FIF2 04 - Khaled Mahmoud

8/11/2019 FIF2 04 - Khaled Mahmoud

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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 EvaluationInspection & Vulnerability AssessmentLoad RatingStrengthening Measures

System-wide VulnerabilitiesBearing FailureJoint Failure

Atmospheric Corrosion

Specific Vulnerabilities:Degradation of Bridge CablesCracking & Deterioration of OrthotropicDeck

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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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 randomlydistributed.

Crossing and broken wires were randomly distributed insome bridge cables.

On some other cables, wire tensile strength was alsorandomly distributed, because of variations in carboncontent.

Cracked and broken wires were observed to be randomlydistributed.

WHY IDENTIFY SAMPLE SIZE?

- To limit invasive wire cutting and splicing.

- To obtain a minimum number of samples to achieve highlevel 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 - FractographicIdentification 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 betterassessment of % of Cracked Wires.

Fracture Toughness Test

Fractographic Examination of ALL Fracture Surfaces ofWires tested in tension (both short & long).


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Analysis of Cracked Wires-BTC Method

BTC Method uses Principles of FractureMechanics to determine Ultimate Strength for

Cracked Wires:

= Measured Fracture Toughness.

= Crack Shape Factor.

= Critical Crack depth obtained from

Fractographic Examination.

( )

c

ccracked

aD

a

Y

K

.)(

)(

=

( )c

K

)(D

a

Y

ca


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Forecast of Cable Service Life-BTC Method

BTC Method uses Data of Wire Strength toforecast 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 inadjacent panels.


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Sensitivity Analysis-BTC Method

Purpose of Sensitivity Analysis:

Identify the key inputs which influencethe estimated cable strength.

Assess whether the estimated cablestrength and the decision makingprocess are likely to be affected byuncertainties.


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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 ofdamage in bridge wire.

Fractographic Examination provides the most accuratedetermination of the proportion of cracked wires.

Fracture-based Analysis of Cracked Wires provides

accurate assessment of the ultimate strength ofcracked wires.

Evaluation of Time-dependent degradation is an

important component necessary in the decisionmaking process and cable strength evaluation.

Monitoring techniques are essential for the conditionassessment of bridge cables.

Conclusions


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CONDITION ASSESSMENT OF BRIDGES & RESEARCH NEEDS

Thank you!

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FIF2 04 - Khaled Mahmoud