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Suggested Citation:"Chapter 1 - Introduction." National Academies of Sciences, Engineering, and Medicine. 2017. Inspection Guidelines for Bridge Post-Tensioning and Stay Cable Systems Using NDE Methods. Washington, DC: The National Academies Press. doi: 10.17226/24779.
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Suggested Citation:"Chapter 1 - Introduction." National Academies of Sciences, Engineering, and Medicine. 2017. Inspection Guidelines for Bridge Post-Tensioning and Stay Cable Systems Using NDE Methods. Washington, DC: The National Academies Press. doi: 10.17226/24779.
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Suggested Citation:"Chapter 1 - Introduction." National Academies of Sciences, Engineering, and Medicine. 2017. Inspection Guidelines for Bridge Post-Tensioning and Stay Cable Systems Using NDE Methods. Washington, DC: The National Academies Press. doi: 10.17226/24779.
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2Introduction Purpose Aims of the Inspection Guidelines The major objective of the inspection guidelines is to assist bridge owners in selecting the most appropriate NDE method for assessing the condition of in-service post-tensioning and stay cable systems. Based on a weighted ranking system, the inspection guidelines provide a list of ranked NDE technolo- gies that are most appropriate for inspecting a particular defect condition, depending on whether metallic or nonmetallic ducts are used as internal or external ducts. The end user also has the option of customizing the weight factors for each of the categories, depending on whether a cost-driven or accuracy- driven approach is sought. The inspection guidelines also pre- sent flowcharts to assist the bridge owners to choose the best possible NDE technology available to detect a particular strand or grout defect of interest. Once the most appropriate NDE method is chosen for a particular situation, the end user is then directed to the corresponding testing procedure, which lays out a detailed procedure to be followed for inspection, including data collection procedure and reporting. Benefits of the Inspection Guidelines The inspection guidelines will present a clear, comprehen- sive way to select NDE methods that allow the information to be readily implemented by the end user. This also will help the end user to select the appropriate NDE method that is best suited for a structure under consideration depending on the most important parameters that are of interest. The inspection guidelines will also help to eliminate any guess- work required in selecting the best appropriate NDE technol- ogy, as each of the technologies that are useful in detecting strand and grout defects in post-tensioning and stay cable systems are ranked based on an overall score that takes into account the precision, accuracy, ease of use, inspection requirements, and cost. Scope The following are the four main topics that are discussed in the inspection guidelines. The scope of each of the four main chapters and the appendices that comprise the inspection guidelines are described in the following paragraphs. Chapter 2: Post-Tensioning and Stay Cable Systems This chapter provides an overview of the post-tensioning sys- tem, which includes both internal and external post-tensioning systems and the stay cable system. The various components of a post-tensioning system, such as tendons, ducts, grout, and anchorage systems, are discussed. This chapter also discusses the components of the stay cable system, such as the main ten- sion elements (MTE), sheathing, corrosion protection systems, saddles, and anchorage systems. Chapter 3: Deterioration Conditions Various deterioration conditions typically found in post- tensioning and stay cable systems are discussed in this chapter. The defects that are considered include: corrosion, section loss, breakage, compromised grout, voids, and water infiltration. The various types and causes of each defect, the significance of these defects, and the NDE methods that are most appropriate in identifying each of the defects are discussed in detail. Chapter 4: Capabilities and Limitations of NDE Methods This chapter discusses the capabilities and limitations of each of the NDE methods considered in the identification of strand and grout defects in post-tensioning and stay cable sys- tems. The capability of the method in detecting the strand and grout defects, its applicability to the internal/external or metal/ nonmetal ducts or anchorage regions, effects of parameters C h a p t e r 1

3 such as concrete cover, layered ducts, and reinforcement congestion, and accessibility requirements are discussed. Chapter 5: Condition Assessment of Post-Tensioning and Stay Cable Systems In this chapter the various aspects relevant to the condi- tion assessment of post-tensioning and stay cable systems are discussed. These include the various types of inspection, the qualifications, responsibilities, and training requirements of the inspectors, and the inspection planning, scheduling and equipment. The various aspects of the evaluation metrics, such as the weighted categories, weight factors, the flowcharts, ranking, and decision-making are discussed. Finally the test procedures, and data processing of the various NDE methods evaluated for the assessment of post-tensioning and stay cable systems are discussed. Appendices Appendix A presents the condition assessment flowcharts, where the user can choose the most appropriate NDE method for assessing a particular defect condition. Flowcharts based on a cost-driven and an accuracy-driven approach are presented. Appendix B presents a different set of flowcharts that helps the user to establish what tendon and/or grout defects can be iden- tified by a particular NDE method. The location of the ducts (internal/external/anchorage regions) and the duct material (metal/nonmetal) are considered in the flowcharts presented in Appendix A and B. Appendix C presents the testing proce- dures for the various NDE methods and a combination of NDE methods. Appendix D presents the procedure in customizing the decision matrix in terms of adding new NDE technologies, or adding new criteria to the decision matrix, and in modifying the weight factors. Finally, Appendix E presents two illustrative examples for the application of the developed decision matrix. Applicability Intended Audience Bridge owners, bridge inspectors, and the bridge engineers, who are involved in evaluating post-tensioning and stay cable systems for various strand and grout defects, are the intended audience of the inspection guidelines. Implementation of the Decision Matrix The decision matrix was developed so that it is simple enough for the end user to make necessary modifications, depending on the parameters that are of importance to them. The considered weighted categories are precision, accuracy, ease of use, inspec- tion requirements, and cost. The various conditions considered in the decision matrix are corrosion, section loss, breakage, compromised grout, voids, and water infiltration. How- ever, the decision matrix provides the end user the flexibility to replace existing or include additional weighted categories, or conditions. The weights of the various categories may also be customized by the end user depending on whether the empha- sis of the inspection is on cost, accuracy or other parameters. Definitions and Terminology Post-Tensioning and Stay Cable Systems Post-tensioning systems essentially consist of prestressing steel tendons placed in longitudinal ducts and tensioned after the con- crete has reached its specified initial compressive strength. Upon release of the prestressing force, the tendons exert compressive stresses on concrete, thus minimizing or completely eliminat- ing tensile stresses in concrete in the tension zones. Depending on the location of the post-tensioning cables, the bridge system may be classified as internal or external post-tensioning systems. Stay cable systems consist of a bridge deck supported by a system of inclined cables, or stays, passing over or attached to towers located at the main abutments or piers. The versatility of stay cable systems lends itself to a wide variety of geometric configurations, and the cable system is economic in terms of weight, material, and overall cost. Deterioration Conditions The deterioration conditions that may be observed in post- tensioning and stay cable systems may be broadly classified as strand defects and grout defects. The strand defects include corrosion, section loss, and breakage of the metal strands. The compromised grout can include segregated grout, unhydrated grout or gassed grout. Other grout deterioration conditions such as voids and water infiltration are also a cause of concern as they offer a conducive environment for tendon corrosion. NDE Methods and Bridge Evaluations The various NDE methods used for evaluating strand and grout defects in post-tensioning and stay cable systems are: • Electromagnetic methods: GPR, infrared thermography (IRT), ECT. • Magnetic methods: magnetic flux leakage (MFL), magnetic main flux method–permanent magnet (MMFM-Permanent), magnetic main flux method–solenoid (MMFM-Solenoid). • Mechanical wave and vibration methods: impact echo (IE), ultrasonic tomography (UST), ultrasonic echo (USE), sonic/ ultrasonic pulse velocity (SPV-UPV), low frequency ultra- sound (LFUT), and sounding. • Electrochemical methods: EIS.

4• Combinations of methods like GPR and USE, GPR and IE, MFL and sounding, MFL and IE, and IRT and USE. Bridge inspection may be classified as: • Tier 1 bridge inspection: Routine maintenance inspection performed on a system or network level. Typically provides some indication of the existence of damages. • Tier 2 bridge inspection: Detailed component condition assessment performed on a project or element level. Typi- cally provides some indication of damage existence, local- ization, and/or severity. • Tier 3 bridge inspection: Material testing inspection performed on a project element level. Typically provides some indication of remaining service life and may include material tests. How to Use the Inspection Guidelines Overview of the Inspection Guidelines The inspection guidelines aid bridge owners and bridge inspectors to evaluate strand and grout defects in post- tensioning and stay cable systems. An overview of the post- tensioning and stay cable systems and their components is presented to help users have a good understanding of the two systems. The typical deterioration conditions seen in these two bridge systems are discussed along with the significance and the NDE methods that may be used in detecting these defects. Detailed information regarding the various inspection methods also is presented for the users to understand the advantages and limitation of each NDE technique. The guidelines also present the evaluation metrics that will help the NDE techniques to be ranked based on weighted categories that include precision, accuracy, ease of use, inspection requirements, and cost. The inspection guidelines will also let end users customize the met- rics for new technologies, or for additional weighted criteria. Finally, the inspection guidelines present tools that aid the users in choosing the inspection technique that best suits the user’s requirements. These tools include flowcharts that help users determine the appropriate NDE method for a given condition, and the defect conditions that can be identified by a particu- lar NDE technique. Flowcharts and inspection procedures for the various NDE techniques are aimed at providing users with a standardized procedure for using the NDE techniques for inspection of post-tensioning and stay cable systems. Structure of the Inspection Guidelines The inspection guidelines consist of a total of five chapters and five appendices. The introduction chapter presents the aim, benefits, scope, applicability, terminology definitions, and how to use the inspection guidelines. Chapter 2 provides an overview of the post-tensioning and the stay cable system. Both internal and external post- tensioning systems and the various components of the post- tensioning system are discussed, followed by an overview of the stay cable system along with an overview of the various components of this system. Chapter 3 discusses the various deterioration conditions typ- ically observed in the post-tensioning and stay cable systems. The deterioration conditions discussed include corrosion, sec- tion loss, breakage, various compromised grout defects, voids, and water infiltration. The types and causes, significance, and NDE methods that may be used to detect each of these condi- tions are discussed in this chapter. Chapter 4 covers the capabilities and limitations of the con- sidered NDE methods that may be used to detect strand and grout defects in the post-tensioning and stay cable systems. The NDE methods presented in this chapter include: electromag- netic methods like GPR, IRT, and ECT; magnetic methods like MFL, MMFM-Permanent, and MMFM-Solenoid; mechanical wave and vibration methods such as IE, UST, USE, SPV-UPV, LFUT, and sounding; visual inspection; electrochemical meth- ods like EIS; and a combinations of methods like GPR and USE, GPR and IE, MFL and sounding, MFL and IE, and IRT and USE. Finally, Chapter 5 presents the various aspects of the con- dition assessment of post-tensioning and stay cable systems. The general aspects of inspection such as the types of inspection; the qualifications, responsibilities and training requirements of inspectors; and planning, scheduling, and equipment for NDE inspection technique are discussed. The evaluation metrics for the various inspection methods discussed in the fourth chapter also are presented here. Finally, the testing procedure and the data processing of each of the methods are presented. The appendices provided at the end of the inspection guidelines provide detailed information regarding the vari- ous aspects of the inspection guidelines. Appendix A presents the flowcharts that may be used to determine the appropriate inspection technique to detect any particular deterioration condition, such as corrosion, section loss, breakage, compro- mised grout, voids, or water infiltration. Appendix B provides the flowcharts for the various NDE techniques and the defects that they can identify. Appendix C presents the testing proce- dures for all the NDE technologies considered in this study. Customizing the decision matrix by including new criteria or by adding new NDE technologies, which may be necessary in the light of rapid technological advancements, are in Appen- dix D. Finally, Appendix E presents two illustrative examples on how to use the inspection guidelines.

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TRB's National Cooperative Highway Research Program (NCHRP) Research Report 848: Inspection Guidelines for Bridge Post-Tensioning and Stay Cable Systems Using NDE Methods describe nondestructive evaluation (NDE) methods for assessing the condition of in-service post-tensioning and stay cable systems. The NDE methods outlined in this report explore different condition assessments, including corrosion, section loss, breakage, grout conditions, voids, water infiltration, and tendon deterioration in the anchorage systems. The NDE methods are ground penetrating radar (GPR), infrared thermography (IRT), electrical capacitance tomography (ECT), magnetic flux leakage (MFL), magnetic main flux method (MMFM), impact echo (IE), ultrasonic tomography (UST), ultrasonic echo (USE), sonic/ultrasonic pulse velocity (S/UPV), low frequency ultrasound (LFUT), sounding, visual testing (VT), and electrochemical impedance spectroscopy (EIS).

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