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Ashland Bridge Rehabilitation Using Advanced Composite Materials

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Ashland Bridge Rehabilitation Using Advanced Composite Materials

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    1. Ashland Bridge Rehabilitation Using Advanced Composite Materials Matt Swinehart August 7, 2002 Advisor: Michael Chajes

    2. Overview Introduction Background Methods Results Conclusions Future research

    3. Introduction Ashland Bridge Ashland Bridge carries SR 82 over Red Clay Creek Floor beams and concrete deck are suspected of deterioration Solution: CFRP plates and replacement of deck

    4. Introduction Location of Bridge

    5. Introduction Fibers are strong when pulled along the fiber direction The matrix in a fiber reinforced polymer gives the material strength in any direction

    6. Introduction

    7. Background University of Delaware Trent Miller Rehabilitation of steel bridge girders using advanced composites Todd West Enhancement to the bond between advanced composite materials and steel for bridge rehabilitation Chajes, et. al Full-scale deck replacement

    8. Methods Bridge load test conducted on June 13 Analysis of peak strain values, impact factor, effective width of floor beams, percent fixity, prediction of change in stress after rehabilitation, inservice monitoring, and natural frequency

    9. Methods

    10. Methods - Passes Six passes with four different routes and two different truck speeds (semi-static and dynamic)

    11. Methods Truck Specifications

    12. Results Peak Strain Values Largest strain from a single truck pass experienced by Through girder = 96.98 e Floor beam = 169.5 e - when the back axle is directly above Overall: minimal strains

    13. Comparison with DelDOT model Simple analytical model vs. experimental data Using DelDOTs model with our truck specifications - maximum floor beam stress = 11.9 ksi Largest stress during load test = 6.6 ksi Possible reasons for differences: incorrect effective width calculation or inherent inaccuracies of theoretical model

    14. Results - Composite vs. Non-composite Composite action between the deck and beam are evident from graphs from load test

    15. Results Composite vs. Non-composite (cont.) Neutral axis of composite is about 24 inches from the bottom of the steel flange

    16. Results - Impact Factor Dynamic loading of the bridge causes an increase in stress: 8% for the through girder 5% for the floor beams Formula:

    17. Results - Percent Fixity Percent fixity = Overall percent fixity values for floor beams are relatively low (range from 1-3.5) Percent fixity values can range from 0 to 100 Can consider the floor beams to not be fixed Model as simply supported

    18. Results - Predictions of Change in Stress Method of transformed sections steel and concrete modeled as steel Change in stress is less than expected at 2% Possible reason: composite action already present

    19. Results In-service Monitoring Installed by Degang Li, University of Delaware June 17 - June 22, 2002, normal traffic Trigger strain of 25 e Bridge experiences very few heavy truck loads Largest strain = 130 e

    20. Results In-service Monitoring Peak Values Peak value was 130 e

    21. Results In-service Monitoring Frequency Infrequent high strains

    22. Results - Natural Frequency Perception of safety The lower damping shows that the through girders vibrate longer Frequency = 3.4 cycles/second Percent Damping around 1% Energy decays slowly

    23. Conclusions There probably is no immediate need for bridge rehabilitation based on the load test Field testing yields more accurate assessments of a bridges capacity than simple analytical models

    24. Conclusions (cont.) Current condition of bridge (before rehab.): Concrete deck and floor beams act as a composite might explain lower than expected stress Experiences little heavy truck traffic Experiences minimal strains/stresses Energy in the bridge is dissipated slowly

    25. Conclusions (cont.) Projected change in stress after rehab. due to bonding of CFRP plates: 2% decrease Change in stress means retrofit increases stiffness of floor beams Decrease is smaller than expected, possibly because already acting compositely

    26. Future Research Post-rehabilitation test on bridge to determine actual effects of CFRP retrofit Long-term durability of CFRP retrofits Long-term monitoring of rehabilitated structures Effects of concurrent environmental factors and fatigue Accurate analysis of effective width (How do you get it

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