Risk-Based Inspection and Strength Evaluation of Suspension Bridge Main Cable Systems (2023) / Chapter Skim
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Pages 78-90
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From page 78... ...
78 C H A P T E R 5 Risk-Based Method for Determining Timing of Next Inspection Introduction One of the needs of bridge owners is a more rigorous method for determining the frequency of internal cable inspections. These can be expensive, intrusive inspections, and a rational method is needed to better determine how often they should be performed.
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From page 79... ...
79 engineering rationale, experience, and typical deterioration patterns to evaluate the reliability characteristics of bridges and the potential outcomes of damage. In the case of Project 12-115 we are focusing on just the suspension system of a single bridge type, so the approach will focus only on the specific elements of the suspension system consisting of the main cable and appurtenances outside the anchorage, the portion of the cable and appurtenances inside the anchorage, and the suspenders and their appurtenances and not the total bridge.
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From page 80... ...
80 use of engineering judgement and past experience to be used in lieu of deterioration curves. The RT has relied heavily on engineering judgement and past experience in estimating the rates of deterioration.
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From page 81... ...
81 That being said, it important that external biennial inspections of the suspension system components be performed to detect potential signs of internal deterioration. Items to be inspected are outlined in Article 2.1.1.2 of the FHWA Primer for the Inspection and Strength Evaluation of Suspension Bridge Cables.
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From page 82... ...
82 Identify Elements of the Suspension System Identify the Damage Modes for Those Element Develop Occurrence Factors Develop Consequence Factors Inspection Practice • Interval • Procedures • Criteria for Reassessment Inspection Reassessment Required? Source: Washer et al.
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From page 83... ...
83 reliability, considering the expected damages, are then identified. The damage modes and attributes are generally identified through an expert panel process and are subsequently used in a rational process that identifies those elements that are more highly reliable and durable and those elements that are more likely to suffer from deterioration and damage.
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From page 84... ...
84 Determining Occurrence Factor (OF) The Occurrence Factor is determined by assigning points to the attributes listed in each of the four categories, Screening, Design, Loading and Condition, as shown in the sections that follow.
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From page 85... ...
85 unless active measures are taken to preclude access. Their waste material, when exposed to moisture, can create an acidic environment which is highly corrosive to steel.
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From page 86... ...
86 C.5–ACOUSTIC EMISSION/ACOUSTIC MONITORING SYSTEM The AE monitoring systems deployed on main cables of suspension bridge are also capable of monitoring wire breaks within the anchorage. As with the main cable, the systems require regular maintenance in order to ensure their continued effectiveness.
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From page 87... ...
87 • Test removed suspenders to failure to determine remaining breaking strength. • Dissect strands after testing and evaluate corrosion.
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From page 88... ...
88 area, impacts to the element's structural and durability characteristics are not obvious. Until an-depth inspection of the affected elements is performed the component should be screened from the general reliability assessment.
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From page 89... ...
89 ADTT greater than 5% but less than or equal to 10% 15 points ADTT greater than 0% but less than or equal to 5% 10 points No permit trucks allowed 0 points L.2–EXTERNAL ENVIRONMENT Environmental exposure of suspender ropes caused by entrapped water and/or debris within or against the suspender and sockets has been the main cause of deterioration. In cases where details have been used that are completely free-draining to prevent the accumulation of debris, as well as allowing unlimited inspection access, the life span of the suspender ropes has been greatly increased.
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From page 90... ...
90 Determining Consequence Factor The CF considers primarily how failure in one element would affect the failure of the entire bridge. The suspender ropes are internally redundant members constructed of hundreds of individual wires.
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