Ashland Bridge Rehabilitation Using Advanced Composite Materials

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Ashland Bridge Rehabilitation Using Advanced
Composite Materials

• Matt Swinehart
• August 7, 2002
• Advisor Michael Chajes

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Overview

• Introduction
• Background
• Methods
• Results
• Conclusions
• Future research

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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

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Introduction Location of Bridge
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Introduction

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

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Introduction
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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

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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

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Methods
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Methods - Passes

• Six passes with four different routes and two
  different truck speeds (semi-static and dynamic)

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Methods Truck Specifications
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Results Peak Strain Values

• Largest strain from a single truck pass
  experienced by
• Through girder 96.98 µe
• Floor beam 169.5 µe - when the back axle is
  directly above
• Overall minimal strains

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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

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Results - Composite vs. Non-composite

• Composite action between the deck and beam are
  evident from graphs from load test

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Results Composite vs. Non-composite (cont.)

• Neutral axis of composite is about 24 inches from
  the bottom of the steel flange

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Results - Impact Factor

• Dynamic loading of the bridge causes an increase
  in stress
• 8 for the through girder
• 5 for the floor beams
• Formula

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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

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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

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Results In-service Monitoring

• Installed by Degang Li, University of Delaware
• June 17 - June 22, 2002, normal traffic
• Trigger strain of 25 µe
• Bridge experiences very few heavy truck loads
• Largest strain 130 µe

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Results In-service Monitoring Peak Values

• Peak value was 130 µe

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Results In-service Monitoring Frequency

• Infrequent high strains

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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

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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

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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

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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

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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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The End
Has anyone seen this bottle?