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50 CHAPTER FOUR MAINTENANCE AND REPAIR OF STAY CABLES REPAIR AND RETROFIT STRATEGIES Deck elevation surveys; AND METHODS Repair procedures including sheathing repair, PVF tape repair, repair of damage to guide pipes, and welded The maintenance manuals of 11 bridges were reviewed in this connections; study. There were major differences between the approaches Safety and traffic control during inspections; and contents of the different manuals. Although a few manu- Description of methods for measuring cable forces; als included procedures for the repair of cable sheathing and Inspection forms; and replacement of cables, others did not provide such information. Deck elevation survey forms. There were major differences as to the level of detail between different manuals, even for the coverage of the same topics. The as-designed and as-built cable forces, deck profile eleva- The examination of the maintenance manuals did not iden- tions, and others, are typically not included in the manuals and tify cases where any of the following methods discussed in are not required to be measured during inspections. Procedures the literature were included in the manuals: for checking for moisture and evidence of vibration problems are generally lacking in many maintenance manuals. Recommendations for baseline measurements of cable frequency, damping ratio, cable sag, and cable inclina- The following is a list of the items found in the different tion angles (at specific points accessible by inspectors). manuals that are related to stay cables: Such measurements can be taken when the effects of creep and shrinkage have dissipated. Such measurements Bridge description; could also include air and structure temperatures. Design considerations; The designer's estimated (calculated) cable frequencies, Loads; sag, and inclination angles (at a specific point) with and Stay cable details: identification numbers, number of without the effects of cross cables or dampers (if used). strands and wires, diameter of cable, mass per unit length, This information could be provided for different ambient inclination angles, length, estimated cable tension at the temperatures. end of construction and after creep and shrinkage effects The designer's estimated (calculated) bending stiffness are taken into account; and damping of cable in the free length and in the Stay cable shop drawings including as-built anchorage anchorage zones. design, materials used, any repairs done during construc- The designer's estimated (calculated) stiffness of neo- tion, and history of problems during construction; prene rings and/or proprietary dampers in contact with Inspection and maintenance frequencies, and qualifica- the cable. tions of inspection teams; Procedures for checking if viscous or other dampers are Information on access: platforms, ladders, and snooper actually working as intended including maintenance pro- trucks; cedures for dampers. Cable retensioning procedures; The designer's estimated (calculated) wind speeds at Cable replacement procedures including traffic patterns which vibrations owing to vortex shedding would be and specific replacement procedures; expected. Inspection procedures for anchorages, guide pipes, neo- The designer's calculated values of the "precursor trans- prene boots, neoprene washers, sheathing, cross cables, formation matrix." This matrix would be required if the dampers, and so forth, including identification of criti- damage detection methodology, Precursor Transforma- cal areas and how and where to look for moisture and tion Method (Tabatabai et al. 1998b), is employed in the corrosion; future. This method uses a linearly elastic finite-element Listing of designers, contractors, and suppliers of stay model of the bridge. In the computer model, the temper- cables and components; ature of the cables are, one by one, raised by say 100 Summary of qualification test results for MTEs; degrees, and the force changes in all other cables are Summary of qualification test results for the entire stay noted. Each column in the transformation matrix would cable system; consist of cable force changes associated with tempera-