and fabricate an automated vibration testing system using a ruggedized laptop "! Real time control of testing and analysis of vibration signal to determine frequency, phase of signal "! Manual controls as well

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19 Project Task 2!!Complete vibration testing and load testing on dowel laminated timber bridge deck sections "!Start with individual deck sections and continue testing during construction until final completion.

20 Bridge 53!! Steel girders with timber deck, timber pile caps and pilings!! 1964!! 22 ft span!! Restricted load ratings

21 Bridge sections

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26 July Completed

27 SLC - Peak 2

28 Project Task 3!!Complete flexural vibration testing and load testing on spike laminated timber bridges in Minnesota

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30 Static Load Testing

31 Bridge 53 Vibration characteristics

32 Average Deflection vs. Frequency

33 Conclusions 1.! Automated testing system has been developed capable of repeatedly and reliability using forced vibration and measuring vibration amplitude. 2.! Each bridge has a unique set of vibration characteristics that were identified using the automated system. 3.! The relationship between the measured frequency and measured EI is stronger for girder bridges than dowel laminated bridges.

34 Future Research Recommendations!! 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 developing future load ratings.!! An accurate means of determining bridge weight and the true measured stiffness is essential for being able to relate the measured frequency against the measured EI product.!! The key question that must be determined is how the vibration response will change due to structural deterioration caused by decay or lack of maintenance.

35 Thank you!