condition assessment of bridges & research needs · condition assessment of bridges &...
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CONDITION ASSESSMENT OF BRIDGES & RESEARCH NEEDS
Khaled Mahmoud, PhD, PE, President Bridge Technology Consulting
New York City, USA www.kmbtc.com
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Outline
• Techniques for Strength Evaluation Inspection & Vulnerability Assessment Load Rating Strengthening Measures
• System-wide Vulnerabilities
Bearing Failure Joint Failure Atmospheric Corrosion
• Specific Vulnerabilities:
Degradation of Bridge Cables Cracking & Deterioration of Orthotropic Deck
• Need for Research & Monitoring Techniques
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Bearing Deterioration
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Bearing Failure
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Joint Failure
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Atmospheric Corrosion
Atmospheric Corrosion
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Suspension Bridge Data
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Corrosion Protection System
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Cable Unwrapping & Inspection
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Cable Force Capacity
LLTDL
CapUlt
P
PSafetyofFactor
++
=..
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BTC Method for Cable Strength Evaluation
• Sample size & Random Sampling
• Basic degradation modeling
• Cracked wire proportion
• Broken wire proportion
• Effect of adjacent panels
• Wire testing program
• Analysis of cracked wires
• Forecast of cable strength
• Sensitivity Analysis
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BTC Method for Cable Strength Evaluation
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Random Sample Size Determination-BTC Method
• WHY RANDOM?
– Because Damage inside bridge cables is mostly randomly distributed.
– Crossing and broken wires were randomly distributed in some bridge cables.
– On some other cables, wire tensile strength was also randomly distributed, because of variations in carbon content.
– Cracked and broken wires were observed to be randomly distributed.
• WHY IDENTIFY SAMPLE SIZE? - To limit invasive wire cutting and splicing. - To obtain a minimum number of samples to achieve high
level of confidence in estimated cable strength.
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Random Sample Size Determination-BTC Method
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Random Sampling Plan
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SEM - Fractographic Identification of Cracks
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Cracked Wire Proportion-BTC Method
• Cracked Wires are Identified as Probabilistic Quantity
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Broken Wire Proportion-BTC Method
• Broken Wires are Identified as Probabilistic Quantity
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Broken Wire Proportion-BTC Method
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Wire Test Program-BTC Method
BTC Method Test Program includes:
• Enhanced Tension Test for Mechanical Properties
• Tensile Test of Long Wires to obtain better assessment of % of Cracked Wires.
• Fracture Toughness Test
• Fractographic Examination of ALL Fracture Surfaces of Wires tested in tension (both short & long).
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Analysis of Cracked Wires-BTC Method
BTC Method uses Principles of Fracture Mechanics to determine Ultimate Strength for Cracked Wires:
= Measured Fracture Toughness.
= Crack Shape Factor.
= Critical Crack depth obtained from Fractographic Examination.
( )c
ccracked
aDaY
K
.)(
)(
πσ =
( )cK)(
DaY
ca
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Forecast of Cable Service Life-BTC Method
• BTC Method uses Data of Wire Strength to forecast service life of cables.
• It relies on degradation of Strength for both:
• Intact Wires
• Cracked Wires • It includes effect of adjacent panels; i.e.,
effect of broken and cracked wires in adjacent panels.
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Sensitivity Analysis-BTC Method
• Purpose of Sensitivity Analysis:
• Identify the key inputs which influence the estimated cable strength.
• Assess whether the estimated cable strength and the decision making process are likely to be affected by uncertainties.
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Sensitivity Analysis-BTC Method
• KEY INPUT For Sensitivity Analysis:
• Effect of adjacent panels
• Proportion of cracked wires
• Ultimate strength of cracked wires
• Proportion of broken wires
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Cable Monitoring
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Cable Monitoring
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Cable Monitoring
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Cable Monitoring
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• Visual Evaluation of bridge cable wire condition is
misleading and provides unreliable results.
• Random Sampling Provides good representation of damage in bridge wire.
• Fractographic Examination provides the most accurate determination of the proportion of cracked wires.
• Fracture-based Analysis of Cracked Wires provides accurate assessment of the ultimate strength of cracked wires.
• Evaluation of Time-dependent degradation is an important component necessary in the decision making process and cable strength evaluation.
• Monitoring techniques are essential for the condition assessment of bridge cables.
Conclusions
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CONDITION ASSESSMENT OF BRIDGES & RESEARCH NEEDS
Thank you!