Risk-Based Inspection and Strength Evaluation of Suspension Bridge Main Cable Systems (2023)

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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. Recent advances in risk-based inspection (RBI) point to a way to better determine inspection frequency. This section details how RBI can be adapted for cable inspections. An illustrative example of applying reliability-based analysis to establish an inspection interval for the main cable of a typical suspension bridge is available in Appendix B of the proposed Guidelines. Risk-Based Inspection of the Suspension System One of the Objectives of NCHRP 12-115 was to develop a RBI approach for the suspension system elements of a suspension bridge. NCHRP Report 782, “Proposed Guidelines for Reliability-Based Bridge Inspection Practices” served as the basis for the development of this approach. NCHRP 782 describes a general methodology for developing a RBI practice that is intended to improve the safety and reliability of bridges by focusing inspection efforts where most needed. The approach, as written, is intended to be a framework for conducting reliability assessments of bridges to develop inspection strategies that are based on an assessment of inspection needs. The approach described takes into consideration characteristics that contribute to the reliability of a bridge such as the structure type, age, condition, importance, environment, loading, and known problems. The procedure contained in NCHRP 782 is intended for “highway bridges of common design characteristics.” Complex bridges, such as suspension bridges, require an approach not entirely consistent with, but similar to, the NCHRP 782 guidelines. The attractiveness of applying the NCHRP 782 approach to suspension systems is its potential promise for a means of assessing the needs of the suspension system resulting in an inspection frequency based on those needs. The recurrence period for the inspection of suspension systems is a common issue for suspension bridge owners and one that must be addressed. To accomplish this, the likelihood of anticipated damage modes to the suspension system and associated consequences must be identified and analyzed. Such an approach results in a focus on the damage and deterioration mechanisms that are most important for suspension system element safety. The process as outlined in NCHRP 782 begins with the establishment of an expert panel to define and assess the durability and reliability characteristics of bridges within a jurisdiction. The expert panel groups the bridge inventory into bridge/structure types and assesses the inspection needs by using

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. The approach as presented in the following discussion does allow for bridges owners to “adjust” the approach to reflect any unique characteristics of their bridge’s suspension system. In addition, given that the modes of deterioration for helical strand bridges are very similar to those of a parallel wire cable, it is the opinion of the RT that the procedure as developed below can be applied to bridges with helical strand main cables as well. It is also the opinion of the RT that the same general process used for determining the inspection cycle of groups or types of bridges as outlined in NCHRP 782 can be used, with some modifications, for the suspension system of a suspension bridge. As presented in NCHRP 782 the process consists of three basic steps: 1. What can go wrong, and how likely is it. In this step, possible damage modes for the elements of a selected bridge are identified. In the case of 12-115, as stated above, focus will be placed on the suspension system elements. Design, loading, and condition characteristics are considered to categorize the likelihood of serious damage occurring. For example, in the case of the main cable, the RT has established that the primary things that can go wrong in the suspension systems are corrosion, leading to section loss, cracking and wire breaks. The likelihood will fall into one of four occurrences factors ranging from very unlikely to very likely. 2. What are the consequences. In this step the consequences resulting from the assumed damage modes are assessed. The potential consequences are categorized into one of four consequence factors ranging from minor effect on safety through any inability of the bridge to safely and reliably perform its intended function. 3. Determine the inspection interval and scope. Based on the results of the above steps, the inspection needs and inspection interval are prioritized. Damage modes that are likely to occur or have a high consequence are prioritized over damage modes that are unlikely to occur or are of little consequence in terms of safety. As stated in NCHRP 782, it is critical to establish what constitutes “when an element is no longer performing its intended function to safely and reliably carry normal loads and maintain serviceability.” The issue with the elements of suspension systems of large suspension bridges is what constitutes “safety and reliability”? Unlike small bridges comprised of easily observed steel and concrete elements that lend themselves to simple determination of the effects of loss, the determination of the effects of damage to the components of suspension system, particularly that of the main cable, is a highly complex and statistically based process. Complicating this issue is the lack of any deterioration curves for the elements of the suspension systems. Elements from different bridges show tremendous variations in the rate of deterioration and the locations of that deterioration. Couple this with the fact that a consistent process for the internal inspections of suspension bridge systems is somewhat recent (NCHRP 534, 2004), establishment of the onset of deterioration has proven to be illusive at best. That being said, NCHRP 782 does allow the

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. It appears that the point when an element is no longer performing its intended function to safely and reliably carry normal loads and maintain serviceability will have to the tied in the case of some elements to an acceptable FOS as determined by inspection and numerical evaluation. This is particularly true in the case of the main cable. Loading in the main cables of suspension bridges is comprised primarily of dead load (about 80-85% of total load in most bridges) and given that most suspension bridges built prior to 1980 have design factors of safety above 3.00, a suspension bridge can “safely and reliably” carry live load after sustaining significant deterioration and loss of strength. Therefore, how “low” the FOS can be considered acceptable will have to rely heavily on cable maintenance/monitoring, engineering judgement and the risk tolerance of the owners. At present, for a conventional cable with no dehumidification or health monitoring systems, most owners have adopted a minimum FOS of 2.0. NCHRP 534 recommends owners start making contingency plans for cable replacement/supplementation when a FOS of 2.15 is reached. Some modern suspension bridges have been designed with factors of safety just over 2.2 and at least one suspension bridge in service has an estimated FOS of approximately 1.75 (It is important to point out that in this particular case, dehumidification, acoustic monitoring and live load monitoring has been put in place to monitor the cable in “real” time.) At this point in the project research the RT is recommending that the proposed reliability-based bridge inspection practices only be applied to bridges with a FOS of 2.0 or greater. Returning to the first step of the NCHRP 782 process “what can go wrong and how likely is it to occur?” As stated in NCHRP 782, what can go wrong addresses the damage modes that affect the bridge elements. In other words, what damage is likely to develop over the service life of the bridge which would lead to the inability of the element to safely and reliably perform its intended function. For example, the damage modes most often seen in suspension bridge main cables is corrosion, leading to cracking and eventual wire breaks. In NCHRP 782, the assessment of bridge inspection needs is based on an Occurrence Factor which is driven by an assessment of the likelihood that a given damage mode will result in in an inability of the element performing its function in a safe and reliable manner during a defined period of time. In the case of NCHRP 782 this time period is 72 months. The present return inspection period as stated in NCHRP 534 for a bridge cable in excellent condition, (only stage 2 wires) is 30 years. If there are stage 4 and broken wires, the period drops to 5 years. These intervals are based solely on condition and not on the likelihood of an element’s inability to perform its intended function. Using the data collected from the questionnaire and previous RT performed inspections, a reasonable means of better defining a “next” inspection cycle has been developed. It is important to realize that “attributes” as defined in NCHRP 782 include characteristics of the system that can contribute to an element’s reliability, durability, or performance. In the case of the main cables such attributes would be the existence of an effective coating systems, de-humidification system, oiling, or acoustic monitoring (or a combination thereof). The existence of such attributes makes it unlikely that failure of the main cable to perform its intended function safely and reliably would occur in some agreed upon time interval without these attributes.

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. Step 2 of the process developed in NCHRP 782 is the assessment of consequences. A consequence is defined as “the likely outcome presuming a given damage mode were to result in element being considered being unable to perform its intended function in a safe and reliable manner.” It is important to note that as stated in NCHRP 782, “failure of an element is not an anticipated event when using a RBI approach, rather the process of assessing the consequences of a failure merely as a tool to rank the importance of a given element relative to other elements for the purpose of prioritizing inspection needs.” The inspection interval will be based on the Occurrence Factor and consequence factors following the procedure presented in NCHRP 782. It is important to understand that the maximum inspection interval, in order to be consistent, is inextricably linked with the assessment interval used to establish the occurrence factors. The entire process is best illustrated in the following flow chart taken from NCHRP 782 with minor modifications:

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. (2014) Figure 31. NCHRP 782 Process for Reliability-Based Bridge Inspection Practices As stated earlier, the first step in the establishment of a RBI approach is to identify the potential damage modes for the elements that have been identified as critical to the suspension system. The likely damage modes are derived from past experience, engineering judgement and commonly known damage modes. The characteristics, or attributes, of those bridge elements that contribute to their NO YES

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. The importance of each attribute’s influence on the reliability and durability of the bridge element is ranked and a rationale based on the damage modes and attributes of the bridge element to estimate the likelihood of serious damage occurring during a specified interval is developed. Element Attributes Attributes are characteristics of a bridge element that affect its reliability. These attributes are typically well-known parameters affecting the performance of the bridge elements during their service lives. An element can have good attributes that are known to provide good service life performance. For example, eyebars in an anchorage chamber that has an operational, well-maintained dehumidification system would be considered to possess a good attribute. Alternatively, elements may have qualities or attributes that contribute to more rapid deterioration or increased likelihood of damage. For example, the main cable of a suspension system with a deteriorated exterior protection system would be an example of an attribute resulting in more rapid deterioration of the wires in the cable. The identification of key attributes is simply a listing of these attributes and a relative ranking of their importance in terms of the reliability and the durability of the element. As stated in NCHRP 782, attributes can be generally grouped into four categories: Screening, Design, Loading and Condition. The attributes listed below are not intended at this time to be an all-inclusive list. A more in- depth list will be prepared as the process is more fully developed. At this time, it is the intention of the RT that the owner will have the option of adding attributes that reflect any unique characteristics of their bridge. The attributes listed below are meant to illustrate the methodology and facilitate the presentation of the example. RBI Approach for Main Cables An illustrative example of applying reliability-based analysis to establish an inspection interval for the main cable of a typical suspension bridge is contained in the following section. A complete example of the approach is available in Appendix B of the proposed Guidelines. Main Cable Strands Inspection Scope Inspections of the main cable strand inside the anchorages. Here the main cable strands are splayed out between the splay saddle and the strand anchoring steel. Regular Inspection Scope The main cable strands are inspected by walking on existing walkways, ladders and floors. Notes are taken of conditions and irregularities found. Any broken wires are noted. Corrosion, paint condition, and stains are typically evaluated. In-depth Inspection Scope In-depth inspection involves hands on inspection of all strands and driving wedges through a select number of strands. The in-depth inspection will provide an estimate of the main cable safety factor at this location.

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. Screening Attributes The screening attributes for the main cable strands are the same as those provided for the main cable. Design Attributes D.1–WIRE COATING Virtually all suspension bridges presently in use were constructed using galvanized wire. The deterioration characteristics of galvanized wire versus “bright” wire appear to be somewhat different, though the data available for bright wire in cables is extremely limited. Galvanizing definitely delays the onset of section loss due to corrosion, but some research has indicated that a by-product of the oxidation of the galvanizing appears to be hydrogen ions that in a closed environment, when mixed with water, contributes to hydrogen embrittlement and cracking. This is only the case in the main cable outside of the anchorage. In the anchorage, the main contributor to wire failure has been ferrous corrosion leading to significant section loss. In this case, galvanizing is a significant contributor to extending the life of the wires. For this reason, galvanized wire is considered advantageous in this analysis and the attribute is rated as follows: Bright wire (ungalvanized) 20 points Galvanized wire 10 points Loading Attributes L.1–ANCHORAGE WATER PENETRATION The environmental exposure of the wires in the anchorage is significantly different than those in the main cable. The primary method of weather protection is the anchorage chamber itself. If the chamber is properly sealed from the outside environment, then the strands will generally be well protected. However, water will always be present in the form of humidity and changes in temperature will cause water vapor to condense on the steel strands as well as the anchorage concrete, leading to corrosion. If water is allowed to enter the chamber then the rate of corrosion can advance rapidly, leading to severe section loss of strands (particularly on wires closest to the floor level, e.g. where they wrap around strand shoes). This attribute is rated as follows: Anchorage has existing water leaks and/or standing water present within the chamber 20 points Anchorage shows evidence of previous water penetration onto strands 15 points Anchorage experiences high humidity levels and/or condensation but no standing water 10 points Anchorage is dry 0 points L.2–ANCHORAGE DEBRIS It is an established fact that animal debris (e.g. pigeon excrement) can lead to advanced deterioration of steel structures. Birds in particular will create their habitat in confined spaces, such as anchorages,

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. Anchorages must be sealed to prevent entry of any type of animal and any debris, if present, must be immediately removed and the steel surfaces cleaned to prevent further deterioration. This attribute is rated as follows: Anchorage strands have significant deposits of animal excrement directly on steel surfaces 20 points Anchorage is not well-sealed but there is no evidence of animal entry 15 points Anchorage shows evidence of previous animal entry but is currently sealed 10 points Anchorage is completely sealed 0 points L.3–INTERNAL ENVIRONMENT Water entering the cable will eventually progress into the anchorage via gravity. Experience indicates that there is no physical barrier that is 100% effective in keeping water out of a cable, hence the reason that the scoring below for no outward evidence of water in a cable still gets a score value greater than 0. The attribute is rated as follows: Water Dripping from the Cable 20 points Rust staining at points along the cable 15 points No outward evidence of water in the cable 10 points Condition Attributes C.1–CONDITION HISTORY/TREND (BASED ON LAST INTERNAL INSPECTION) The condition of the wires in anchorage as observed during periodic inspections give an excellent indication of the likelihood of continued deterioration. This attribute is rated as follows: Stage 4 wires with wire breaks 20 points Stage 4 wires without breaks 15 points Stage 3 wires 10 points Stage 2 wires 0 points C.4–ANCHORAGE DEHUMIDIFICATION SYSTEM Dehumidification of anchorages and tower tops has been used in the Unites States for over 30 years. The effectiveness in stopping corrosion in those cases has been established. It is reasonable to assume that a well-maintained dehumidification system (i.e maintaining humidity levels below 40%) is beneficial in extending the useful like of steel components within the anchorage. This attribute is rated as follows: No Dehumidification 20 points Dehumidification system not maintained/not fully operational 20 points Dehumidification system maintains RH < 40% 0 points

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. This attribute is rated as follows: No AE system (or existing AE system has not been regularly maintained) 20 points AE system installed and properly maintained – increase in number of detected breaks 20 points AE system installed and properly maintained – number of detected breaks at steady state 5 points Determining Consequence Factor The Consequence Factor (CF) for the main cable strands is determined in the same way as that of the main cable. Anchorage Eyebars Inspection Scope Inspection of the main cable strand anchoring steel inside the anchorages. In-depth inspection involves eyebars, strand shoes, sockets, anchoring rods or other components anchoring the main cable strands to the anchoring mass. The type of anchoring system varies greatly between suspension bridges. Inspection of the strand anchoring steel may be done as part of the bridge’s regular inspection. Regular Inspection Scope Eyebars – measure corrosion section loss In-depth Inspection Scope No in-depth inspection required unless issues found during regular inspection. Suspender Ropes Inspection Scope Regular Inspection Scope • Visually inspect the suspender. Note the condition of the protection system (paint, galvanization sleeve). Note any corrosion and staining. Note any broken wires (typically near sockets). In-depth Inspection Scope • Hands on inspection of all suspender connections. Note any broken wires and condition. • Inspect all attachments to the suspenders (gatherers, separators, signs etc.) • Evaluate 15% of ropes with magnetostriction (MS). • Replace rope at midspan, minimum one per cable. • Replace worst rope found by MS, minimum one per cable. • Replace rope with most broken wires or worst corrosion, minimum one per cable.

87 • Test removed suspenders to failure to determine remaining breaking strength. • Dissect strands after testing and evaluate corrosion. 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. Screening Attributes S.1–CURRENT CONDITION OF THE MAIN CABLE This screening attribute is scored based on whether the most recent internal inspection resulted in a calculated FOS of less than 2.5. Current FOS is less than or equal to 2.5 Suspenders should receive an in-depth inspection every 5 years until load restrictions or suspender replacement has been implemented Current FOS is greater than 2.5 Continue with Procedure S.2–FIRE DAMAGE Though rare, fires on a suspension bridge have occurred in the past. These fires are usually the result of vehicular accidents but secondary causes such as vandalism or terrorism are possible. If a fire has occurred on the bridge, an appropriate assessment should be conducted to determine how the fire has affected the load carrying capacity and the durability characteristics of the suspension system. Typically, an assessment of the damage is made immediately after the incident based on exterior indicators. Since many of the components of the suspension system are “enclosed”, impacts to the element’s structural and durability characteristics might not be readily available. Until an internal inspection of the affected elements is performed, the component should be screened from the general reliability assessment. Fire Incident has occurred and an internal inspection within 12 months of the fire has not occurred Suspension system is not eligible for reliability assessment of inspection interval until inspection confirms the system is structurally undamaged and elements contributing to its durability are functioning There has been no fire incident on the bridge, or an internal inspection has been conducted within 12 months of a fire incident confirming that the suspension system and those elements providing durability are undamaged Continue with Procedure S.3–COLLISION DAMAGE Collision with the main cables and suspenders of a suspension bridge, though rare, have occurred in the past. These incidents are usually the result of vehicular accidents or oversize loads but secondary causes such as terrorism are possible. If a collision with the cable or suspender has occurred, an appropriate assessment must be conducted to determine how the impact has affected the load carrying capacity and the durability characteristics of the suspension system. Typically, an assessment of the damage is made immediately after the incident based on exterior indicators. Since many of the components of the suspension system are “enclosed” and in some cases some distance from the impact

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. Impact incident has occurred and a detailed inspection within 12 months of the fire has not occurred Suspension system is not eligible for reliability assessment of inspection interval until inspection confirms the system is structurally undamaged and elements contributing to its durability are functioning There has been no impact incident on the bridge or an internal inspection has been conducted within 12 months of an impact incident confirming that the suspension system and those elements providing durability are undamaged Continue with Procedure Design Attributes D.1–WIRE COATING Suspenders are typically galvanized wire rope with a Class A coating, but wires are available with additional coating thicknesses (Class B or Class C), as well as other coating systems (e.g. aluminum- mischmetal alloy). The attribute is rated as follows: Galvanized, Class A coating 20 points Galvanized, Class B coating 15 points Galvanized, Class C or Aluminum-Mischmetal Alloy (any Class) 10 points D.2–CONNECTION DETAILS Deterioration of suspenders has typically been observed at locations of vulnerable details, either as a result of the original design or due to modifications during the course of its service life. These details result in deterioration due to stress concentrations, debris collection or due to limited inspection access. The attribute is rated as follows: Anchor sockets with closely spaced stiffeners 20 points Deviation points with small radius bends 15 points Clamps or other attachments to rope 15 points Open sockets with clear inspection access 0 points Loading Attributes L.1–ADTT (SUSPENDERS) Though live load represents a small percentage of the total load on a suspension bridge main cable, there are elements of the suspension system that are more directly impacted by live load. The suspenders on a suspension bridge and the attachment details of the suspenders to the cables and the superstructure have a much higher live load to dead load ratio. For this reason, ADTT should be taken into consideration as an attribute for the suspenders. The attribute is rated as follows: ADTT greater than 10% 20 points

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. This attribute is rated as follows: Constrained connection details with entrapped debris and/or water 20 points Enclosure around rope and/or sockets limiting air movement and/or inspection access 15 points Open sockets with free-draining details and no evidence of debris or entrapped water 0 points Condition Attributes C.1–EXISTING FACTOR OF SAFETY OF SUSPENDER ROPES The FOS for the suspenders should be compared against the original specified (as-built) minimum breaking strength. The Rating Factor is determined by dividing the original specified (as-built) breaking strength by the tested breaking strength. To use this attribute, the bridge must have had at least one in-depth inspection, including laboratory testing of removed ropes to determine the existing breaking strength. This attribute is rated as follows: Rating Factor is less than 0.75 20 points FOS ≥ 0.75 but < 0.85 15 points FOS ≥ 0.85 but < 1.0 10 points Rating Factor ≥ 1.0 5 points C.2–CONDITION HISTORY/TREND (BASED ON LAST INTERNAL INSPECTION) The condition of the suspender ropes as observed during periodic inspections give an excellent indication of the likelihood of continued deterioration. This attribute is rated as follows: Broken wires observed at end sockets or connections 20 points Broken wires observed along straight portion of rope 10 points No broken wires 0 points

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. Corrosion and/or failure individual wires would not result in a collapse of the bridge, though failures of wires do result in section loss and an accompanying reduction in the safety factor of the cable. Suspension bridges with more than two suspenders per cable band have a higher redundancy and are thus more tolerant of losses to an individual rope. As such, bridges with one suspender rope (2 legs) per cable band are considered to have a “Moderate” consequence on safety while bridges with two suspender ropes (4 legs) per cable band have a “Minor” consequence on safety. Note that is it assumed that the two suspender ropes are independent and that the failure of one suspender would not directly affect one of the other suspenders at that panel point. The other consideration of this factor is serviceability, that is, the effect that the operation of the bridge (or lack thereof) has on the community. A closure of a high-volume bridge in a large urban area would have a more significant consequence on serviceability than a closure of a low-volume bridge in a rural area. For purposes of this analysis, two levels are considered: one for “high-volume” bridges [high average annual daily traffic (AADT)] and one for “low-volume” bridges (low AADT). Based on a review of existing suspension bridges and their average traffic counts, an AADT value of 30,000 was selected as the dividing line between high-volume and low-volume. Therefore, bridges with AADT ≥ 30,000 are considered to have a “Major” impact on serviceability, while those with AADT < 30,000 have a “Moderate” impact on serviceability. Smaller bridges with lower traffic volumes may be still very important to the community. In such cases a “Major” value may be used. Conversely, some bridges may have operational redundancy that would limit the effect of a closure on the community. In such cases a “Moderate” or “Minor” value may be used. Once the consequences of Safety and Serviceability have been determined using the above approach, the CF may be determined from the table of CF Levels. Cable Band Bolts Inspection Scope Inspection of cable band bolt tensions. Regular Inspection Scope No regular inspection required. In-depth Inspection Scope Cable band bolt tensions should be checked during the in-depth inspection of the main cables. If the aggregate cable band bolt tension of all bolts on an individual band are found to be less than 50% of the original specified value, a programmatic inspection of all cable band bolts should be performed.