Risk-Based Inspection and Strength Evaluation of Suspension Bridge Main Cable Systems (2023) / Chapter Skim
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Pages 5-34
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5 C H A P T E R 2 Literature Review and Synthesis Literature Review Purpose of Literature Review NCHRP 534 represents the current guidelines followed by bridge owners for planning and conducting inspections of main cables of suspension bridges and for estimating their remaining strength. The literature review for the present project used this previous NCHRP effort as a starting point.
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6 members of this research team, contains an up-to-date review of NDT technologies, e.g. Acoustic Emission, Magnetostrictive, Flux Leakage, used in practice and research and was used as the starting point for the work done in this study.
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7 4) using Monte Carlo simulations reflecting the EVD (simulating independent and identically distributed random variables)
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8 establish the percentage of cracked and broken wires. The methodology contained in NCHRP 534 is, at present, the only approach that is being used.
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9 main cable, and that they are sufficiently durable to survive the rigors of field installation. The ability to monitor variables such as temperature and humidity can be used as indirect indicators of the potential for corrosion activity.
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10 As stated above, for reasons of security, most of the bridge owners requested that the data provided not be specifically associated with their bridge. Q3.0 Description of Suspension Bridge.
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11 Figure 2. Total Length of Bridge (in feet)
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12 Figure 4. Length of Side Spans Supported by Main Cables (in feet)
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13 Q3.7 Sidewalks. (21 Responses)
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14 Figure 7. Sag Ratio versus Age Q4.3 Cable Diameters.
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15 had previously been opened. The remaining two bridges are reported to have a zinc chromate paste.
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16 Figure 9. Number of Wires in Parallel Wire Cables Q4.6.3 Number of wires in the side Spans.
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17 Q4.6.5 Are the Wires galvanized? Eighteen respondents reported that the wires in their main cables are galvanized.
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18 Q5.2 What Acoustical Monitoring System Is Used? Of the seven bridges reported to have an acoustical monitoring system three were installed by Pure and four were installed by MISTRAS.
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19 Figure 13. Number of Times Cables Have Been Inspected Q6.3 Is the Cable Inspected on a Regular Basis?
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20 Q6.4 Number of Panels Opened During Each Inspection. (20 Responses)
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21 Figure 16. Selection Criteria for Opening Panels Q6.6 Were Field Inspection Forms Prepared for Your Bridge?
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22 Figure 17. Number of Samples and Specimens Q6.9 What Tests Were Conducted on the Specimens?
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23 Q6.14 Describe the Method Used to Tension New Wires? (17 Responses)
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24 on methods used for wire cutting and wire repair for the interior wires in order to come up with a recommendation on how to utilize more wires from the interior of the cable in the wire sampling.
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25 pieces of wire for testing. The Guidelines calculations also assumes (3.2.1)
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26 a. Though pointed out in the Problem Statement of the second top priority "Development of models to predict the strength of deteriorated cables" at the NCHRP-sponsored "Workshop on Safety Appraisal of Suspension Bridge Main Cables" (2)
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27 Figure 18. FOS as of Last Inspection Q6.18 Location of the Panel With the Lowest Factor of Safety?
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28 Of the 17 parallel wire bridges none reported any use of NDE on the cable. One owner reported field instrumentation of selected eye-bar elements.
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29 Figure 19. Age of Anchorage Dehumidification System Q7.2 Do you inspect the strands in the anchorages as part of your biennial inspection?
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30 Q8.0 Suspender Information Q8.1 Panel length between suspenders and diameter of suspenders? (21 Responses)
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31 Q8.7 Have any suspenders been replaced?
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32 protect the main cables, more so, because higher risks of service interruptions exist and can manifest themselves on other structural elements far sooner. Respondent #2 New/updated guideline should include details of helical structural strands inspections, testing and strength evaluation techniques, reliable NDT methods to determine in situ cable conditions, any technique to conduct internal inspections at saddles, vibrations based tension measurements techniques and applications, wire sample collections and repair techniques for helical strands, condition rating and remaining life estimation techniques, protection system-wrap-paint vs dehumidification - cost-benefit approach, inspection frequency and timing for helical strands.
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33 • Wire samples containing mixed corrosion stage specimens provide lower values of the theoretical sample minimum strength between cable bands than wires in worse condition throughout. • Wire samples are classified according to the worst corrosion stage found anywhere along their lengths.
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34 • Inspection frequency and number of panels to be opened need to take into consideration any previous findings and extenuating circumstances such as the use of a dehumidification system or an acoustical monitoring system. Should the number of panels be based more on length of cable rather than a fixed number of panels per bridge?
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